Nicholas L. Abbott, PhD

Dr. Abbott is a Professor of Chemical Engineering at the University of Wisconsin-Madison. His research interests span colloid, interface, and surfactant science. A particular focus is directed toward the design of new surfactants that can be placed under active control, the use of liquid crystalline materials to amplify biomolecular interactions, and the design of interfaces with chemistry and topography patterned on nanometer dimensions. His work has been recognized by honors, which include a Presidential Early Career Award in Science and Engineering, a Camille Dreyfus Teacher-Scholar Award and a Fulbright Fellowship. He has published in leading journals, including Science, Journal of the American Chemical Society, Physical Review Letters and Langmuir.

Recent Publications

2018

Related Articles

Amphiphile Induced Phase Transition of Liquid Crystals at Aqueous Interfaces.

ACS Appl Mater Interfaces. 2018 Oct 04;:

Authors: Ramezani-Dakhel H, Rahimi M, Pendery J, Kim YK, Thayumanavan S, Roux B, Abbott NL, de Pablo JJ

Related Articles

Amphiphile Induced Phase Transition of Liquid Crystals at Aqueous Interfaces.

ACS Appl Mater Interfaces. 2018 Oct 04;:

Authors: Ramezani-Dakhel H, Rahimi M, Pendery J, Kim YK, Thayumanavan S, Roux B, Abbott NL, de Pablo JJ

Abstract
Monolayer assemblies of amphiphiles at planar interfaces between thermotropic liquid crystals (LCs) and an aqueous phase can give rise to configurational transitions of the underlying LCs. A common assumption has been that a reconfiguration of the LC phase is caused by an interdigitation of the hydrophobic tails of amphiphiles with the molecules of the LC at the interface. A different mechanism is discovered here, whereby reorientation of the LC systems is shown to occur through lowering of the orientation-dependent surface energy of the LC due to formation of a thin isotropic layer at the aqueous interface. Using a combination of simulations and experiments, we demonstrate that a monolayer of specific amphiphiles at an aqueous interface can cause a local nematic-to-isotropic phase transition of the LC by disturbing the antiparallel configuration of the LC molecules. These results provide new insights into the interfacial, molecular-level organization of LCs that can be exploited for rational design of biological sensors and responsive systems.

PMID: 30285408 [PubMed - as supplied by publisher]

Related Articles

Amphiphile Induced Phase Transition of Liquid Crystals at Aqueous Interfaces.

ACS Appl Mater Interfaces. 2018 Oct 04;:

Authors: Ramezani-Dakhel H, Rahimi M, Pendery J, Kim YK, Thayumanavan S, Roux B, Abbott NL, de Pablo JJ

Machine Learning Algorithms for Liquid Crystals-Based Sensors.

ACS Sens. 2018 Oct 05;:

Authors: Cao Y, Yu H, Abbott NL, Zavala VM

Machine Learning Algorithms for Liquid Crystals-Based Sensors.

ACS Sens. 2018 Oct 05;:

Authors: Cao Y, Yu H, Abbott NL, Zavala VM

Abstract
We present a machine learning (ML) framework to optimize the specificity and speed of liquid crystal (LC)-based chemical sensors. We demonstrate that ML can be used to automatically extract feature information from LCs to accurately classify surface-driven orientational transitions (and the corresponding optical responses) triggered by the presence of different gas-phase analytes. To demonstrate the utility of the approach, we designed an LC system that exhibited optical responses to a stream of nitrogen containing either 10 ppmv dimethyl-methylphosphonate (DMMP) or 30% relative humidity (RH). ML was used to classify thousands of images (optical micrographs) collected collected during the LC responses and to show that classification (sensing) accuracies of over 99% can be achieved. For the same experimental system, we demonstrate that traditional features used in characterizing LC responses (such as average brightness) can only achieve sensing accuracies of 60%. We also find that high accuracies can be achieved by using time snapshots collected early in the LC response, thus providing the ability to create fast sensors. We thus argue that ML techniques can be used to more systematically analyze the quality of information embedded in LC responses and to filter out noise that arises from imperfect LC designs and from sample variations. We evaluate a range of classifiers and features and conclude that linear support vector machines are preferred and that high accuracies can only be achieved by simultaneously exploiting multiple sources of feature information.

PMID: 30289249 [PubMed - as supplied by publisher]

Machine Learning Algorithms for Liquid Crystals-Based Sensors.

ACS Sens. 2018 Oct 05;:

Authors: Cao Y, Yu H, Abbott NL, Zavala VM

Related Articles

Oligomers as Triggers for Responsive Liquid Crystals.

Langmuir. 2018 Jul 31;:

Authors: Kim YK, Raghupathi KR, Pendery JS, Khomein P, Sridhar U, de Pablo JJ, Thayumanavan S, Abbott NL

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Oligomers as Triggers for Responsive Liquid Crystals.

Langmuir. 2018 Jul 31;:

Authors: Kim YK, Raghupathi KR, Pendery JS, Khomein P, Sridhar U, de Pablo JJ, Thayumanavan S, Abbott NL

Abstract
We report an investigation of the influence of aqueous solutions of amphiphilic oligomers on the ordering of micrometer-thick films of thermotropic liquid crystals (LCs), thus addressing the gap in knowledge arising from previous studies of the interactions of monomeric and polymeric amphiphiles with LCs. Specifically, we synthesized amphiphilic oligomers (with decyl hydrophobic and pentaethylenegylcol hydrophilic domains) in monomer, dimer and trimer forms, and incubated aqueous solutions of the oligomers against nematic films of 4'-pentyl-4-biphenylcarbonitrile (5CB). All amphiphilic oligomers caused sequential surface-driven orientational (planar to homeotropic) and then bulk phase transitions (nematic to isotropic) with dynamics depending strongly on degree of oligomerization. The dynamics of the orientational transitions accelerated from monomer to trimer, consistent with the effects of an increase in adsorption free energy. The mechanism underlying the orientational transition, however, involved a decrease in anchoring energy and not change in easy axis of the LC. In contrast, the rate of the phase transition induced by absorption of oligomers into the LC decreased from monomer to trimer, suggesting that constraints on configurational degrees of freedom influence the absorption free energies of the oligomers. Interestingly, the oligomer-induced transition from the nematic to isotropic phase of 5CB was observed to nucleate at the aqueous-5CB interface, consistent with surface-induced disorder underlying the above-reported decrease in anchoring energy caused by the oligomers. Finally, we provided proof-of-concept experiments of the triggering of LCs using a trimeric amphiphile that is photocleaved by UV illumination into monomeric fragments. Overall, our results provide insight into the rational design of oligomers that can be used as triggers to create responsive LCs.

PMID: 30064213 [PubMed - as supplied by publisher]

Related Articles

Oligomers as Triggers for Responsive Liquid Crystals.

Langmuir. 2018 Jul 31;:

Authors: Kim YK, Raghupathi KR, Pendery JS, Khomein P, Sridhar U, de Pablo JJ, Thayumanavan S, Abbott NL

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Redox-Triggered Orientational Responses of Liquid Crystals to Chlorine Gas.

Angew Chem Int Ed Engl. 2018 Jun 22;:

Authors: Szilvási T, Bao N, Nayani K, Yu H, Rai P, Twieg RJ, Mavrikakis M, Abbott NL

Related Articles

Redox-Triggered Orientational Responses of Liquid Crystals to Chlorine Gas.

Angew Chem Int Ed Engl. 2018 Jun 22;:

Authors: Szilvási T, Bao N, Nayani K, Yu H, Rai P, Twieg RJ, Mavrikakis M, Abbott NL

Abstract
Surface-supported liquid crystals (LCs) that exhibit orientational and thus optical responses upon exposure to ppb concentrations of Cl2 gas are reported. Computations identified Mn cations as candidate surface binding sites that undergo redox-triggered changes in the strength of binding to nitrogen-based LCs upon exposure to Cl2 gas. Guided by these predictions, μm-thick films of nitrile- or pyridine-containing LCs were prepared on surfaces decorated with Mn2+ binding sites as perchlorate salts. Following exposure to Cl2 , formation of Mn4+ (in the form of MnO2 microparticles) was confirmed and an accompanying change in the orientation and optical appearance of the supported LC films was measured. In unoptimized systems, the LC orientational transitions provided the sensitivity and response times needed for monitoring human exposure to Cl2 gas. The response was also selective to Cl2 over other oxidizing agents such as air or NO2 and other chemical targets such as organophosphonates.

PMID: 29931784 [PubMed - as supplied by publisher]

Related Articles

Redox-Triggered Orientational Responses of Liquid Crystals to Chlorine Gas.

Angew Chem Int Ed Engl. 2018 Jun 22;:

Authors: Szilvási T, Bao N, Nayani K, Yu H, Rai P, Twieg RJ, Mavrikakis M, Abbott NL

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Liquid Crystals with Interfacial Ordering that Enhances Responsiveness to Chemical Targets.

Adv Mater. 2018 May 21;:e1706707

Authors: Nayani K, Rai P, Bao N, Yu H, Mavrikakis M, Twieg RJ, Abbott NL

Related Articles

Liquid Crystals with Interfacial Ordering that Enhances Responsiveness to Chemical Targets.

Adv Mater. 2018 May 21;:e1706707

Authors: Nayani K, Rai P, Bao N, Yu H, Mavrikakis M, Twieg RJ, Abbott NL

Abstract
The development of stimuli-responsive materials suitable for use in wearable sensors is a key unresolved challenge. Liquid crystals (LCs) are particularly promising, as they do not require power, are light-weight, and can be tuned to respond to a range of targeted chemical stimuli. Here, an advance is reported in the design of LCs for chemical sensors with the discovery of LCs that assume parallel orientations at free surfaces and yet retain their chemoresponsiveness. The resulting LC-based sensors are more sensitive and exhibit faster responses than previous LC sensor designs.

PMID: 29782666 [PubMed - as supplied by publisher]

Related Articles

Liquid Crystals with Interfacial Ordering that Enhances Responsiveness to Chemical Targets.

Adv Mater. 2018 May 21;:e1706707

Authors: Nayani K, Rai P, Bao N, Yu H, Mavrikakis M, Twieg RJ, Abbott NL

Related Articles

The role of anions in adsorbate-induced anchoring transitions of liquid crystals on surfaces with discrete cation binding sites.

Soft Matter. 2018 Jan 08;:

Authors: Szilvási T, Bao N, Yu H, Twieg RJ, Mavrikakis M, Abbott NL

Related Articles

The role of anions in adsorbate-induced anchoring transitions of liquid crystals on surfaces with discrete cation binding sites.

Soft Matter. 2018 Jan 08;:

Authors: Szilvási T, Bao N, Yu H, Twieg RJ, Mavrikakis M, Abbott NL

Abstract
We report a combined theoretical and experimental effort to elucidate systematically for the first time the influence of anions of transition metal salt-decorated surfaces on the orientations of supported films of nematic liquid crystals (LCs) and adsorbate-induced orientational transitions of these LC films. Guided by computational chemistry predictions, we find that nitrate anions weaken the binding of 4'-n-pentyl-4-biphenylcarbonitrile (5CB) to transition metal cations, as compared to perchlorate salts, although binding is still sufficiently strong to induce homeotropic (perpendicular) orientations of 5CB. In addition, we find the orientations of the LC to be correlated across all metal cations investigated by a molecular anchoring energy density that is calculated as the product of the single-site binding energy and metal cation binding site density on the surface. The weaker single-site binding energy caused by nitrate also facilitates competitive binding of adsorbates to the metal cations, leading to more facile orientational transitions induced by adsorbates. Finally, our analysis suggests that nitrate anions recruit water via hydrogen bonding to the metal binding sites, modulating further the relative net binding energies of 5CB and adsorbates to surfaces decorated with metal nitrates. After accounting for the presence of water, we find a universal exponential relationship between the calculated displacement free energies and measured dynamic response of LCs to adsorbates for all metal salts studied, independent of the metal salt anion.

PMID: 29308482 [PubMed - as supplied by publisher]

Related Articles

The role of anions in adsorbate-induced anchoring transitions of liquid crystals on surfaces with discrete cation binding sites.

Soft Matter. 2018 Jan 08;:

Authors: Szilvási T, Bao N, Yu H, Twieg RJ, Mavrikakis M, Abbott NL

2017

Related Articles

Non-Additive Interactions Mediated by Water at Chemically Heterogeneous Surfaces: Non-ionic Polar Groups and Hydrophobic Interactions.

J Am Chem Soc. 2017 Nov 11;:

Authors: Wang C, Ma CD, Yeon H, Wang X, Gellman SH, Abbott NL

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Non-Additive Interactions Mediated by Water at Chemically Heterogeneous Surfaces: Non-ionic Polar Groups and Hydrophobic Interactions.

J Am Chem Soc. 2017 Nov 11;:

Authors: Wang C, Ma CD, Yeon H, Wang X, Gellman SH, Abbott NL

Abstract
We explore how two non-ionic polar groups (primary amine and primary amide) influence hydrophobic interactions of neighboring non-polar domains. We designed stable β-peptide sequences that generated globally amphiphilic (GA) heli-ces, each with a non-polar domain formed by six cyclohexyl side chains arranged along one side of the 14-helix. The other side of the helix was dominated by three polar side chains, from β3-homolysine (K) and/or β3-homoglutamine (Q) resi-dues. Variations in this polar side chain array included exclusively β3-hLys (GA-KKK) and β3-hLys/β3-hGln mixtures (e.g., GA-QKK and GA-QQK). Chemical force measurements in aqueous solution vs. methanol allowed quantification of the hydrophobic interactions of the β-peptide with the non-polar tip of an atomic force microscope (AFM). At pH 10.5, where the K side chain is deprotonated, we measured hydrophobic adhesive interactions mediated by GA-KKK to be 0.61 ± 0.04 nN, by GA-QKK to be 0.54 ± 0.01 nN, by GA-QQK to be 0 ± 0.01 nN. This finding suggests that replacing an amine group (K side chain) with a primary amide group (Q side chain) weakens the hydrophobic interaction generated by the six cy-clohexyl side chains. AFM studies with solid-supported mixed monolayers containing an alkyl component (60%) and a component bearing either a terminal amide or amine group (40%) revealed analogous trends. These observations from two distinct experiment systems indicate that proximal non-ionic polar groups have pronounced effects on hydrophobic interactions generated by a neighboring non-polar domain, and that the magnitude of the effect depends strongly on polar group identity.

PMID: 29129065 [PubMed - as supplied by publisher]

Related Articles

Non-Additive Interactions Mediated by Water at Chemically Heterogeneous Surfaces: Non-ionic Polar Groups and Hydrophobic Interactions.

J Am Chem Soc. 2017 Nov 11;:

Authors: Wang C, Ma CD, Yeon H, Wang X, Gellman SH, Abbott NL

Related Articles

Redox-triggered mixing and demixing of surfactants within assemblies formed in solution and at surfaces.

J Colloid Interface Sci. 2017 Sep 15;502:122-133

Authors: Smith TJ, Wang C, Abbott NL

Related Articles

Redox-triggered mixing and demixing of surfactants within assemblies formed in solution and at surfaces.

J Colloid Interface Sci. 2017 Sep 15;502:122-133

Authors: Smith TJ, Wang C, Abbott NL

Abstract
We report experiments that test the hypothesis that redox-triggered changes in the architectures of surfactants permit control of mixing of surfactants within assemblies. Specifically, we describe surface tension, light scattering, atomic force microscopy, and quartz crystal microbalance measurements that characterize the redox-dependent behaviors of cationic surfactants with a ferrocene group located either at the surfactant terminus (11-ferrocenylundecyl-trimethylammonium bromide; FTMA) or head (N,N-dimethylferrocenylmethyldecylammonium bromide; DMFA). In bulk solution, we find that reduced and oxidized FTMA do not mix within micellar assemblies but that reduced and oxidized DMFA do form mixed micelles. Because oxidized FTMA has the architecture of a bolaform surfactant whereas oxidized DMFA has a conventional surfactant architecture with a divalent head group, these results suggest that redox-triggered changes in molecular architecture permit control of the extent of mixing of surfactants in micellar assemblies in bulk solution. This conclusion receives further support from measurements performed with mixtures of dodecyltrimethylammonium bromide and FTMA, with FTMA in either reduced or oxidized states, and was found to extend to hemimicellar assemblies formed at hydrophobic solid surfaces but not to mixed monolayers formed at the surface of water. The latter is attributed to differences in the conformations of surfactants within monolayers and micellar assemblies. Overall, these results provide insight into the design of surfactant assemblies within which mixing can be controlled reversibly using redox processes.

PMID: 28478219 [PubMed - in process]

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Redox-triggered mixing and demixing of surfactants within assemblies formed in solution and at surfaces.

J Colloid Interface Sci. 2017 Sep 15;502:122-133

Authors: Smith TJ, Wang C, Abbott NL

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Active Janus Particles at Interfaces of Liquid Crystals.

Langmuir. 2017 Aug 29;:

Authors: Mangal R, Nayani K, Kim YK, Bukusoglu E, Córdova-Figueroa UM, Abbott NL

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Active Janus Particles at Interfaces of Liquid Crystals.

Langmuir. 2017 Aug 29;:

Authors: Mangal R, Nayani K, Kim YK, Bukusoglu E, Córdova-Figueroa UM, Abbott NL

Abstract
We report an investigation of the active motion of silica-palladium Janus particles (JPs) adsorbed at interfaces formed between nematic liquid crystals (LCs) and aqueous phases containing hydrogen peroxide (H2O2). In comparison to isotropic oil-aqueous interfaces, we observe the elasticity and anisotropic viscosity of the nematic phase to change qualitatively the active motion of the JPs at the LC interfaces. Although contact line pinning on the surface of the JPs is observed to restrict out-of-plane rotational diffusion of the JPs at LC interfaces, orientational anchoring of nematic LCs on the silica (planar) and palladi-um (homeotropic) hemispheres bias JP in-plane orientations to generate active motion almost exclusively along the director of the LC at low concentrations of H2O2 (0.5wt% ). In contrast, displacements perpendicular to the director exhibit the character-istics of Brownian diffusion. At higher concentrations of H2O2 (1wt % - 3wt%), we observe an increasing population of JPs propelled parallel and perpendicular to the LC director in a manner consistent with active motion. In addition, under these con-ditions, we also observe a subpopulation of JPs (approximately 10%) that exhibit active motion exclusively perpendicular to the LC director. These results are discussed in light of independent measurements of the distribution of azimuthal orientations of the JPs at the LC interfaces and calculations of the elastic energies that bias JP orientations. We also contrast our observa-tions at LC interfaces to past studies of self-propulsion of particles within and at the interfaces of isotropic liquids.

PMID: 28850782 [PubMed - as supplied by publisher]

Related Articles

Active Janus Particles at Interfaces of Liquid Crystals.

Langmuir. 2017 Aug 29;:

Authors: Mangal R, Nayani K, Kim YK, Bukusoglu E, Córdova-Figueroa UM, Abbott NL

Related Articles

Influence of Order within Nonpolar Monolayers on Hydrophobic Interactions.

Langmuir. 2017 May 16;33(19):4628-4637

Authors: Yeon H, Wang C, Van Lehn RC, Abbott NL

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Influence of Order within Nonpolar Monolayers on Hydrophobic Interactions.

Langmuir. 2017 May 16;33(19):4628-4637

Authors: Yeon H, Wang C, Van Lehn RC, Abbott NL

Abstract
We report an experimental investigation of the influence of molecular-level order (crystallinity) within nonpolar monolayers on hydrophobic interactions. The measurements were performed using gold film-supported monolayers formed from alkanethiols (CH3(CH2)nSH, with n ranging from 3 to 17), which we confirmed by using polarization-modulation infrared reflection-adsorption spectroscopy to exhibit chain-length-dependent order (methylene peak moves from 2926 to 2919 cm(-1), corresponding to a transition from liquid- to quasi-crystalline-like order) in the absence of substantial changes in chain density (constant methyl peak intensity). By using monolayer-covered surfaces immersed in either aqueous triethanolamine (TEA, 10 mM, pH 7.0) or pure methanol, we quantified hydrophobic and van der Waals contributions to adhesive interactions between identical pairs of surfaces (measured using an atomic force microscope) as a function of the length and order of the aliphatic chains within the monolayers. In particular, we measured pull-off forces arising from hydrophobic adhesion to increase in a nonlinear manner with chain length (abrupt increase between n = 5 and 6 from 2.1 ± 0.3 to 14.1 ± 0.7 nN) and to correlate closely with a transition from a liquid-like to crystalline-like monolayer phase. In contrast, adhesion in methanol increased gradually with chain length from 0.3 ± 0.1 to 3.2 ± 0.3 nN for n = 3 to 7 and then did not change further with an increase in chain length. These results lead to the hypothesis that order within nonpolar monolayers influences hydrophobic interactions. Additional support for this hypothesis was obtained from measurements reported in this paper using long-chain alkanethiols (ordered) and alkenethiols (disordered). The results are placed into the context of recent spectroscopic studies of hydrogen bonding of water at nonpolar monolayers. Overall, our study provides new insight into factors that influence hydrophobic interactions at nonpolar monolayers.

PMID: 28420228 [PubMed - in process]

Related Articles

Influence of Order within Nonpolar Monolayers on Hydrophobic Interactions.

Langmuir. 2017 May 16;33(19):4628-4637

Authors: Yeon H, Wang C, Van Lehn RC, Abbott NL

Related Articles

Generation of Gaseous ClO2 from Thin Films of Solid NaClO2 by Sequential Exposure to Ultraviolet Light and Moisture.

ACS Appl Mater Interfaces. 2017 May 17;9(19):16594-16603

Authors: Jain R, Abbasi R, Nelson K, Busche D, Lynn DM, Abbott NL

Related Articles

Generation of Gaseous ClO2 from Thin Films of Solid NaClO2 by Sequential Exposure to Ultraviolet Light and Moisture.

ACS Appl Mater Interfaces. 2017 May 17;9(19):16594-16603

Authors: Jain R, Abbasi R, Nelson K, Busche D, Lynn DM, Abbott NL

Abstract
We report that thin films of solid sodium chlorite (NaClO2) can be photochemically activated by irradiation with ultraviolet (UV) light to generate gaseous chlorine dioxide (ClO2) upon subsequent exposure to moisture. The limiting role of water in the reaction is evidenced by an increase in yield of ClO2 with relative humidity of the gas stream passed over the UV-activated salt. The UV-activated state of the NaClO2 was found to possess a half-life of 48 h, revealing the presence of long-lived UV activated species that subsequently react with water to produce gaseous ClO2. The yield of ClO2 was determined to be proportional to the surface area of NaClO2 particles projected to the incident illumination, consistent with activation of a ∼10 nm-thick layer of NaClO2 at the surface of the micrometer-sized salt crystals (for an activation wavelength of 254 nm). We also found that the quantity of ClO2 released can be tuned ∼10-fold by varying wavelength of UV irradiation and relative humidity of the gas stream passed over the UV-activated NaClO2. The UV-activated species were not detectable by electron paramagnetic resonance spectroscopy, indicating that the activated intermediate is not an excited triplet state of ClO2(-). Additionally, neither X-ray photoelectron spectroscopy, nor Raman spectroscopy, nor attenuated total reflection infrared spectroscopy revealed the identity of the activated intermediate species. The ability to preactivate solid phase chlorite salt for subsequent generation of ClO2 upon exposure to moisture suggests the basis of new materials and methods that permit triggered release of ClO2 in contexts that use its disinfectant properties.

PMID: 28409922 [PubMed - in process]

Related Articles

Generation of Gaseous ClO2 from Thin Films of Solid NaClO2 by Sequential Exposure to Ultraviolet Light and Moisture.

ACS Appl Mater Interfaces. 2017 May 17;9(19):16594-16603

Authors: Jain R, Abbasi R, Nelson K, Busche D, Lynn DM, Abbott NL

Related Articles

Segregation of liquid crystal mixtures in topological defects.

Nat Commun. 2017 Apr 28;8:15064

Authors: Rahimi M, Ramezani-Dakhel H, Zhang R, Ramirez-Hernandez A, Abbott NL, de Pablo JJ

Related Articles

Segregation of liquid crystal mixtures in topological defects.

Nat Commun. 2017 Apr 28;8:15064

Authors: Rahimi M, Ramezani-Dakhel H, Zhang R, Ramirez-Hernandez A, Abbott NL, de Pablo JJ

Abstract
The structure and physical properties of liquid crystal (LC) mixtures are a function of composition, and small changes can have pronounced effects on observables, such as phase-transition temperatures. Traditionally, LC mixtures have been assumed to be compositionally homogenous. The results of chemically detailed simulations presented here show that this is not the case; pronounced deviations of the local order from that observed in the bulk at defects and interfaces lead to significant compositional segregation effects. More specifically, two disclination lines are stabilized in this work by introducing into a nematic liquid crystal mixture a cylindrical body that exhibits perpendicular anchoring. It is found that the local composition deviates considerably from that of the bulk at the interface with the cylinder and in the defects, thereby suggesting new assembly and synthetic strategies that may capitalize on the unusual molecular environment provided by liquid crystal mixtures.

PMID: 28452347 [PubMed - in process]

Related Articles

Segregation of liquid crystal mixtures in topological defects.

Nat Commun. 2017 Apr 28;8:15064

Authors: Rahimi M, Ramezani-Dakhel H, Zhang R, Ramirez-Hernandez A, Abbott NL, de Pablo JJ

An Engineered Surface-immobilized Enzyme that Retains High Levels of Catalytic Activity in Air.

J Am Chem Soc. 2017 Feb 13;:

Authors: Badieyan S, Wang Q, Zou X, Li Y, Herron M, Abbott NL, Chen Z, Marsh EN

An Engineered Surface-immobilized Enzyme that Retains High Levels of Catalytic Activity in Air.

J Am Chem Soc. 2017 Feb 13;:

Authors: Badieyan S, Wang Q, Zou X, Li Y, Herron M, Abbott NL, Chen Z, Marsh EN

Abstract
In the absence of aqueous buffer most enzymes retain little or no activity; however, "water-free" enzymes would have many diverse applications. Here we describe the chemically precise immobilization of an enzyme on an engineered surface designed to support catalytic activity in air at ambient humidity. Covalent immobilization of haloalkane dehalogenase on a surface support displaying poly-(sorbitol methacrylate) chains resulted in ~ 40-fold increase in activity over lyophilized enzyme powders for the gas-phase dehalogenation of 1-bromopropane. The activity of the immobilized enzyme in air approaches 25 % of the activity obtained in buffer for the immobilized enzyme. Poly-(sorbitol methacrylate) appears to enhance activity by replacing protein-water interactions, thereby preserving the protein structure.

PMID: 28191945 [PubMed - as supplied by publisher]

An Engineered Surface-immobilized Enzyme that Retains High Levels of Catalytic Activity in Air.

J Am Chem Soc. 2017 Feb 13;:

Authors: Badieyan S, Wang Q, Zou X, Li Y, Herron M, Abbott NL, Chen Z, Marsh EN

Related Articles

Molecular Structure of Canonical Liquid Crystal Interfaces.

J Am Chem Soc. 2017 Feb 08;:

Authors: Sadati M, Ramezani-Dakhel H, Bu W, Sevgen E, Liang Z, Erol C, Rahimi M, Taheri Qazvini N, Lin B, Abbott NL, Roux B, Schlossman ML, de Pablo JJ

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Molecular Structure of Canonical Liquid Crystal Interfaces.

J Am Chem Soc. 2017 Feb 08;:

Authors: Sadati M, Ramezani-Dakhel H, Bu W, Sevgen E, Liang Z, Erol C, Rahimi M, Taheri Qazvini N, Lin B, Abbott NL, Roux B, Schlossman ML, de Pablo JJ

Abstract
Numerous applications of liquid crystals (LC) rely on control of molecular orientation at an interface. However, little is known about the precise molecular structure of such interfaces. In this work, synchrotron X-ray reflectivity measurements, accompanied by large-scale atomistic molecular dynamics simulations, are used for the first time to reconstruct the air-liquid crystal interface of a nematic material, namely 5CB (4-Pentyl-4'-Cyanobiphenyl). The results are compared to those for 8CB (4-Octyl-4'-Cyanobiphenyl) which, in addition to isotropic and nematic states, can also form a smectic phase. Our findings indicate that the air interface imprints a highly ordered structure into the material; such a local structure then propagates well into the bulk of the liquid crystal, particularly for nematic and smectic phases.

PMID: 28177227 [PubMed - as supplied by publisher]

Related Articles

Molecular Structure of Canonical Liquid Crystal Interfaces.

J Am Chem Soc. 2017 Feb 08;:

Authors: Sadati M, Ramezani-Dakhel H, Bu W, Sevgen E, Liang Z, Erol C, Rahimi M, Taheri Qazvini N, Lin B, Abbott NL, Roux B, Schlossman ML, de Pablo JJ

2016

Related Articles

Positioning colloids at the surfaces of cholesteric liquid crystal droplets.

Soft Matter. 2016 Oct 26;12(42):8781-8789

Authors: Bukusoglu E, Wang X, Zhou Y, Martínez-González JA, Rahimi M, Wang Q, de Pablo JJ, Abbott NL

Related Articles

Positioning colloids at the surfaces of cholesteric liquid crystal droplets.

Soft Matter. 2016 Oct 26;12(42):8781-8789

Authors: Bukusoglu E, Wang X, Zhou Y, Martínez-González JA, Rahimi M, Wang Q, de Pablo JJ, Abbott NL

Abstract
We report on the internal configurations of aqueous dispersions of droplets of cholesteric liquid crystals (LCs; 5-50 μm-in-diameter; comprised of 4-cyano-4'-pentylbiphenyl and 4-(1-methylheptyloxycarbonyl)phenyl-4-hexyloxybenzoate) and their influence on the positioning of surface-adsorbed colloids (0.2 or 1 μm-in-diameter polystyrene (PS)). When N = 2D/P was less than 4, where D is the droplet diameter and P is the cholesteric pitch, the droplets adopted a twisted bipolar structure (TBS) and colloids were observed to assume positions at either the poles or equator of the droplets. A statistical analysis of the distribution of locations of the colloids revealed a potential well of depth 2.7 kBT near the equator, a conclusion that was supported by computer simulations performed via the minimization of the Landau-de Gennes free energy (well depth of 7 kBT from simulation). In contrast, for N > 4, a majority of the droplets exhibited a radial spherical structure (RSS) characterized by a pair of closely spaced surface defects (angle of separation with respect to the center of the droplet θ < 5°) connected by a disclination winding to/from the droplet center, which led to the positioning of pairs of colloids with well-defined spacing at these surface defects. The separation of the pairs of surface-adsorbed colloids was colloid size-dependent, ranging from 1.11 ± 0.04 μm for 1 μm-in-diameter colloids to 1.7 ± 0.2 μm for 200 nm-in-diameter colloids. We also observed long-lived metastable configurations in which the two surface point defects were separated by much larger distances (corresponding to populations with angles of θ = 20 ± 10° and 85 ± 10° with respect to the center), and observed these pairs of defects to also position pairs of colloids. A third configuration, the diametrical spherical structure (DSS) was also observed. Consistent with the predictions of computer simulations, we found experimentally that the DSS is indeed composed of disconnected defect rings positioned along the diameter of the droplet. Overall, these results reveal that the rich palette of defects exhibited by confined cholesteric LC systems (equilibrium and metastable) provide the basis of a versatile class of templates that enable the surface positioning of colloids in ways that are not possible with achiral LC droplets.

PMID: 27722427 [PubMed - in process]

Related Articles

Positioning colloids at the surfaces of cholesteric liquid crystal droplets.

Soft Matter. 2016 Oct 26;12(42):8781-8789

Authors: Bukusoglu E, Wang X, Zhou Y, Martínez-González JA, Rahimi M, Wang Q, de Pablo JJ, Abbott NL

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Interfacial Stacks of Polymeric Nanofilms on Soft Biological Surfaces that Release Multiple Agents.

ACS Appl Mater Interfaces. 2016 Oct 03;

Authors: Herron M, Schurr MJ, Murphy CJ, McAnulty JF, Czuprynski CJ, Abbott NL

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Interfacial Stacks of Polymeric Nanofilms on Soft Biological Surfaces that Release Multiple Agents.

ACS Appl Mater Interfaces. 2016 Oct 03;

Authors: Herron M, Schurr MJ, Murphy CJ, McAnulty JF, Czuprynski CJ, Abbott NL

Abstract
We report a general and facile method that permits the transfer (stacking) of multiple independently fabricated and nanoscopically thin polymeric films, each containing a distinct bioactive agent, onto soft biomedically relevant surfaces (e.g., collagen-based wound dressings). By using polyelectrolyte multilayer films (PEMs) formed from poly(allyl amine hydrochloride) and poly(acrylic acid) as representative polymeric nanofilms and micrometer-thick water-soluble poly(vinyl alcohol) sacrificial films to stack the PEMs, we demonstrate that it is possible to create stacked polymeric constructs containing multiple bioactive agents (e.g., antimicrobial and antibiofilm agents) on soft and chemically complex surfaces onto which PEMs cannot be routinely transferred by stamping. We illustrate the characteristics and merits of the approach by fabricating stacks of Ga(3+) (antibiofilm agent)- and Ag(+) (antimicrobial agent)-loaded PEMs as prototypical examples of agent-containing PEMs and demonstrate that the stacked PEMs incorporate precise loadings of the agents and provide flexibility in terms of tuning release rates. Specifically, we show that simultaneous release of Ga(3+) and Ag(+) from the stacked PEMs on collagen-based wound dressings can lead to synergistic effects on bacteria, killing and dispersing biofilms formed by Pseudomonas aeruginosa (two strains: ATCC 27853 and MPAO1) at sufficiently low loadings of agents such that cytotoxic effects on mammalian cells are avoided. The approach is general (a wide range of bioactive agents other than Ga(3+) and Ag(+) can be incorporated into PEMs), and the modular nature of the approach potentially allows end-user functionalization of soft biological surfaces for programmed release of multiple bioactive agents.

PMID: 27579573 [PubMed - as supplied by publisher]

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Interfacial Stacks of Polymeric Nanofilms on Soft Biological Surfaces that Release Multiple Agents.

ACS Appl Mater Interfaces. 2016 Oct 03;

Authors: Herron M, Schurr MJ, Murphy CJ, McAnulty JF, Czuprynski CJ, Abbott NL

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Controlled deformation of vesicles by flexible structured media.

Sci Adv. 2016 Aug;2(8):e1600978

Authors: Zhang R, Zhou Y, Martínez-González JA, Hernández-Ortiz JP, Abbott NL, de Pablo JJ

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Controlled deformation of vesicles by flexible structured media.

Sci Adv. 2016 Aug;2(8):e1600978

Authors: Zhang R, Zhou Y, Martínez-González JA, Hernández-Ortiz JP, Abbott NL, de Pablo JJ

Abstract
Liquid crystalline (LC) materials, such as actin or tubulin networks, are known to be capable of deforming the shape of cells. Here, elements of that behavior are reproduced in a synthetic system, namely, a giant vesicle suspended in a LC, which we view as a first step toward the preparation of active, anisotropic hybrid systems that mimic some of the functionality encountered in biological systems. To that end, we rely on a coupled particle-continuum representation of deformable networks in a nematic LC represented at the level of a Landau-de Gennes free energy functional. Our results indicate that, depending on its elastic properties, the LC is indeed able to deform the vesicle until it reaches an equilibrium, anisotropic shape. The magnitude of the deformation is determined by a balance of elastic and surface forces. For perpendicular anchoring at the vesicle, a Saturn ring defect forms along the equatorial plane, and the vesicle adopts a pancake-like, oblate shape. For degenerate planar anchoring at the vesicle, two boojum defects are formed at the poles of the vesicle, which adopts an elongated, spheroidal shape. During the deformation, the volume of the topological defects in the LC shrinks considerably as the curvature of the vesicle increases. These predictions are confirmed by our experimental observations of spindle-like shapes in experiments with giant unilamellar vesicles with planar anchoring. We find that the tension of the vesicle suppresses vesicle deformation, whereas anchoring strength and large elastic constants promote shape anisotropy.

PMID: 27532056 [PubMed - in process]

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Controlled deformation of vesicles by flexible structured media.

Sci Adv. 2016 Aug;2(8):e1600978

Authors: Zhang R, Zhou Y, Martínez-González JA, Hernández-Ortiz JP, Abbott NL, de Pablo JJ

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Structural Transitions in Cholesteric Liquid Crystal Droplets.

ACS Nano. 2016 Jul 26;10(7):6484-90

Authors: Zhou Y, Bukusoglu E, Martínez-González JA, Rahimi M, Roberts TF, Zhang R, Wang X, Abbott NL, de Pablo JJ

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Structural Transitions in Cholesteric Liquid Crystal Droplets.

ACS Nano. 2016 Jul 26;10(7):6484-90

Authors: Zhou Y, Bukusoglu E, Martínez-González JA, Rahimi M, Roberts TF, Zhang R, Wang X, Abbott NL, de Pablo JJ

Abstract
Confinement of cholesteric liquid crystals (ChLC) into droplets leads to a delicate interplay between elasticity, chirality, and surface energy. In this work, we rely on a combination of theory and experiments to understand the rich morphological behavior that arises from that balance. More specifically, a systematic study of micrometer-sized ChLC droplets is presented as a function of chirality and surface energy (or anchoring). With increasing chirality, a continuous transition is observed from a twisted bipolar structure to a radial spherical structure, all within a narrow range of chirality. During such a transition, a bent structure is predicted by simulations and confirmed by experimental observations. Simulations are also able to capture the dynamics of the quenching process observed in experiments. Consistent with published work, it is found that nanoparticles are attracted to defect regions on the surface of the droplets. For weak anchoring conditions at the nanoparticle surface, ChLC droplets adopt a morphology similar to that of the equilibrium helical phase observed for ChLCs in the bulk. As the anchoring strength increases, a planar bipolar structure arises, followed by a morphological transition to a bent structure. The influence of chirality and surface interactions are discussed in the context of the potential use of ChLC droplets as stimuli-responsive materials for reporting molecular adsorbates.

PMID: 27249186 [PubMed - in process]

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Structural Transitions in Cholesteric Liquid Crystal Droplets.

ACS Nano. 2016 Jul 26;10(7):6484-90

Authors: Zhou Y, Bukusoglu E, Martínez-González JA, Rahimi M, Roberts TF, Zhang R, Wang X, Abbott NL, de Pablo JJ

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Straining soft colloids in aqueous nematic liquid crystals.

Proc Natl Acad Sci U S A. 2016 May 17;113(20):5564-9

Authors: Mushenheim PC, Pendery JS, Weibel DB, Spagnolie SE, Abbott NL

Related Articles

Straining soft colloids in aqueous nematic liquid crystals.

Proc Natl Acad Sci U S A. 2016 May 17;113(20):5564-9

Authors: Mushenheim PC, Pendery JS, Weibel DB, Spagnolie SE, Abbott NL

Abstract
Liquid crystals (LCs), because of their long-range molecular ordering, are anisotropic, elastic fluids. Herein, we report that elastic stresses imparted by nematic LCs can dynamically shape soft colloids and tune their physical properties. Specifically, we use giant unilamellar vesicles (GUVs) as soft colloids and explore the interplay of mechanical strain when the GUVs are confined within aqueous chromonic LC phases. Accompanying thermal quenching from isotropic to LC phases, we observe the elasticity of the LC phases to transform initially spherical GUVs (diameters of 2-50 µm) into two distinct populations of GUVs with spindle-like shapes and aspect ratios as large as 10. Large GUVs are strained to a small extent (R/r < 1.54, where R and r are the major and minor radii, respectively), consistent with an LC elasticity-induced expansion of lipid membrane surface area of up to 3% and conservation of the internal GUV volume. Small GUVs, in contrast, form highly elongated spindles (1.54 < R/r < 10) that arise from an efflux of LCs from the GUVs during the shape transformation, consistent with LC-induced straining of the membrane leading to transient membrane pore formation. A thermodynamic analysis of both populations of GUVs reveals that the final shapes adopted by these soft colloids are dominated by a competition between the LC elasticity and an energy (∼0.01 mN/m) associated with the GUV-LC interface. Overall, these results provide insight into the coupling of strain in soft materials and suggest previously unidentified designs of LC-based responsive and reconfigurable materials.

PMID: 27140607 [PubMed]

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Straining soft colloids in aqueous nematic liquid crystals.

Proc Natl Acad Sci U S A. 2016 May 17;113(20):5564-9

Authors: Mushenheim PC, Pendery JS, Weibel DB, Spagnolie SE, Abbott NL

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Surface-controlled orientational transitions in elastically strained films of liquid crystal that are triggered by vapors of toluene.

ACS Appl Mater Interfaces. 2016 Apr 12;

Authors: Bedolla-Pantoja M, Abbott NL

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Surface-controlled orientational transitions in elastically strained films of liquid crystal that are triggered by vapors of toluene.

ACS Appl Mater Interfaces. 2016 Apr 12;

Authors: Bedolla-Pantoja M, Abbott NL

Abstract
We report the fabrication of chemically patterned microwells that enable the rapid and facile preparation (by spin coating and patterned dewetting) of thin films of liquid crystals (LCs) that have precise thicknesses (0.7-30 µm), are supported on chemically defined substrates, and have free upper surfaces. We use these microwells to prepare elastically-strained nematic LC films supported on silica glass, gold or polystyrene substrates and thereby characterize the response of the strained LC films to vapors of toluene. We report that low concentrations of toluene vapor (<500ppm) can partition into the LC to lower the anchoring energy of the LC on these substrates, thus allowing the elastic energy of the strained LC film to drive the LC films through an orientational transition. The central role of the toluene-induced change in surface anchoring energy is supported by additional experiments in which the response of the nematic LC to changes in film thickness and substrate identity are quantified. A simple thermodynamic model captures these trends and yielded estimates of anchoring energies (8 - 22 J/m2). Significantly, the orientational transitions observed in these strained LC thin films occur at concentrations of toluene vapor that are almost an order of magnitude below those which lead to bulk phase transitions, and they are not triggered by exposure to water vapor. Overall, these results hint at principles for the design of responsive LC-based materials that can be triggered by concentrations of aromatic volatile aromatic compounds that are relevant to human health.

PMID: 27070511 [PubMed - as supplied by publisher]

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Surface-controlled orientational transitions in elastically strained films of liquid crystal that are triggered by vapors of toluene.

ACS Appl Mater Interfaces. 2016 Apr 12;

Authors: Bedolla-Pantoja M, Abbott NL

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Interaction of the Hydrophobic Tip of an Atomic Force Microscope with Oligopeptides Immobilized Using Short and Long Tethers.

Langmuir. 2016 Mar 29;32(12):2985-95

Authors: Ma CD, Acevedo-Vélez C, Wang C, Gellman SH, Abbott NL

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Interaction of the Hydrophobic Tip of an Atomic Force Microscope with Oligopeptides Immobilized Using Short and Long Tethers.

Langmuir. 2016 Mar 29;32(12):2985-95

Authors: Ma CD, Acevedo-Vélez C, Wang C, Gellman SH, Abbott NL

Abstract
We report an investigation of the adhesive force generated between the hydrophobic tip of an atomic force microscope (AFM) and surfaces presenting oligopeptides immobilized using either short (∼1 nm) or long (∼60 nm) tethers. Specifically, we used either sulfosuccinimidyl-4-(N-maleimidomethyl)cyclohexane-1-carboxylate (SSMCC) or 10 kDa polyethylene glycol (PEG) end-functionalized with maleimide and N-hydroxysuccinimide groups to immobilize helical oligomers of β-amino acids (β-peptides) to mixed monolayers presenting tetraethylene glycol (EG4) and amine-terminated EG4 (EG4N) groups. When SSMCC was used to immobilize the β-peptides, we measured the adhesive interaction between the AFM tip and surface to rupture through a single event with magnitude consistent with the interaction of a single β-peptide with the AFM tip. Surprisingly, this occurred even when, on average, multiple β-peptides were located within the interaction area between the AFM tip and surface. In contrast, when using the long 10 kDa PEG tether, we observed the magnitude of the adhesive interaction as well as the dynamics of the rupture events to unmask the presence of the multiple β-peptides within the interaction area. To provide insight into these observations, we formulated a simple mechanical model of the interaction of the AFM tip with the immobilized β-peptides and used the model to demonstrate that adhesion measurements performed using short tethers (but not long tethers) are dominated by the interaction of single β-peptides because (i) the mechanical properties of the short tether are highly nonlinear, thus causing one β-peptide to dominate the adhesion force at the point of rupture, and (ii) the AFM cantilever is mechanically unstable following the rupture of the adhesive interaction with a single β-peptide. Overall, our study reveals that short tethers offer the basis of an approach that facilitates measurement of adhesive interactions with single molecules presented at surfaces.

PMID: 26895750 [PubMed - in process]

Related Articles

Interaction of the Hydrophobic Tip of an Atomic Force Microscope with Oligopeptides Immobilized Using Short and Long Tethers.

Langmuir. 2016 Mar 29;32(12):2985-95

Authors: Ma CD, Acevedo-Vélez C, Wang C, Gellman SH, Abbott NL

2015

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Liquid Crystals: Liquid Crystal Interfaces Programmed with Enzyme-Responsive Polymers and Surfactants (Small 43/2015).

Small. 2015 Nov;11(43):5722

Authors: Ma CD, Adamiak L, Miller DS, Wang X, Gianneschi NC, Abbott NL

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Liquid Crystals: Liquid Crystal Interfaces Programmed with Enzyme-Responsive Polymers and Surfactants (Small 43/2015).

Small. 2015 Nov;11(43):5722

Authors: Ma CD, Adamiak L, Miller DS, Wang X, Gianneschi NC, Abbott NL

Abstract
Complex signaling cascades, ubiquitous in living systems, inspire the pursuit of advanced materials that can amplify molecular-level interactions into multi-length scale signal transduction processes. N. C. Gianneschi, N. L. Abbott, and co-workers seek to combine stimuli-responsive polymers with liquid crystals (LC), which are ideally suited to dynamically report on biological events occurring at LC interfaces. On page 5747, they envision that the integration of these materials can lead to the generation of a range of macroscopic signals, each triggered by subtle molecular cues.

PMID: 26767912 [PubMed - in process]

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Liquid Crystals: Liquid Crystal Interfaces Programmed with Enzyme-Responsive Polymers and Surfactants (Small 43/2015).

Small. 2015 Nov;11(43):5722

Authors: Ma CD, Adamiak L, Miller DS, Wang X, Gianneschi NC, Abbott NL

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Blue-phase liquid crystal droplets.

Proc Natl Acad Sci U S A. 2015 Oct 27;112(43):13195-200

Authors: Martínez-González JA, Zhou Y, Rahimi M, Bukusoglu E, Abbott NL, de Pablo JJ

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Blue-phase liquid crystal droplets.

Proc Natl Acad Sci U S A. 2015 Oct 27;112(43):13195-200

Authors: Martínez-González JA, Zhou Y, Rahimi M, Bukusoglu E, Abbott NL, de Pablo JJ

Abstract
Blue phases of liquid crystals represent unique ordered states of matter in which arrays of defects are organized into striking patterns. Most studies of blue phases to date have focused on bulk properties. In this work, we present a systematic study of blue phases confined into spherical droplets. It is found that, in addition to the so-called blue phases I and II, several new morphologies arise under confinement, with a complexity that increases with the chirality of the medium and with a nature that can be altered by surface anchoring. Through a combination of simulations and experiments, it is also found that one can control the wavelength at which blue-phase droplets absorb light by manipulating either their size or the strength of the anchoring, thereby providing a liquid-state analog of nanoparticles, where dimensions are used to control absorbance or emission. The results presented in this work also suggest that there are conditions where confinement increases the range of stability of blue phases, thereby providing intriguing prospects for applications.

PMID: 26460039 [PubMed - in process]

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Blue-phase liquid crystal droplets.

Proc Natl Acad Sci U S A. 2015 Oct 27;112(43):13195-200

Authors: Martínez-González JA, Zhou Y, Rahimi M, Bukusoglu E, Abbott NL, de Pablo JJ

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Effects of confinement, surface-induced orientations and strain on dynamical behaviors of bacteria in thin liquid crystalline films.

Soft Matter. 2015 Sep 14;11(34):6821-31

Authors: Mushenheim PC, Trivedi RR, Roy SS, Arnold MS, Weibel DB, Abbott NL

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Effects of confinement, surface-induced orientations and strain on dynamical behaviors of bacteria in thin liquid crystalline films.

Soft Matter. 2015 Sep 14;11(34):6821-31

Authors: Mushenheim PC, Trivedi RR, Roy SS, Arnold MS, Weibel DB, Abbott NL

Abstract
We report on the organization and dynamics of bacteria (Proteus mirabilis) dispersed within lyotropic liquid crystal (LC) films confined by pairs of surfaces that induce homeotropic (perpendicular) or hybrid (homeotropic and parallel orientations at each surface) anchoring of the LC. By using motile vegetative bacteria (3 µm in length) and homeotropically aligned LC films with thicknesses that exceed the length of the rod-shaped cells, a key finding reported in this paper is that elastic torques generated by the LC are sufficiently large to overcome wall-induced hydrodynamic torques acting on the cells, thus leading to LC-guided bacterial motion near surfaces that orient LCs. This result extends to bacteria within LC films with hybrid anchoring, and leads to the observation that asymmetric strain within a hybrid aligned LC rectifies motions of motile cells. In contrast, when the LC film thickness is sufficiently small that confinement prevents alignment of the bacteria cells along a homeotropically aligned LC director (achieved using swarm cells of length 10-60 µm), the bacterial cells propel in directions orthogonal to the director, generating transient distortions in the LC that have striking "comet-like" optical signatures. In this limit, for hybrid LC films, we find LC elastic stresses deform the bodies of swarm cells into bent configurations that follow the LC director, thus unmasking a coupling between bacterial shape and LC strain. Overall, these results provide new insight into the influence of surface-oriented LCs on dynamical bacterial behaviors and hint at novel ways to manipulate bacteria using confined LC phases that are not possible in isotropic solutions.

PMID: 26224035 [PubMed - in process]

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Effects of confinement, surface-induced orientations and strain on dynamical behaviors of bacteria in thin liquid crystalline films.

Soft Matter. 2015 Sep 14;11(34):6821-31

Authors: Mushenheim PC, Trivedi RR, Roy SS, Arnold MS, Weibel DB, Abbott NL

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Bacterial transport of colloids in liquid crystalline environments.

Soft Matter. 2015 Sep 18;

Authors: Trivedi RR, Maeda R, Abbott NL, Spagnolie SE, Weibel DB

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Bacterial transport of colloids in liquid crystalline environments.

Soft Matter. 2015 Sep 18;

Authors: Trivedi RR, Maeda R, Abbott NL, Spagnolie SE, Weibel DB

Abstract
We describe the controlled transport and delivery of non-motile eukaryotic cells and polymer microparticles by swimming bacteria suspended in nematic liquid crystals. The bacteria push reversibly attached cargo in a stable, unidirectional path (or along a complex patterned director field) over exceptionally long distances. Numerical simulations and analytical predictions for swimming speeds provide a mechanistic insight into the hydrodynamics of the system. This study lays the foundation for using cargo-carrying bacteria in engineering applications and for understanding interspecies interactions in polymicrobial communities.

PMID: 26382153 [PubMed - as supplied by publisher]

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Bacterial transport of colloids in liquid crystalline environments.

Soft Matter. 2015 Sep 18;

Authors: Trivedi RR, Maeda R, Abbott NL, Spagnolie SE, Weibel DB

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Dynamic anchoring transitions at aqueous-liquid crystal interfaces induced by specific and non-specific binding of vesicles to proteins.

J Colloid Interface Sci. 2015 Jul 1;449:452-61

Authors: Tan LN, Abbott NL

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Dynamic anchoring transitions at aqueous-liquid crystal interfaces induced by specific and non-specific binding of vesicles to proteins.

J Colloid Interface Sci. 2015 Jul 1;449:452-61

Authors: Tan LN, Abbott NL

Abstract
This paper reports on the dynamics of continuous anchoring transitions at interfaces formed between nematic liquid crystals (LCs, 4'-pentyl-4-cyanobiphenyl (5CB)) and immiscible aqueous phases that are induced by either non-specific or specific interactions between phospholipid vesicles and proteins adsorbed at the LC interfaces. By analyzing the dynamic response of LCs to non-specific adsorption of lipids onto bovine serum albumin (BSA)-decorated LC interfaces, we provide evidence that the LC anchoring transitions are slower than diffusion-controlled accumulation of lipid at the interface, consistent with the hypothesis that the LC transition involves lateral reorganization of proteins and lipids at the interface. Significantly, optical measurements of the tilt angle of the LC as a function of the amount of lipid captured at the interface were found to be quantitatively consistent with theoretical predictions of LC anchoring directed by nanoscopic domains of molecules that cause planar (protein) and homeotropic (lipid) anchoring of the LC. Finally, specific binding interactions between the antibody-decorated LC interfaces and vesicles (through antibody-antigen recognition) greatly accelerated the continuous LC anchoring transitions, with dynamics that were measured to scale with the logarithm of the ligand composition of the vesicles (over four orders of magnitude). The latter dynamics were found to be strongly influenced by addition of synthetic surfactants, consistent with our proposal that the rate-limiting step underlying the response of the LC was the transfer of lipids from captured vesicles into the protein-decorated LC interface. Overall, the results presented in this paper provide quantitative insight into the origin of continuous anchoring transitions triggered by vesicles at protein-decorated LC interfaces and, more broadly, guidance for the design of stimuli-responsive LC systems.

PMID: 25731912 [PubMed - in process]

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Dynamic anchoring transitions at aqueous-liquid crystal interfaces induced by specific and non-specific binding of vesicles to proteins.

J Colloid Interface Sci. 2015 Jul 1;449:452-61

Authors: Tan LN, Abbott NL

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Hierarchical microstructures formed by bidisperse colloidal suspensions within colloid-in-liquid crystal gels.

ACS Appl Mater Interfaces. 2015 Apr 8;7(13):7153-62

Authors: Diestra-Cruz H, Bukusoglu E, Abbott NL, Acevedo A

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Hierarchical microstructures formed by bidisperse colloidal suspensions within colloid-in-liquid crystal gels.

ACS Appl Mater Interfaces. 2015 Apr 8;7(13):7153-62

Authors: Diestra-Cruz H, Bukusoglu E, Abbott NL, Acevedo A

Abstract
Past studies have reported that colloids of a single size dispersed in the isotropic phase of a mesogenic solvent can form colloid-rich networks (and gels) upon thermal quenching of the system across the isotropic-nematic phase boundary of the mesogens. Herein we report the observation and characterization of complex hierarchical microstructures that form when bidisperse colloidal suspensions of nanoparticles (NPs; iron oxide with diameters of 188 ± 20 nm or poly(methyl methacrylate) with diameters of 150 ± 15 nm) and microparticles (MPs; polystyrene with diameters of 2.77 ± 0.20 μm) are dispersed in the isotropic phase of 4-pentyl-4'-cyanobiphenyl (5CB) and thermally quenched. Specifically, we document microstructuring that results from three sequential phase separation processes that occur at distinct temperatures during stepwise cooling of the ternary mixture from its miscibility region. The first phase transition demixes the system into coexisting MP-rich and NP-rich phases; the second promotes formation of a particle network within the MP-rich phase; and the third, which coincides with the isotropic-to-nematic phase transition of 5CB, produces a second colloidal network within the NP-rich phase. We quantified the dynamics of each demixing process by using optical microscopy and Fourier transform image analysis to establish that the phase transitions occur through (i) surface-directed spinodal decomposition, (ii) spinodal decomposition, and (iii) nucleation and growth, respectively. Significantly, the observed series of phase transitions leads to a hierarchical organization of cellular microstructures not observed in colloid-in-liquid crystal gels formed from monodisperse colloids. The results of this study suggest new routes to the synthesis of colloidal materials with hierarchical microstructures that combine large surface areas and organized porosity with potential applications in catalysis, separations, chemical sensing, or tissue engineering.

PMID: 25706308 [PubMed - in process]

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Hierarchical microstructures formed by bidisperse colloidal suspensions within colloid-in-liquid crystal gels.

ACS Appl Mater Interfaces. 2015 Apr 8;7(13):7153-62

Authors: Diestra-Cruz H, Bukusoglu E, Abbott NL, Acevedo A

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Nanoparticle self-assembly at the interface of liquid crystal droplets.

Proc Natl Acad Sci U S A. 2015 Apr 13;

Authors: Rahimi M, Roberts TF, Armas-Pérez JC, Wang X, Bukusoglu E, Abbott NL, de Pablo JJ

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Nanoparticle self-assembly at the interface of liquid crystal droplets.

Proc Natl Acad Sci U S A. 2015 Apr 13;

Authors: Rahimi M, Roberts TF, Armas-Pérez JC, Wang X, Bukusoglu E, Abbott NL, de Pablo JJ

Abstract
Nanoparticles adsorbed at the interface of nematic liquid crystals are known to form ordered structures whose morphology depends on the orientation of the underlying nematic field. The origin of such structures is believed to result from an interplay between the liquid crystal orientation at the particles' surface, the orientation at the liquid crystal's air interface, and the bulk elasticity of the underlying liquid crystal. In this work, we consider nanoparticle assembly at the interface of nematic droplets. We present a systematic study of the free energy of nanoparticle-laden droplets in terms of experiments and a Landau-de Gennes formalism. The results of that study indicate that, even for conditions under which particles interact only weakly at flat interfaces, particles aggregate at the poles of bipolar droplets and assemble into robust, quantized arrangements that can be mapped onto hexagonal lattices. The contributions of elasticity and interfacial energy corresponding to different arrangements are used to explain the resulting morphologies, and the predictions of the model are shown to be consistent with experimental observations. The findings presented here suggest that particle-laden liquid crystal droplets could provide a unique and versatile route toward building blocks for hierarchical materials assembly.

PMID: 25870304 [PubMed - as supplied by publisher]

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Nanoparticle self-assembly at the interface of liquid crystal droplets.

Proc Natl Acad Sci U S A. 2015 Apr 13;

Authors: Rahimi M, Roberts TF, Armas-Pérez JC, Wang X, Bukusoglu E, Abbott NL, de Pablo JJ

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An evolved Mxe GyrA intein for enhanced production of fusion proteins.

ACS Chem Biol. 2015 Feb 20;10(2):527-38

Authors: Marshall CJ, Grosskopf VA, Moehling TJ, Tillotson BJ, Wiepz GJ, Abbott NL, Raines RT, Shusta EV

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An evolved Mxe GyrA intein for enhanced production of fusion proteins.

ACS Chem Biol. 2015 Feb 20;10(2):527-38

Authors: Marshall CJ, Grosskopf VA, Moehling TJ, Tillotson BJ, Wiepz GJ, Abbott NL, Raines RT, Shusta EV

Abstract
Expressing antibodies as fusions to the non-self-cleaving Mxe GyrA intein enables site-specific, carboxy-terminal chemical modification of the antibodies by expressed protein ligation (EPL). Bacterial antibody-intein fusion protein expression platforms typically yield insoluble inclusion bodies that require refolding to obtain active antibody-intein fusion proteins. Previously, we demonstrated that it was possible to employ yeast surface display to express properly folded single-chain antibody (scFv)-intein fusions, therefore permitting the direct small-scale chemical functionalization of scFvs. Here, directed evolution of the Mxe GyrA intein was performed to improve both the display and secretion levels of scFv-intein fusion proteins from yeast. The engineered intein was shown to increase the yeast display levels of eight different scFvs by up to 3-fold. Additionally, scFv- and green fluorescent protein (GFP)-intein fusion proteins can be secreted from yeast, and while fusion of the scFvs to the wild-type intein resulted in low expression levels, the engineered intein increased scFv-intein production levels by up to 30-fold. The secreted scFv- and GFP-intein fusion proteins retained their respective binding and fluorescent activities, and upon intein release, EPL resulted in carboxy-terminal azide functionalization of the target proteins. The azide-functionalized scFvs and GFP were subsequently employed in a copper-free, strain-promoted click reaction to site-specifically immobilize the proteins on surfaces, and it was demonstrated that the functionalized, immobilized scFvs retained their antigen binding specificity. Taken together, the evolved yeast intein platform provides a robust alternative to bacterial intein expression systems.

PMID: 25384269 [PubMed - in process]

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An evolved Mxe GyrA intein for enhanced production of fusion proteins.

ACS Chem Biol. 2015 Feb 20;10(2):527-38

Authors: Marshall CJ, Grosskopf VA, Moehling TJ, Tillotson BJ, Wiepz GJ, Abbott NL, Raines RT, Shusta EV

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Modulation of hydrophobic interactions by proximally immobilized ions.

Nature. 2015 Jan 15;517(7534):347-50

Authors: Ma CD, Wang C, Acevedo-Vélez C, Gellman SH, Abbott NL

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Modulation of hydrophobic interactions by proximally immobilized ions.

Nature. 2015 Jan 15;517(7534):347-50

Authors: Ma CD, Wang C, Acevedo-Vélez C, Gellman SH, Abbott NL

Abstract
The structure of water near non-polar molecular fragments or surfaces mediates the hydrophobic interactions that underlie a broad range of interfacial, colloidal and biophysical phenomena. Substantial progress over the past decade has improved our understanding of hydrophobic interactions in simple model systems, but most biologically and technologically relevant structures contain non-polar domains in close proximity to polar and charged functional groups. Theories and simulations exploring such nanometre-scale chemical heterogeneity find it can have an important effect, but the influence of this heterogeneity on hydrophobic interactions has not been tested experimentally. Here we report chemical force microscopy measurements on alkyl-functionalized surfaces that reveal a dramatic change in the surfaces' hydrophobic interaction strengths on co-immobilization of amine or guanidine groups. Protonation of amine groups doubles the strength of hydrophobic interactions, and guanidinium groups eliminate measurable hydrophobic interactions in all pH ranges investigated. We see these divergent effects of proximally immobilized cations also in single-molecule measurements on conformationally stable β-peptides with non-polar subunits located one nanometre from either amine- or guanidine-bearing subunits. Our results demonstrate the importance of nanometre-scale chemical heterogeneity, with hydrophobicity not an intrinsic property of any given non-polar domain but strongly modulated by functional groups located as far away as one nanometre. The judicious placing of charged groups near hydrophobic domains thus provides a strategy for tuning hydrophobic driving forces to optimize molecular recognition or self-assembly processes.

PMID: 25592540 [PubMed - indexed for MEDLINE]

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Modulation of hydrophobic interactions by proximally immobilized ions.

Nature. 2015 Jan 15;517(7534):347-50

Authors: Ma CD, Wang C, Acevedo-Vélez C, Gellman SH, Abbott NL

2014

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Surfactant-induced ordering and wetting transitions of droplets of thermotropic liquid crystals "caged" inside partially filled polymeric capsules.

Langmuir. 2014 Dec 16;30(49):14944-53

Authors: Carlton RJ, Zayas-Gonzalez YM, Manna U, Lynn DM, Abbott NL

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Surfactant-induced ordering and wetting transitions of droplets of thermotropic liquid crystals "caged" inside partially filled polymeric capsules.

Langmuir. 2014 Dec 16;30(49):14944-53

Authors: Carlton RJ, Zayas-Gonzalez YM, Manna U, Lynn DM, Abbott NL

Abstract
We report a study of the wetting and ordering of thermotropic liquid crystal (LC) droplets that are trapped (or "caged") within micrometer-sized cationic polymeric microcapsules dispersed in aqueous solutions of surfactants. When they were initially dispersed in water, we observed caged, nearly spherical droplets of E7, a nematic LC mixture, to occupy ∼40% of the interior volume of the polymeric capsules [diameter of 6.7 ± 0.3 μm, formed via covalent layer-by-layer assembly of branched polyethylenimine and poly(2-vinyl-4,4-dimethylazlactone)] and to contact the interior surface of the capsule wall at an angle of ∼157 ± 11°. The internal ordering of LC within the droplets corresponded to the so-called bipolar configuration (distorted by contact with the capsule walls). While the effects of dodecyltrimethylammonium bromide (DTAB) and sodium dodecyl sulfate (SDS) on the internal ordering of "free" LC droplets are similar, we observed the two surfactants to trigger strikingly different wetting and configurational transitions when LC droplets were caged within polymeric capsules. Specifically, upon addition of SDS to the aqueous phase, we observed the contact angles (θ) of caged LC on the interior surface of the capsule to decrease, resulting in a progression of complex droplet shapes, including lenses (θ ≈ 130 ± 10°), hemispheres (θ ≈ 89 ± 5°), and concave hemispheres (θ < 85°). The wetting transitions induced by SDS also resulted in changes in the internal ordering of the LC to yield states topologically equivalent to axial and radial configurations. Although topologically equivalent to free droplets, the contributions that surface anchoring, LC elasticity, and topological defects make to the free energy of caged LC droplets differ from those of free droplets. Overall, these results and others reported herein lead us to conclude that caged LC droplets offer a platform for new designs of LC-droplet-based responsive soft matter that cannot be realized in dispersions of free droplets.

PMID: 24911044 [PubMed - in process]

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Surfactant-induced ordering and wetting transitions of droplets of thermotropic liquid crystals "caged" inside partially filled polymeric capsules.

Langmuir. 2014 Dec 16;30(49):14944-53

Authors: Carlton RJ, Zayas-Gonzalez YM, Manna U, Lynn DM, Abbott NL

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Organized assemblies of colloids formed at the poles of micrometer-sized droplets of liquid crystal.

Soft Matter. 2014 Nov 28;10(44):8821-8

Authors: Wang X, Miller DS, de Pablo JJ, Abbott NL

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Organized assemblies of colloids formed at the poles of micrometer-sized droplets of liquid crystal.

Soft Matter. 2014 Nov 28;10(44):8821-8

Authors: Wang X, Miller DS, de Pablo JJ, Abbott NL

Abstract
We report on the formation of organized assemblies of 1 μm-in-diameter colloids (polystyrene (PS)) at the poles of water-dispersed droplets (diameters 7-20 μm) of nematic liquid crystal (LC). For 4-cyano-4'-pentylbiphenyl droplets decorated with two to five PS colloids, we found 32 distinct arrangements of the colloids to form at the boojums of bipolar droplet configurations. Significantly, all but one of these configurations (a ring comprised of five PS colloids) could be mapped onto a local (non-close packed) hexagonal lattice. To provide insight into the origin of the hexagonal lattice, we investigated planar aqueous-LC interfaces, and found that organized assemblies of PS colloids did not form at these interfaces. Experiments involving the addition of salts revealed that a repulsive interaction of electrostatic origin prevented formation of assemblies at planar interfaces, and that regions of high splay near the poles of the LC droplets generated cohesive interactions between colloids that could overcome the repulsion. Support for this interpretation was obtained from a model that included (i) a long-range attraction between adsorbed colloids and the boojum due to the increasing rate of strain (splay) of LC near the boojum (splay attraction), (ii) an attractive inter-colloid interaction that reflects the quadrupolar symmetry of the strain in the LC around the colloids, and (iii) electrostatic repulsion between colloids. The model predicts that electrostatic repulsion between colloids can lead to a ∼1000kBT energy barrier at planar interfaces of LC films, and that the repulsive interaction can be overcome by splay attraction of the colloids to the boojums of the LC droplets. Overall, the results reported in this paper advance our understanding of the directed assembly of colloids at interfaces of LC droplets.

PMID: 25284139 [PubMed - in process]

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Organized assemblies of colloids formed at the poles of micrometer-sized droplets of liquid crystal.

Soft Matter. 2014 Nov 28;10(44):8821-8

Authors: Wang X, Miller DS, de Pablo JJ, Abbott NL

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Hierarchical organization in liquid crystal-in-liquid crystal emulsions.

Soft Matter. 2014 Nov 21;10(43):8627-34

Authors: Mushenheim PC, Abbott NL

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Hierarchical organization in liquid crystal-in-liquid crystal emulsions.

Soft Matter. 2014 Nov 21;10(43):8627-34

Authors: Mushenheim PC, Abbott NL

Abstract
We report the formation and characterization of hierarchical ordering in systems comprised of micrometer-sized droplets of thermotropic nematic liquid crystals (LCs) dispersed in continuous nematic phases of a lyotropic chromonic LC (disodium cromoglycate (DSCG)). Significantly, we find the orientations of the two LC phases to be coupled, with nematic droplets of 4'-pentyl-4-cyanobiphenyl (5CB) exhibiting a bipolar configuration with an axis of symmetry aligned orthogonal to the far-field director of the DSCG phase. We determine that this coupling of orientations does not result from either anisometric LC droplet shape or interfacial ionic phenomena but rather is consistent with the influence of van der Waals interactions that arise from the anisotropic polarizabilities of nematic 5CB (Δn = +0.18) and DSCG (Δn = -0.02) phases. We also find that it is possible to rotate and uniformly align the nematic droplets by using a weak magnetic field (B ∼ 0.3 T). An analysis of the dynamics of relaxation of the orientations of the 5CB droplets following removal of the magnetic field reveals the DSCG and 5CB droplets to be coupled by energies of ∼10(4) kT, consistent with a simple theoretical estimate of the influence of anisotropic van der Waals interactions. We also observed the nematic 5CB droplets to form dimers and larger assemblies mediated by the elasticity of the nematic DSCG. Overall, these results reveal that LC-in-LC emulsions define a new class of hierarchically ordered soft matter in which both thermotropic and lyotropic LCs are coupled in their ordering.

PMID: 25278032 [PubMed - in process]

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Hierarchical organization in liquid crystal-in-liquid crystal emulsions.

Soft Matter. 2014 Nov 21;10(43):8627-34

Authors: Mushenheim PC, Abbott NL

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Reversible Switching of Liquid Crystalline Order Permits Synthesis of Homogeneous Populations of Dipolar Patchy Microparticles.

Adv Funct Mater. 2014 Oct 22;24(39):6219-6226

Authors: Wang X, Miller DS, de Pablo JJ, Abbott NL

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Reversible Switching of Liquid Crystalline Order Permits Synthesis of Homogeneous Populations of Dipolar Patchy Microparticles.

Adv Funct Mater. 2014 Oct 22;24(39):6219-6226

Authors: Wang X, Miller DS, de Pablo JJ, Abbott NL

Abstract
The spontaneous positioning of colloids on the surfaces of micrometer-sized liquid crystalline droplets and their subsequent polymerization offers the basis of a general and facile method for the synthesis of patchy microparticles. The existence of multiple local energetic minima, however, can generate kinetic traps for colloids on the surfaces of the liquid crystal (LC) droplets and result in heterogeneous populations of patchy microparticles. To address this issue, here we demonstrate that adsorbate-driven switching of the internal configurations of LC droplets can be used to sweep colloids to a single location on the LC droplet surfaces, thus resulting in the synthesis of homogeneous populations of patchy microparticles. The surface-driven switching of the LC can be triggered by addition of surfactant or salts, and permits the synthesis of dipolar microparticles as well as "Janus-like" microparticles. By using magnetic colloids, we illustrate the utility of the approach by synthesizing magnetically-responsive patchy microdroplets of LC with either dipolar or quadrupolar symmetry that exhibit distinct optical responses upon application of an external magnetic field.

PMID: 25484850 [PubMed - as supplied by publisher]

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Reversible Switching of Liquid Crystalline Order Permits Synthesis of Homogeneous Populations of Dipolar Patchy Microparticles.

Adv Funct Mater. 2014 Oct 22;24(39):6219-6226

Authors: Wang X, Miller DS, de Pablo JJ, Abbott NL

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Helical versus all-trans conformations of oligo(ethylene glycol)-terminated alkanethiol self-assembled monolayers.

Langmuir. 2014 Sep 2;30(34):10263-9

Authors: Johnson PS, Goel M, Abbott NL, Himpsel FJ

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Helical versus all-trans conformations of oligo(ethylene glycol)-terminated alkanethiol self-assembled monolayers.

Langmuir. 2014 Sep 2;30(34):10263-9

Authors: Johnson PS, Goel M, Abbott NL, Himpsel FJ

Abstract
The complex mixture of conformational states exhibited by oligo(ethylene glycol)-terminated alkanethiols on Ag and Au surfaces is explored by polarization-dependent X-ray absorption spectroscopy. Three self-assembled monolayers (SAMs) with known helical or all-trans conformations are used as references to characterize a SAM with unknown conformations. This case study is used as a prototype for developing a systematic framework to extract the conformations of SAMs from the polarization dependence of several orbitals. In the case at hand, these are associated with the C-H/Rydberg bonds of the alkane, the C-H/Rydberg bonds of ethylene glycol, and the C-C bonds of the backbone. The C-H/Rydberg orbitals of the alkane and ethylene glycol are distinguished via the chemical shift of the corresponding C 1s core levels.

PMID: 25133805 [PubMed - indexed for MEDLINE]

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Helical versus all-trans conformations of oligo(ethylene glycol)-terminated alkanethiol self-assembled monolayers.

Langmuir. 2014 Sep 2;30(34):10263-9

Authors: Johnson PS, Goel M, Abbott NL, Himpsel FJ

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Using liquid crystals to reveal how mechanical anisotropy changes interfacial behaviors of motile bacteria.

Biophys J. 2014 Jul 1;107(1):255-65

Authors: Mushenheim PC, Trivedi RR, Weibel DB, Abbott NL

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Using liquid crystals to reveal how mechanical anisotropy changes interfacial behaviors of motile bacteria.

Biophys J. 2014 Jul 1;107(1):255-65

Authors: Mushenheim PC, Trivedi RR, Weibel DB, Abbott NL

Abstract
Bacteria often inhabit and exhibit distinct dynamical behaviors at interfaces, but the physical mechanisms by which interfaces cue bacteria are still poorly understood. In this work, we use interfaces formed between coexisting isotropic and liquid crystal (LC) phases to provide insight into how mechanical anisotropy and defects in LC ordering influence fundamental bacterial behaviors. Specifically, we measure the anisotropic elasticity of the LC to change fundamental behaviors of motile, rod-shaped Proteus mirabilis cells (3 μm in length) adsorbed to the LC interface, including the orientation, speed, and direction of motion of the cells (the cells follow the director of the LC at the interface), transient multicellular self-association, and dynamical escape from the interface. In this latter context, we measure motile bacteria to escape from the interfaces preferentially into the isotropic phase, consistent with the predicted effects of an elastic penalty associated with strain of the LC about the bacteria when escape occurs into the nematic phase. We also observe boojums (surface topological defects) present at the interfaces of droplets of nematic LC (tactoids) to play a central role in mediating the escape of motile bacteria from the LC interface. Whereas the bacteria escape the interface of nematic droplets via a mechanism that involved nematic director-guided motion through one of the two boojums, for isotropic droplets in a continuous nematic phase, the elasticity of the LC generally prevented single bacteria from escaping. Instead, assemblies of bacteria piled up at boojums and escape occurred through a cooperative, multicellular phenomenon. Overall, our studies show that the dynamical behaviors of motile bacteria at anisotropic LC interfaces can be understood within a conceptual framework that reflects the interplay of LC elasticity, surface-induced order, and topological defects.

PMID: 24988359 [PubMed - in process]

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Using liquid crystals to reveal how mechanical anisotropy changes interfacial behaviors of motile bacteria.

Biophys J. 2014 Jul 1;107(1):255-65

Authors: Mushenheim PC, Trivedi RR, Weibel DB, Abbott NL

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Liquid crystals anchored on mixed monolayers of chiral versus achiral molecules: continuous change in orientation as a function of enantiomeric excess.

Angew Chem Int Ed Engl. 2014 Jul 28;53(31):8079-83

Authors: Bai Y, Abbasi R, Wang C, Abbott NL

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Liquid crystals anchored on mixed monolayers of chiral versus achiral molecules: continuous change in orientation as a function of enantiomeric excess.

Angew Chem Int Ed Engl. 2014 Jul 28;53(31):8079-83

Authors: Bai Y, Abbasi R, Wang C, Abbott NL

Abstract
The orientations of liquid crystals (LCs) anchored on monolayers formed from mixtures of chiral versus achiral molecules were compared. Changes in the enantiomeric excess of mixed monolayers of chiral dipeptides gave rise to continuous changes in the orientations of nematic LCs, allowing arbitrary tuning of the azimuthal orientations of LCs over a range of ≈100°. In contrast, the same LCs exhibited discontinuous changes in orientation on surfaces presenting mixtures of achiral molecules. These striking differences in the anchoring of LCs on surfaces presenting chiral versus achiral molecules provide insights into the molecular origins of ordering transitions of LCs, and provide new principles based on chiral monolayers for the rational design of surfaces that permit continuous tuning of the orientations of LCs.

PMID: 24841757 [PubMed - in process]

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Liquid crystals anchored on mixed monolayers of chiral versus achiral molecules: continuous change in orientation as a function of enantiomeric excess.

Angew Chem Int Ed Engl. 2014 Jul 28;53(31):8079-83

Authors: Bai Y, Abbasi R, Wang C, Abbott NL

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Comparison of the influence of humidity and D-mannitol on the organization of tetraethylene glycol-terminated self-assembled monolayers and immobilized antimicrobial peptides.

Langmuir. 2014 Jun 24;30(24):7143-51

Authors: Goel M, Marsh EN, Chen Z, Abbott NL

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Comparison of the influence of humidity and D-mannitol on the organization of tetraethylene glycol-terminated self-assembled monolayers and immobilized antimicrobial peptides.

Langmuir. 2014 Jun 24;30(24):7143-51

Authors: Goel M, Marsh EN, Chen Z, Abbott NL

Abstract
We report the use of polarization-modulation infrared reflection-absorption spectroscopy (PM-IRRAS) to characterize the effects of relative humidity (RH) and d-mannitol on the conformations of tetraethylene glycol (EG4)-terminated self-assembled monolayers (SAMs) and immobilized antimicrobial peptides (Cecropin P1 and a hybrid of Cecropin A (1-8) and Melittin (1-18)). These results are used to assess the extent to which d-mannitol can substitute for water in promoting conformational states of the SAMs and oligopeptides similar to those induced by hydration. Our measurements reveal a red shift of the COC asymmetric stretching vibration of the EG4-terminated SAMs with increasing humidity, consistent with a transition from a mixed all-trans/helical (7/2 helix) conformation at 0% RH to a predominantly helical conformation at 90% RH. Significantly, under dry conditions, a thin (2 nm in thickness) overlayer of d-mannitol generated the COC spectroscopic signature of the EG4-terminated SAM measured at high humidity. Comparisons of the effects of humidity and d-mannitol on the secondary structure of the two oligopeptides also revealed both to cause the amide I peak positions, which were measured in dry air (and without d-mannitol) to correspond to α-helical conformations, to undergo red-shifts. The magnitudes of the red-shifts, however, were more pronounced for dry d-mannitol than for high RH, with Cecropin P1 and the hybrid peptide exhibiting amide I peak positions under d-mannitol consistent with bulk aqueous solution secondary structures (random and β-sheet, respectively). These results are discussed in the context of prior reports of the tendency of d-mannitol to form glassy states in the absence of water. Overall, the results presented in this paper support the hypothesis that d-mannitol can substitute, in at least some ways, for the influence of water on the conformational states of biologically relevant molecules at interfaces. The results provide guidance for the design of interfaces for water-free biologics.

PMID: 24854220 [PubMed - indexed for MEDLINE]

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Comparison of the influence of humidity and D-mannitol on the organization of tetraethylene glycol-terminated self-assembled monolayers and immobilized antimicrobial peptides.

Langmuir. 2014 Jun 24;30(24):7143-51

Authors: Goel M, Marsh EN, Chen Z, Abbott NL

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Liquid crystal droplet-based amplification of microvesicles that are shed by mammalian cells.

Analyst. 2014 May 21;139(10):2386-96

Authors: Tan LN, Wiepz GJ, Miller DS, Shusta EV, Abbott NL

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Liquid crystal droplet-based amplification of microvesicles that are shed by mammalian cells.

Analyst. 2014 May 21;139(10):2386-96

Authors: Tan LN, Wiepz GJ, Miller DS, Shusta EV, Abbott NL

Abstract
Membrane-derived microvesicles (MVs) shed by cells are being investigated for their role in intercellular communication and as potential biomarkers of disease, but facile and sensitive methods for their analysis do not exist. Here we demonstrate new principles for analysis of MVs that use micrometer-sized droplets of liquid crystals (LCs) to amplify MVs that are selectively captured via antibody-mediated interactions. The influence of the MVs on the micrometer-sized LC droplets is shown to be readily quantified via use of flow cytometry. The methodology was developed using MVs shed by epidermoid carcinoma A431 cells that contain epidermal growth factor receptor (EGFR) as an important and representative example of MVs containing signaling proteins that play a central role in cancer. The LC droplets were found to be sensitive to 10(6) MVs containing EGFR (relative to controls using isotype control antibody) and to possess a dynamic range of response across several orders of magnitude. Because the 100 nm-sized MVs captured via EGFR generate an optical response in the micrometer-sized LC droplets that can be readily detected by flow cytometry in light scattering mode, the approach possesses significant advantages over direct detection of MVs by flow cytometry. The LC droplets are also substantially more sensitive than techniques such as immunoblotting because the lipid-component of the MVs serves to amplify the antibody-mediated capture of the target proteins in the MVs. Other merits of the approach are defined and discussed in the paper.

PMID: 24667742 [PubMed - in process]

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Liquid crystal droplet-based amplification of microvesicles that are shed by mammalian cells.

Analyst. 2014 May 21;139(10):2386-96

Authors: Tan LN, Wiepz GJ, Miller DS, Shusta EV, Abbott NL

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Influence of the Phase State of Self-Assembling Redox Mediators on their Electrochemical Activity.

AIChE J. 2014 Apr 1;60(4):1381-1392

Authors: Muller JP, Aytar BS, Kondo Y, Lynn DM, Abbott NL

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Influence of the Phase State of Self-Assembling Redox Mediators on their Electrochemical Activity.

AIChE J. 2014 Apr 1;60(4):1381-1392

Authors: Muller JP, Aytar BS, Kondo Y, Lynn DM, Abbott NL

Abstract
Self-assembling redox mediators have the potential to be broadly useful in a range of interfacial electrochemical contexts because the oxidation state and state of assembly of the mediator are closely coupled. In this paper, we report an investigation of the self-assembly of single- and double-tailed ferrocenyl amphiphiles (FTMA and BFDMA, respectively) at the surfaces of Pt electrodes and the impact of the dynamic assembled state of the amphiphiles on their rate of oxidation. We conclude that frozen aggregates of BFDMA adsorb to the surfaces of the Pt electrodes, and that slow dynamics of reorganization BFDMA within these aggregates limits the rate of electrooxidation of BFDMA. In contrast, FTMA, while forming assemblies on the surfaces of Pt electrodes, is characterized by fast reorganization dynamics and a corresponding rate of oxidation that is an order of magnitude greater than BFDMA.

PMID: 24882870 [PubMed - as supplied by publisher]

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Influence of the Phase State of Self-Assembling Redox Mediators on their Electrochemical Activity.

AIChE J. 2014 Apr 1;60(4):1381-1392

Authors: Muller JP, Aytar BS, Kondo Y, Lynn DM, Abbott NL

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Colloid-in-liquid crystal gels formed via spinodal decomposition.

Soft Matter. 2014 Mar 14;10(10):1602-10

Authors: Bukusoglu E, Pal SK, de Pablo JJ, Abbott NL

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Colloid-in-liquid crystal gels formed via spinodal decomposition.

Soft Matter. 2014 Mar 14;10(10):1602-10

Authors: Bukusoglu E, Pal SK, de Pablo JJ, Abbott NL

Abstract
We report that colloid-in-liquid crystal (CLC) gels can be formed via a two-step process that involves spinodal decomposition of a dispersion of colloidal particles in an isotropic phase of mesogens followed by nucleation of nematic domains within the colloidal network defined by the spinodal process. This pathway contrasts to previously reported routes leading to the formation of CLC gels, which have involved entanglement of defects or exclusion of particles from growing nematic domains. The new route provides the basis of simple design rules that enable control of the microstructure and dynamic mechanical properties of the gels.

PMID: 24651134 [PubMed - indexed for MEDLINE]

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Colloid-in-liquid crystal gels formed via spinodal decomposition.

Soft Matter. 2014 Mar 14;10(10):1602-10

Authors: Bukusoglu E, Pal SK, de Pablo JJ, Abbott NL

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Measuring liquid crystal elastic constants with free energy perturbations.

Soft Matter. 2014 Feb 14;10(6):882-93

Authors: Joshi AA, Whitmer JK, Guzmán O, Abbott NL, de Pablo JJ

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Measuring liquid crystal elastic constants with free energy perturbations.

Soft Matter. 2014 Feb 14;10(6):882-93

Authors: Joshi AA, Whitmer JK, Guzmán O, Abbott NL, de Pablo JJ

Abstract
A first principles method is proposed to calculate the Frank elastic constants of nematic liquid crystals. These include the constants corresponding to standard splay, twist and bend deformations, and an often-ignored surface-like contribution known as saddle-splay. The proposed approach is implemented on the widely studied Gay-Berne (3, 5, 2, 1) model [J. G. Gay and B. J. Berne, J. Chem. Phys., 1981, 74, 3316], and the effects of temperature and system size on the elastic constants are examined in the nematic phase. The results of simulations for splay, twist, and bend elastic constants are consistent with those from previous literature reports. The method is subsequently applied to the saddle-splay elastic constant k24 which is found to exist at the limits of the Ericksen inequalities governing positive definite free energy. Finally, extensions of the method are discussed that present a new paradigm for in silico measurements of elastic constants.

PMID: 24837037 [PubMed - indexed for MEDLINE]

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Measuring liquid crystal elastic constants with free energy perturbations.

Soft Matter. 2014 Feb 14;10(6):882-93

Authors: Joshi AA, Whitmer JK, Guzmán O, Abbott NL, de Pablo JJ

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Adsorbate-induced anchoring transitions of liquid crystals on surfaces presenting metal salts with mixed anions.

ACS Appl Mater Interfaces. 2014 Feb 26;6(4):2362-9

Authors: Hunter JT, Abbott NL

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Adsorbate-induced anchoring transitions of liquid crystals on surfaces presenting metal salts with mixed anions.

ACS Appl Mater Interfaces. 2014 Feb 26;6(4):2362-9

Authors: Hunter JT, Abbott NL

Abstract
We report that metal salts composed of mixtures of anions of differing coordination strength can be used to increase the sensitivity and selectivity of adsorbate-induced anchoring transitions of liquid crystals (LCs) supported on surfaces decorated with the metal salts. Specifically, the dynamics of anchoring transitions triggered by the adsorbate dimethyl methylphosphonate (DMMP) on surfaces of aluminum(III) salts were analyzed within the framework of a model for mass transport to reveal that the sensitivity of a nitrile-containing nematic LC to DMMP increased from 250 to 25 ppb when the composition of the (counter) anion was changed from 100% perchlorate to 90% nitrate and 10% perchlorate (by mole percent). To provide insight into these observations, polarization-modulation infrared reflectance-absorbance spectroscopy (PM-IRRAS) was used to show that the intensity of the absorption band in the IR spectrum corresponding to the coordinated state of the nitrile group (but not the position of the peak) decreased with the increase in the mole fraction of the strongly coordinating anion (nitrate) in the anion mixture, thus suggesting that the addition of the strongly coordinating anion decreased the number of coordination interactions (per unit area of the interface) but not the strength of the individual coordination interactions between the metal cation and the LC. We also measured the incorporation of the nitrate anion into the metal salt to decrease the effect of humidity on the dynamic response of the LC to DMMP, a result that is consistent with weaker interactions between the nitrate anion and water as compared to the perchlorate anion and water. Finally, the bidentate anion acetylacetonate was measured to cause a similar increase in sensitivity to DMMP when mixed with perchlorate in a 1:1 ratio (the resulting sensitivity of the system to DMMP was 100 ppb). Overall, these results suggest that tailoring the identity of the anion represents a general and facile approach for tuning the orientational response of LCs supported on metal salts to targeted analytes.

PMID: 24369715 [PubMed - indexed for MEDLINE]

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Adsorbate-induced anchoring transitions of liquid crystals on surfaces presenting metal salts with mixed anions.

ACS Appl Mater Interfaces. 2014 Feb 26;6(4):2362-9

Authors: Hunter JT, Abbott NL

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Design of Functional Materials based on Liquid Crystalline Droplets.

Chem Mater. 2014 Jan 14;26(1):496-506

Authors: Miller DS, Wang X, Abbott NL

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Design of Functional Materials based on Liquid Crystalline Droplets.

Chem Mater. 2014 Jan 14;26(1):496-506

Authors: Miller DS, Wang X, Abbott NL

Abstract
This brief perspective focuses on recent advances in the design of functional soft materials that are based on confinement of low molecular weight liquid crystals (LCs) within micrometer-sized droplets. While the ordering of LCs within micrometer-sized domains has been explored extensively in polymer-dispersed LC materials, recent studies performed with LC domains with precisely defined size and interfacial chemistry have unmasked observations of confinement-induced ordering of LCs that do not follow previously reported theoretical predictions. These new findings, which are enabled in part by advances in the preparation of LCs encapsulated in polymeric shells, are opening up new opportunities for the design of soft responsive materials based on surface-induced ordering transitions. These materials are also providing new insights into the self-assembly of biomolecular and colloidal species at defects formed by LCs confined to micrometer-sized domains. The studies presented in this perspective serve additionally to highlight gaps in knowledge regarding the ordering of LCs in confined systems.

PMID: 24882944 [PubMed - as supplied by publisher]

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Design of Functional Materials based on Liquid Crystalline Droplets.

Chem Mater. 2014 Jan 14;26(1):496-506

Authors: Miller DS, Wang X, Abbott NL

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Dynamic self-assembly of motile bacteria in liquid crystals.

Soft Matter. 2014 Jan 7;10(1):88-95

Authors: Mushenheim PC, Trivedi RR, Tuson HH, Weibel DB, Abbott NL

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Dynamic self-assembly of motile bacteria in liquid crystals.

Soft Matter. 2014 Jan 7;10(1):88-95

Authors: Mushenheim PC, Trivedi RR, Tuson HH, Weibel DB, Abbott NL

Abstract
This paper reports an investigation of dynamical behaviors of motile rod-shaped bacteria within anisotropic viscoelastic environments defined by lyotropic liquid crystals (LCs). In contrast to passive microparticles (including non-motile bacteria) that associate irreversibly in LCs via elasticity-mediated forces, we report that motile Proteus mirabilis bacteria form dynamic and reversible multi-cellular assemblies when dispersed in a lyotropic LC. By measuring the velocity of the bacteria through the LC (8.8 ± 0.2 μm s(-1)) and by characterizing the ordering of the LC about the rod-shaped bacteria (tangential anchoring), we conclude that the reversibility of the inter-bacterial interaction emerges from the interplay of forces generated by the flagella of the bacteria and the elasticity of the LC, both of which are comparable in magnitude (tens of pN) for motile Proteus mirabilis cells. We also measured the dissociation process, which occurs in a direction determined by the LC, to bias the size distribution of multi-cellular bacterial complexes in a population of motile Proteus mirabilis relative to a population of non-motile cells. Overall, these observations and others reported in this paper provide insight into the fundamental dynamic behaviors of bacteria in complex anisotropic environments and suggest that motile bacteria in LCs are an exciting model system for exploration of principles for the design of active materials.

PMID: 24652584 [PubMed - indexed for MEDLINE]

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Dynamic self-assembly of motile bacteria in liquid crystals.

Soft Matter. 2014 Jan 7;10(1):88-95

Authors: Mushenheim PC, Trivedi RR, Tuson HH, Weibel DB, Abbott NL

2013

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Liquid crystal chemical sensors that cells can wear.

Angew Chem Int Ed Engl. 2013 Dec 23;52(52):14011-5

Authors: Manna U, Zayas-Gonzalez YM, Carlton RJ, Caruso F, Abbott NL, Lynn DM

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Liquid crystal chemical sensors that cells can wear.

Angew Chem Int Ed Engl. 2013 Dec 23;52(52):14011-5

Authors: Manna U, Zayas-Gonzalez YM, Carlton RJ, Caruso F, Abbott NL, Lynn DM

PMID: 24288229 [PubMed - indexed for MEDLINE]

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Liquid crystal chemical sensors that cells can wear.

Angew Chem Int Ed Engl. 2013 Dec 23;52(52):14011-5

Authors: Manna U, Zayas-Gonzalez YM, Carlton RJ, Caruso F, Abbott NL, Lynn DM

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Applied physics. Colloid science collides with liquid crystals.

Science. 2013 Dec 13;342(6164):1326-7

Authors: Abbott NL

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Applied physics. Colloid science collides with liquid crystals.

Science. 2013 Dec 13;342(6164):1326-7

Authors: Abbott NL

PMID: 24337282 [PubMed]

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Applied physics. Colloid science collides with liquid crystals.

Science. 2013 Dec 13;342(6164):1326-7

Authors: Abbott NL

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Nematic-field-driven positioning of particles in liquid crystal droplets.

Phys Rev Lett. 2013 Nov 27;111(22):227801

Authors: Whitmer JK, Wang X, Mondiot F, Miller DS, Abbott NL, de Pablo JJ

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Nematic-field-driven positioning of particles in liquid crystal droplets.

Phys Rev Lett. 2013 Nov 27;111(22):227801

Authors: Whitmer JK, Wang X, Mondiot F, Miller DS, Abbott NL, de Pablo JJ

Abstract
Common nematic oils, such as 5CB, experience planar anchoring at aqueous interfaces. When these oils are emulsified, this anchoring preference and the resulting topological constraints lead to the formation of droplets that exhibit one or two point defects within the nematic phase. Here, we explore the interactions of adsorbed particles at the aqueous interface through a combination of experiments and coarse-grained modeling, and demonstrate that surface-active particles, driven by elastic forces in the droplet, readily localize to these defect regions in a programmable manner. When droplets include two nanoparticles, these preferentially segregate to the two poles, thereby forming highly regular dipolar structures that could serve for hierarchical assembly of functional structures. Addition of sufficient concentrations of surfactant changes the interior morphology of the droplet, but pins defects to the interface, resulting in aggregation of the two particles.

PMID: 24329470 [PubMed]

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Nematic-field-driven positioning of particles in liquid crystal droplets.

Phys Rev Lett. 2013 Nov 27;111(22):227801

Authors: Whitmer JK, Wang X, Mondiot F, Miller DS, Abbott NL, de Pablo JJ

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Analysis of the internal configurations of droplets of liquid crystal using flow cytometry.

Anal Chem. 2013 Nov 5;85(21):10296-303

Authors: Miller DS, Wang X, Buchen J, Lavrentovich OD, Abbott NL

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Analysis of the internal configurations of droplets of liquid crystal using flow cytometry.

Anal Chem. 2013 Nov 5;85(21):10296-303

Authors: Miller DS, Wang X, Buchen J, Lavrentovich OD, Abbott NL

Abstract
We report the use of flow cytometry to identify the internal ordering (director configurations) of micrometer-sized droplets of thermotropic liquid crystals (LCs) dispersed in aqueous solutions of adsorbates (surfactants and phospholipids). We reveal that changes in the configurations of the LC droplets induced by the adsorbates generate distinct changes in light scattering plots (side versus forward scattering). Specifically, when compared to bipolar droplets, radial droplets generate a narrower distribution of side scattering intensities (SSC, large angle light scattering) for a given intensity of forward scattering (FSC, small angle light scattering). This difference is shown to arise from the rotational symmetry of a radial LC droplet which is absent for the bipolar configuration of the LC droplet. In addition, the scatter plots for radial droplets possess a characteristic "S-shape", with two or more SSC intensities observed for each intensity of FSC. The origin of the experimentally observed S-shape is investigated via calculation of form factors and established to be due to size-dependent interference effects that differ for the forward and side scattered light. Finally, by analyzing emulsions composed of mixtures of bipolar and radial droplets at rates of up to 10,000 droplets per second, we demonstrate that flow cytometry permits precise determination of the percentage of radial droplets within the mixture with a coefficient of determination of 0.98 (as validated by optical microscopy). Overall, the results presented in this paper demonstrate that flow cytometry provides a promising approach for high throughput quantification of the internal configurations of LC emulsion microdroplets. Because large numbers of droplets can be characterized, it enables statistically robust analyses of LC droplets. The methodology also appears promising for quantification of chemical and biological assays based on adsorbate-induced ordering transitions within LC droplets.

PMID: 24079265 [PubMed - indexed for MEDLINE]

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Analysis of the internal configurations of droplets of liquid crystal using flow cytometry.

Anal Chem. 2013 Nov 5;85(21):10296-303

Authors: Miller DS, Wang X, Buchen J, Lavrentovich OD, Abbott NL

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Spatial control of cell transfection using soluble or solid-phase redox agents and a redox-active ferrocenyl lipid.

ACS Appl Mater Interfaces. 2013 Sep 11;5(17):8283-8

Authors: Aytar BS, Muller JP, Kondo Y, Abbott NL, Lynn DM

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Spatial control of cell transfection using soluble or solid-phase redox agents and a redox-active ferrocenyl lipid.

ACS Appl Mater Interfaces. 2013 Sep 11;5(17):8283-8

Authors: Aytar BS, Muller JP, Kondo Y, Abbott NL, Lynn DM

Abstract
We report principles for active, user-defined control over the locations and timing with which DNA is expressed in cells. Our approach exploits unique properties of a ferrocenyl cationic lipid that is inactive when oxidized, but active when chemically reduced. We show that methods that exert spatial control over the administration of reducing agents can lead to local activation of lipoplexes and spatial control over gene expression. The versatility of this approach is demonstrated using both soluble and solid-phase reducing agents. These methods provide control over cell transfection, including methods for remote activation and the patterning of expression using solid-phase redox agents, that are difficult to achieve using conventional lipoplexes.

PMID: 23965341 [PubMed - indexed for MEDLINE]

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Spatial control of cell transfection using soluble or solid-phase redox agents and a redox-active ferrocenyl lipid.

ACS Appl Mater Interfaces. 2013 Sep 11;5(17):8283-8

Authors: Aytar BS, Muller JP, Kondo Y, Abbott NL, Lynn DM

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Facile chemical functionalization of proteins through intein-linked yeast display.

Bioconjug Chem. 2013 Sep 18;24(9):1634-44

Authors: Marshall CJ, Agarwal N, Kalia J, Grosskopf VA, McGrath NA, Abbott NL, Raines RT, Shusta EV

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Facile chemical functionalization of proteins through intein-linked yeast display.

Bioconjug Chem. 2013 Sep 18;24(9):1634-44

Authors: Marshall CJ, Agarwal N, Kalia J, Grosskopf VA, McGrath NA, Abbott NL, Raines RT, Shusta EV

Abstract
Intein-mediated expressed protein ligation (EPL) permits the site-specific chemical customization of proteins. While traditional techniques have used purified, soluble proteins, we have extended these methods to release and modify intein fusion proteins expressed on the yeast surface, thereby eliminating the need for soluble protein expression and purification. To this end, we sought to simultaneously release yeast surface-displayed proteins and selectively conjugate with chemical functionalities compatible with EPL and click chemistry. Single-chain antibodies (scFv) and green fluorescent protein (GFP) were displayed on the yeast surface as fusions to the N-terminus of the Mxe GyrA intein. ScFv and GFP were released from the yeast surface with either a sulfur nucleophile (MESNA) or a nitrogen nucleophile (hydrazine) linked to an azido group. The hydrazine azide permitted the simultaneous release and azido functionalization of displayed proteins, but nonspecific reactions with other yeast proteins were detected, and cleavage efficiency was limited. In contrast, MESNA released significantly more protein from the yeast surface while also generating a unique thioester at the carboxy-terminus of the released protein. These protein thioesters were subsequently reacted with a cysteine alkyne in an EPL reaction and then employed in an azide-alkyne cycloaddition to immobilize the scFv and GFP on an azide-decorated surface with >90% site-specificity. Importantly, the immobilized proteins retained their activity. Since yeast surface display is also a protein engineering platform, these approaches provide a particularly powerful tool for the rapid assessment of engineered proteins.

PMID: 23924245 [PubMed - indexed for MEDLINE]

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Facile chemical functionalization of proteins through intein-linked yeast display.

Bioconjug Chem. 2013 Sep 18;24(9):1634-44

Authors: Marshall CJ, Agarwal N, Kalia J, Grosskopf VA, McGrath NA, Abbott NL, Raines RT, Shusta EV

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Colloid-in-liquid crystal gels that respond to biomolecular interactions.

Small. 2013 Aug 26;9(16):2785-92, 2784

Authors: Agarwal A, Sidiq S, Setia S, Bukusoglu E, de Pablo JJ, Pal SK, Abbott NL

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Colloid-in-liquid crystal gels that respond to biomolecular interactions.

Small. 2013 Aug 26;9(16):2785-92, 2784

Authors: Agarwal A, Sidiq S, Setia S, Bukusoglu E, de Pablo JJ, Pal SK, Abbott NL

Abstract
This paper advances the design of stimuli-responsive materials based on colloidal particles dispersed in liquid crystals (LCs). Specifically, thin films of colloid-in-liquid crystal (CLC) gels undergo easily visualized ordering transitions in response to reversible and irreversible (enzymatic) biomolecular interactions occurring at the aqueous interfaces of the gels. In particular, LC ordering transitions can propagate across the entire thickness of the gels. However, confinement of the LC to small domains with lateral sizes of ∼10 μm does change the nature of the anchoring transitions, as compared to films of pure LC, due to the effects of confinement on the elastic energy stored in the LC. The effects of confinement are also observed to cause the response of individual domains of the LC within the CLC gel to vary significantly from one to another, indicating that manipulation of LC domain size and shape can provide the basis of a general and facile method to tune the response of these LC-based physical gels to interfacial phenomena. Overall, the results presented in this paper establish that CLC gels offer a promising approach to the preparation of self-supporting, LC-based stimuli-responsive materials.

PMID: 23554243 [PubMed - indexed for MEDLINE]

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Colloid-in-liquid crystal gels that respond to biomolecular interactions.

Small. 2013 Aug 26;9(16):2785-92, 2784

Authors: Agarwal A, Sidiq S, Setia S, Bukusoglu E, de Pablo JJ, Pal SK, Abbott NL

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Liquid crystal-based emulsions for synthesis of spherical and non-spherical particles with chemical patches.

J Am Chem Soc. 2013 Jul 10;135(27):9972-5

Authors: Mondiot F, Wang X, de Pablo JJ, Abbott NL

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Liquid crystal-based emulsions for synthesis of spherical and non-spherical particles with chemical patches.

J Am Chem Soc. 2013 Jul 10;135(27):9972-5

Authors: Mondiot F, Wang X, de Pablo JJ, Abbott NL

Abstract
We report the use of liquid crystal (LC)-in-water emulsions for the synthesis of either spherical or non-spherical particles with chemically distinct domains located at the poles of the particles. The approach involves the localization of solid colloids at topological defects that form predictably at surfaces of water-dispersed LC droplets. By polymerizing the LC droplets displaying the colloids at their surface defects, we demonstrate formation of both spherical and, upon extraction of the mesogen, anisotropic composite particles with colloids located at either one or both of the poles. Because the colloids protrude from the surfaces of the particles, they also define organized, chemical patches with functionality controlled by the colloid surface.

PMID: 23600692 [PubMed - indexed for MEDLINE]

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Liquid crystal-based emulsions for synthesis of spherical and non-spherical particles with chemical patches.

J Am Chem Soc. 2013 Jul 10;135(27):9972-5

Authors: Mondiot F, Wang X, de Pablo JJ, Abbott NL

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Redox-based control of the transformation and activation of siRNA complexes in extracellular environments using ferrocenyl lipids.

J Am Chem Soc. 2013 Jun 19;135(24):9111-20

Authors: Aytar BS, Muller JP, Kondo Y, Talmon Y, Abbott NL, Lynn DM

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Redox-based control of the transformation and activation of siRNA complexes in extracellular environments using ferrocenyl lipids.

J Am Chem Soc. 2013 Jun 19;135(24):9111-20

Authors: Aytar BS, Muller JP, Kondo Y, Talmon Y, Abbott NL, Lynn DM

Abstract
We report physical characterization and biological evaluation of complexes of small interfering RNA (siRNA) formed using a cationic lipid [bis(11-ferrocenylundecyl)dimethylammonium bromide (BFDMA)] containing redox-active ferrocenyl groups at the end of each hydrophobic tail. We demonstrate that control over the redox state of BFDMA can be used to influence key physical properties and control the activities of lipoplexes formed using siRNA-based constructs. Specifically, lipoplexes of siRNA and reduced BFDMA lead to high levels of sequence-specific gene silencing in cells, but lipoplexes formed using oxidized BFDMA do not. Lipoplexes of oxidized BFDMA can be activated in situ to induce high levels of silencing by addition of a chemical reducing agent, demonstrating a basis for external control over the activation/delivery of siRNA in cellular environments. Differences in activity arise from the inability of oxidized BFDMA to promote efficient internalization of siRNA; these differences also correlated to significant differences in the nanostructures of these lipoplexes (determined by cryo-TEM) and their ζ potentials as a function of oxidation state. These results are considered in view of recent studies characterizing the nanostructures, properties, and behaviors of lipoplexes formed using BFDMA and macromolecular plasmid DNA. We find that several key structural features and aspects of redox control observed for lipoplexes of plasmid DNA are maintained in complexes formed using smaller and more rigid siRNA. The ability to transform BFDMA in complex media presents opportunities to exert control over the nanostructures and behaviors of siRNA lipoplexes in ways not possible using conventional lipids. The approaches reported here could thus prove useful in both fundamental and applied contexts.

PMID: 23701636 [PubMed - indexed for MEDLINE]

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Redox-based control of the transformation and activation of siRNA complexes in extracellular environments using ferrocenyl lipids.

J Am Chem Soc. 2013 Jun 19;135(24):9111-20

Authors: Aytar BS, Muller JP, Kondo Y, Talmon Y, Abbott NL, Lynn DM

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Introduction to optical methods for characterizing liquid crystals at interfaces.

Langmuir. 2013 Mar 12;29(10):3154-69

Authors: Miller DS, Carlton RJ, Mushenheim PC, Abbott NL

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Introduction to optical methods for characterizing liquid crystals at interfaces.

Langmuir. 2013 Mar 12;29(10):3154-69

Authors: Miller DS, Carlton RJ, Mushenheim PC, Abbott NL

Abstract
This Instructional Review describes methods and underlying principles that can be used to characterize both the orientations assumed spontaneously by liquid crystals (LCs) at interfaces and the strength with which the LCs are held in those orientations (so-called anchoring energies). The application of these methods to several different classes of LC interfaces is described, including solid and aqueous interfaces as well as planar and nonplanar interfaces (such as those that define a LC-in-water emulsion droplet). These methods, which enable fundamental studies of the ordering of LCs at polymeric, chemically functionalized, and biomolecular interfaces, are described in this Instructional Review on a level that can be easily understood by a nonexpert reader such as an undergraduate or graduate student. We focus on optical methods because they are based on instrumentation that is found widely in research and teaching laboratories.

PMID: 23347378 [PubMed - indexed for MEDLINE]

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Introduction to optical methods for characterizing liquid crystals at interfaces.

Langmuir. 2013 Mar 12;29(10):3154-69

Authors: Miller DS, Carlton RJ, Mushenheim PC, Abbott NL

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Modeling the polydomain-monodomain transition of liquid crystal elastomers.

Phys Rev E Stat Nonlin Soft Matter Phys. 2013 Feb;87(2):020502

Authors: Whitmer JK, Roberts TF, Shekhar R, Abbott NL, de Pablo JJ

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Modeling the polydomain-monodomain transition of liquid crystal elastomers.

Phys Rev E Stat Nonlin Soft Matter Phys. 2013 Feb;87(2):020502

Authors: Whitmer JK, Roberts TF, Shekhar R, Abbott NL, de Pablo JJ

Abstract
We study the mechanism of the polydomain-monodomain transition in liquid crystalline elastomers at the molecular scale. A coarse-grained model is proposed in which mesogens are described as ellipsoidal particles. Molecular dynamics simulations are used to examine the transition from a polydomain state to a monodomain state in the presence of uniaxial strain. Our model demonstrates soft elasticity, similar to that exhibited by side-chain elastomers in the literature. By analyzing the growth dynamics of nematic domains during uniaxial extension, we provide direct evidence that at a molecular level the polydomain-monodomain transition proceeds through cluster rotation and domain growth.

PMID: 23496448 [PubMed - indexed for MEDLINE]

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Modeling the polydomain-monodomain transition of liquid crystal elastomers.

Phys Rev E Stat Nonlin Soft Matter Phys. 2013 Feb;87(2):020502

Authors: Whitmer JK, Roberts TF, Shekhar R, Abbott NL, de Pablo JJ

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Influence of droplet size, pH and ionic strength on endotoxin-triggered ordering transitions in liquid crystalline droplets.

Soft Matter. 2013 Jan 14;9(2):374-382

Authors: Miller DS, Abbott NL

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Influence of droplet size, pH and ionic strength on endotoxin-triggered ordering transitions in liquid crystalline droplets.

Soft Matter. 2013 Jan 14;9(2):374-382

Authors: Miller DS, Abbott NL

Abstract
We report an investigation of ordering transitions that are induced in water-dispersed, micrometer-sized droplets of a thermotropic liquid crystal (LC) by the bacterial lipopolysaccharide endotoxin. We reveal that the ordering transitions induced by endotoxin - from a bipolar state of the droplets to a radial state - are strongly dependent on the size of the LC droplets. Specifically, as the diameters of the LC droplets increase from 2 μm to above 10 μm (in phosphate buffered saline with an ionic strength of 90 mM and a pH of 7.2), we measured the percentage of droplets exhibiting a radial configuration in the presence of 100 pg/mL endotoxin to decrease from 98 ± 1 % to 3 ± 2 %. In addition, we measured a decrease in either the ionic strength or pH of the aqueous phase to reduce the percentage of droplets exhibiting a radial configuration in the presence of endotoxin. These results, when interpreted within the context of a simple thermodynamic model that incorporates the contributions of elasticity and surface anchoring to the free energies of the LC droplets, lead us to conclude that (i) the elastic constant K24 plays a central role in determining the size-dependent response of the LC droplets to endotoxin, and (ii) endotoxin-triggered ordering transitions occur only under solution conditions (pH, ionic strength) where the combined contributions of elasticity and surface anchoring to the free energies of the bipolar and radial configurations of the LC droplets are similar in magnitude. Our analysis also suggests that the presence of endotoxin perturbs the free energies of the LC droplets by ~10(-17) J/droplet, which is comparable to the standard free energy of self-association of ~10(3) endotoxin molecules. These results, when combined with prior reports of localization of endotoxin at the center of LC droplets, are consistent with the hypothesis that self-assembly of endotoxin within micrometer-sized LC droplets provides the driving force for the ordering transitions. Overall, these results advance our understanding of ordering transitions triggered by the interactions of analytes with LC droplets and, more broadly, provide guidance to the design of LC droplet systems as the basis of stimuli-responsive soft materials.

PMID: 23675387 [PubMed - as supplied by publisher]

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Influence of droplet size, pH and ionic strength on endotoxin-triggered ordering transitions in liquid crystalline droplets.

Soft Matter. 2013 Jan 14;9(2):374-382

Authors: Miller DS, Abbott NL

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Amplification of the stereochemistry of biomolecular adsorbates by deracemization of chiral domains in bent-core liquid crystals.

Adv Mater. 2013 Jan 11;25(2):245-9

Authors: Lee G, Carlton RJ, Araoka F, Abbott NL, Takezoe H

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Amplification of the stereochemistry of biomolecular adsorbates by deracemization of chiral domains in bent-core liquid crystals.

Adv Mater. 2013 Jan 11;25(2):245-9

Authors: Lee G, Carlton RJ, Araoka F, Abbott NL, Takezoe H

Abstract
Assemblies of chiral phospholipids that form spontaneously at interfaces between aqueous phases and bent-core liquid crystals can deracemize mixtures of chiral domains that otherwise form in the liquid crystal phase. An enantiomeric excess of chiral domains is induced by adsorption of either L- or D-phospholipid with the same sense of optical rotation.

PMID: 23109049 [PubMed - indexed for MEDLINE]

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Amplification of the stereochemistry of biomolecular adsorbates by deracemization of chiral domains in bent-core liquid crystals.

Adv Mater. 2013 Jan 11;25(2):245-9

Authors: Lee G, Carlton RJ, Araoka F, Abbott NL, Takezoe H

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Chemical and biological sensing using liquid crystals.

Liq Cryst Rev. 2013;1(1):29-51

Authors: Carlton RJ, Hunter JT, Miller DS, Abbasi R, Mushenheim PC, Tan LN, Abbott NL

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Chemical and biological sensing using liquid crystals.

Liq Cryst Rev. 2013;1(1):29-51

Authors: Carlton RJ, Hunter JT, Miller DS, Abbasi R, Mushenheim PC, Tan LN, Abbott NL

Abstract
The liquid crystalline state of matter arises from orientation-dependent, non-covalent interaction between molecules within condensed phases. Because the balance of intermolecular forces that underlies formation of liquid crystals is delicate, this state of matter can, in general, be easily perturbed by external stimuli (such as an electric field in a display). In this review, we present an overview of recent efforts that have focused on exploiting the responsiveness of liquid crystals as the basis of chemical and biological sensors. In this application of liquid crystals, the challenge is to design liquid crystalline systems that undergo changes in organization when perturbed by targeted chemical and biological species of interest. The approaches described below revolve around the design of interfaces that selectively bind targeted species, thus leading to surface-driven changes in the organization of the liquid crystals. Because liquid crystals possess anisotropic optical and dielectric properties, a range of different methods can be used to read out the changes in organization of liquid crystals that are caused by targeted chemical and biological species. This review focuses on principles for liquid crystal-based sensors that provide an optical output.

PMID: 24795857 [PubMed - as supplied by publisher]

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Chemical and biological sensing using liquid crystals.

Liq Cryst Rev. 2013;1(1):29-51

Authors: Carlton RJ, Hunter JT, Miller DS, Abbasi R, Mushenheim PC, Tan LN, Abbott NL

2012

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Improving liquid-crystal-based biosensing in aqueous phases.

ACS Appl Mater Interfaces. 2012 Dec;4(12):6884-90

Authors: Iglesias W, Abbott NL, Mann EK, Jákli A

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Improving liquid-crystal-based biosensing in aqueous phases.

ACS Appl Mater Interfaces. 2012 Dec;4(12):6884-90

Authors: Iglesias W, Abbott NL, Mann EK, Jákli A

Abstract
Liquid crystal (LC)-based biological sensors permit the study of aqueous biological samples without the need for the labeling of biological species with fluorescent dyes (which can be laborious and change the properties of the biological sample under study). To date, studies of LC-based biosensors have explored only a narrow range of the liquid crystal/alignment layer combinations essential to their operation. Here, we report a study of the role of LC elastic constants and the surface anchoring energy in determining the sensitivity of LC-based biosensors. By investigating a mixture of rod-shape and bent-shape mesogens, and three different alignment layers, we were able to widen the useful detection range of a LC-based sensor by providing an almost-linear mapping of effective birefringence with anionic surfactant concentrations between 0.05 mM and 1 mM (model target analyte). These studies pave the way for optimization of LC-based biosensors and reveal the importance of the choice of both the LC material and the alignment layer in determining sensor properties.

PMID: 23157269 [PubMed - indexed for MEDLINE]

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Improving liquid-crystal-based biosensing in aqueous phases.

ACS Appl Mater Interfaces. 2012 Dec;4(12):6884-90

Authors: Iglesias W, Abbott NL, Mann EK, Jákli A

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Microfluidic sensing devices employing in situ-formed liquid crystal thin film for detection of biochemical interactions.

Lab Chip. 2012 Oct 7;12(19):3746-53

Authors: Liu Y, Cheng D, Lin IH, Abbott NL, Jiang H

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Microfluidic sensing devices employing in situ-formed liquid crystal thin film for detection of biochemical interactions.

Lab Chip. 2012 Oct 7;12(19):3746-53

Authors: Liu Y, Cheng D, Lin IH, Abbott NL, Jiang H

Abstract
Although biochemical sensing using liquid crystals (LC) has been demonstrated, relatively little attention has been paid towards the fabrication of in situ-formed LC sensing devices. Herein, we demonstrate a highly reproducible method to create uniform LC thin film on treated substrates, as needed, for LC sensing. We use shear forces generated by the laminar flow of aqueous liquid within a microfluidic channel to create LC thin films stabilized within microfabricated structures. The orientational response of the LC thin films to targeted analytes in aqueous phases was transduced and amplified by the optical birefringence of the LC thin films. The biochemical sensing capability of our sensing devices was demonstrated through experiments employing two chemical systems: dodecyl trimethylammonium bromide (DTAB) dissolved in an aqueous solution, and the hydrolysis of phospholipids by the enzyme phospholipase A(2) (PLA(2)).

PMID: 22842797 [PubMed - indexed for MEDLINE]

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Microfluidic sensing devices employing in situ-formed liquid crystal thin film for detection of biochemical interactions.

Lab Chip. 2012 Oct 7;12(19):3746-53

Authors: Liu Y, Cheng D, Lin IH, Abbott NL, Jiang H

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Influence of specific anions on the orientational ordering of thermotropic liquid crystals at aqueous interfaces.

Langmuir. 2012 Sep 4;28(35):12796-805

Authors: Carlton RJ, Ma CD, Gupta JK, Abbott NL

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Influence of specific anions on the orientational ordering of thermotropic liquid crystals at aqueous interfaces.

Langmuir. 2012 Sep 4;28(35):12796-805

Authors: Carlton RJ, Ma CD, Gupta JK, Abbott NL

Abstract
We report that specific anions (of sodium salts) added to aqueous phases at molar concentrations can trigger rapid, orientational ordering transitions in water-immiscible, thermotropic liquid crystals (LCs; e.g., nematic phase of 4'-pentyl-4-cyanobiphenyl, 5CB) contacting the aqueous phases. Anions classified as chaotropic, specifically iodide, perchlorate, and thiocyanate, cause 5CB to undergo continuous, concentration-dependent transitions from planar to homeotropic (perpendicular) orientations at LC-aqueous interfaces within 20 s of addition of the anions. In contrast, anions classified as relatively more kosmotropic in nature (fluoride, sulfate, phosphate, acetate, chloride, nitrate, bromide, and chlorate) do not perturb the LC orientation from that observed without added salts (i.e., planar orientation). Surface pressure-area isotherms of Langmuir films of 5CB supported on aqueous salt solutions reveal ion-specific effects ranking in a manner similar to the LC ordering transitions. Specifically, chaotropic salts stabilized monolayers of 5CB to higher surface pressures and areal densities (12.6 mN/m at 27 Å(2)/molecule for NaClO(4)) and thus smaller molecular tilt angles (30° from the surface normal for NaClO(4)) than kosmotropic salts (5.0 mN/m at 38 Å(2)/molecule with a corresponding tilt angle of 53° for NaCl). These results and others reported herein suggest that anion-specific interactions with 5CB monolayers lead to bulk LC ordering transitions. Support for the proposition that these ion-specific interactions involve the nitrile group was obtained by using a second LC with nitrile groups (E7; ion-specific effects similar to 5CB were observed) and a third LC with fluorine-substituted aromatic groups (TL205; weak dipole and no ion-specific effects were measured). Finally, we also establish that anion-induced orientational transitions in micrometer-thick LC films involve a change in the easy axis of the LC. Overall, these results provide new insights into ionic phenomena occurring at LC-aqueous interfaces, and reveal that the long-range ordering of LC oils can amplify ion-specific interactions at these interfaces into macroscopic ordering transitions.

PMID: 22866677 [PubMed - indexed for MEDLINE]

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Influence of specific anions on the orientational ordering of thermotropic liquid crystals at aqueous interfaces.

Langmuir. 2012 Sep 4;28(35):12796-805

Authors: Carlton RJ, Ma CD, Gupta JK, Abbott NL

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Imide photodissociation investigated by X-ray absorption spectroscopy.

J Phys Chem B. 2012 Jun 21;116(24):7048-54

Authors: Johnson PS, Cook PL, Liu X, Yang W, Bai Y, Abbott NL, Himpsel FJ

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Imide photodissociation investigated by X-ray absorption spectroscopy.

J Phys Chem B. 2012 Jun 21;116(24):7048-54

Authors: Johnson PS, Cook PL, Liu X, Yang W, Bai Y, Abbott NL, Himpsel FJ

Abstract
X-ray absorption spectroscopy is used to investigate the photodissociation of the imides PMDI (pyromellitic diimide) and SSMCC (sulfosuccinimidyl 4-(N-maleimidomethyl) cyclohexane-1-carboxylate). PMDI contains only one type of imide, and its photodissociation can be explained by a simple conversion from imide to a mix of imine and nitrile after desorption of the oxygens from the imide. SSMCC contains two different imides. One reacts like PMDI, the other in a more complex multistep process. Eventually, N(2) is formed in the bulk of the sample at high radiation density. The sequence of reactions is inferred from the π* peaks in total electron yield and fluorescence yield absorption spectra at the N 1s and O 1s edges. First-order rate equations are used to model the evolution of the peak areas versus radiation dose.

PMID: 22594563 [PubMed]

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Imide photodissociation investigated by X-ray absorption spectroscopy.

J Phys Chem B. 2012 Jun 21;116(24):7048-54

Authors: Johnson PS, Cook PL, Liu X, Yang W, Bai Y, Abbott NL, Himpsel FJ

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Ordering transitions triggered by specific binding of vesicles to protein-decorated interfaces of thermotropic liquid crystals.

Langmuir. 2012 Apr 17;28(15):6364-76

Authors: Tan LN, Orler VJ, Abbott NL

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Ordering transitions triggered by specific binding of vesicles to protein-decorated interfaces of thermotropic liquid crystals.

Langmuir. 2012 Apr 17;28(15):6364-76

Authors: Tan LN, Orler VJ, Abbott NL

Abstract
We report that specific binding of ligand-functionalized (biotinylated) phospholipid vesicles (diameter = 120 ± 19 nm) to a monolayer of proteins (streptavidin or anti-biotin antibody) adsorbed at an interface between an aqueous phase and an immiscible film of a thermotropic liquid crystal (LC) [nematic 4'-pentyl-4-cyanobiphenyl (5CB)] triggers a continuous orientational ordering transition (continuous change in the tilt) in the LC. Results presented in this paper indicate that, following the capture of the vesicles at the LC interface via the specific binding interaction, phospholipids are transferred from the vesicles onto the LC interface to form a monolayer, reorganizing and partially displacing proteins from the LC interface. The dynamics of this process are accelerated substantially by the specific binding event relative to a protein-decorated interface of a LC that does not bind the ligands presented by the vesicles. The observation of the continuous change in the ordering of the LC, when combined with other results presented in this paper, is significant, as it is consistent with the presence of suboptical domains of proteins and phospholipids on the LC interface. An additional significant hypothesis that emerges from the work reported in this paper is that the ordering transition of the LC is strongly influenced by the bound state of the protein adsorbed on the LC interface, as evidenced by the influence on the LC of (i) "crowding" of the protein within a monolayer formed at the LC interface and (ii) aging of the proteins on the LC interface. Overall, these results demonstrate that ordering transitions in LCs can be used to provide fundamental insights into the competitive adsorption of proteins and lipids at oil-water interfaces and that LC ordering transitions have the potential to be useful for reporting specific binding events involving vesicles and proteins.

PMID: 22372743 [PubMed - indexed for MEDLINE]

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Ordering transitions triggered by specific binding of vesicles to protein-decorated interfaces of thermotropic liquid crystals.

Langmuir. 2012 Apr 17;28(15):6364-76

Authors: Tan LN, Orler VJ, Abbott NL

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Liquid Crystalline Materials for Biological Applications.

Chem Mater. 2012 Mar 13;24(5):746-758

Authors: Lowe AM, Abbott NL

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Liquid Crystalline Materials for Biological Applications.

Chem Mater. 2012 Mar 13;24(5):746-758

Authors: Lowe AM, Abbott NL

Abstract
Liquid crystals have a long history of use as materials that respond to external stimuli (e.g., electrical and optical fields). More recently, a series of investigations have reported the design of liquid crystalline materials that undergo ordering transitions in response to a range of biological interactions, including interactions involving proteins, nucleic acids, viruses, bacteria and mammalian cells. A central challenge underlying the design of liquid crystalline materials for such applications is the tailoring of the interface of the materials so as to couple targeted biological interactions to ordering transitions. This review describes recent progress toward design of interfaces of liquid crystalline materials that are suitable for biological applications. Approaches addressed in this review include the use of lipid assemblies, polymeric membranes containing oligopeptides, cationic surfactant-DNA complexes, peptide-amphiphiles, interfacial protein assemblies and multi-layer polymeric films.

PMID: 22563142 [PubMed - as supplied by publisher]

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Liquid Crystalline Materials for Biological Applications.

Chem Mater. 2012 Mar 13;24(5):746-758

Authors: Lowe AM, Abbott NL

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Incorporation of DOPE into Lipoplexes formed from a Ferrocenyl Lipid leads to Inverse Hexagonal Nanostructures that allow Redox-Based Control of Transfection in High Serum.

Soft Matter. 2012 Jan 1;8(24):2608-2619

Authors: Muller JP, Aytar BS, Kondo Y, Lynn DM, Abbott NL

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Incorporation of DOPE into Lipoplexes formed from a Ferrocenyl Lipid leads to Inverse Hexagonal Nanostructures that allow Redox-Based Control of Transfection in High Serum.

Soft Matter. 2012 Jan 1;8(24):2608-2619

Authors: Muller JP, Aytar BS, Kondo Y, Lynn DM, Abbott NL

Abstract
We report small angle X-ray and neutron scattering measurements that reveal that mixtures of the redox-active lipid bis(11-ferrocenylundecyl)dimethylammonium bromide (BFDMA) and dioleoylphosphatidylethanolamine (DOPE) spontaneously form lipoplexes with DNA that exhibit inverse hexagonal nanostructure (H(II) (c)). In contrast to lipoplexes of DNA and BFDMA only, which exhibit a multilamellar nanostructure (L(α) (c)) and limited ability to transfect cells in the presence of serum proteins, we measured lipoplexes of BFDMA and DOPE with the H(II) (c) nanostructure to survive incubation in serum and to expand significantly the range of media compositions (e.g., up to 80% serum) over which BFDMA can be used to transfect cells with high efficiency. Importantly, we also measured the oxidation state of the ferrocene within the BFDMA/DNA lipoplexes to have a substantial influence on the transfection efficiency of the lipoplexes in media containing serum. Specifically, whereas lipoplexes of reduced BFDMA and DOPE transfect cells with high efficiency, lipoplexes of oxidized BFDMA and DNA lead to low levels of transfection. Complementary measurements using SAXS reveal that the low transfection efficiency of the lipoplexes of oxidized BFDMA and DOPE correlates with the presence of weak Bragg peaks and thus low levels of H(II) (c) nanostructure in solution. Overall, these results provide support for our hypothesis that DOPE-induced formation of the H(II) (c) nanostructure of the BFDMA-containing lipoplexes underlies the high cell transfection efficiency measured in the presence of serum, and that the oxidation state of BFDMA within lipoplexes with DOPE substantially regulates the formation of the H(II) (c) nanostructure and thus the ability of the lipoplexes to transfect cells with DNA. More generally, the results presented in this paper suggest that lipoplexes formed from BFDMA and DOPE may offer the basis of approaches that permit active and external control of transfection of cells in the presence of high (physiologically relevant) levels of serum.

PMID: 22707977 [PubMed - as supplied by publisher]

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Incorporation of DOPE into Lipoplexes formed from a Ferrocenyl Lipid leads to Inverse Hexagonal Nanostructures that allow Redox-Based Control of Transfection in High Serum.

Soft Matter. 2012 Jan 1;8(24):2608-2619

Authors: Muller JP, Aytar BS, Kondo Y, Lynn DM, Abbott NL

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Influence of simple electrolytes on the orientational ordering of thermotropic liquid crystals at aqueous interfaces.

Langmuir. 2012 Jan 10;28(1):31-6

Authors: Carlton RJ, Gupta JK, Swift CL, Abbott NL

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Influence of simple electrolytes on the orientational ordering of thermotropic liquid crystals at aqueous interfaces.

Langmuir. 2012 Jan 10;28(1):31-6

Authors: Carlton RJ, Gupta JK, Swift CL, Abbott NL

Abstract
We report orientational anchoring transitions at aqueous interfaces of a water-immiscible, thermotropic liquid crystal (LC; nematic phase of 4'-pentyl-4-cyanobiphenyl (5CB)) that are induced by changes in pH and the addition of simple electrolytes (NaCl) to the aqueous phase. Whereas measurements of the zeta potential on the aqueous side of the interface of LC-in-water emulsions prepared with 5CB confirm pH-dependent formation of an electrical double layer extending into the aqueous phase, quantification of the orientational ordering of the LC leads to the proposition that an electrical double layer is also formed on the LC-side of the interface with an internal electric field that drives the LC anchoring transition. Further support for this conclusion is obtained from measurements of the dependence of LC ordering on pH and ionic strength, as well as a simple model based on the Poisson-Boltzmann equation from which we calculate the contribution of an electrical double layer to the orientational anchoring energy of the LC. Overall, the results presented herein provide new fundamental insights into ionic phenomena at LC-aqueous interfaces, and expand the range of solutes known to cause orientational anchoring transitions at LC-aqueous interfaces beyond previously examined amphiphilic adsorbates.

PMID: 22106820 [PubMed - indexed for MEDLINE]

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Influence of simple electrolytes on the orientational ordering of thermotropic liquid crystals at aqueous interfaces.

Langmuir. 2012 Jan 10;28(1):31-6

Authors: Carlton RJ, Gupta JK, Swift CL, Abbott NL

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Enantiomeric interactions between liquid crystals and organized monolayers of tyrosine-containing dipeptides.

J Am Chem Soc. 2012 Jan 11;134(1):548-58

Authors: Bai Y, Abbott NL

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Enantiomeric interactions between liquid crystals and organized monolayers of tyrosine-containing dipeptides.

J Am Chem Soc. 2012 Jan 11;134(1):548-58

Authors: Bai Y, Abbott NL

Abstract
We have examined the orientational ordering of nematic liquid crystals (LCs) supported on organized monolayers of dipeptides with the goal of understanding how peptide-based interfaces encode intermolecular interactions that are amplified into supramolecular ordering. By characterizing the orientations of nematic LCs (4-cyano-4'-pentylbiphenyl and TL205 (a mixture of mesogens containing cyclohexane-fluorinated biphenyls and fluorinated terphenyls)) on monolayers of l-cysteine-l-tyrosine, l-cysteine-l-phenylalanine, or l-cysteine-l-phosphotyrosine formed on crystallographically textured films of gold, we conclude that patterns of hydrogen bonds generated by the organized monolayers of dipeptides are transduced via macroscopic orientational ordering of the LCs. This conclusion is supported by the observation that the ordering exhibited by the achiral LCs is specific to the enantiomers used to form the dipeptide-based monolayers. The dominant role of the -OH group of tyrosine in dictating the patterns of hydrogen bonds that orient the LCs was also evidenced by the effects of phosphorylation of the tyrosine on the ordering of the LCs. Overall, these results reveal that crystallographic texturing of gold films can direct the formation of monolayers of dipeptides with long-range order, thus unmasking the influence of hydrogen bonding, chirality, and phosphorylation on the macroscopic orientational ordering of LCs supported on these surfaces. These results suggest new approaches based on supramolecular assembly for reporting the chemical functionality and stereochemistry of synthetic and biological peptide-based molecules displayed at surfaces.

PMID: 22091988 [PubMed - indexed for MEDLINE]

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Enantiomeric interactions between liquid crystals and organized monolayers of tyrosine-containing dipeptides.

J Am Chem Soc. 2012 Jan 11;134(1):548-58

Authors: Bai Y, Abbott NL

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Addition of ascorbic acid to the extracellular environment activates lipoplexes of a ferrocenyl lipid and promotes cell transfection.

J Control Release. 2012 Jan 30;157(2):249-59

Authors: Aytar BS, Muller JP, Golan S, Hata S, Takahashi H, Kondo Y, Talmon Y, Abbott NL, Lynn DM

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Addition of ascorbic acid to the extracellular environment activates lipoplexes of a ferrocenyl lipid and promotes cell transfection.

J Control Release. 2012 Jan 30;157(2):249-59

Authors: Aytar BS, Muller JP, Golan S, Hata S, Takahashi H, Kondo Y, Talmon Y, Abbott NL, Lynn DM

Abstract
The level of cell transfection mediated by lipoplexes formed using the ferrocenyl lipid bis(11-ferrocenylundecyl)dimethylammonium bromide (BFDMA) depends strongly on the oxidation state of the two ferrocenyl groups of the lipid (reduced BFDMA generally mediates high levels of transfection, but oxidized BFDMA mediates very low levels of transfection). Here, we report that it is possible to chemically transform inactive lipoplexes (formed using oxidized BFMDA) to "active" lipoplexes that mediate high levels of transfection by treatment with the small-molecule reducing agent ascorbic acid (vitamin C). Our results demonstrate that this transformation can be conducted in cell culture media and in the presence of cells by addition of ascorbic acid to lipoplex-containing media in which cells are growing. Treatment of lipoplexes of oxidized BFDMA with ascorbic acid resulted in lipoplexes composed of reduced BFDMA, as characterized by UV/vis spectrophotometry, and lead to activated lipoplexes that mediated high levels of transgene expression in the COS-7, HEK 293T/17, HeLa, and NIH 3T3 cell lines. Characterization of internalization of DNA by confocal microscopy and measurements of the zeta potentials of lipoplexes suggested that these large differences in cell transfection result from (i) differences in the extents to which these lipoplexes are internalized by cells and (ii) changes in the oxidation state of BFDMA that occur in the extracellular environment (i.e., prior to internalization of lipoplexes by cells). Characterization of lipoplexes by small-angle neutron scattering (SANS) and by cryogenic transmission electron microscopy (cryo-TEM) revealed changes in the nanostructures of lipoplexes upon the addition of ascorbic acid, from aggregates that were generally amorphous, to aggregates with a more extensive multilamellar nanostructure. The results of this study provide guidance for the design of redox-active lipids that could lead to methods that enable spatial and/or temporal control of cell transfection.

PMID: 21963768 [PubMed - indexed for MEDLINE]

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Addition of ascorbic acid to the extracellular environment activates lipoplexes of a ferrocenyl lipid and promotes cell transfection.

J Control Release. 2012 Jan 30;157(2):249-59

Authors: Aytar BS, Muller JP, Golan S, Hata S, Takahashi H, Kondo Y, Talmon Y, Abbott NL, Lynn DM

2011

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Lyotropic liquid crystals formed from ACHC-rich β-peptides.

J Am Chem Soc. 2011 Aug 31;133(34):13604-13

Authors: Pomerantz WC, Yuwono VM, Drake R, Hartgerink JD, Abbott NL, Gellman SH

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Lyotropic liquid crystals formed from ACHC-rich β-peptides.

J Am Chem Soc. 2011 Aug 31;133(34):13604-13

Authors: Pomerantz WC, Yuwono VM, Drake R, Hartgerink JD, Abbott NL, Gellman SH

Abstract
We have examined the effect of β-peptide modifications on the propensity of these helical molecules to form lyotropic liquid crystalline (LC) phases in water. All of the β-peptides we have examined contain 10 residues. In each case, at least three residues are derived from trans-2-aminocyclohexanecarboxylic acid (ACHC), which strongly promotes folding to a 14-helical conformation. The structural features varied include the number of ACHC residues, the nature and spatial arrangement of charged side chains (cationic vs anionic), and the identity of groups at the β-peptide termini. We found that relatively small changes (e.g., swapping the positions of a cationic and an anionic side chain) could have large effects, such as abrogation of LC phase formation. The trends revealed by sequence-property studies led to the design of LC-forming β-peptides that bear biomolecular recognition groups (biotin or the tripeptide Arg-Gly-Asp). Structural analysis via circular dichroism and cryo-transmission electron microscopy revealed the existence of two different types of self-associated species, globular aggregates and nanofibers. Nanofibers are the predominant assembly formed at concentrations that lead to LC phase formation, and we conclude that these nanofibers are the functional mesogens. Overall, these studies show how the modularity of β-peptide oligomers enables elucidation of the relationship between molecular structure and large-scale self-assembly behavior.

PMID: 21815636 [PubMed - indexed for MEDLINE]

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Lyotropic liquid crystals formed from ACHC-rich β-peptides.

J Am Chem Soc. 2011 Aug 31;133(34):13604-13

Authors: Pomerantz WC, Yuwono VM, Drake R, Hartgerink JD, Abbott NL, Gellman SH

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Universal mechanism for breaking amide bonds by ionizing radiation.

J Chem Phys. 2011 Jul 28;135(4):044702

Authors: Johnson PS, Cook PL, Liu X, Yang W, Bai Y, Abbott NL, Himpsel FJ

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Universal mechanism for breaking amide bonds by ionizing radiation.

J Chem Phys. 2011 Jul 28;135(4):044702

Authors: Johnson PS, Cook PL, Liu X, Yang W, Bai Y, Abbott NL, Himpsel FJ

Abstract
The photodissociation of the amide bond by UV light and soft x-rays is investigated by x-ray absorption spectroscopy at the C, N, and O 1s edges. Irradiation leaves a clear and universal signature for a wide variety of amides, ranging from oligopeptides to large proteins and synthetic polyamides, such as nylon. As the π∗ peak of the amide bond shrinks, two new π∗ peaks appear at the N 1s edge with a characteristic splitting of 1.1 eV. An additional characteristic is the overall intensity reduction of both the π∗ and σ∗ features at the O 1s edge, which indicates loss of oxygen. The spectroscopic results are consistent with the release of the O atom from the amide bond, followed by the migration of the H atom from the N to one of its two C neighbors. Migration to the carbonyl C leads to an imine, and migration to the C(α) of the amino acid residue leads to a nitrile. Imine and nitrile produce the two characteristic π∗ transitions at the N 1s edge. A variety of other models is considered and tested against the N 1s spectra of reference compounds.

PMID: 21806150 [PubMed - indexed for MEDLINE]

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Universal mechanism for breaking amide bonds by ionizing radiation.

J Chem Phys. 2011 Jul 28;135(4):044702

Authors: Johnson PS, Cook PL, Liu X, Yang W, Bai Y, Abbott NL, Himpsel FJ

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Influence of biological media on the structure and behavior of ferrocene-containing cationic lipid/DNA complexes used for DNA delivery.

Langmuir. 2011 Jun 7;27(11):6615-21

Authors: Golan S, Aytar BS, Muller JP, Kondo Y, Lynn DM, Abbott NL, Talmon Y

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Influence of biological media on the structure and behavior of ferrocene-containing cationic lipid/DNA complexes used for DNA delivery.

Langmuir. 2011 Jun 7;27(11):6615-21

Authors: Golan S, Aytar BS, Muller JP, Kondo Y, Lynn DM, Abbott NL, Talmon Y

Abstract
Biological media affect the physicochemical properties of cationic lipid-DNA complexes (lipoplexes) and can influence their ability to transfect cells. To develop new lipids for efficient DNA delivery, the influence of serum-containing media on the structures and properties of the resulting lipoplexes must be understood. To date, however, a clear and general picture of how serum-containing media influences the structures of lipoplexes has not been established. Some studies suggest that serum can disintegrate lipoplexes formed using certain types of cationic lipids, resulting in the inhibition of transfection. Other studies have demonstrated that lipoplexes formulated from other lipids are stable in the presence of serum and are able to transfect cells efficiently. In this article, we describe the influence of serum-containing media on lipoplexes formed using the redox-active cationic lipid bis(n-ferrocenylundecyl)dimethylammonium bromide (BFDMA). This lipoplex system promotes markedly decreased levels of transgene expression in COS-7 cells as serum concentrations are increased from 0 to 2, 5, 10, and 50% (v/v). To understand the cause of this decrease in transfection efficiency, we used cryogenic transmission electron microscopy (cryo-TEM) and measurements of zeta potential to characterize lipoplexes in cell culture media supplemented with 0, 2, 5, 10, and 50% serum. Cryo-TEM revealed that in serum-free media BFDMA lipoplexes form onionlike, multilamellar nanostructures. However, the presence of serum in the media caused disassociation of the intact multilamellar lipoplexes. At low serum concentrations (2 and 5%), DNA threads appeared to separate from the complex, leaving the nanostructure of the lipoplexes disrupted. At higher serum concentration (10%), disassociation increased and bundles of multilamellae were discharged from the main multilamellar complex. In contrast, lipoplexes characterized in serum-free aqueous salt (Li(2)SO(4)) medium and in OptiMEM cell culture medium (no serum) did not exhibit significant structural changes. The zeta potentials of lipoplexes in serum-free media (salt medium and cell culture medium) were similar (e.g., approximately -35 mV). Interestingly, the presence of serum caused the zeta potentials to become less negative (about -20 mV in OptiMEM and -10 mV in Li(2)SO(4)), even though serum contains negatively charged entities that have been demonstrated to lead to more negative zeta potentials in other lipoplex systems. The combined measurements of zeta potential and cryo-TEM are consistent with the proposition that DNA threads separate from the lipoplex in the presence of serum, resulting in a decrease in the net negative charge of the surface of the lipoplex.

PMID: 21528933 [PubMed - indexed for MEDLINE]

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Influence of biological media on the structure and behavior of ferrocene-containing cationic lipid/DNA complexes used for DNA delivery.

Langmuir. 2011 Jun 7;27(11):6615-21

Authors: Golan S, Aytar BS, Muller JP, Kondo Y, Lynn DM, Abbott NL, Talmon Y

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Recent advances in colloidal and interfacial phenomena involving liquid crystals.

Langmuir. 2011 May 17;27(10):5719-38

Authors: Bai Y, Abbott NL

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Recent advances in colloidal and interfacial phenomena involving liquid crystals.

Langmuir. 2011 May 17;27(10):5719-38

Authors: Bai Y, Abbott NL

Abstract
This feature article describes recent advances in several areas of research involving the interfacial ordering of liquid crystals (LCs). The first advance revolves around the ordering of LCs at bio/chemically functionalized surfaces. Whereas the majority of past studies of surface-induced ordering of LCs have involved surfaces of solids that present a limited diversity of chemical functional groups (surfaces at which van der Waals forces dominate surface-induced ordering), recent studies have moved to investigate the ordering of LCs on chemically complex surfaces. For example, surfaces decorated with biomolecules (e.g., oligopeptides and proteins) and transition-metal ions have been investigated, leading to an understanding of the roles that metal-ligand coordination interactions, electrical double layers, acid-base interactions, and hydrogen bonding can play in the interfacial ordering of LCs. The opportunity to create chemically responsive LCs capable of undergoing ordering transitions in the presence of targeted molecular events (e.g., ligand exchange around a metal center) has emerged from these fundamental studies. A second advance has focused on investigations of the ordering of LCs at interfaces with immiscible isotropic fluids, particularly water. In contrast to prior studies of surface-induced ordering of LCs on solid surfaces, LC-aqueous interfaces are deformable and molecules at these interfaces exhibit high levels of mobility and thus can reorganize in response to changes in the interfacial environment. A range of fundamental investigations involving these LC-aqueous interfaces have revealed that (i) the spatial and temporal characteristics of assemblies formed from biomolecular interactions can be reported by surface-driven ordering transitions in the LCs, (ii) the interfacial phase behavior of molecules and colloids can be coupled to (and manipulated via) the ordering (and nematic elasticity) of LCs, and (iii) the confinement of LCs leads to unanticipated size-dependent ordering (particularly in the context of LC emulsion droplets). The third and final advance addressed in this article involves interactions between colloids mediated by LCs. Recent experiments involving microparticles deposited at the LC-aqueous interface have revealed that LC-mediated interactions can drive interfacial assemblies of particles through reversible ordering transitions (e.g., from 1D chains to 2D arrays with local hexagonal symmetry). In addition, recent single-nanoparticle measurements suggest that the ordering of LCs about nanoparticles differs substantially from micrometer-sized particles and that the interactions between nanoparticles mediated by the LCs are far weaker than predicted by theory (sufficiently weak that the interactions are reversible and thus enable self-assembly). Finally, LC-mediated interactions between colloidal particles have also been shown to lead to the formation of colloid-in-LC gels that possess mechanical properties relevant to the design of materials that interface with living biological systems. Overall, these three topics serve to illustrate the broad opportunities that exist to do fundamental interfacial science and discovery-oriented research involving LCs.

PMID: 21090596 [PubMed - indexed for MEDLINE]

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Recent advances in colloidal and interfacial phenomena involving liquid crystals.

Langmuir. 2011 May 17;27(10):5719-38

Authors: Bai Y, Abbott NL

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Lateral transport of solutes in microfluidic channels using electrochemically generated gradients in redox-active surfactants.

Anal Chem. 2011 Apr 15;83(8):3033-41

Authors: Liu X, Abbott NL

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Lateral transport of solutes in microfluidic channels using electrochemically generated gradients in redox-active surfactants.

Anal Chem. 2011 Apr 15;83(8):3033-41

Authors: Liu X, Abbott NL

Abstract
We report principles for a continuous flow process that can separate solutes based on a driving force for selective transport that is generated by a lateral concentration gradient of a redox-active surfactant across a microfluidic channel. Microfluidic channels fabricated with gold electrodes lining each vertical wall were used to electrochemically generate concentration gradients of the redox-active surfactant 11-ferrocenylundecyl-trimethylammonium bromide (FTMA) in a direction perpendicular to the flow. The interactions of three solutes (a hydrophobic dye, 1-phenylazo-2-naphthylamine (yellow AB), an amphiphilic molecule, 2-(4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene-3-pentanoyl)-1-hexadecanoyl-sn-glycero-3-phosphocholine (BODIPY C(5)-HPC), and an organic salt, 1-methylpyridinium-3-sulfonate (MPS)) with the lateral gradients in surfactant/micelle concentration were shown to drive the formation of solute-specific concentration gradients. Two distinct physical mechanisms were identified to lead to the solute concentration gradients: solubilization of solutes by micelles and differential adsorption of the solutes onto the walls of the microchannels in the presence of the surfactant concentration gradient. These two mechanisms were used to demonstrate delipidation of a mixture of BODIPY C(5)-HPC (lipid) and MPS and purification of BODIPY C(5)-HPC from a mixture of BODIPY C(5)-HPC and yellow AB. Overall, the results of this study demonstrate that lateral concentration gradients of redox-active surfactants formed within microfluidic channels can be used to transport solutes across the microfluidic channels in a solute-dependent manner. The approach employs electrical potentials (<1 V) that are sufficiently small to avoid electrolysis of water, can be performed in solutions having high ionic strength (>0.1M), and offers the basis of continuous processes for the purification or separation of solutes in microscale systems.

PMID: 21446653 [PubMed - indexed for MEDLINE]

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Lateral transport of solutes in microfluidic channels using electrochemically generated gradients in redox-active surfactants.

Anal Chem. 2011 Apr 15;83(8):3033-41

Authors: Liu X, Abbott NL

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Single-molecule force spectroscopy of β-peptides that display well-defined three-dimensional chemical patterns.

J Am Chem Soc. 2011 Mar 23;133(11):3981-8

Authors: Acevedo-Vélez C, Andre G, Dufrêne YF, Gellman SH, Abbott NL

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Single-molecule force spectroscopy of β-peptides that display well-defined three-dimensional chemical patterns.

J Am Chem Soc. 2011 Mar 23;133(11):3981-8

Authors: Acevedo-Vélez C, Andre G, Dufrêne YF, Gellman SH, Abbott NL

Abstract
Oligomers of β-amino acids ("β-peptides") can be designed to fold into stable helices that display side chains with a diverse range of chemical functionality in precise arrangements. We sought to determine whether the predictable, three-dimensional side-chain patterns generated by β-peptides could be used in combination with single-molecule force spectroscopy to quantify how changes in nanometer-scale chemical patterns affect intermolecular interactions. To this end, we synthesized β-peptides that were designed to be either globally amphiphilic (GA), i.e., display a global segregation of side chains bearing hydrophobic and cationic functional groups, or non-globally amphiphilic (iso-GA), i.e., display a more uniform distribution of hydrophobic and cationic functional groups in three-dimensions. Single-molecule force measurements of β-peptide interactions with hydrophobic surfaces through aqueous solution (triethanolamine buffer, pH 7.2) reveal that the GA and iso-GA isomers give rise to qualitatively different adhesion force histograms. The data are consistent with the display of a substantial nonpolar domain by the GA oligomer, which leads to strong hydrophobic interactions, and the absence of a comparable domain on the iso-GA oligomer. This interpretation is supported by force measurements in the presence of methanol, which is known to disrupt hydrophobic interactions. Our ability to associate changes in measured forces with changes in three-dimensional chemical nanopatterns projected from conformationally stable β-peptide helices highlights a contrast between this system and conventional peptides (α-amino acid residues): conventional peptides are more conformationally flexible, which leads to uncertainty in the three-dimensional nanoscopic chemical patterns that underlie measured forces. Overall, we conclude that β-peptide oligomers provide a versatile platform for quantifying intermolecular interactions that arise from specific functional group nanopatterns.

PMID: 21361359 [PubMed - indexed for MEDLINE]

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Single-molecule force spectroscopy of β-peptides that display well-defined three-dimensional chemical patterns.

J Am Chem Soc. 2011 Mar 23;133(11):3981-8

Authors: Acevedo-Vélez C, Andre G, Dufrêne YF, Gellman SH, Abbott NL

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Ordering transitions in nematic liquid crystals induced by vesicles captured through ligand-receptor interactions.

Langmuir. 2011 Feb 15;27(4):1419-29

Authors: Tan LN, Bertics PJ, Abbott NL

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Ordering transitions in nematic liquid crystals induced by vesicles captured through ligand-receptor interactions.

Langmuir. 2011 Feb 15;27(4):1419-29

Authors: Tan LN, Bertics PJ, Abbott NL

Abstract
We report that phospholipid vesicles incorporating ligands, when captured from solution onto surfaces presenting receptors for these ligands, can trigger surface-induced orientational ordering transitions in nematic phases of 4'-pentyl-4-cyanobiphenyl (5CB). Specifically, whereas avidin-functionalized surfaces incubated against vesicles composed of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) were observed to cause the liquid crystal (LC) to adopt a parallel orientation at the surface, the same surfaces incubated against biotinylated vesicles (DOPC and 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-(biotinyl) (biotin-DOPE)) caused the homeotropic (perpendicular) ordering of the LC. The use of a combination of atomic force microscopy (AFM), ellipsometry and quantitative fluorimetry, performed as a function of vesicle composition and vesicle concentration in solution, revealed the capture of intact vesicles containing 1% biotin-DOPE from buffer at the avidin-functionalized surfaces. Subsequent exposure to water prior to contact with the LC, however, resulted in the rupture of the majority of vesicles into interfacial multilayer assemblies with a maximum phospholipid loading set by random close packing of the intact vesicles initially captured on the surface (5.1 ± 0.2 phospholipid molecules/nm(2)). At high concentrations of biotinylated lipid (>10% biotin-DOPE) in the vesicles, the limiting lipid loading was measured to be 4.0 ± 0.3 phospholipid molecules/nm(2), consistent with the maximum phospholipid loading set by the spontaneous formation of a bilayer during incubation with the biotinylated vesicles. We measured the homeotropic ordering of the LC on the surfaces independently of the initial morphology of the phospholipid assembly captured on the surface (intact vesicle, planar multilayer). We interpret this result to infer the reorganization of the phospholipid bilayers either prior to or upon contact with the LCs such that interactions of the acyl chains of the phospholipid and the LC dominate the ordering of the LC, a conclusion that is further supported by quantitative measurements of the orientation of the LC as a function of the phospholipid surface density (>1.8 molecules/nm(2) is required to cause the homeotropic ordering of the LC). These results and others presented herein provide fundamental insights into the interactions of phospholipid-decorated interfaces with LCs and thereby provide guidance for the design of surfaces on which phospholipid assemblies captured through ligand-receptor recognition can be reported via ordering transitions in LCs.

PMID: 21142099 [PubMed - indexed for MEDLINE]

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Ordering transitions in nematic liquid crystals induced by vesicles captured through ligand-receptor interactions.

Langmuir. 2011 Feb 15;27(4):1419-29

Authors: Tan LN, Bertics PJ, Abbott NL

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Effect of trehalose on the interaction of Alzheimer's Aβ-peptide and anionic lipid monolayers.

Biochim Biophys Acta. 2011 Jan;1808(1):26-33

Authors: Izmitli A, Schebor C, McGovern MP, Reddy AS, Abbott NL, de Pablo JJ

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Effect of trehalose on the interaction of Alzheimer's Aβ-peptide and anionic lipid monolayers.

Biochim Biophys Acta. 2011 Jan;1808(1):26-33

Authors: Izmitli A, Schebor C, McGovern MP, Reddy AS, Abbott NL, de Pablo JJ

Abstract
The interaction of amyloid β-peptide (Aβ) with cell membranes is believed to play a central role in the pathogenesis of Alzheimer's disease. In particular, recent experimental evidence indicates that bilayer and monolayer membranes accelerate the aggregation and amyloid fibril formation rate of Aβ. Understanding that interaction could help develop therapeutic strategies for treatment of the disease. Trehalose, a disaccharide of glucose, has been shown to be effective in preventing the aggregation of numerous proteins. It has also been shown to delay the onset of certain amyloid-related diseases in a mouse model. Using Langmuir monolayers and molecular simulations of the corresponding system, we study several thermodynamic and kinetic aspects of the insertion of Aβ peptide into DPPG monolayers in water and trehalose subphases. In the water subphase, the insertion of the Aβ peptide into the monolayer exhibits a lag time which decreases with increasing temperature of the subphase. In the presence of trehalose, the lag time is completely eliminated and peptide insertion is completed within a shorter time period compared to that observed in pure water. Molecular simulations show that more peptide is inserted into the monolayer in the water subphase, and that such insertion is deeper. The peptide at the monolayer interface orients itself parallel to the monolayer, while it inserts with an angle of 50° in the trehalose subphase. Simulations also show that trehalose reduces the conformational change that the peptide undergoes when it inserts into the monolayer. This observation helps explain the experimentally observed elimination of the lag time by trehalose and the temperature dependence of the lag time in the water subphase.

PMID: 20920466 [PubMed - indexed for MEDLINE]

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Effect of trehalose on the interaction of Alzheimer's Aβ-peptide and anionic lipid monolayers.

Biochim Biophys Acta. 2011 Jan;1808(1):26-33

Authors: Izmitli A, Schebor C, McGovern MP, Reddy AS, Abbott NL, de Pablo JJ

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Lyotropic liquid crystalline phases from helical β-peptides as alignment media.

Chem Commun (Camb). 2011 Jan 7;47(1):502-4

Authors: Thiele CM, Pomerantz WC, Abbott NL, Gellman SH

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Lyotropic liquid crystalline phases from helical β-peptides as alignment media.

Chem Commun (Camb). 2011 Jan 7;47(1):502-4

Authors: Thiele CM, Pomerantz WC, Abbott NL, Gellman SH

Abstract
Lyotropic liquid crystalline (LLC) phases from helical β-peptides are proposed as novel water-based alignment media. In contrast to α-peptides, β-peptides form LLCs at very short chain lengths and at concentrations as low as 1 percent. Spectra obtained in these LLC phases are artefact-free and lead to RDCs of the desired size. First indications towards enantiodiscrimination are provided.

PMID: 20972503 [PubMed - indexed for MEDLINE]

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Lyotropic liquid crystalline phases from helical β-peptides as alignment media.

Chem Commun (Camb). 2011 Jan 7;47(1):502-4

Authors: Thiele CM, Pomerantz WC, Abbott NL, Gellman SH

2010

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Characterization of the nanostructure of complexes formed by single- or double-stranded oligonucleotides with a cationic surfactant.

J Phys Chem B. 2010 Dec 2;114(47):15554-64

Authors: Liu X, Abbott NL

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Characterization of the nanostructure of complexes formed by single- or double-stranded oligonucleotides with a cationic surfactant.

J Phys Chem B. 2010 Dec 2;114(47):15554-64

Authors: Liu X, Abbott NL

Abstract
We report the use of dynamic light scattering (DLS), small-angle neutron scattering (SANS), and small-angle X-ray scattering (SAXS) to characterize the nanostructure of complexes formed by either single- or double-stranded oligonucleotides with a cationic surfactant (cetyltrimethylammonium bromide, CTAB) in aqueous solution (1 mM Li(2)SO(4)). For single-stranded oligonucleotides 5'-A(20)-3' and 5'-CCCCATTCTAGCAGCCCGGG-3', both the appearance of two Bragg peaks (at 0.14 and 0.28 Å(-1)) in SAXS spectra with a spacing of 1:2 and form factor fits to SANS spectra are consistent with the presence of multilamellar vesicles (with, on average, 6-9 layers with a periodicity of 45-48 Å). Some samples showed evidence of an additional Bragg peak (at 0.20 Å(-1)) associated with periodic packing (with a periodicity of 31 Å) of the oligonucleotides within the lamellae of the nanostructure. The nucleotide composition of the single-stranded oligonucleotides was also found to impact the number and size of the complexes formed with CTAB. In contrast to 5'-A(20)-3' and 5'-CCCCATTCTAGCAGCCCGGG-3', 5'-T(20)-3' did not change the state of aggregation of CTAB (globular micelles) over a wide range of oligonucleotide:CTAB charge ratios. These results support the proposition that hydrophobic interactions, as well as electrostatics, play a central role in the formation of complexes between cationic amphiphiles and single-stranded oligonucleotides and thus give rise to nanostructures that depend on nucleotide composition. In contrast to the single-stranded oligonucleotides, for double-stranded oligonucleotides mixed with CTAB, three Bragg peaks (0.13, 0.23, and 0.25 Å(-1)) in SAXS spectra with a spacing ratio of 1:√3:√4 and characteristic changes in SANS spectra indicate formation of a hexagonal nanostructure. Also, the composition of the double-stranded oligonucleotides did not measurably impact the nanostructure of complexes formed with CTAB, suggesting that electrostatic interactions dominate the formation of these complexes. Overall, these results provide insights into the intermolecular interactions that occur between cationic amphiphiles and oligonucleotides and establish that single and double-stranded oligonucleotides form complexes with cationic surfactants that differ in nanostructure. The results also provide guidance for the design of oligonucleotide complexes with cationic amphiphiles.

PMID: 21062067 [PubMed - indexed for MEDLINE]

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Characterization of the nanostructure of complexes formed by single- or double-stranded oligonucleotides with a cationic surfactant.

J Phys Chem B. 2010 Dec 2;114(47):15554-64

Authors: Liu X, Abbott NL

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Spontaneous formation of water droplets at oil-solid interfaces.

Langmuir. 2010 Sep 7;26(17):13797-804

Authors: Yang Z, Abbott NL

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Spontaneous formation of water droplets at oil-solid interfaces.

Langmuir. 2010 Sep 7;26(17):13797-804

Authors: Yang Z, Abbott NL

Abstract
We report observations of spontaneous formation of micrometer-sized water droplets within micrometer-thick films of a range of different oils (isotropic and nematic 4-cyano-4'-pentylbiphenyl (5CB) and silicone, olive and corn oil) that are supported on glass substrates treated with octadecyltrichlorosilane (OTS) and immersed under water. Confocal imaging was used to determine that the water droplets nucleate and grow at the interface between the oils and OTS-treated glass with a contact angle of approximately 130 degrees. A simple thermodynamic model based on macroscopic interfacial energetic arguments consistent with the contact angle of 130 degrees, however, fails to account for the spontaneous formation of the water droplets. zeta-potential measurements performed with OTS-treated glass (-59.0 +/- 16.4 mV) and hydrophobic monolayers formed on gold films (2.0 +/- 0.7 mV), when combined with the observed absence of droplet formation under films of oil supported on the latter surfaces, suggest that the charge of the oil-solid interface promotes partitioning of water to the interfacial region. The hydrophobic nature of the OTS-treated glass promotes dewetting of water accumulated in the interfacial region into droplets (a thin film of water is seen to form on bare glass). The inhibitory effect on droplet formation of both salt (NaCl) and sucrose (0.1-500 mM) added to the aqueous phase was similar, indicating that both solutes lower the chemical potential of the bulk water (osmotic effect) sufficiently to prevent partitioning of the water to the interface between the oil and supporting substrates. These results suggest that charged, hydrophobic surfaces can provide routes to spontaneous formation of surface-supported, water-in-oil emulsions.

PMID: 20712383 [PubMed - indexed for MEDLINE]

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Spontaneous formation of water droplets at oil-solid interfaces.

Langmuir. 2010 Sep 7;26(17):13797-804

Authors: Yang Z, Abbott NL

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Design of Biomolecular Interfaces using Liquid Crystals Containing Oligomeric Ethylene Glycol.

Adv Funct Mater. 2010 Jul 9;20(13):2098-2106

Authors: Yang Z, Gupta JK, Kishimoto K, Shoji Y, Kato T, Abbott NL

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Design of Biomolecular Interfaces using Liquid Crystals Containing Oligomeric Ethylene Glycol.

Adv Funct Mater. 2010 Jul 9;20(13):2098-2106

Authors: Yang Z, Gupta JK, Kishimoto K, Shoji Y, Kato T, Abbott NL

Abstract
We report an investigation of nematic LCs formed from miscible mixtures of 4-cyano-4'-pentylbiphenyl (5CB) and 2-(2-[2-{2-(2,3-difluoro-4-{4-(4-trans-pentylcyclohexyl)-phenyl-phenoxy)ethoxy}ethoxy]ethoxy)ethanol (EG4-LC), the latter being a mesogen with a tetra(ethylene glycol) tail. Quantitative characterization of the ordering of this LC mixture at biologically-relevant aqueous interfaces revealed that addition of EG4-LC (1-5% by weight) to 5CB causes a continuous transition in the ordering of the LC from a planar (pure 5CB) to a perpendicular (homeotropic) orientation. The homeotropic ordering is also seen in aqueous dispersions of micrometer-sized droplets of the LC mixture, which exhibit enhanced stability against coalescence. These observations and others, all of which suggest partitioning of the EG4-LC from the bulk of the LC to its aqueous interface, were complemented by measurements of the adsorption of bovine serum albumin (BSA) to the aqueous-LC interface. Whereas adsorption of BSA to the interface of a LC mixture containing 1% wt/wt of EG4-LC triggered an ordering transition, higher concentrations of EG4-LC (>2% wt/wt) prevented this ordering transition, consistent with a decrease in adsorption of BSA. This conclusion is supported by epifluorescence measurements using fluorescently labeled BSA and comparisons to LC interfaces at which EG4-containing lipids are adsorbed. Overall, these results demonstrate a general and facile approach to the design of LCs with interfaces that present biologically relevant chemical functional groups, assume well-defined orientations at aqueous interfaces, and lower non-specific protein adsorption. The bulk of the LC serves as a reservoir of EG4-LC, thus permitting easy preparation of these interfaces and the potential for spontaneous repair of the EG4-decorated interfaces during contact with biological systems.

PMID: 22199989 [PubMed - as supplied by publisher]

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Design of Biomolecular Interfaces using Liquid Crystals Containing Oligomeric Ethylene Glycol.

Adv Funct Mater. 2010 Jul 9;20(13):2098-2106

Authors: Yang Z, Gupta JK, Kishimoto K, Shoji Y, Kato T, Abbott NL

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Immobilization of polymer-decorated liquid crystal droplets on chemically tailored surfaces.

Langmuir. 2010 Jun 15;26(12):10234-42

Authors: Kinsinger MI, Buck ME, Abbott NL, Lynn DM

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Immobilization of polymer-decorated liquid crystal droplets on chemically tailored surfaces.

Langmuir. 2010 Jun 15;26(12):10234-42

Authors: Kinsinger MI, Buck ME, Abbott NL, Lynn DM

Abstract
We demonstrate that the assembly of an amphiphilic polyamine on the interfaces of micrometer-sized droplets of a thermotropic liquid crystal (LC) dispersed in aqueous solutions can be used to facilitate the immobilization of LC droplets on chemically functionalized surfaces. Polymer 1 was designed to contain both hydrophobic (alkyl-functionalized) and hydrophilic (primary and tertiary amine-functionalized) side chain functionality. The assembly of this polymer at the interfaces of aqueous dispersions of LC droplets was achieved by the spontaneous adsorption of polymer from aqueous solution. Polymer adsorption triggered transitions in the orientational ordering of the LCs, as observed by polarized light and bright-field microscopy. We demonstrate that the presence of polymer 1 on the interfaces of these droplets can be exploited to immobilize LC droplets on planar solid surfaces through covalent bond formation (e.g., for surfaces coated with polymer multilayers containing reactive azlactone functionality) or through electrostatic interactions (e.g., for surfaces coated with multilayers containing hydrolyzed azlactone functionality). The characterization of immobilized LC droplets by polarized, fluorescence, and laser scanning confocal microscopy revealed the general spherical shape of the polymer-coated LC droplets to be maintained after immobilization, and that immobilization led to additional ordering transitions within the droplets that were dependent on the nature of the surfaces with which they were in contact. Polymer 1-functionalized LC droplets were not immobilized on polymer multilayers treated with poly(ethylene imine) (PEI). We demonstrate that the ability to design surfaces that promote or prevent the immobilization of polymer-functionalized LC droplets can be exploited to pattern the immobilization of LC droplets on surfaces. The results of this investigation provide the basis of an approach that could be used to tailor the properties of dispersed LC emulsions and to immobilize these droplets on functional surfaces of interest in a broad range of fundamental and applied contexts.

PMID: 20405867 [PubMed - indexed for MEDLINE]

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Immobilization of polymer-decorated liquid crystal droplets on chemically tailored surfaces.

Langmuir. 2010 Jun 15;26(12):10234-42

Authors: Kinsinger MI, Buck ME, Abbott NL, Lynn DM

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Characterization of surfaces presenting covalently immobilized oligopeptides using near-edge X-ray absorption fine structure spectroscopy.

Langmuir. 2010 May 4;26(9):6464-70

Authors: Bai Y, Liu X, Cook P, Abbott NL, Himpsel FJ

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Characterization of surfaces presenting covalently immobilized oligopeptides using near-edge X-ray absorption fine structure spectroscopy.

Langmuir. 2010 May 4;26(9):6464-70

Authors: Bai Y, Liu X, Cook P, Abbott NL, Himpsel FJ

Abstract
This study addresses the need for methods that validate the surface chemistry leading to the immobilization of biomolecules and provide information about the resulting structural configurations. We report on the use of near-edge X-ray absorption fine structure spectroscopy (NEXAFS) to characterize a widely employed immobilization chemistry that leads to the covalent attachment of a biologically relevant oligopeptide to a surface. The oligopeptide used in this study is a kinase substrate of the epidermal growth factor receptor (EGFR), a protein that is a common target for cancer therapeutics. By observing changes in the pi* and sigma* orbitals of specific nitrogen and carbon atoms (amide, imide, carbonyl), we are able to follow the sequential reactions leading to immobilization of the oligopeptide. We also show that it is possible to use NEXAFS to extend this characterization method to submonolayer densities that are relevant to biological assays. Such an element-specific chemical characterization of small peptides on surfaces fills an unmet need and establishes NEXAFS as useful technique for characterizing the immobilization of small biomolecules on surfaces.

PMID: 20387822 [PubMed - indexed for MEDLINE]

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Characterization of surfaces presenting covalently immobilized oligopeptides using near-edge X-ray absorption fine structure spectroscopy.

Langmuir. 2010 May 4;26(9):6464-70

Authors: Bai Y, Liu X, Cook P, Abbott NL, Himpsel FJ

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Design of surfaces for liquid crystal-based bioanalytical assays.

ACS Appl Mater Interfaces. 2010 Mar;2(3):722-31

Authors: Lowe AM, Ozer BH, Bai Y, Bertics PJ, Abbott NL

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Design of surfaces for liquid crystal-based bioanalytical assays.

ACS Appl Mater Interfaces. 2010 Mar;2(3):722-31

Authors: Lowe AM, Ozer BH, Bai Y, Bertics PJ, Abbott NL

Abstract
Surface-induced ordering of liquid crystals (LCs) offers the basis of a label-free analytical technique for the detection of surface-bound biomolecules. The orientation-dependent energy of interaction of a LC with a surface (anchoring energy of LC), in particular, is both sensitive to the presence of surface-bound molecules and easily quantified. Herein, we report a study that analyzes a simple model of twisted nematic LC systems and thereby identifies surfaces with LC anchoring energies in the range of 0.5 microJ/m(2) to 2.0 microJ/m(2) to be optimal for use with LC-based analytical methods. Guided by these predictions, we demonstrate that analytic surfaces possessing anchoring energies within this range can be fabricated with a high level of precision (< 0.1 microJ/m(2)) through formation of monolayers of organothiols (with omega-functional groups corresponding to oligoethyleneglycols and amines) on gold films deposited by physical vapor deposition at oblique angles of incidence. Finally, by using the human epidermal growth factor receptor (EGFR) as a model protein analyte, we have characterized the influence of the anchoring energies of the surfaces on the response of the LC to the presence of surface-bound EGFR. These results, when combined with (32)P-radiolabeling of the EGFR to independently quantify the surface concentration of EGFR, permit identification of surfaces that allow use of LCs to report surface densities of EGFR of 30-40 pg/mm(2). Overall, the results reported in this paper guide the design of surfaces for use in LC-based analytical systems.

PMID: 20356273 [PubMed - indexed for MEDLINE]

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Design of surfaces for liquid crystal-based bioanalytical assays.

ACS Appl Mater Interfaces. 2010 Mar;2(3):722-31

Authors: Lowe AM, Ozer BH, Bai Y, Bertics PJ, Abbott NL

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Langmuir films of flexible polymers transferred to aqueous/liquid crystal interfaces induce uniform azimuthal alignment of the liquid crystal.

J Colloid Interface Sci. 2010 Jan 1;341(1):124-35

Authors: Kinsinger MI, Buck ME, Meli MV, Abbott NL, Lynn DM

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Langmuir films of flexible polymers transferred to aqueous/liquid crystal interfaces induce uniform azimuthal alignment of the liquid crystal.

J Colloid Interface Sci. 2010 Jan 1;341(1):124-35

Authors: Kinsinger MI, Buck ME, Meli MV, Abbott NL, Lynn DM

Abstract
We reported recently that amphiphilic polymers can be assembled at interfaces created between aqueous phases and thermotropic liquid crystals (LCs) in ways that: (i) couple the organization of the polymer to the order of the LC and (ii) respond to changes in the properties of aqueous phases that can be characterized as changes in the optical appearance of the LC. This investigation sought to characterize the behavior of aqueous-LC interfaces decorated with uniaxially compressed thin films of polymers transferred by Langmuir-Schaefer (LS) transfer. Here, we report physicochemical characterization of interfaces created between aqueous phases and the thermotropic LC 4-cyano-4'-pentylbiphenyl (5CB) decorated with Langmuir films of a novel amphiphilic polymer (polymer 1), synthesized by the addition of hydrophobic and hydrophilic side chains to poly(2-vinyl-4,4'-dimethylazlactone). Initial characterization of this system resulted in the unexpected observation of uniform azimuthal alignment of 5CB after LS transfer of the polymer films to aqueous-5CB interfaces. This paper describes characterization of Langmuir films of polymer 1 hosted at aqueous-5CB interfaces as well as the results of our investigations into the origins of the uniform ordering of the LC observed upon LS transfer. Our results, when combined, support the conclusion that uniform azimuthal alignment of 5CB is the result of long-range ordering of polymer chains in the Langmuir films (in a preferred direction orthogonal to the direction of compression) that is generated during uniaxial compression of the films prior to LS transfer. Although past studies of Langmuir films of polymers at aqueous-air interfaces have demonstrated that in-plane alignment of polymer backbones can be induced by uniaxial compression, these past reports have generally made use of polymers with rigid backbones. One important outcome of this current study is thus the observation of anisotropy and long-range order in Langmuir films of a novel flexible polymer. A second important outcome is the observation that the existence, extent, and dynamics of this order can be identified and characterized optically by transfer of the Langmuir film to a thin film of LC. Additional characterization of Langmuir films of two other flexible polymers [poly(methyl methacrylate) and poly(vinyl stearate)] using this method also resulted in uniform azimuthal alignment of 5CB, suggesting that the generation of long-range order in uniaxially compressed Langmuir films of polymers may also occur more generally over a broader range of polymers with flexible backbones.

PMID: 19836025 [PubMed - indexed for MEDLINE]

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Langmuir films of flexible polymers transferred to aqueous/liquid crystal interfaces induce uniform azimuthal alignment of the liquid crystal.

J Colloid Interface Sci. 2010 Jan 1;341(1):124-35

Authors: Kinsinger MI, Buck ME, Meli MV, Abbott NL, Lynn DM