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

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.

SUBMITTER: Yang Z

PROVIDER: S-EPMC3245687 | biostudies-literature | 2010 Jul

REPOSITORIES: biostudies-literature

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

Yang Zhongqiang Z Gupta Jugal K JK Kishimoto Kenji K Shoji Yoshiko Y Kato Takashi T Abbott Nicholas L NL

Advanced functional materials 20100701 13

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 ...[more]

PMID: 22199989

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Project description:Stimuli-responsive biomaterials are used to facilitate drug and gene delivery by shielding the drug/gene during circulation times and selectively releasing the cargo at the desired target. Within stimuli-responsive materials, pH-responsive materials are exploited for delivery to specific organs, intracellular compartments, cancer cells, site of inflammation or infection as those sites are characterized by pH that is different from the blood pH. In this paper we use molecular dynamics (MD) simulations to design such pH-responsive biomaterials where the balance between the various intermolecular interactions (e.g., electrostatics, van der Waals) within the biomaterials allow biofunctional molecules to be reversibly shielded and exposed to the environment with change in pH. In our model the shielding aspect is imparted by a polyethylene glycol (PEG) brush and the pH-responsive component is a PEG-tethered oligopeptide that undergoes changes in conformations via protonation of residues upon changes in pH. Starting with a PEG-tethered peptide in a monodisperse short PEG brush, we first vary the composition and sequence of histidine (H), lysine (K), and glutamate (E) along the oligopeptide sequence to find the design parameters that maximize the shielding and exposure of the oligopeptide at pH ? 7.0 and pH < 7.0, respectively. Then, we probe the effect of the PEG brush on the conformations of the oligopeptides by simulating PEG-tethered peptide in a bimodal PEG brush containing short PEG and long PEG chains. We characterize the intermolecular interactions involving the PEG, peptide, and solvent that influence the shielded and exposed conformations of the oligopeptides at the two different pHs. In a short monodisperse PEG brush, with a longer PEG-tethered peptide containing large blocks of histidines that undergo change in protonation state as a response to pH change, placed between a protonated lysine and deprotonated glutamate, the PEG brush exhibits maximum shielding and exposure with pH change. This change from shielded to exposed state is driven by electrostatic repulsion upon H protonation. The presence of long PEG chains in a bimodal PEG brush leads to dominating PEG-peptide attractive interactions that reduces the contrast in shielded and exposed conformations of the PEG-tethered peptide upon protonation of histidines.

Project description:Soft matter that undergoes programmed macroscopic responses to molecular analytes has potential utility in a range of health and safety-related contexts. In this study, we report the design of a nematic liquid crystal (LC) composition that forms through dimerization of carboxylic acids and responds to the presence of vapors of organoamines by undergoing a visually distinct phase transition to an isotropic phase. Specifically, we screened mixtures of two carboxylic acids, 4-butylbenzoic acid and trans-4-pentylcyclohexanecarboxylic acid, and found select compositions that exhibited a nematic phase from 30.6 to 111.7 °C during heating and 110.6 to 3.1 °C during cooling. The metastable nematic phase formed at ambient temperatures was found to be long-lived (>5 days), thus enabling the use of the LC as a chemoresponsive optical material. By comparing experimental infrared (IR) spectra of the LC phase with vibrational frequencies calculated using density functional theory (DFT), we show that it is possible to distinguish between the presence of monomers, homodimers and heterodimers in the mixture, leading us to conclude that a one-to-one heterodimer is the dominant species within this LC composition. Further support for this conclusion is obtained by using differential scanning calorimetry. Exposure of the LC to 12 ppm triethylamine (TEA) triggers a phase transition to an isotropic phase, which we show by IR spectroscopy to be driven by an acid-base reaction, leading to the formation of ammonium carboxylate salts. We characterized the dynamics of the phase transition and found that it proceeds via a characteristic spatiotemporal pathway involving the nucleation, growth, and coalescence of isotropic domains, thus amplifying the atomic-scale acid-base reaction into an information-rich optical output. In contrast to TEA, we determined via both experiment and computation that neither hydrogen bonding donor or acceptor molecules, such as water, dimethyl methylphosphonate, ethylene oxide or formaldehyde, disrupt the heterodimers formed in the LC, hinting that the phase transition (including spatial-temporal characteristics of the pathway) induced in this class of hydrogen bonded LC may offer the basis of a facile and chemically selective way of reporting the presence of volatile amines. This proposal is supported by exploratory experiments in which we show that it is possible to trigger a phase transition in the LC by exposure to volatile amines emitted from rotting fish. Overall, these results provide new principles for the design of chemoresponsive soft matter based on hydrogen bonded LCs that may find use as the basis of low-cost visual indicators of chemical environments.

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

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

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