Liquid Crystalline Membranes Research Articles

Electrochemical Detection of Selective Anion Transport through Subnanopores in Liquid-Crystalline Water Treatment Membranes.

The anion-selective transport through subnanoporous liquid-crystalline (LC) water treatment membranes was quantitatively detected by the deposition and electrochemical analysis of the LC membrane on the GaN electrode. The time course of the capacitance and Warburg resistance of the LC membrane suggest that the interaction of the LC membrane with monovalent Cl- ions is distinctly different from that with SO42- ions. A continuous decay in capacitance suggests the condensation of Cl- ions in subnanopores, whereas the interaction between SO42- ions and the inner wall of subnanopores is much weaker. The chronoamperometry data further suggest that SO42- ions are transported through subnanoporous channels 10 times faster than Cl- ions. These results, together with the previous X-ray emission spectroscopy, suggest that SO42- ions, which possess similar hydrogen-bonded structures to the hydrogen-bonded networks inside the subnanopores, can exchange the associated water molecules and hop along the network of water molecules, but Cl- ions bind and accumulate inside subnanopores. The well-controlled supramolecular self-assembly of LC building blocks opens a large potential toward the fine adjustment of hydrogen-bonding networks in nanospace providing materials new functions, which cannot be realized by bulk water.

Hydrogen-Bonded Structures of Water Molecules in Hydroxy-Functionalized Nanochannels of Columnar Liquid Crystalline Nanostructured Membranes Studied by Soft X-ray Emission Spectroscopy.

Here, we report a synchrotron-based high-resolution soft X-ray emission spectroscopy study on hydrogen-bonded structures of water molecules in the self-organized, hydroxy-group-functionalized one-dimensional nanochannels of liquid crystalline nanostructured membranes. The water molecules confined in the uncharged hydroxy-functionalized nanochannels (which have a diameter of about 1.5 nm) exhibit hydrogen-bonded structures close to those of bulk liquid water, even directly interacting with diol groups. These hydrogen-bonded structures contrast with the more distorted hydrogen bonding of water molecules confined in self-organized channels with a diameter of 0.6 nm formed by an analogous nanostructured membrane with a cationic moiety, which was explained by the ability of the channel functional groups to donate and accept hydrogen bonds in a confined space and the nanochannel diameter.

A general overview of the multifactorial adaptation to cold: biochemical mechanisms and strategies.

Cold environments are more frequent than people think. They include deep oceans, cold lakes, snow, permafrost, sea ice, glaciers, cold soils, cold deserts, caves, areas at elevations greater than 3000m, and also artificial refrigeration systems. These environments are inhabited by a diversity of eukaryotic and prokaryotic organisms that must adapt to the hard conditions imposed by cold. This adaptation is multifactorial and includes (i) sensing the cold, mainly through the modification of the liquid-crystalline membrane state, leading to the activation of a two-component system that transduce the signal; (ii) adapting the composition of membranes for proper functions mainly due to the production of double bonds in lipids, changes in hopanoid composition, and the inclusion of pigments; (iii) producing cold-adapted proteins, some of which show modifications in the composition of amino acids involved in stabilizing interactions and structural adaptations, e.g., enzymes with high catalytic efficiency; and (iv) producing ice-binding proteins and anti-freeze proteins, extracellular polysaccharides and compatible solutes that protect cells from intracellular and extracellular ice. However, organisms also respond by reprogramming their metabolism and specifically inducing cold-shock and cold-adaptation genes through strategies such as DNA supercoiling, distinctive signatures in promoter regions and/or the action of CSPs on mRNAs, among others. In this review, we describe the main findings about how organisms adapt to cold, with a focus in prokaryotes and linking the information with findings in eukaryotes.

Fluctuating Flexoelectric Membranes in Asymmetric Viscoelastic Media: Power Spectrum through Mechanical Network and Transfer Function Models

Flexoelectric liquid crystalline membranes immersed in asymmetric viscoelastic media is a material system model with physiological applications such as outer hair cells (OHCs), where membrane oscillations generate bulk flow. Motivated by this physiological process, here we extend our previous work by characterizing the force transmission output of our model in addition to viscoelastic fluid flow, since solid–fluid interactions are an essential feature of confined physiological flow and flow in immersed elastic structures. In this work, the rigidity of the confinement results in a passive force reception, while more complete solid–fluid interactions will be considered in the future. A significant contribution of this work is a new asymmetry linear viscoelastic electro-rheological model and the obtained implicit relation between force transmission and flow generation and how this relation is modulated by electric field frequency and the material properties of the device. Maximal force and flow are found at resonant frequencies of asymmetry viscoelastic bulk phases, flexoelectric and dispersion mechanisms through the elastic and Womersley numbers.

Poly(ionic liquid) membranes preserving liquid crystalline microstructures for lithium-ion enrichment

The combination of membrane separation technology and hydrometallurgy has opened up new possibilities for the recovery and recycling of lithium from ever-growing spent lithium-ion batteries. Herein, we prepared a series of positively charged poly(ionic liquid) membranes preserving liquid crystal mesophases and investigated the monatomic ion separation capacity of the liquid crystalline membranes by diffusion dialysis experiments using the simulative spent battery leachate. The results revealed that liquid crystalline membranes with bicontinuous cubic liquid crystal structure possessed great potential as precise ion separation membranes for lithium-ion enrichment. Compared to the other topological structures, the bicontinuous cubic liquid crystal structure enhanced both the Li+ flux and ion selectivity of the membranes. The ion flux of the membrane with this structure was three times higher than that of amorphous membranes. Meanwhile, the Li+/Ni2+ selectivity was up to 7.40, which was significantly higher than that of hexagonal liquid crystalline membranes (2.59) and commercial membranes AMI-7001S (5.71). Moreover, the preservation of liquid crystal structures obviously improved the water management capacity and mechanical strength of the membranes.

Collective dynamics of domain structures in liquid crystalline lipid bilayers

Objectives. Numerous studies of biosystems indicate the distinct role of quasi-one-dimensional molecular structures in the transport of energy, charges, and information. Of particular interest are the studies on the collective dynamics of quasi-one-dimensional lateral structures in liquid crystalline membranes and the possibility of local excitation transfer through such structures. In this paper, we developed a model for the collective dynamics of quasi-one-dimensional domain structures in lipid bilayers interacting with the environment. The objective is to study the mechanisms of the directed energy transport in liquid crystalline lipid membranes.Methods. In this paper, the percolation domain structures formed as a result of phase separation in multicomponent lipid membranes are considered to be quasi-one-dimensional domain structures. The model distinguishes two subsystems interacting with each other and differing in their structural and dynamic properties, i.e., the membrane surface formed by polar groups of lipid molecules and the internal hydrophilic region of the membrane formed by acyl chains of lipids. The acyl chain subsystem is simulated using the Ginzburg-Landau Hamiltonian which considers the dependence of its dynamics on temperature close to the lipid melting phase transition temperature Tc.Results. Analysis of dynamic states has shown that elastic excitations moving at constant rate in the form of solitons may exist near temperatures Tc in the considered quasi-one-dimensional domain structures. In addition, motion of the elastic excitation region (kink) along domain structures in the acyl chain region causes the formation of acoustic soliton, i.e., the compression region in the polar group subsystem moving in concert with the kink displacement. The soliton localization region covers about 10 molecules and depends significantly on the interaction parameter of the polar group and acyl chain subsystems. Soliton moves at a subsonic speed determined, in particular, by the magnitude of an external force.Conclusions. The model developed in this paper shows that liquid crystalline domain structures in lipid membranes exhibit properties of active media, wherein the formation and displacement of localized elastic excitations on macroscopic spatial and temporal scales may occur. The proposed molecular mechanism of the soliton transport along quasi-one-dimensional domain structures may be used for describing the directed energy transfer along lateral domain channels in biomembranes and the cooperative functioning of the membrane bioenergetic and receptor complexes.

Effect of lipid saturation on the topology and oligomeric state of helical membrane polypeptides

Natural liquid crystalline membranes are made up of many different lipids carrying a mixture of saturated and unsaturated fatty acyl chains. Whereas in the past considerable attention has been paid to cholesterol content, the phospholipid head groups and the membrane surface charge the detailed fatty acyl composition was often considered less important. However, recent investigations indicate that the detailed fatty acyl chain composition has pronounced effects on the oligomerization of the transmembrane helical anchoring domains of the MHC II receptor or the membrane alignment of the cationic antimicrobial peptide PGLa. In contrast the antimicrobial peptides magainin 2 and alamethicin are less susceptible to lipid saturation. Using histidine-rich LAH4 designer peptides the high energetic contributions of lipid saturation in stabilizing transmembrane helical alignments are quantitatively evaluated. These observations can have important implications for the biological regulation of membrane proteins and should be taken into considerations during biophysical or structural experiments.

Removal of viruses from their cocktail solution by liquid-crystalline water-treatment membranes

Liquid-crystalline (LC) water-treatment membranes obtained by in situ photopolymerization of ionic mesogenic monomers have been shown to efficiently remove viruses. In our previous works, bicontinuous cubic (Cubbi) and smectic (Sm) LC membranes prepared from ionic taper- and rod-shaped polymerizable mesogens, respectively, were used for this purpose. Here, we report the results of virus removal by columnar (Col) LC water-treatment membranes having ionic nanochannels obtained from ionic taper-shaped mesogens. These effects are compared with those obtained for Cubbi membranes. The effects of these Col and Cubbi LC ionic membranes on the removal of several viruses from their cocktail solution are also examined.

Structure and activation mechanism of the hexameric plasma membrane H+-ATPase

The S. cerevisiae plasma membrane H+-ATPase, Pma1, is a P3A-type ATPase and the primary protein component of the membrane compartment of Pma1 (MCP). Like other plasma membrane H+-ATPases, Pma1 assembles and functions as a hexamer, a property unique to this subfamily among the larger family of P-type ATPases. It has been unclear how Pma1 organizes the yeast membrane into MCP microdomains, or why it is that Pma1 needs to assemble into a hexamer to establish the membrane electrochemical proton gradient. Here we report a high-resolution cryo-EM study of native Pma1 hexamers embedded in endogenous lipids. Remarkably, we found that the Pma1 hexamer encircles a liquid-crystalline membrane domain composed of 57 ordered lipid molecules. The Pma1-encircled lipid patch structure likely serves as the building block of the MCP. At pH 7.4, the carboxyl-terminal regulatory α-helix binds to the phosphorylation domains of two neighboring Pma1 subunits, locking the hexamer in the autoinhibited state. The regulatory helix becomes disordered at lower pH, leading to activation of the Pma1 hexamer. The activation process is accompanied by a 6.7 Å downward shift and a 40° rotation of transmembrane helices 1 and 2 that line the proton translocation path. The conformational changes have enabled us to propose a detailed mechanism for ATP-hydrolysis-driven proton pumping across the plasma membrane. Our structures will facilitate the development of antifungal drugs that target this essential protein.

Improvement of oxygen permselectivity of a rigid helical polyphenylacetylene: Effect of flexible groups, degree of polymerization, composites, thickness, orientation, and network formation

In order to improve oxygen permselectivity of a rigid helical poly(alkenylphenylacetylene) membrane having a columnar liquid crystalline structure, several chemical and membrane structures including the degree of polymerization and the orientation of the macromolecules were modified and controlled. Introduction of longer alkenyl or flexible siloxane groups significantly enhanced oxygen permeability (PO2) and by reducing the degree of polymerization and the thickness of the membranes, or by the formation of network structures oxygen permselectivity (α = PO2/PN2) was effectively enhanced. The membranes from polymers with very small degree of polymerization and perpendicular orientation had extremely high α. In spite of the membranes from the polymers having the identical chemical structure, their performances could be optimized by controlling several membrane structures.

Self-healing and shape memory functions exhibited by supramolecular liquid-crystalline networks formed by combination of hydrogen bonding interactions and coordination bonding.

We here report a new approach to develop self-healing shape memory supramolecular liquid-crystalline (LC) networks through self-assembly of molecular building blocks via combination of hydrogen bonding and coordination bonding. We have designed and synthesized supramolecular LC polymers and networks based on the complexation of a forklike mesogenic ligand with Ag+ ions and carboxylic acids. Unidirectionally aligned fibers and free-standing films forming layered LC nanostructures have been obtained for the supramolecular LC networks. We have found that hybrid supramolecular LC networks formed through metal–ligand interactions and hydrogen bonding exhibit both self-healing properties and shape memory functions, while hydrogen-bonded LC networks only show self-healing properties. The combination of hydrogen bonds and metal–ligand interactions allows the tuning of intermolecular interactions and self-assembled structures, leading to the formation of the dynamic supramolecular LC materials. The new material design presented here has potential for the development of smart LC materials and functional LC membranes with tunable responsiveness.

Structure, membrane topology and influence of cholesterol of the membrane proximal region: transmembrane helical anchor sequence of gp41 from HIV

During the first steps of HIV infection the Env subunit gp41 is thought to establish contact between the membranes and to be the main driver of fusion. Here we investigated in liquid crystalline membranes the structure and cholesterol recognition of constructs made of a gp41 external region carrying a cholesterol recognition amino acid consensus (CRAC) motif and a hydrophobic membrane anchoring sequence. CD- und ATR-FTIR spectroscopies indicate that the constructs adopt a high degree of helical secondary structure in membrane environments. Furthermore, 15N and 2H solid-state NMR spectra of gp41 polypeptides reconstituted into uniaxially oriented bilayers agree with the CRAC domain being an extension of the transmembrane helix. Upon addition of cholesterol the CRAC NMR spectra remain largely unaffected when being associated with the native gp41 transmembrane sequence but its topology changes when anchored in the membrane by a hydrophobic model sequence. The 2H solid-state NMR spectra of deuterated cholesterol are indicative of a stronger influence of the model sequence on this lipid when compared to the native gp41 sequence. These observations are suggestive of a strong coupling between the transmembrane and the membrane proximal region of gp41 possibly enforced by oligomerization of the transmembrane helical region.

Hydrogen-bond filtration.

Self-organization of water molecules around solute ions can affect how they permeate through nanoporous liquid-crystalline membranes.

Influence of chain interaction and ordered structures in polymer dispersed liquid crystalline membranes on thermal conductivity

Abstract Polymer dispersed liquid crystalline (PDLC) membrane with intrinsic thermal conductivity was prepared by dispersing liquid crystalline polysiloxane containing crosslinked structure (liquid crystalline polysiloxane elastomer (LCPE)) into polyvinyl alcohol (PVA). Chemical structures were characterized by Fourier transform infrared (FT-IR) and 1H-NMR, and microscopic structures were analyzed by polarizing optical microscope (POM), scanning electron microscope (SEM) and X-ray diffraction (XRD). The thermal conductivity of PDLC membrane was characterized by hot disk thermal constants analyzer, and the tensile properties were measured by tensile testing machine. Thermal properties were characterized by differential scanning calorimeter (DSC) and thermal gravimetric analyzer (TGA). The results show that LCPE was dispersed in PVA uniformly, and the mesogenic monomer of LCPE formed microscopic ordered structures in PDLC membrane. Meanwhile, hydrogen-bond interaction was formed between LCPE and PVA chain. Both microscopic-ordered structure and the hydrogen-bond interaction improved the phonon transmission path, and the thermal conductivity of PDLC membrane was up to 0.74 W/m⋅K, which was 6 times higher than that of pure PVA film. PDLC membrane possessed proper tensile strength and elongation at break, respectively 5.18 MPa and 338%. As a result, PDLC membrane can be used as thermal conductive membrane in electronic packaging and other related fields.

High Virus Removal by Self‐Organized Nanostructured 2D Liquid‐Crystalline Smectic Membranes for Water Treatment

To obtain high quality of drinking water free from biocontaminants is especially important issue. A new strategy employing smectic liquid-crystalline ionic membranes exhibiting 2D structures of layered nanochannels for water treatment is proposed for efficient virus removal and sufficient water flux. The smectic A (SmA) liquid-crystalline membranes obtained by in situ polymerization of an ionic mesogenic monomer are examined for removal of three distinct viruses with small size: Qβ bacteriophage, MS2 bacteriophage, and Aichi virus. The semi-bilayer structure of the SmA significantly obstructs the virus penetration with an average log reduction value of 7.3 log10 or the equivalent of reducing 18 million viruses down to 1. Furthermore, the layered nanochannels of the SmA liquid crystal allow efficient water permeation compared to other types of liquid-crystalline membrane consisting of nanopores.

On the Origin of the Anomalous Behavior of Lipid Membrane Properties in the Vicinity of the Chain-Melting Phase Transition

Biomembranes are key objects of numerous studies in biology and biophysics of great importance to medicine. A few nanometers thin quasi two-dimensional liquid crystalline membranes with bending rigidity of a few kT exhibit unusual properties and they are the focus of theoretical and experimental physics. The first order chain-melting phase transition of lipid membranes is observed to be accompanied by a pseudocritical behavior of membrane physical-chemical properties. However, the investigation of the nature of the anomalous swelling of a stack of lipid membranes in the vicinity of the transition by different groups led to conflicting conclusions about the level of critical density fluctuations and their impact on the membrane softening. Correspondingly, conclusions about the contribution of Helfrich’s undulations to the effect of swelling were different. In our work we present a comprehensive complementary neutron small-angle and spin-echo study directly showing the presence of significant critical fluctuations in the vicinity of the transition which induce membrane softening. However, contrary to the existing paradigm, we demonstrate that the increased undulation forces cannot explain the anomalous swelling. We suggest that the observed effect is instead determined by the dominating increase of short-range entropic repulsion.

Promotion of anhydrous proton conduction by polyvinyl alcohol in liquid crystalline composite membranes containing 1-tetradecyl-3-methylimidazolium hydrogen sulfate

Composite membranes composed of liquid crystalline 1-tetradecyl-3-methylimidazolium hydrogen sulfate and polyvinyl alcohol are prepared for anhydrous proton conduction. The composite membranes exhibit smectic A liquid crystal phase in which polyvinyl alcohol chains aggregate into lamellas between the bilayers formed by the alkyl imidazolium hydrogen sulfate. Smectic order of hydrogen sulfate anions ensures formation of hydrogen-bonded chains for proton conduction via a hopping mechanism. Electrochemical measurements reveal that temperature-dependent ionic conductivity of the composite membranes approximately follows an Arrhenius-type law and reaches 20.5 mS cm−1 at 140 °C, which is twice that of the pure ionic liquid crystal. Potentiostatic polarization measurements show that proton transfer number of the composite membrane is also promoted. Polyvinyl alcohol promotes anhydrous proton conduction by constructing additional hybrid hydrogen-bonded chains consisting of hydroxyl groups of PVA and hydrogen sulfate anions. The ionic liquid crystalline composite membranes possess the potential application in intermediate temperature fuel cells.

Stiffening of Phosphocholine Membranes by Cholesterol

Cholesterol is a key molecule in controlling membrane fluidity, packing state, and various functions in eukaryotic cell membranes. It also regulates antibiotic drug resistance by augmenting the mechanical properties of its host membrane against structural damage. While, structurally, cholesterol exhibits universal condensing effects on fluid lipid membranes (saturated and unsaturated), its effects on membrane mechanics are presumed to be non-universal. Specifically, cholesterol causes strong stiffening in saturated lipid membranes, yet its mechanical effects on unsaturated lipid membranes remain controversial. Previous studies on di-monounsaturated lipids, such as DOPC, have shown that cholesterol has little effect on the bending rigidity of such membranes, despite clear evidence of a condensing effect. In contrast, neutron spin echo (NSE) spectroscopy shows that cholesterol yields a non-trivial stiffening of DOPC membranes over NSE timescales [1]. Here, we report similar observations using solid-state 2H-NMR spectroscopy. The model-free functional dependence of spin lattice relaxation rates (R1Z) on segmental order parameters (SCD), unambiguously indicates increased membrane bending rigidity with cholesterol [2]. These results are contextualized within the fluctuation-dissipation theorem which connects relaxations from thermal fluctuations in liquid-crystalline membranes to quasi-elastic deformation on mesoscopic length scales. Parallel studies on membranes with different lipid unsaturation (e.g. POPC vs. DOPC) indicate that cholesterol-induced stiffening is dependent on chain unsaturation and is present in all studied membranes. Our dynamical results - as well as structural SANS/SAXS and ESR data - are in excellent agreement with real-space fluctuation analysis from molecular dynamics simulations on cognate DOPC-cholesterol bilayers and with standard theories of membrane mechanics. Our findings have significant biological implications and encourage reassessment of mechanical measurements of cholesterol-containing membranes over length and time scales relevant to biological processes. [1] R. Ashkar et al. Biophys. J. (2019) 116, 328a. [2] T.R. Molugu et al. (2016) Chem. Phys. Lipids 1848, 246.

Transport mechanisms of water molecules and ions in sub-nano channels of nanostructured water treatment liquid-crystalline membranes: a molecular dynamics simulation study

Transport mechanisms of water molecules and ions in the liquid crystalline (LC) membranes with sub-nano channels formed by self-organization of thermotropic ionic LC compounds were elucidated by molecular dynamics simulations.

Polymerizable Photocleavable Columnar Liquid Crystals for Nanoporous Water Treatment Membranes.

Here, we describe a strategy to obtain nanoporous liquid-crystalline (LC) membranes by incorporating a photocleavable ortho-nitrobenzyl group in polymerizable columnar liquid crystals. Two derivatives were synthesized with propylene and nonylene spacers, respectively, between the ionic and the photocleavable moieties to introduce various size nanopores after photocleavage. The membranes were prepared by photopolymerization in the LC states, followed by photocleavage and washing with methanol. The resulting membranes show a virus rejection of 99.99%. Although the rejection value remained almost the same for the two membranes, water flux increased with increasing the length of the alkyl spacers. These membranes were found to be almost free from pinhole defects. The present study offers a new methodology for the development of nanoporous membranes with organized nanostructures for separation technologies.