Polymer sailing on rafts within lipid membranes

Comparison of the property of homogeneous and heterogeneous ion exchange membranes during electrodialysis process

Bidirectional Light-Driven Ion Transport through Porphyrin Metal–Organic Framework-Based van der Waals Heterostructures via pH-Induced Band Alignment Inversion

Structural (volume fractions of the gel phase and the intergel solution) and transport (electrical conductivity, diffusion permeability, transport numbers of counterions and coions) characteristics of cation-exchange (CMX, MK-40) and anion-exchange (AMX, MA-41) membranes in NaCl, CaCl2, and Na2SO4 solutions have been studied. The investigated membranes have the same chemical nature of the ion-exchange matrix and similar values of ion-exchange capacity, but they differ in the degree of heterogeneity and chemical nature of the reinforcing materials. The difference in the properties between heterogeneous (MK-40 and MA-41) and (conventionally) homogeneous (CMX and AMX) membranes is due to the fact that the heterogeneous membranes have macropores, whereas the homogeneous membranes do not have such pores. It has been shown that the largest macropores, which basically determine the high diffusion permeability of heterogeneous membranes, are formed at the boundaries of reinforcing fabric threads and the composite material. Regarding the influence of the electrolyte nature, the sorption of coions of the membrane gel phase (not containing macropores) is of primary importance; the sorption of coions, as well as diffusion permeability and the transport number of coions, increase in the order: 1 : 2 < 1 : 1 < 2 : 1, where the first numeral is the charge of the counterion and the second one is that of the coion. An important role, especially in the case of heterogeneous membranes, is played by the electrolyte diffusion coefficients in the electroneutral solution that fills the central part of meso- and macropores.

Membrane fusion is a common course in innumerable biological processes that helps in the survival of eukaryotes. Enveloped viruses utilize this process to enter the host cells. Generally, the membrane lipid compositions play an important role in membrane fusion by modulating the membrane's physical properties and the behavior of membrane proteins in the cellular milieu. In this work, we have demonstrated the role of polyunsaturated fatty acids (PUFAs), such as eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids, on the organization, dynamics, and fusion of homogeneous and heterogeneous membranes. We have exploited arrays of steady-state and time-resolved fluorescence spectroscopic methods and polyethylene glycol-induced membrane fusion assay to elucidate the behavior of EPA and DHA on dioleoyl phosphatidylcholine (DOPC)/cholesterol (CH) homogeneous and DOPC/sphingomyelin/CH heterogeneous membranes. Our results suggest that EPA and DHA display differential effects on two different membranes. The effects of PUFAs in homogeneous membranes are majorly attributed to their flexible chain dynamics, whereas the ability of PUFA-induced cholesterol transfer from the lo to the ld phase rules their behavior in heterogeneous membranes. Overall, our results provide detailed information on the effect of PUFAs on homogeneous and heterogeneous membranes.

In the desalination of recycled water, the triple demand for a high recovery ratio, low energy consumption, and fouling resistance can be met by electrodialysis (ED) under certain conditions: high recovery is an inherent property of the process, while low energy consumption and fouling resistance can be obtained by the use of modified heterogeneous membranes. To this end, heterogeneous polyethylene-based anionexchange membranes were modified by a hydrophilic anion-exchange coating, having an ion-exchange capacity of 2.2 to 2.9 mEq/g (dry weight) and a specific conductance of 70 to 110 mS/cm. The coating was found to be stable in continuous ED operation (66 days). The modification suppressed water splitting and brought the performance of the coated heterogeneous membranes into line with that of homogeneous commercial anion-exchange membranes. Direct measurement of the polarization at the coated membranes indicated that this phenomenon decreased as a result of the coating. Mathematical modeling showed that the strong antipolarizing effect of the thin charged coating could be explained in terms of the change of ion distribution caused by the coating. A fixed charge density much smaller than that within the membrane bulk sufficed to increase the limiting current to the value obtained with homogeneous membranes, and electroneutrality kept a finite concentration of mobile ions near the entrance to the membrane even at very high current density. Current–voltage curves predicted from the model showed a decrease of polarization for the coated membranes, as was indeed obtained experimentally. Fouling was studied by the addition of dodecylbenzyl sulfonate (DBS) as a model foulant to the feed solution. The modified membranes showed a smaller fouling tendency than commercial anion-exchange membranes.

Ion transport through homogeneous and heterogeneous ion-exchange membranes in single salt and multicomponent electrolyte solutions

The effect of N,N-dimethylacetamide on the selectivity of heterogeneous (MK-40, MA-40, and MA-41) and homogeneous (MF-4SK) ion-exchange membranes is studied for the first time. Concentration dependences of electrical conductivity and diffusion permeability of the membranes were measured experimentally over wide lithium chloride concentrations; on their basis, electrodiffusion coefficients of the co- and counterions were calculated. The interrelation between the electrodiffusion coefficients and the specific moisture capacity of the heterogeneous and homogeneous membranes (which affect their selectivity) is revealed. The calculated electrodiffusion coefficients were used in the calculations of the electromigration transport numbers of counterions in the initial membranes and those processed in mixed solvent. It is shown that the heterogeneous membrane selectivity either increased under the action of the aprotic solvent to polymer material (MA-40, MA-41) or remained practically unchanged (MK-40); the selectivity of homogeneous perfluorinated membranes (e.g., MF-4SK) decreased, thus approaching that of the studied heterogeneous anion-exchange membranes.

The experimental results of the chosen salts permeation with selected heterogeneous and homogenous membranes were analysed as a part of modelling of mass transport in electrodialysis metathesis process (ED-M) for synthesis of KNO3. Heterogeneous membranes swelled more in aqueous solutions and they had higher water uptake than homogeneous membranes. Heterogeneous membranes were also more permeable for both the solute and the solvent, which was attributed to higher solubility of salts in heterogeneous membrane’s material. Diffusion coefficients in ion-exchange membranes tested in this study were found to be dependent on concentration of the upstream solution, with an exception of Ca2+ in anion-exchange membranes and NO3- in cation-exchange membranes. The role of osmosis in water transport in ED-M process was found negligible.

Cholesterol Lipids of Borrelia burgdorferi Form Lipid Rafts and Are Required for the Bactericidal Activity of a Complement-Independent Antibody

During vertebrate development, oligodendrocytes wrap their plasma membrane around axons to produce myelin, a specialized membrane highly enriched in galactosylceramide (GalC) and cholesterol. Here, we studied the formation of myelin membrane sheets in a neuron-glia co-culture system. We applied different microscopy techniques to visualize lipid packing and dynamics in the oligodendroglial plasma membrane. We used the fluorescent dye Laurdan to examine the lipid order with two-photon microscopy and observed that neurons induce a dramatic lipid condensation of the oligodendroglial membrane. On a nanoscale resolution, using stimulated emission depletion and fluorescence resonance energy transfer microscopy, we demonstrated a neuronal-dependent clustering of GalC in oligodendrocytes. Most importantly these changes in lipid organization of the oligodendroglial plasma membrane were not observed in shiverer mice that do not express the myelin basic protein. Our data demonstrate that neurons induce the condensation of the myelin-forming bilayer in oligodendrocytes and that MBP is involved in this process of plasma membrane rearrangement. We propose that this mechanism is essential for myelin to perform its insulating function during nerve conduction.

Effects of the surface layer structure of the heterogeneous ion-exchange membranes on their impedance

Localization of the death receptor Fas to specialized membrane microdomains is crucial to Fas-mediated cell death signaling. Here, we report that the post-translational modification of Fas by palmitoylation at the membrane proximal cysteine residue in the cytoplasmic region is the targeting signal for Fas localization to lipid rafts, as demonstrated in both cell-free and living cell systems. Palmitoylation is required for the redistribution of Fas to actin cytoskeleton-linked rafts upon Fas stimulation and for the raft-dependent, ezrin-mediated cytoskeleton association, which is necessary for the efficient Fas receptor internalization, death-inducing signaling complex assembly and subsequent caspase cascade leading to cell death.

Sorting and Clustering of Transmembrane Helices in Coexisting Fluid Domains in Model Membranes

Plasma membrane heterogeneity is a key biophysical regulatory principle of membrane protein dynamics, which further influences downstream signal transduction. Although extensive biophysical and cell biology studies have proven membrane heterogeneity is essential to cell fate, the direct link between membrane heterogeneity regulation to cellular function remains unclear. Heterogeneous structures on plasma membranes, such as lipid rafts, are transiently assembled, thus hard to study via regular techniques. Indeed, it is nearly impossible to perturb membrane heterogeneity without changing plasma membrane compositions. In this study, we developed a high-spatial resolved DNA-origami-based nanoheater system with specific lipid heterogeneity targeting to manipulate the local lipid environmental temperature under near-infrared (NIR) laser illumination. Our results showed that the targeted heating of the local lipid environment influences the membrane thermodynamic properties, which further triggers an integrin-associated cell migration change. Therefore, the nanoheater system was further applied as an optimized therapeutic agent for wound healing. Our strategy provides a powerful tool to dynamically manipulate membrane heterogeneity and has the potential to explore cellular function through changes in plasma membrane biophysical properties.

Editorial: Synthetic biology--ready for application.