Ion‐Channel Gating in Transmembrane Receptor Proteins: Functional Activity in Tethered Lipid Membranes

Through thiolipids a planar lipid bilayer (1) was immobilized on a gold support (2) for use as an electrode. This allows the detection of the ligand‐gating function of the natural transmembrane channel protein OmpF (3) reconstituted in the artificial membrane: the binding of a domain (4) of the toxin colicin N, observed by surface plasmon resonance, induces the blocking of the OmpF channel protein, as shown by impedance spectroscopy.     

Vesicle formation from a synthetic adenosine based lipid

We report the synthesis of a novel purine based amphiphile; di-oleyladenosinephosphocholine (DOAPC). Light microscopy, TEM and QELS studies on DOAPC in aqueous media support the formation of lamellar systems. These investigations indicate that the presence of adenine does not prohibit the formation of lamellar organizations. Stable small unilamellar vesicles can be prepared by using extrusion techniques.     

Sol-Gel Routes to Zeolite Membranes and Thin Films

The synthesis of zeolite membranes and thin films using the secondary growth process is briefly described. In this process colloidal zeolite particles (sols) are prepared hydrothermally and then subsequently deposited on substrates to produce uniform layers of controlled thickness, as illustrated with silicalite and zeolite-A. The formation and growth of the zeolite sols has been investigated in situ by small angle neutron scattering (SANS). SANS measurements on silicalite sols at progressively higher concentrations have provided details of the colloid interactions which lead to zeolite gel-layer structures which are uniform and free of defects.     

Asymmetric Membranes: Preparation and Applications

The separation of molecular mixtures by semipermeable membranes under the driving force of hydrostatic pressure has assumed major importance in recent years. Among other factors the development of membranes with asymmetric structure which, while having the same separating properties, afford a filtration output many times greater than that of the previously known symmetrical membranes, was decisive for this method. In the present progress report the structures of asymmetric membranes are discussed, as well as their preparation from various polymers and their application to the separation of molecular mixtures.     

Gas Separation with Polymer Membranes

Gas-selective polymer membranes have long been used in industrial applications. Studies of polymers with well-defined flexible phenyl ether segments such as 1 should contribute to the understanding of the selection mechanism and thus ultimately lead to the synthesis of optimized membrane materials. Various different bridging groups X were used in the studies.     

Fluorescence Studies of the Existence and Functional Importance of Regular Distributions in Liposomal Membranes

Abstract

Liposomes containing rigid and bulky lipid molecules such as sterols and pyrene‐labeled lipids can exhibit biphasic changes in membrane properties at several specific mole fractions predicted by the theory of lipid regular distributions (e.g., superlattices) in the plane of the membrane. This phenomenon has been observed in two‐component as well as multicomponent liquid‐crystalline liposomal membranes. The extent of sterol regular distribution plays a role in drug partitioning into membranes, the activities of surface‐acting enzymes such as cholesterol oxidase and phospholipase A2, and in free‐radical‐induced sterol oxidation. This article summarizes the original fluorescence studies of lipid superlattices, reviews the recent findings in this area, and discusses the current controversial issues related to lipid regular distributions.     

Selective Vesicle Formation from Calixarenes by Self‐Assembly

Amphiphilic polyhydroxy macrocycles self‐assemble in water to form vesicles selectively. These vesicles are uniform in size (50–200 nm; see representation) and stable both in aqueous solution and in dried form. The selective mode of aggregation can be correlated with structural characteristics of the phenolic amphiphiles, in particular, the macrocyclic moiety and intra‐ and intermolecular hydrogen bonds between the phenolic OH groups.     

Emulsion Filtration Through Surface Modified Ceramic Membranes

In this work we studied the influence of membrane hydrophobicity on the filtration of oil/water (O/W) emulsions with a dispersed phase content of 30% (V/V). The membrane filtration process was realized by using ceramic tubular hydrophilic or hydrophobic membranes with different mean pore size (0.2 pm, 1.2 pm, and 1.4 pm of mean pore radius). Hydrophobic character was obtained by modifying superficially the membrane surface with a very thin polymer layer. The results obtained showed that the emulsion viscosity and droplet size distribution depend on the shearing forces and transmembrane pressure. The operating conditions and the nature of the membrane surface/emulsion interaction are the main parameters which control the type and nature of emulsion changes, such as modification of the mean droplet size, concentration into oleic phase or breaking.     

聚电解质和表面活性剂混合体系中多价金属离子诱导的囊泡聚集

利用浊度和电镜观察等方法研究了水解的苯乙烯-马来酸酐共聚物(SMA)和十二烷基三乙基溴化铵(DEAB)混合体系中多价金属离子诱导的囊泡聚集现象. 提出了关于多价金属离子诱导囊泡聚集的机理.     

Preparation and Properties of Nanoporous Triblock Copolymer Membranes

“ Unplug those pores!” could be a slogan common to cosmetologists and polymer chemists. Membranes with nanochannels can be obtained by first forming a film by casting a solution of a triblock and homopolymer mixture, then selectively cross-linking domains in the film by photolysis, and finally forming nanochannels through removal of the homopolymer by solvent extraction. Such membranes are not liquid permeable but have gas-permeability constants about six orders of magnitude higher than that of low-density polyethylene films.     

Vesicle formation in oleyldimethylamine oxide/sodium oleate mixtures

Vesicle formation in a mixture of oleyldimethylamine oxide (OleylDMAO) and sodium oleate (NaOl) was investigated by viscoelastic measurements and cryoscopic transmission electron micrograph (cryo-TEM) observations. The viscoelastic properties changed with increasing mole fraction of NaOl (X _NaOl) from the Maxwell behavior of OleylDMAO solutions (X _NaOl=0) suggesting a transient network of long flexible chains. For X _NaOl=0.2 and 0.4 mixtures, both the shear storage modulus G and the shear loss modulus G showed weak dependences on angular frequency with a relation G>G. From cryo-TEM observations, vesicles coexisted with threadlike micelles in mixtures of X _NaOl=0.2 and 0.3. As X _NaOl increased further (X _NaOl=0.5 and 0.6), threadlike micelles disappeared and the coexistence of vesicles and globular micelles was observed. At X _NaOl=0.5, the viscosity decreased remarkably, which was consistent with the disappearance of threadlike micelles. The results indicated that vesicles were formed by the addition of NaOl to OleylDMAO solutions, contrary to the expectation of a decrease of the packing parameter with the introduction of electric charges.     

Digitonin as a Chemical Trigger for the Selective Transformation of Giant Vesicles

The rupture of cationic giant vesicles (see the picture) in the presence of anionic vesicles, or the reverse, on exposure to digitonin is dependent on the respective cholesterol levels (0–50 mol%). Thus a disparate giant vesicle population can be chemically induced to release the contents from only a portion of its members.     

Synthetic Bilayer Membranes: Molecular Design,Self-Organization,and Application

Lipid bilayers are a most central building block of the biological molecular organization. Their two-dimensional self-assembly is essential to the generation of biological shapes and sizes on the molecular level. The observation that a totally synthetic amphiphile in water is spontaneously assembled to a bilayer structure suggested that bilayer formation is a general physicochemical phenomenon that is not restricted to particular structures of biolipid molecules. Bilayer formation is now observed for a large variety of synthetic amphiphiles which contain one, two, three, or four alkyl tails. The flexible alkyl tail may be replaced by perfluoroalkyl chains. The supramolecular structures obtained therefrom can be related to the component's molecular structure in many cases. The structural variety and the ease of molecular design make the synthetic bilayer an attractive vehicle for organizing covalently bound functional units and guest molecules. In addition, stable monolayers on water, planar lipid membranes (BLM), and free-standing cast films are obtainable because of the self-assembling property of bilayer-forming compounds. These molecular organizations display common supramolecular features. The use of the cast film as a molecular template provides exciting potential for the production of novel two-dimensional materials.     

Two-Dimensional MFI-Type Zeolite Flow Battery Membranes

Vanadium flow battery (VFB) is one of the most reliable stationary electrochemical energy-storage technologies, and a membrane with high vanadium resistance and proton conductivity is essential for manufacturing high-performance VFBs. In this study, a two-dimensional (2D) MFI-type zeolite membrane was fabricated from zeolite nanosheet modules, which displayed excellent vanadium resistance (0.07 mmol L⁻¹ h⁻¹) and proton conductivity (0.16 S cm⁻¹), yielding a coulombic efficiency of 93.9 %, a voltage efficiency of 87.6 %, and an energy efficiency of 82.3 % at 40 mA cm⁻². The self-discharge period of a VFB equipped with 2D MFI-type zeolite membrane increased up to 116.2 h, which was significantly longer than that of the commercial perfluorinated sulfonate membrane (45.9 h). Furthermore, the corresponding battery performance remained stable over 1000 cycles (>1500 h) at 80 mA cm⁻². These findings demonstrate that 2D MFI-type membranes are promising ion-conductive membranes applicable for stationary electrochemical energy-storage devices.     

Spiroligomer-Based Macrocycles for Atomically Precise Membranes

Here, we report a new class of peptidomimetic macrocycles with well-defined three-dimensional structures and low conformational flexibility. They are assembled from fused-ring spiro-ladder oligomers (spiroligomers) by modular solid-phase synthesis. Two-dimensional nuclear magnetic resonance confirms their shape persistency. Triangular macrocycles of tunable sizes assemble into membranes with atomically precise pores, which exhibit size and shape-dependent molecular sieving towards a series of structurally similar compounds. The exceptional structural diversity and stability of spiroligomer-based macrocycles will be explored for more applications.     

Phospholipids as Functional Constituents of Biomembranes

This article describes new methods for the synthesis of biologically active phospholipids. The physical properties of such compounds are directly related to their chemical structure, the position of the substituents esterified with glycerol not only influencing the physical properties but also the biological function of the phospholipids. Phase transitions can be induced by temperature changes and—in biological systems—by changes in the surface charge or the degree of protonation. In model studies, the properties of lipid phases differ sufficiently to influence and control biological membrane processes. Alkyl glycerides can modify the properties of biological membranes quickly and reversibly to increase the permeation of active compounds. An important example is the improved transport of cytostatic drugs across the blood-brain barrier. Knowledge about the substrate specificity of enzymes that metabolize phospholipids allows the synthesis of tailored cytotoxic phospholipids which selectively accumulate in malignant tissues. Thus, the interplay of chemical synthesis and investigations of physical structure lays a foundation for the understanding of simple membrane processes on a molecular level, and the experience gained with such model systems can, in turn, be used to influence natural membranes, such as those of the blood-brain barrier or of tumors, in a directed way.     

Polymer Vesicle Sensor through the Self-assembly of Hyperbranched Polymeric Ionic Liquids for the Detection of SO2 Derivatives

This work reports a SO_2 derivative-detecting and colorful hyperbranched polymeric ionic liquid(HBPIL) vesicle through aqueous self-assembly. By a simple anion-exchange, we achieved the combination of functional small-molecule probe of acid fuchsin with HBPILs. The obtained HBPIL vesicle displayed ultraviolet absorption at 544 nm, and was used as a novel SO_2 derivative sensor with high sensitivity and visualization. Due to the functional ion pairs enriching on the surface, the SO32-detection limit of the HBPILs vesicles was as low as 0.138 μmol/L, which was about 1.5 orders of magnitude lower than that of acid fuchsin.     

Vesicle formation in hydrocarbons assisted with microbial hydrolases and biosurfactants

The present study demonstrates the role of microbial hydrolases in the transformation of hydrocarbons (soybean, sunflower, groundnut and gingelly oil, etc.) to vesicles. The combined effect of lipolytic enzyme generation and biosurfactants production during microbial growth at optimized media and environmental conditions mediates this transformation. Among the microbial species, Candida albicans exhibit complete transformation compared to Pseudomonads and Bacillus sps. Within hydrocarbons, only soybean and sunflower oils transformed to solid mass and no change with the remaining oils. Characterization of the vesicles revealed an increase in total weight by 160-180% compared to the original weight of hydrocarbon taken for the study and more than 73% increases in viscosity. Acid value and saponification value also showed an increase, respectively, by 78 and 84%. The bound water content estimated was 26%. Light microscopic analysis exhibit, presence of unilamellar and bi-lamellar structures.