Showing papers on "Membrane published in 1996"
TL;DR: Supporting lipid-protein bilayers form versatile models of low-dimensionality complex fluids, which can be used to study interfacial forces and wetting phenomena, and enable the design of phantom cells to explore the interplay of lock-and-key forces and universal forces for cell adhesion.
Abstract: Scientific and practical applications of supported lipid-protein bilayers are described. Membranes can be covalently coupled to or separated from solids by ultrathin layers of water or soft polymer cushions. The latter systems maintain the structural and dynamic properties of free bilayers, forming a class of models of biomembranes that allow the application of a manifold of surface-sensitive techniques. They form versatile models of low-dimensionality complex fluids, which can be used to study interfacial forces and wetting phenomena, and enable the design of phantom cells to explore the interplay of lock-and-key forces (such as receptor-ligand binding) and universal forces for cell adhesion. Practical applications are the design of (highly selective) receptor surfaces of biosensors on electrooptical devices or the biofunctionalization of inorganic solids.
2,123 citations
TL;DR: A complete interfacial hydrophobicity scale that includes the contribution of the peptide bond was determined from the partitioning of two series of small model peptides into the interfaces of neutral (zwitterionic) phospholipid membranes.
Abstract: The partitioning of membrane-active oligopeptides into membrane interfaces promotes the formation of secondary structure. A quantitative description of the coupling of structure formation to partitioning, which may provide a basis for understanding membrane protein folding and insertion, requires an appropriate free energy scale for partitioning. A complete interfacial hydrophobicity scale that includes the contribution of the peptide bond was therefore determined from the partitioning of two series of small model peptides into the interfaces of neutral (zwitterionic) phospholipid membranes. Aromatic residues are found to be especially favoured at the interface while charged residues, and the peptide bond, are disfavoured about equally. Reduction of the high cost of partitioning the peptide bond through hydrogen bonding may be important in the promotion of structure formation in the membrane interface.
1,531 citations
TL;DR: In this paper, the template method is used to synthesize nanotubules and fibrils of polymers, metals, semiconductors, carbons, and other materials.
Abstract: This paper reviews a relatively new method for preparing nanomaterials: membrane-based synthesis. This method entails the synthesis of the desired material within the pores of a nanoporous membrane. Because the membranes employed contain cylindrical pores of uniform diameter, monodisperse nanocylinders of the desired material, whose dimensions can be carefully controlled, are obtained. These nanocylinders may be either hollow (a tubule) or solid (a fibril or nanowire). We call this approach the “template” method because the pores in the nanoporous membranes are used as templates for forming the desired material. This template method is a very general approach; it has been used to prepare nanotubules and fibrils of polymers, metals, semiconductors, carbons, and other materials.
1,419 citations
TL;DR: In this article, a review of new experimental and theoretical physical research related to the formation of polymeric membranes by phase separation of a polymer solution, and to the morphology of these membranes is presented.
1,246 citations
01 Jan 1996
TL;DR: In this article, the performance and productivity of the ~-cyclodextrin (CD) membrane reactor indicate an improvement of CD stability, and the effect of different average degree of ~-CD carbonate substitution (DS), the amount of immobilized carbonate and operating stirring speeds have been examined under a constant substrate concentration and constant permeation rate.
Abstract: Membranes of PEEKlWC containing carbonate derivative ~-cyclodextrin (~-CD) have been prepared and their catalytic behaviour for the p-nitrophenylacetate (PNPA) hydrolysis has been investigated. The effect of different average degree of ~-CD carbonate substitution (DS), the amount of immobilized ~-CD carbonate and operating stirring speeds have been examined under a constant substrate concentration and constant permeation rate. The performance and productivity of the ~-CD membrane reactor indicate an improvement of CD stability.
1,220 citations
980 citations
TL;DR: Bacteriorhodopsin crystals were obtained from bicontinuous cubic phases, but not from micellar systems, implying a critical role of the continuity of the diffusion space (the bilayer) on crystal growth.
Abstract: Understanding the mechanisms of action of membrane proteins requires the elucidation of their structures to high resolution. The critical step in accomplishing this by x-ray crystallography is the routine availability of well-ordered three-dimensional crystals. We have devised a novel, rational approach to meet this goal using quasisolid lipidic cubic phases. This membrane system, consisting of lipid, water, and protein in appropriate proportions, forms a structured, transparent, and complex three-dimensional lipidic array, which is pervaded by an intercommunicating aqueous channel system. Such matrices provide nucleation sites ("seeding") and support growth by lateral diffusion of protein molecules in the membrane ("feeding"). Bacteriorhodopsin crystals were obtained from bicontinuous cubic phases, but not from micellar systems, implying a critical role of the continuity of the diffusion space (the bilayer) on crystal growth. Hexagonal bacteriorhodopsin crystals diffracted to 3.7 A resolution, with a space group P6(3), and unit cell dimensions of a = b = 62 A, c = 108 A; alpha = beta = 90 degrees and gamma = 120 degrees.
974 citations
TL;DR: In this paper, a streaming potential analyzer was used to investigate the effect of solution chemistry on the surface charge of four commercial reverse osmosis and nanofiltration membranes, and the curves of zeta potential versus solution pH for all membranes display a shape characteristic of amphoteric surfaces with acidic and basic functional groups.
948 citations
TL;DR: A survey of the studies made in recent years on perfluorinated membranes, structure properties and applications can be found in this paper, where the properties and structure of these membranes were mainly studied by SAXS, SANS, NMR, ESR conductance and IR spectroscopy.
787 citations
TL;DR: In this paper, a toroidal wormhole model was proposed to detect helical magainin 2 in the skin of Xenopus laevis, where a substantial fraction of the peptide is oriented perpendicular to the membrane.
Abstract: Magainin, found in the skin of Xenopus laevis, belongs to a broad class of antimicrobial peptides which kill bacteria by permeabilizing the cytoplasmic membrane but do not lyse eukaryotic cells. The 23-residue peptide has been shown to form an amphiphilic helix when associated with membranes. However, its molecular mechanism of action has been controversial. Oriented circular dichroism has detected helical magainin oriented perpendicular to the plane of the membrane at high peptide concentrations, but Raman, fluorescence, differential scanning calorimetry, and NMR all indicate that the peptide is associated with the head groups of the lipid bilayer. Here we show that neutron in-plane scattering detects pores formed by magainin 2 in membranes only when a substantial fraction of the peptide is oriented perpendicular to the membrane. The pores are almost twice as large as the alamethicin pores. On the basis of the in-plane scattering data, we propose a toroidal (or wormhole) model, which differs from the barrel-stave model of alamethicin in that the lipid bends back on itself like the inside of a torus. The bending requires a lateral expansion in the head group region of the bilayer. Magainin monomers play the role of fillers in the expansion region thereby stabilizing the pore. This molecular configuration is consistent with all published magainin data.
761 citations
TL;DR: Local control of the domain orientation in diblock copolymer thin films can be obtained by the application of electric fields on micrometer-length scales by spin-coated onto substrates previously patterned with planar electrodes.
Abstract: Local control of the domain orientation in diblock copolymer thin films can be obtained by the application of electric fields on micrometer-length scales. Thin films of an asymmetric polystyrene-polymethylmethacrylate diblock copolymer, with cylindrical polymethylmethacrylate microdomains, were spin-coated onto substrates previously patterned with planar electrodes. The substrates, 100-nanometer-thick silicon nitride membranes, allow direct observation of the electrodes and the copolymer domain structure by transmission electron microscopy. The cylinders aligned parallel to the electric field lines for fields exceeding 30 kilovolts per centimeter, after annealing at 250°C in an inert atmosphere for 24 hours. This technique could find application in nanostructure fabrication.
TL;DR: The formation of basement membranes requires cooperation between different cell types since nidogen, for example, is usually synthesized by cells other than those exposed to the basement membranes.
Abstract: Basement membranes are thin sheets of extracellular proteins situated in close contact with cells at various locations in the body. They have a great influence on tissue compartmentalization and cellular phenotypes from early embryonic development onwards. The major constituents of all basement membranes are collagen IV and laminin, which both exist as multiple isoforms and each form a huge irregular network by self assembly. These networks are connected by nidogen, which also binds to several other components (proteoglycans, fibulins). Basement membranes are connected to cells by several receptors of the integrin family, which bind preferentially to laminins and collagen IV, and via some lectin-type interactions. The formation of basement membranes requires cooperation between different cell types since nidogen, for example, is usually synthesized by cells other than those exposed to the basement membranes. Thus many molecular interactions, of variable affinities, determine the final shape of basement membranes and their preferred subanatomical localization.
TL;DR: A.J. Burggraaf et al. as mentioned in this paper proposed a method for the characterisation of porous structure in Membrane Materials and applied it in liquid phase separation with Inorganic and Hybrid Membranes.
Abstract: Preface. List of contributors. 1. General Overview, Trends and Prospects (A.J. Burggraaf, L. Cot). 2. Important Characteristics of Inorganic Membranes (A.J. Burggraaf). 3. Adsorption Phenomena in Membrane Systems (Y.H. Ma). 4. Methods for the Characterisation of Porous Structure in Membrane Materials (A. Julbe, J.D.F. Ramsay). 5. Ceramic Processing Techniques of Support Systems for Membranes Synthesis (A. Larbot). 6. Preparation of Asymmetric Ceramic Membrane Supports by Dip-coating (B.C. Bonekamp). 7. Sol-Gel Chemistry and its Application to Porous Membrane Processing (C. Guizard). 8. Fundamentals of Membrane Top-Layer Synthesis and Processing (A.J. Burggraaf). 9. Transport and Separation Properties of Membranes with Gases and Vapours (A.J. Burggraaf). 10. Dense Ceramic Membranes for Oxygen Separation (H.J.M. Bouwmeester, A.J. Burggraaf). 11. Current Developments and Future Research in Catalytic Membrane Reactors (J. Sanchez, T.T. Tsotsis). 12. Transport and Fouling Phenomena in Liquid Phase Separation with Inorganic and Hybrid Membranes (C. Guizard, G. Rios). 13. Applications of Ceramic Membranes in Liquid Filtration (C.A.M. Siskens). 14. Feasibility of the Application of Porous Inorganic Gas Separation Membranes in some Large-Scale Chemical Processes (H.M. van Veen, M. Bracht, E. Hamoen, P.T. Alderliesten). Subject Index.
TL;DR: In this article, a decal transfer method was used to apply thin-film catalyst/ionomer composite layers to Nation® membranes and achieved a maximum power density of 250 mW/cm2.
Abstract: Direct methanol fuel cells (DMFCs) using Pt‐Ru electrocatalysts and perfluorosulfonic acid membranes provide high performances if operated above 100°C with optimized catalyst layers. A decal transfer method is used to apply thin‐film catalyst/ionomer composite layers to Nation® membranes. A Nation 112 membrane/electrode assembly operating on 5 atm oxygen at 130°C yields a current of 670 mA/cm2 at 0.5 V cell voltage. Peak power density is 400 mW/cm2. The same cell operating on 3 atm air at 110°C yields 370 mA/cm2 at 0.5 V and provides a maximum power density of 250 mW/cm2.
TL;DR: In this article, the rejection of single electrolytes at six nanofiltration membranes has been experimentally studied using a model based on the extended Nernst-Planck equation, which accounts for the hindered nature of transport in the membranes.
Book•
01 Jan 1996
TL;DR: Water treatment membrane processes, Water treatment membranes processes, کتابخانه مرکزی دانشگاه علوم پزشدکی ایران
Abstract: Part 1 An overview of membrane processes and their application in water treatment: the emergence of membranes in water and wastewater treatment membrane applications - a contaminant-based perspective categories of membrane technologies. Part 2 Principles of membrane performance: models of rejection in dP processes models for sensitivity in electrodialysis models for selectivity in multiphase processes mass transport and permeate flux in dP processes biofouling of membranes. Part 3 Process applications: field evaluation and piloting reverse osmosis nanofiltration ultrafiltration microfiltration electrodialysis. Part 4 Membrane reactors: PAC/membrane reactors coagulation and membrane separation membrane bioreactors ion exchange membrane reactors. Part 5 Future developments.
TL;DR: Chemical cross-linking is shown, followed by electrophoresis and immunoblotting, that three rat brain glutamate transporter proteins (GLAST, GLT and EAAC) form homomultimers, postulate that the glutamate transporters operate as homomULTimeric complexes.
TL;DR: In this article, a PBI-poly poly[2,2′-(m-phenylene)-5,5′-bibenzimidazole (PBI) was used in a H 2 O 2 fuel cell.
TL;DR: In this paper, a mechanism for the formation of nodular structures in the top layer of ultra-filtration membranes is presented, and structures arising from polymer crystallization during immersion precipitation are discussed.
TL;DR: It is reported here that at cytotoxic concentrations, amylin forms voltage-dependent, relatively nonselective, ion-permeable channels in planar phospholipid bilayer membranes, suggesting that channel formation may be the mechanism of cytotoxicity of humanAmylin.
TL;DR: In this article, strategies for the preparation of zeolite molecular sieve membranes and layers on different substrates are reviewed, and the resulting nanoporous layers have been applied in highly selective sensors, for the alignment of NLO chromophores and for molecular separations.
Abstract: Strategies for the preparation of zeolite molecular sieve membranes and layers on different substrates are reviewed. Membranes (and continuous thin films) have been synthesized with ZSM-5 (MFI) type molecular sieves and other zeolites, either as free-standing specimens, grown on various supports according to several schemes, or embedded in polymer matrices. The membranes have been studied for molecule-selective separations and for catalytic reactions. Layers of presynthesized molecular sieves have been deposited by means of sol−gel matrixes and other bonding agents, molecular attachment layers, and via sputtering or laser ablation techniques. The resulting nanoporous layers have been applied in highly selective sensors, for the alignment of NLO chromophores and for molecular separations. Finally, oriented molecular sieve layers have been grown on self-assembled organic mono- and multilayers presenting phosphonate groups at the interface. Mixed phosphonate/alkyl films show profound effects on the surface c...
TL;DR: In this article, a self-humidifying electrolyte membrane is proposed to solve the problem of water management in the electrolyte, which allows the use of very thin membranes, simultaneously allowing high performance of the cell.
Abstract: Polymer electrolyte fuel cells have attracted enormous interest as a primary power source for electric vehicles. Water management in the electrolyte is one of the complicated problems to be overcome. A new self-humidifying electrolyte membrane is proposed to solve this problem. Self-humidification allows the use of very thin membranes, simultaneously allowing high performance of the cell. Use of the new, thin membranes makes the system very simple and ready for cold starts and also amenable to abrupt load changes. The electrolyte is comprised of 50 {micro}m thick Nafion membrane containing 0.07 mg/cm{sup 2} of platinum catalyst particles (d = 1 to 2 nm) and a few weight percent of a hygroscopic material such as silica or titania (d = ca. 5 to 7 nm). The platinum particles catalyze the oxidation of crossover hydrogen with oxygen to generate water, which in turn is adsorbed by the oxide particles. The cell shows exceptionally stable and high performance even under ambient pressure conditions when operated with hydrogen saturated with water at 20 C and dry oxygen. The internal resistance was measured to be 0.06 {Omega} cm{sup 2}, and the output of the cell was 0.63 W/cm{sup 2}, i.e., 0.9 A/cm{sup 2} at 0.7more » V with an energy efficiency of 60%. The output was 1 W/cm{sup 2} in the voltage region of 0.6 to 0.4 V yielding current densities of 1.6 to 2.5 A/cm{sup 2}. Hydrogen depleted for self-humidification was estimated to be less than a few percent under these operating conditions.« less
TL;DR: It is concluded that the free energy of solvation mainly determines the shape of the permeation resistance profile, and for hydrophobic particles the membrane interior will act as a trap instead of a barrier.
Abstract: The transport of small molecules across a phospholipid membrane is studied by molecular dynamics simulations. The effects of size, hydrophobicity, and asphericity of the penetrants on the permeation process are investigated. For this purpose, permeability coefficients of oxygen and ammonia are computed using an inhomogeneous solubility−diffusion model and compared to the previously computed results of the permeation of water. Furthermore, solubility and diffusion data are computed for a series of Lennard-Jones particles that differ in size and shape. The results are discussed within the framework of the four-region model and are especially related to the free volume characteristics of the membrane. It is concluded that the free energy of solvation mainly determines the shape of the permeation resistance profile. For hydrophobic particles the membrane interior will act as a trap instead of a barrier. Moderately hydrophilic and hydrophilic penetrants experience the largest resistance to permeation in the de...
TL;DR: The giant liposomes were stable and retained a concentration gradient of K+ across the membrane, as evidenced in fluorescence images of the K(+)-indicator PBFI encapsulated in the liposome.
TL;DR: In this paper, the authors present a set of terms applicable to non-living Terminology for membranes and membrane processes and their definitions represent a core set that will allow uniform understanding and eliminate most ambiguity or confusion caused by conflicting terminology now in use.
Abstract: Republication or reproduction of this report or its storage and/or dissemination by electronic means is permitted without the need for formal IUPACpermission on condition that an acknowledgement, with full reference to the source along with use of the copyright symbol 0, the name IUPAC and the year of publication are prominently visible. Publication of a translation into another language is subject to the additional condition of prior approval from the relevant IUPAC National Adhering Organization. SYNOPSIS membranes and membrane processes. The terms include the key vocabulary used in the literature concerned with scientific, technical and commercial aspects of the membrane field. Processes and membranes based on synthetic or modified natural polymers as well as ceramic and metallic membranes are covered. The resultant terms and their definitions represent a core set that will allow uniform understanding and eliminate most ambiguity or confusion caused by conflicting terminology now in use. The terms and definitions selected for inclusion reflect the majority preference of the membrane community. To avoid irreconcilable differences, definitions and descriptions involving interpretations of phenomena were minimized. Some terms were deleted in cases where majority preferences were not apparent. This strategy was adopted with the understanding that the current core group of terms, which enjoy majority support, can be augmented as evolution of the field occurs. This project has involved assembling a basic set of terms applicable to non-living Terminology for membranes and membrane processes
TL;DR: The morphological and biochemical data are consistent with the hypothesis that autophagy or a similar host process is involved in the formation of the poliovirus-induced membranes.
Abstract: Poliovirus RNA replicative complexes are associated with cytoplasmic membranous structures that accumulate during viral infection. These membranes were immunoisolated by using a monoclonal antibody against the viral nonstructural protein 2C. Biochemical analysis of the isolated membranes revealed that several organelles of the host cell (lysosomes, trans-Golgi stack and trans-Golgi network, and endoplasmic reticulum) contributed to the virus-induced membranous structures. Electron microscopy of infected cells preserved by high-pressure freezing revealed that the virus-induced membranes contain double lipid bilayers that surround apparently cytosolic material. Immunolabeling experiments showed that poliovirus proteins 2C and 3D were localized to the same membranes as the cellular markers tested. The morphological and biochemical data are consistent with the hypothesis that autophagy or a similar host process is involved in the formation of the poliovirus-induced membranes.
TL;DR: This work has shown that the membrane skeleton provides both confining and binding effects on the movement of membrane proteins, and that it can play a pivotal role in the molecular organization of the plasma membrane, especially in the formation of special membrane domains.
TL;DR: Hydrophilized PSf-g-HEMA membranes can provide improved performance in protein ultrafiltration over unmodified PSf UF membranes because pore etching effects are compensated for by the grafted layer yielding both improved filtrate flux (>30%) and protein retention of bovine serum albumin.
TL;DR: It is concluded that the regulation of the acyl chain composition in wild-type cells of E. coli is necessary for the organism to be able to grow in a “window” between a lamellar gel phase and reversed non-lamellar phases.
TL;DR: In this article, a solution method for the pervaporation separation of acetic acid-water mixtures was proposed, in which dry PVA films were crosslinked by immersion for two days at 40°C in reaction solutions which contained different contents of GA, acetone and a catalyst, HCl.