Showing papers on "Membrane published in 1991"

Basic Principles of Membrane Technology

Abstract: I: Introduction. II: Materials and Material Properties. III. Preparation of Synthetic Membranes. IV: Characterisation of Membranes. V: Transport in Membranes. VI: Membrane Processes. VII: Polarisation Phenomena and Membrane Fouling. VIII: Module and Process Design. Appendix 1. Appendix 2. Answers to Exercises: Solved Problems. Answers to Exercises: Unsolved Problems. List of Symbols. Index.

Polymer Electrolyte Fuel Cell Model

Abstract: We present here an isothermal, one-dimensional, steady-state model for a complete polymer electrolyte fuel cell (PEFC) with a 117 Nation | membrane. In this model we employ water diffusion coefficients electro-osmotic drag coefficients, water sorption isotherms, and membrane conductivities, all measured in our laboratory as functions of membrane water content. The model pre.dicts a net-water-per-proton flux ratio of 0.2 H20/H § under typical operating conditions, which is much less than the measured electro-osmotic drag coefficient for a fully hydrated membrane. It also predicts an increase in membrane resistance with increased current density and demonstrates the great advantage of a thinner membrane in alleviating this resistance problem. Both of these predictions were verified experimentally under certain conditions.

Collagen family of proteins.

Abstract: Collagen molecules are structural macro-molecules of the extracellular matrix that include in their structure one or several domains that have a characteristic triple helical conformation. They have been classified by types that define distinct sets of polypeptide chains that can form homo- and heterotrimeric assemblies. All the collagen molecules participate in supramolecular aggregates that are stabilized in part by interactions between triple helical domains. Fourteen collagen types have been defined so far. They form a wide range of structures. Most notable are 1) fibrils that are found in most connective tissues and are made by alloys of fibrillar collagens (types I, II, III, V, and XI) and 2) sheets constituting basement membranes (type IV collagen), Descemet's membrane (type VIII collagen), worm cuticle, and organic exoskeleton of sponges. Other collagens, present in smaller quantities in tissues, play the role of connecting elements between these major structures and other tissue components. The f...

Determination of water diffusion coefficients in perfluorosulfonate ionomeric membranes

Abstract: Pulsed field gradient spin-echo 1 H NMR measurements of 1 H intradiffusion coefficients at 30 o C in hydrated Nafion membranes are reported. The dependence of the 1 H self-diffusion coefficient on membrane water content was a central part of this investigation. 1 H diffusion coefficients ranged from 0.6×10 −6 to 5.8×10 −6 cm 2 /s for the range of membrane water content 2-14 water molecules per sulfonate

The conformation of membranes

Abstract: Membranes composed of amphiphilic molecules are highly flexible surfaces that determine the architecture of biological systems and provide a basic structural element for complex fluids such as microemulsions. Physical theories have been developed to describe many aspects of their conformational behaviour, such as the preferred shapes and shape transformations of closed vesicles, and the shape fluctuations, random-surface configurations, and adhesion and unbinding of interacting membranes. Understanding of these phenomena has been much improved through fruitful interactions between theory and experiment.

Physical properties of the fluid lipid-bilayer component of cell membranes: a perspective.

Abstract: The motivation for this review arises from the conviction that, as a result of the mass of experimental data and observations collected in recent years, the study of the physical properties of membranes is now entering a new stage of development. More and more, experiments are being designed to answer specific, detailed questions about membranes which will lead to a quantitative understanding of the way in which the physical properties of membranes are related to and influence their biological function.

ATP-sensitive K+ channel in the mitochondrial inner membrane

Abstract: MITOCHONDRIA take up and extrude various inorganic and organic ions, as well as larger substances such as proteins1–4. The technique of patch clamping should provide real-time information on such transport and on energy transduction in oxidative phosphorylation. It has been applied to detect microscopic currents from mitochondrial membranes and conductances of ion channels in the 5–1,000 pS range in the outer and inner membranes5–10. These pores are not, however, selective for particular ions. Here we use fused giant mitoplasts prepared from rat liver mitochondria to identify a small conductance channel highly selective for K+ in the inner mitochondrial membrane. This channel can be reversibly inactivated by ATP applied to the matrix side under inside-out patch configuration; it is also inhibited by 4-aminopyridine and by glybenclamide. The slope conductance of the unitary currents measured at negative membrane potentials was 9.7±1.0pS (mean ± s.d., n = 6) when the pipette solution contained 100 mM K+ and the bathing solution 33.3 mM K+. Our results indicate that mitochondria depolarize by generating a K+ conducta-ance when ATP in the matrix is deficient.

Catalytic palladium‐based membrane reactors: A review

Abstract: This paper is an extensive review of the literature dealing with the class of catalytic membrane reactors which involves hydrogen permeable membranes made of palladium and palladium alloys. The fundamental factors which affect hydrogen permeability are first discussed. A classification of the many reactions which have been conducted in such reactors at both laboratory and commercial scales is then presented. The various techniques for the preparation of palladium- based membranes are described and the literature on modeling and design of these reactors is also reviewed.

Phospholipid synthesis and lipid composition of subcellular membranes in the unicellular eukaryote Saccharomyces cerevisiae.

Abstract: Subcellular membranes of Saccharomyces cerevisiae, including mitochondria, microsomes, plasma membranes, secretory vesicles, vacuoles, nuclear membranes, peroxisomes, and lipid particles, were isolated by improved procedures and analyzed for their lipid composition and their capacity to synthesize phospholipids and to catalyze sterol delta 24-methylation. The microsomal fraction is heterogeneous in terms of density and classical microsomal marker proteins and also with respect to the distribution of phospholipid-synthesizing enzymes. The specific activity of phosphatidylserine synthase was highest in a microsomal subfraction which was distinct from heavier microsomes harboring phosphatidylinositol synthase and the phospholipid N-methyltransferases. The exclusive location of phosphatidylserine decarboxylase in mitochondria was confirmed. CDO-diacylglycerol synthase activity was found both in mitochondria and in microsomal membranes. Highest specific activities of glycerol-3-phosphate acyltransferase and sterol delta 24-methyltransferase were observed in the lipid particle fraction. Nuclear and plasma membranes, vacuoles, and peroxisomes contain only marginal activities of the lipid-synthesizing enzymes analyzed. The plasma membrane and secretory vesicles are enriched in ergosterol and in phosphatidylserine. Lipid particles are characterized by their high content of ergosteryl esters. The rigidity of the plasma membrane and of secretory vesicles, determined by measuring fluorescence anisotropy by using trimethylammonium diphenylhexatriene as a probe, can be attributed to the high content of ergosterol.

Fluorescence assay for phospholipid membrane asymmetry.

Abstract: Highly fluorescent 7-nitro-2,1,3-benzoxadiazol-4-yl-lipid (NBD-lipid) analogues are widely used to examine lipid transport and membrane structure. We have developed a method for chemically modifying NBD-labeled lipids in both artificial and biological membranes. This was achieved by treating fluorescently labeled membranes with dithionite (S2O4(-2)). When small unilamellar vesicles containing NBD-labeled phospholipids were reacted with dithionite, only the fluorescent lipid located on the outer leaflet of the vesicles' bilayer was reduced. Seven different NBD-lipid analogues, including a fluorescent sterol, were reduced by treatment with dithionite to nonfluorescent 7-amino-2,1,3-benzoxadiazol-4-yl-lipid derivatives. To assess the feasibility of using this reagent in biological systems, N-(7-nitro-2,1,3-benzoxadiazol-4-yl)dioleoylphosphatidylethanol ami ne was inserted into the outer leaflet of the plasma membrane of CHO-K1 cells. Subsequent incubation of these cells with a nontoxic concentration of dithionite resulted in the complete loss of fluorescence from the plasma membrane. In contrast, when cells were permitted to endocytose some of their fluorescently labeled plasma membrane and then treated with dithionite, fluorescence at the plasma membrane was eliminated, while intracellular labeling was not affected. These data suggest that dithionite reacts with NBD-labeled lipids in the outer leaflet of membrane bilayers, producing nonfluorescent derivatives. We demonstrate how reduction of NBD-lipids with dithionite can be used to prepare asymmetrically labeled liposomes and to measure transverse-membrane asymmetry in vesicles. This method should be useful in many biochemical investigations, including the measurement of phospholipid translocase activity.

Pervaporation membrane separation processes

Abstract: 1. Introduction to Pervaporation (J. Neel). 2. Separation Characteristics of Pervaporation Membrane Separation Processes (R.Y.M. Huang, J.W. Rhim). 3. Engineering Aspects of Pervaporation: Calculation of Transport Resistances, Module Optimization and Plant Design (R. Rautenbach, C. Herion and U. Meyer-Blumenroth). 4. Thermodynamic Principles of Pervaporation (M.H.V. Mulder). 5. Estimation and Evaluation of Polymeric Materials for Pervaporation Membranes (G.H. Koops and C.A. Smolders). 6. Sorption and Diffusion in Pervaporation Membranes (A. Heintz, H. Funke and R.N. Lichtenhaler). 7. Synthesis of Novel Copolymer Membranes for Pervaporation (T. Shimidzu and M. Yoshikawa). 8. Pervaporation in Biotechnology (H. Strathmann and W. Gudernatsch). 9. Recent Progress in Pervaporation Membranes for Water/Ethanol Separation (Y. Maeda and M. Kai). 10. Selective Pervaporation of Organics from Water (K.W. Boddeker and G. Bengtson). 11. Plasma Grafted Pervaporation Membranes (T. Hirotsu). 12. Pervaporation Membrane Plant. Industrial Experience and Plant Design in Japan (T. Asada). 13. Development of Vapour Permeation for Industrial Application (U.H.F. Sander). Subject index.

A 'molten-globule' membrane-insertion intermediate of the pore-forming domain of colicin A.

Abstract: THE 'molten' globular conformation of a protein is compact with a native secondary structure but a poorly defined tertiary structure1,2. Molten globular states are intermediates in protein folding and unfolding3–5 and they may be involved in the translocation or insertion of proteins into membranes6. Here we investigate the membrane insertion of the pore-forming domain of colicin A, a bacteriocin that depolarizes the cytoplasmic membrane of sensitive cells7–9. We find that this poreforming domain, the insertion of which depends on pH (refs 10,11), undergoes a native to molten globule transition at acidic pH. The variation of the kinetic constant of membrane insertion of the protein into negatively charged lipid vesicles as a function of the interfacial pH correlates with the appearance of the acidic molten globular state, indicating that this state could be an intermediate formed during the insertion of colicin A into membranes.

Inorganic membranes : synthesis, characteristics, and applications

Abstract: The developing use of inorganic membranes: a historical perspective. Synthesis of inorganic membranes. General characteristics of inorganic membranes. Permeation and separation characteristics of inorganic membranes in liquid phase applications. Liquid filtration and separation with inorganic membranes: operating considerations and some aspects of system design. Gas separations with inorganic membranes. Inorganic membrane reactors to enhance the productivity of chemical processes. Inorganic membranes in food and biotechnology applications. Inorganic membranes for the filtration of water. Wastewater treatment and process industry filtration applications.

Conjugated polymer films for gas separations

Abstract: Permeabilities for a series of gases through free-standing films of the conjugated polymer polyaniline are reported. A remarkable selectivity has been achieved for important gas pairs incuding hydrogen-nitrogen, oxygen-nitrogen, and carbon dioxide-methane. The selectivity values of 3590 for H(2)/N(2), 30 for O(2)/N(2), and 336 for CO(2)/CH(4) surpass the highest previously reported values of 313, 16, and 60 for the nonconjugated polymers poly(trifluorochloroethylene), cellulose nitrate, and a fluorinated polyimide, respectively. The process for tailoring gas selectivity of a polyaniline membrane involves first enhancing the permeabilities of gases with small diameters [ 3.5 A diameter) through controlled redoping of the polymer. The permanent morphological changes induced in this conjugated polymer system and others indicate the potential for development of universal membranes for gas separations.

Voltage-sensing residues in the S4 region of a mammalian K+ channel.

Abstract: THE ability of ion-channel proteins to respond to a change of the transmembrane voltage is one of the basic mechanisms underlying electrical excitability of nerve and muscle membranes. The voltage sensor has been postulated to be the fourth putative transmembrane segment1 (S4) of voltage-activated Na+, Ca2+ and K+ channels1–5. Mutations of positively charged residues within S4 alter gating of Na4 and Shaker-type K+ channels5, but quantitative correlations between the charge or a residue in S4 and the gating valence of the channel have not yet been established. Here, with improved resolution of the voltage dependence of steady-state activation, we present estimates of the equivalent gating valence with sufficient precision to allow quantitative examination of the contribution of individual charged residues to the gating valence of a mammalian non-inactivating K+ channel. We conclude that at least part of the gating charge associated with channel activation is indeed contributed by charged residues within the S4 segment.

Influence of chemisorption on the photodecomposition of salicylic acid and related compounds using suspended TiO2 ceramic membranes

Abstract: The adsorption and photodecomposition on semiconducting membranes of molecules with different functional groups were studied. Ceramic membranes, prepared by a sol-gel technique, were employed because this technique provides some control over surface area, porosity, and crystal form of these materials, properties which affect their photochemical behavior. Salicylic acid was chosen as a prototype molecule. 3-Chlorosalicylic acid, benzoic acid, phenol, and 4-chlorophenol were also investigated. The adsorption densities of salicylic and 3-chlorosalicylic acids decreased with both increasing solution pH and membrane firing temperature, in correlation with the number of positive adsorption sites on TiO2 surface. No adsorption for benzoic acid, phenol, and 4-chlorophenol was observed. Photodecomposition rates were found to depend on the adsorption characteristics of the organic compound; for salicylic acid the degradation rate diminished with increasing pH. Benzoic acid, whose degradation products adsorb on the oxide surface, showed a similar trend. No dependence on pH was detected for phenols. Methanol was found to affect the degradation rate of salicylic acid only under conditions of high pH. It is proposed that, for chemisorbing organics, the initial step of the photodecomposition process is governed by two different mechanisms that depend on the adsorption behavior of the organic compound at a particular pH. For adsorbed salicylate, an orbital configuration of the chelate ring is proposed to interpret direct electron transfer from the organic molecule to the semiconductor.

One-sided action of amphotericin B on cholesterol-containing membranes is determined by its self-association in the medium.

Abstract: The inducement of K+ permeability through membranes by the polyene antibiotic amphotericin B (AmB) has been analyzed as a measure of the antibiotic activity. Dose-response curves have been obtained with cholesterol- and ergosterol-containing egg yolk phosphatidylcholine large unilamellar vesicles (LUVs), human erythrocytes, and Saccharomyces cerevisiae cells. Conductance changes induced by AmB in sterol-containing planar bilayer membranes have also been studied. AmB self-association in aqueous buffer was determined by circular dichroism (CD) as a function of the antibiotic concentration. Electronic absorption and CD spectra of AmB were recorded in the presence of LUVs. For given AmB concentrations, the extent of permeability inducement is dependent on the lipid concentration. On the other hand, for cholesterol-containing LUVs or erythrocytes, a critical AmB concentration had to be reached before any permeability is observed. Independent of lipid concentration, this concentration was directly related to antibiotic self-association in the aqueous buffer. The same observation was made for erythrocytes and nystatin. The AmB absorption and CD spectra were totally different for ergosterol- and cholesterol-containing LUVs. Formation of single channels by one-sided addition of AmB could be observed only in ergosterol-containing membranes. These data lead us to propose that the permeability pathways induced by amphotericin B or nystatin, in ergosterol- and in cholesterol-containing membranes, are of different natures. In the latter case the antibiotics are only active, by single-sided addition, in the self-associated form. These findings offer important clues for the design of less toxic derivatives of AmB: they should have a low degree of self-association in water.

Controlled absorption naproxen formulation for once-daily administration

Abstract: A diltiazem pellet formulation for oral administration comprises a core of diltiazem or a pharmaceutically acceptable salt thereof in association with an organic acid, and a multi-layer membrane surrounding the core and containing a major proportion of a pharmaceutically acceptable film-forming, water insoluble synthetic polymer and a minor proportion of a pharmaceutically acceptable film-forming, water soluble synthetic polymer. The number of layers in the membrane and the ratio of the water soluble to water insoluble polymer being effective to permit release of the diltiazem from the pellet at a rate allowing controlled absorption thereof over a twenty four hour period following oral administration.