Showing papers on "Membrane published in 1993"
TL;DR: A review of the field of thin film composite reverse osmosis membranes, with emphasis on the chemistry and composition of these membranes, is given in this article, with particular attention given to composite membranes that have found commercial use, whether in the present or past.
1,627 citations
TL;DR: In this article, the diffusion coefficient and relaxation time of water in the membrane and the protonic conductivity of the membrane as functions of membrane water content were measured, and the ratio of water molecules carried across the membrane per proton transported, the electro-osmotic drag coefficient, was determined for a limited number of water contents.
Abstract: Water uptake and transport properties of Nafion[reg sign] 117 membranes at 30 C are reported here. Specifically, the authors have determined the amount of water taken up by membranes immersed in liquid water and by membranes exposed to water vapor of variable water activity. Transport parameters measured are the diffusion coefficient and relaxation time of water in the membrane and the protonic conductivity of the membrane as functions of membrane water content. The ratio of water molecules carried across the membrane per proton transported, the electro-osmotic drag coefficient, also was determined for a limited number of membrane water contents. The drag coefficient is contrasted with the experimentally determined net water transport across an operating PEM fuel cell.
1,412 citations
Book•
17 Dec 1993
TL;DR: In this paper, the authors present the basic approaches of materials science of polymeric membranes for gas and vapor separation, and the relations between the polymer structure and transport properties of rubbery and glassy membrane materials are considered.
Abstract: This short Perspective conveys to the general reader of Macromolecules basic approaches of materials science of polymeric membranes for gas and vapor separation. The relations between the polymer structure and transport properties of rubbery and glassy membrane materials are considered. On the basis of acquired information, several methods for quantitative prediction of permeability were developed, and their comparative analysis is given in the Perspective. The past decade was marked by the appearance of a number of novel interesting membrane materials, which will be briefly described in the text. In conclusion, novel approaches for achieving highly permeable and permselective materials (e.g., mixed matrix membranes) will be considered as well as several relevant but not solved so far problems of membrane gas separation.
1,232 citations
TL;DR: This work has shown that a 16-residue peptide has a characteristic beta-sheet circular dichroism spectrum in water and spontaneously assembles to form a macroscopic membrane, which may be a model for studying the insoluble peptides found in certain neurological disorders.
Abstract: A 16-residue peptide [(Ala-Glu-Ala-Glu-Ala-Lys-Ala-Lys)2] has a characteristic beta-sheet circular dichroism spectrum in water. Upon the addition of salt, the peptide spontaneously assembles to form a macroscopic membrane. The membrane does not dissolve in heat or in acidic or alkaline solutions, nor does it dissolve upon addition of guanidine hydrochloride, SDS/urea, or a variety of proteolytic enzymes. Scanning EM reveals a network of interwoven filaments approximately 10-20 nm in diameter. An important component of the stability is probably due to formation of complementary ionic bonds between glutamic and lysine side chains. This phenomenon may be a model for studying the insoluble peptides found in certain neurological disorders. It may also have implications for biomaterials and origin-of-life research.
1,221 citations
TL;DR: The different channel types obtained by recombinant means and the genetic mechanisms controlling the expression of functionally important channel structures are described.
915 citations
TL;DR: In this article, water uptake and transport parameters measured at 30 C for several available perfluorosulfonic acid membranes are compared and water sorption characteristics, diffusion coefficient of water, electroosmotic drag, and protonic conductivity were determined for Nafion 117, Membrane C, and Dow XUS 13204.10 developmental fuel cell membrane.
Abstract: Water uptake and transport parameters measured at 30 C for several available perfluorosulfonic acid membranes are compared. The water sorption characteristics, diffusion coefficient of water, electroosmotic drag, and protonic conductivity were determined for Nafion 117, Membrane C, and Dow XUS 13204.10 developmental fuel cell membrane. The diffusion coefficient and conductivity of each of these membranes were determined as functions of membrane water content. Experimental determination of transport parameters, enables one to compare membranes without the skewing effects of extensive features such as membrane thickness which contributes in a nonlinear fashion to performance in polymer electrolyte fuel cells.
648 citations
TL;DR: Electroporation of isolated cells has also been used for introduction of enzymes, antibodies, and other biochemical reagents for intracellular assays, and more recently, tissue electroporation has begun to be explored, with potential applications including enhanced cancer tumor chemotherapy, gene therapy, transdermal drug delivery, and noninvasive sampling for biochemical measurement.
Abstract: Electroporation is a fascinating cell membrane phenomenon with several existing biological applications and others likely. Although DNA introduction is the most common use, electroporation of isolated cells has also been used for: (1) introduction of enzymes, antibodies, and other biochemical reagents for intracellular assays; (2) selective biochemical loading of one size cell in the presence of many smaller cells; (3) introduction of virus and other particles; (4) cell killing under nontoxic conditions; and (5) insertion of membrane macromolecules into the cell membrane. More recently, tissue electroporation has begun to be explored, with potential applications including: (1) enhanced cancer tumor chemotherapy, (2) gene therapy, (3) transdermal drug delivery, and (4) noninvasive sampling for biochemical measurement. As presently understood, electroporation is an essentially universal membrane phenomenon that occurs in cell and artificial planar bilayer membranes. For short pulses (microsecond to ms), electroporation occurs if the transmembrane voltage, U(t), reaches 0.5-1.5 V. In the case of isolated cells, the pulse magnitude is 10(3)-10(4) V/cm. These pulses cause reversible electrical breakdown (REB), accompanied by a tremendous increase molecular transport across the membrane. REB results in a rapid membrane discharge, with the elevated U(t) returning to low values within a few microseconds of the pulse. However, membrane recovery can be orders of magnitude slower. An associated cell stress commonly occurs, probably because of chemical influxes and effluxes leading to chemical imbalances, which also contribute to eventual survival or death. Basic phenomena, present understanding of mechanism, and the existing and potential applications are briefly reviewed.
623 citations
TL;DR: The lipid phase behavior was consistent with the temperature range over which cooling was damaging for pig and shrimp sperm, and the with the extent of damage produced in pig and human sperm, the first direct evidence that cold shock results from lipid phase transitions in cell membranes.
Abstract: When cells are cooled to temperatures above the freezing point of water at rates greater than a few degrees per minute, they sustain irreversible injury. Reduction of this "cold shock" damage could increase the survival of animals and plants at low environmental temperatures and improve the cryopreservation of plant and animal cells. Leakage of solutes across membranes, associated with thermotropic phase transitions in membrane lipids, is thought to be responsible, but this hypothesis has not been tested directly. Using Fourier transform infrared spectroscopy (FTIR), we measured the lipid phase transitions in intact, living sperm, the animal cell in which cold shock has been studied most extensively. A shift in the CH2 absorbance peaks indicates the transition from liquid-crystalline to gel phase. The phase transition in sperm membranes occurred at a lower temperature for a marine shrimp than for the pig. In each case, potassium leakage, which is a hallmark of cold shock damage, increased abruptly near the end of the phase transition. Human sperm are quite resistant to cold shock, and an abrupt lipid phase transition was not detected. This phase behavior is typical of membranes containing a high proportion of cholesterol, and human sperm have an unusually high sterol content. High cholesterol levels are known to stabilize membranes during cooling. Overall, the lipid phase behavior was consistent with the temperature range over which cooling was damaging for pig and shrimp sperm, and the with the extent of damage produced in pig and human sperm. This is the first direct evidence that cold shock results from lipid phase transitions in cell membranes.
546 citations
TL;DR: The observations above suggest that dye extrusion by MDR1 may occur without a cytoplasmic appearance of the AM compounds, and call attention to the possible interaction of widely used hydrophobic fluorescent indicators with MDR 1.
495 citations
TL;DR: The evidence for fouling both on the membrane surface and within the membrane pores is described, and the effect of the feed properties, membrane properties and the operating conditions on membrane behaviour and fouling are discussed.
TL;DR: The data demonstrate that HIV-1 and HIV-2-L select specific lipid domains within the surface membrane of their host cells through which to emerge during viral maturation.
Abstract: Previous studies have indicated that human immunodeficiency virus (HIV) is enclosed with a lipid envelope similar in composition to cell plasma membranes and to other viruses. Further, the fluidity, as measured by spin resonance spectroscopy, is low and the viral envelope is among the most highly ordered membranes analyzed. However, the relationship between viral envelope lipids and those of the host cell is not known. Here we demonstrate that the phospholipids within the envelopes of HIV-1RF and HIV-2-L are similar to each other but significantly different from their respective host cell surface membranes. Further, we demonstrate that the cholesterol-to-phospholipid molar ratio of the viral envelope is approximately 2.5 times that of the host cell surface membranes. Consistent with the elevated cholesterol-to-phospholipid molar ratio, the viral envelopes of HIV-1RF and HIV-2-L were shown to be 7.5% and 10.5% more ordered than the plasma membranes of their respective host cells. These data demonstrate that HIV-1 and HIV-2-L select specific lipid domains within the surface membrane of their host cells through which to emerge during viral maturation.
TL;DR: In this paper, lipophilic borate salts are used as anionic additives in potentiometric and optical cation-selective sensors based on solvent polymeric membranes, which is attributed to their strong association with positively charged species in the membrane phase.
Book•
01 Jan 1993
TL;DR: Theory of Gas Transport in Membranes Membrane Polymers Physical Structure Fabrication Processes Configurations, Packaging and Engineering/System Design Applications as discussed by the authors...
Abstract: Theory of Gas Transport in Membranes Membrane Polymers Physical Structure Fabrication Processes Configurations, Packaging and Engineering/System Design Applications
TL;DR: In this paper, the authors estimate the lipid composition-dependent free energies of intermediate structures of different geometries, and then infer which fusion mechanism is the best explanation of observed behavior in different systems by selecting the mechanism that requires the least energy.
TL;DR: In this paper, the diffusion coefficient and conductivity of each of these membranes were determined as functions of membrane water content and contact angle measurements indicated that the surface of a perfluorosulfonic acid membrane exposed to water vapor is quite hydrophobic, even in the presence of saturated water vapor.
Patent•
01 Feb 1993
TL;DR: In this paper, a contour drawing of the shape of the structure, determining the dimensions of thin cross-sectional layers of a shape, forming porous polymer membranes corresponding to dimensions of the layers, and laminating the membranes together to form a three-dimensional matrix having the desired shape.
Abstract: Biocompatible porous polymer membranes are prepared by dispersing salt particles in a biocompatible polymer solution. The solvent in which the polymer is dissolved is evaporated to produce a polymer/salt composite membrane. The polymer can then be heated and cooled at a predetermined constant rate to provide the desired amount of crystallinity. Salt particles are leached out of the membrane by immersing the membrane in water or another solvent for the salt but not the polymer. The membrane is dried, resulting in a porous, biocompatible membrane to which dissociated cells can attach and proliferate. A three-dimensional structure can be manufactured using the polymer membranes by preparing a contour drawing of the shape of the structure, determining the dimensions of thin cross-sectional layers of the shape, forming porous polymer membranes corresponding to the dimensions of the layers, and laminating the membranes together to form a three-dimensional matrix having the desired shape.
TL;DR: It is concluded that membrane-bound ARF confers to Golgi membranes all of the requirements for specific beta-COP binding, and that myristoylated, but not non-myristoylation, ARF is the required species.
TL;DR: One‐ and two‐dimensional solid‐state 15N NMR spectra of specifically 15N‐labeled magainin 2 in oriented bilayer samples show that the secondary structure of essentially the entire peptide is α‐helix, immobilized by its interactions with the phospholipids, and oriented parallel to the membrane surface.
Abstract: Magainin 2 is a 23-residue peptide that forms an amphipathic alpha-helix in membrane environments. It functions as an antibiotic and is known to disrupt the electrochemical gradients across the cell membranes of many bacteria, fungi, and some tumor cells, although it does not lyse red blood cells. One- and two-dimensional solid-state 15N NMR spectra of specifically 15N-labeled magainin 2 in oriented bilayer samples show that the secondary structure of essentially the entire peptide is alpha-helix, immobilized by its interactions with the phospholipids, and oriented parallel to the membrane surface.
TL;DR: In this paper, a novel nanoporous carbon membrane produced by carbonization of poly(vinylidene chloride) is described, which separates gas mixtures by selective adsorption and surface diffusion of the more strongly adsorbed components.
TL;DR: In this paper, a long-range interaction between foreign inclusions (e.g. mobile proteins) in a fluid membrane which is mediated by the membrane itself was found, which can be attractive or repulsive depending on the temperature and the elastic properties of the inclusion and the membrane, and for large distances is large compared with electrostatic, van der Waals, and other lipid mediated forces.
Abstract: We find a new long-range interaction between foreign inclusions (e.g. mobile proteins) in a fluid membrane which is mediated by the membrane itself. The interaction falls off as 1/R4, can be attractive or repulsive depending on the temperature and the elastic properties of the inclusion and the membrane, and for large distances is large compared with electrostatic, van der Waals, and other lipid-mediated forces.
TL;DR: Theories explaining electroporation of the cell membrane and applications of the nonthermal PEF process are reviewed in this paper.
Abstract: Pulses of high voltage electric fields (PEF) are potentially a most important cold pasteurization/sterilization food preservation technique to replace or partially substitute for thermal processes. During the PEF process, lysis of micro-organisms is caused by irreversible structural changes in the membranes, leading to pore formation and destruction of the semipermeable barrier of the membrane. Theories explaining electroporation of the cell membrane and applications of the nonthermal PEF process are reviewed in this paper.
TL;DR: The results show that the association of the AP-1 complex with Golgi membranes, like the coatomer complex, requires ARF, which accounts for the sensitivity of both to brefeldin A and GTP, and provide the basis for a model for the early biochemical events that lead to clathrin-coated vesicle formation on the TGN.
Abstract: Recruitment of the Golgi-specific AP-1 adaptor complex onto Golgi membranes is thought to be a prerequisite for clathrin coat assembly on the TGN. We have used an in vitro assay to examine the translocation of cytosolic AP-1 onto purified Golgi membranes. Association of AP-1 with the membranes required GTP or GTP analogues and was inhibited by the fungal metabolite, brefeldin A. In the presence of GTP gamma S, binding of AP-1 to Golgi membranes was strictly dependent on the concentration of cytosol added to the assay. AP-1 recruitment was also found to be temperature dependent, and relatively rapid at 37 degrees C, following a lag period of 3 to 4 min. Using only an adaptor-enriched fraction from cytosol, purified myristoylated ARF1, and Golgi membranes, the GTP gamma S-dependent recruitment of AP-1 could be reconstituted. Our results show that the association of the AP-1 complex with Golgi membranes, like the coatomer complex, requires ARF, which accounts for the sensitivity of both to brefeldin A. In addition, they provide the basis for a model for the early biochemical events that lead to clathrin-coated vesicle formation on the TGN.
TL;DR: The results show that the ability of lipophilic acids to permeate a PC bilayer rapidly is dependent on the presence of the un-ionized acid in the membrane interface, and it is unlikely that there is a universal need for a transport protein to enhance movement of FA across membrane bilayers.
Abstract: How lipophilic acids move across membranes, either model or biological, is the subject of controversy. We describe experiments which better define the mechanism and rates in protein-free phospholipid bilayers. The transbilayer movement of lipophilic acids [fatty acids (FA), covalently-labeled FA, bile acids, and retinoic acid] was monitored by entrapping pyranin, a water-soluble, pH-sensitive fluorescent molecule to measure pH inside unilamellar vesicles [Kamp, F., & Hamilton, J.A. (1992) Proc. Natl. Acad. Sci. U.S.A. 89, 11367-11370]. Equations for the pseudo-unimolecular rate constants for transbilayer movement of un-ionized (kappa FAH) and ionized (kappa FA-) acids are derived. All FA studied (octanoic, lauric, myristic, palmitic, stearic, oleic, elaidic, linoleic, linolelaidic, and arachidonic) and retinoic acid exhibited rapid transbilayer movement (t 1/2 1 h). A further application of the pyranin method was to measure the partitioning of FA and bile acids among water, albumin, and PC vesicles. Our results show that the ability of lipophilic acids to permeate a PC bilayer rapidly is dependent on the presence of the un-ionized acid in the membrane interface. Considering the fast unfacilitated movement of FA across protein-free phospholipid bilayers, it is unlikely that there is a universal need for a transport protein to enhance movement of FA across membrane bilayers. Physiological implications of proton movement accompanying fast movement of un-ionized lipophilic acids (and the consequent generation of a pH gradient) are discussed.
TL;DR: The first observations of giant, long-existing, stabilized pores in vesicle membranes are presented, using a new experimental technique for studying the electro-permeabilization of lipid membranes.
TL;DR: The application of impedance analysis to biosensor devices based on supported lipid/protein membranes is explored and the preparation of planar membranes by fusion of vesicles onto charged surfaces is demonstrated.
Abstract: The application of impedance analysis to biosensor devices based on supported lipid/protein membranes is explored Lipid membranes with a high degree of surface coverage (≃995%) have been prepared by two methods Firstly, very stable high-resistance bilayers are formed by deposition of a covalently bound monolayer of mercaptoalkyls on gold-covered substrates and subsequent transfer of a lipid monolayer via monolayer transfer Secondly, the preparation of planar membranes by fusion of vesicles onto charged surfaces is demonstrated
TL;DR: In this paper, a microheterogeneous model for the description of inhomogeneities on the micro-phase scale of ion exchange membranes is proposed and a set of tests are proposed for determination of model structural-kinetic parameters of membranes.
TL;DR: The focus of this article is on poor membrane permeation and presystemic degradation problems; solubility/dissolution rate problems are discussed only briefly.