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Membrane Surface (membrane + surface)
Terms modified by Membrane Surface Selected AbstractsInfluence of the Non-Perfect Step Input Concentration at the Feed Side of the Membrane Surface on the Diffusion Coefficient EvaluationMACROMOLECULAR THEORY AND SIMULATIONS, Issue 3 2006Jirina Cermakova Abstract Summary: Vapor diffusion coefficients in polymeric membranes were evaluated from dynamic permeation experiments. A membrane separated the diffusion cell into two parts , upstream and downstream. At the start of the experiment the concentration change in the upstream part (feed side) was made by substituting the input stream of pure nitrogen by the stream of permeant vapors. The solution of the Fick's second law with the step input concentration function is used for the evaluation of diffusion coefficients. The realization of the step input function can be difficult and its imperfection can negatively influence the evaluation process. This contribution deals with the description of the experimentally obtained input function and the study of its influence on evaluated values of diffusion coefficients. The mathematical model, which includes the non-perfect step input concentration function and the transport through a polymer was developed. The results of this study enable the estimation of diffusion coefficient evaluation errors as dependence on the experimental arrangements and on the membrane transport properties. Diffusion apparatus for measurement of the steady-state permeation process. [source] Self-Supporting, Double Stimuli-Responsive Porous Membranes From Polystyrene- block -poly(N,N -dimethylaminoethyl methacrylate) Diblock CopolymersADVANCED FUNCTIONAL MATERIALS, Issue 7 2009Felix Schacher Abstract Asymmetric membranes are prepared via the non-solvent-induced phase separation (NIPS) process from a polystyrene- block -poly(N,N -dimethylaminoethyl methacrylate) (PS- b -PDMAEMA) block copolymer. The polymer is prepared via sequential living anionic polymerization. Membrane surface and volume structures are characterized by scanning electron microscopy. Due to their asymmetric character, resulting in a thin separation layer with pores below 100,nm on top and a macroporous volume structure, the membranes are self-supporting. Furthermore, they exhibit a defect-free surface over several 100,µm2. Polystyrene serves as the membrane matrix, whereas the pH- and temperature-sensitive minority block, PDMAEMA, renders the material double stimuli-responsive. Therefore, in terms of water flux, the membranes are able to react on two independently applicable stimuli, pH and temperature. Compared to the conditions where the lowest water flux is obtained, low temperature and pH, activation of both triggers results in a seven-fold permeability increase. The pore size distribution and the separation properties of the obtained membranes were tested through the pH-dependent filtration of silica particles with sizes of 12,100,nm. [source] Study of the MR relaxation of microglia cells labeled with Gd-DTPA-bearing nanoparticlesCONTRAST MEDIA & MOLECULAR IMAGING, Issue 3 2009Emeline Julie Ribot Abstract Therapies involving cells as vehicles need to visualize in situ the trafficking of the cells concerned. This cellular imaging can be driven by cell contrast agent-based nanoparticle internalization and non-invasive MRI (magnetic resonance imaging) detection. Here, microglial cells, that would transport a suicide gene to a glioma, were incubated for different times, with various concentrations of silica nanoparticles on which numerous Gd-DTPA were grafted. The goal of this study was to investigate the repartition of cell-associated particles. MRI was used to quantitatively follow the particle uptake process. Fluorescence microscopy images showed that, although most of the nanoparticles were internalized, some remained adsorbed on the extracellular membrane surface. The cells were then submitted to various treatments: glycine to release bound nanoparticles and/or ultrasound to destroy the cell membranes. The R1 relaxation rates were measured at 4.7 T. R1 was maximal for 4,h of incubation, decreased after 8,h and remained stable for the 24 following hours. The magnetic resonance signal of ultrasonicated and glycine-treated cells made it possible to quantify the loss of bound nanoparticles after 8,h. Nevertheless, this release did not prevent cell detection since the internalized nanoparticles are enough concentrated to visualize the labeled cells even after 4 days of cell growth. These results highlight the compartmentalization of nanoparticles in microglia and the evolution of the MR signal of the labeled cells. This study could be of importance to interpret in vivo the MR signal changes that could occur after administration of such nanoparticle-labeled cells in therapeutic strategies. Copyright © 2009 John Wiley & Sons, Ltd. [source] Influence of Aprotic Solvent on Selectivity of an Amperometric Sensor with Nafion MembraneELECTROANALYSIS, Issue 5 2006B. Chachulski Abstract This paper presents the results of investigation on selectivity of the sulfur dioxide amperometric sensor with Nafion membrane in the presence of carbon monoxide and nitrogen dioxide as the interferents. There have been compared selectivity coefficients, for the sensors containing the following internal electrolytes: solution of sulfuric acid (concentration 5,mol dm,3) in pure water (A) and solution of sulfuric acid (concentration 5,mol dm,3) in mixed solvent dimethylsulfoxide-water with an DMSO: H2O mole ratio of 1,:,2 (B). Values of the selectivity coefficients have been calculated based on the calibration curves. Analysis of both calibration curves and selectivity coefficients plays a significant role in optimization of a working point of a particular sensor. The investigated sensor operates in a three-electrode system, where the working and counter electrodes are vacuum sublimation deposited on the membrane surface. [source] Evaluation of factors influencing membrane performanceENVIRONMENTAL PROGRESS & SUSTAINABLE ENERGY, Issue 4 2005Weihua Peng Abstract Three commercial water treatment membranes, TFC-S (Koch membranes, San Diego, CA), ESPA1, and NTR7450 (Hydranautics, San Diego, CA), were tested under various physical and chemical conditions to investigate their fouling behaviors. It was found that TFC-S always displayed the greatest rate of flux decline, ESPA1 displayed a mild trend in flux decline, and NTR7450 presented a nearly stable flux. Multivariable regression models showed that the flux decline rates for TFC-S and ESPA1 were controlled by the initial permeate flux, whereas their initial (that is, instantaneous) foulings were controlled by the interaction between permeate drag and electrostatic repulsions. Feed bacteria concentration also contributed to the initial fouling of ESPA1 as a result of cell deposition on the membrane surface. NTR7450 showed an initial decline in flux followed by a steady flux, and its initial fouling was significantly affected by feed water total organic carbon (TOC) arising from the initial accumulation of colloidal organic particles on the surface. © 2005 American Institute of Chemical Engineers Environ Prog, 2005 [source] Segregation of two endocannabinoid-hydrolyzing enzymes into pre- and postsynaptic compartments in the rat hippocampus, cerebellum and amygdalaEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 2 2004A. I. Gulyas Abstract Fatty acid amide hydrolase (FAAH) and monoglyceride lipase (MGL) catalyse the hydrolysis of the endocannabinoids anandamide and 2-arachidonoyl glycerol. We investigated their ultrastructural distribution in brain areas where the localization and effects of cannabinoid receptor activation are known. In the hippocampus, FAAH was present in somata and dendrites of principal cells, but not in interneurons. It was located mostly on the membrane surface of intracellular organelles known to store Ca2+ (e.g. mitochondria, smooth endoplasmic reticulum), less frequently on the somatic or dendritic plasma membrane. MGL immunoreactivity was found in axon terminals of granule cells, CA3 pyramidal cells and some interneurons. In the cerebellum, Purkinje cells and their dendrites are intensively immunoreactive for FAAH, together with a sparse axon plexus at the border of the Purkinje cell/granule cell layers. Immunostaining for MGL was complementary, the axons in the molecular layer were intensively labelled leaving the Purkinje cell dendrites blank. FAAH distribution in the amygdala was similar to that of the CB1 cannabinoid receptor: evident signal in neuronal somata and proximal dendrites in the basolateral nucleus, and hardly any labelling in the central nucleus. MGL staining was restricted to axons in the neuropil, with similar relative signal intensities seen for FAAH in different nuclei. Thus, FAAH is primarily a postsynaptic enzyme, whereas MGL is presynaptic. FAAH is associated with membranes of cytoplasmic organelles. The differential compartmentalization of the two enzymes suggests that anandamide and 2-AG signalling may subserve functional roles that are spatially segregated at least at the stage of metabolism. [source] Conformational studies on a unique bis-sulfated glycolipid using NMR spectroscopy and molecular dynamics simulationsFEBS JOURNAL, Issue 23 2000Naoko Iida-Tanaka The time-averaged solution conformation of a unique bis-sulfated glycolipid (HSO3)2 -2,6Man,-2Glc,-1- sn -2,3- O -alkylglycerol, was studied in terms of the torsional angles of two glycosidic linkages, , (H1-C1-O-Cx) and , (C1-O-Cx-Hx), derived from heteronuclear three-bond coupling constants (3JC,H), and inter-residual proton,proton distances from J-HMBC 2D and ROESY experiments, respectively. The dihedral angles of Glc,1Gro in glycolipids were determined for the first time. The C1-C4 diagonal line of the ,-glucose ring makes an angle of ,,120 ° with the glycerol backbone, suggesting that the ,-glucose ring is almost parallel to the membrane surface in contrast with the perpendicular orientation of the ,-isomer. Furthermore, minimum-energy states around the conformation were estimated by Monte Carlo/stochastic dynamics (MCSD) mixed-mode simulations and the energy minimization with assisted model building and energy refinement (AMBER) force field. The Glc,1Gro linkage has a single minimum-energy structure. On the other hand, three conformers were observed for the Man,2Glc linkage. The flexibility of Man,2Glc was further confirmed by the absence of inter-residual hydrogen bonds which were judged from the temperature coefficients of the chemical shifts, d,/dT (,10,3 p.p.m.·°C,1), of hydroxy protons. The conformational flexibility may facilitate interaction of extracellular substances with both sulfate groups. [source] Conductivity and Methanol Permeability of Nafion,Zirconium Phosphate Composite Membranes Containing High Aspect Ratio Filler Particles,FUEL CELLS, Issue 4 2009M. Casciola Abstract Gels of exfoliated ,-zirconium phosphate (ZrPexf) in dimethylformamide (DMF) were used to prepare Nafion/ZrPexf composite membranes with filler loadings up to 7,wt.-% by casting mixtures of Nafion 1100 solutions in DMF and suitable amounts of 2,wt.-% ZrP gels in DMF. TEM pictures showed that the ZrPexf particles had aspect ratio of at least 20. All samples were characterised by methanol permeability (P) and through-plane (,thp) and in-plane (,inp) conductivity measurements at 40,°C and 100% RH. The methanol permeability of Nafion membranes containing in situ grown ZrP particles with low aspect ratio (Nafion/ZrPisg) was also determined. The methanol permeability and the swelling behaviour of the composite membranes turned out to be strongly dependent on the filler morphology. As a general trend, both permeability and swelling decreased according to the sequence: Nafion/ZrPisg > Nafion > Nafion/ZrPexf. The maximum selectivity (,thp/P,=,1.4,×,105,S,cm,3,s) was found for the membrane filled with 1,wt.-% ZrPexf: this value is seven times higher than that of Nafion. For the Nafion/ZrPexf membranes, the ratio ,inp/,thp increases with the filler loading, thus indicating that the preferred orientation of the ZrP sheets is parallel to the membrane surface. [source] pH-dependent translocation of ,-tocopherol transfer protein (,-TTP) between hepatic cytosol and late endosomesGENES TO CELLS, Issue 10 2003Masakuni Horiguchi Background:, ,-Tocopherol transfer protein (,-TTP), a member of the Sec14 protein family, plays an important role in transporting ,-tocopherol, a major lipid-soluble anti-oxidant, in the cytosolic compartment of hepatocytes and is known as a product of the causative gene for familial isolated vitamin E deficiency. It has been shown that the secretion of hepatocyte ,-tocopherol taken up with plasma lipoproteins is facilitated by ,-TTP. To explore the mechanism of ,-TTP mediated ,-tocopherol secretion, we investigated drugs which may affect this secretion. Results:, We found that, in a hepatocyte cell culture system, intracellular ,-tocopherol transport is impaired by chloroquine, an agent known for its function of elevating the pH in acidic compartments. Under chloroquine treatment, the diffuse cytosolic distribution of ,-TTP changes to a punctate pattern. Double-staining experiments with endocytosis markers revealed that ,-TTP accumulates transiently on the cytoplasmic surface of late endosomal membranes. This phenomenon is specific for hepatoma cell lines or primarily cultured hepatocytes. Other members of the Sec14 family, such as cellular retinaldehyde-binding protein (CRALBP) and supernatant protein factor (SPF), do not show this accumulation. Furthermore, we elucidate that the obligatory amino acid sequence for this function is located between amino acids 21 and 50, upstream of the N-terminal end of the lipid-binding domain. Conclusion:, We hypothesize that a liver-specific target molecule for ,-TTP exists on the late endosomal membrane surface. This transient binding may explain the mechanism of how ,-tocopherol is transferred from late endosomes to cytosolic ,-TTP. [source] Solid-state NMR Structure DeterminationIUBMB LIFE, Issue 9 2003Alison Drechsler Abstract Biological applications of solid-state NMR (SS-NMR) have been predominantly in the area of model membrane systems. Increasingly the focus has been membrane peptides and proteins. SS-NMR is able to provide information about how the peptides or proteins interact with the lipids or other peptides/proteins in the membrane, their effect on the membrane and the location of the peptides or proteins relative to the membrane surface. Recent developments in biological SS-NMR have been made possible by improvements in labelling and NMR techniques. This review discusses aligned systems and magic angle spinning techniques, bilayers and bicelles, and measurement of chemical shift anisotropy and dipolar coupling. A number of specific experiments such as cross polarization, rotational resonance, REDOR, PISEMA, MAOSS and multidimensional experiments are described. In addition to 2H, 13C and 15N, recent solid-sate 1H, 19F and 17O NMR work is discussed. Several examples of the use of SS-NMR to determine the structure of membrane peptides and proteins are given. IUBMB Life, 55: 515-523, 2003 [source] Chemical modification of polyethersulfone nanofiltration membranes: A reviewJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2009B. Van der Bruggen Abstract Polysulfone (PS) and poly(ether)sulfone (PES) are often used for synthesis of nanofiltration membranes, due to their chemical, thermal, and mechanical stability. The disadvantage for applying PS/PES is their high hydrophobicity, which increases membrane fouling. To optimize the performance of PS/PES nanofiltration membranes, membranes can be modified. An increase in membrane hydrophilicity is a good method to improve membrane performance. This article reviews chemical (and physicochemical) modification methods applied to increase the hydrophilicity of PS/PES nanofiltration membranes. Modification of poly(ether)sulfone membranes in view of increasing hydrophilicity can be carried out in several ways. Physical or chemical membrane modification processes after formation of the membrane create more hydrophilic surfaces. Such modification processes are (1) graft polymerization that chemically attaches hydrophilic monomers to the membrane surface; (2) plasma treatment, that introduces different functional groups to the membrane surface; and (3) physical preadsorption of hydrophilic components to the membrane surface. Surfactant modification, self-assembly of hydrophilic nanoparticles and membrane nitrification are also such membrane modification processes. Another approach is based on modification of polymers before membrane formation. This bulk modification implies the modification of membrane materials before membrane synthesis of the incorporation of hydrophilic additives in the membrane matrix during membrane synthesis. Sulfonation, carboxylation, and nitration are such techniques. To conclude, polymer blending also results in membranes with improved surface characteristics. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Synthesis of charged ultrafiltration poly(styrene- co -divinyl benzene) composite membraneJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008Sonny Sachdeva Abstract A ceramic supported crosslinked polystyrene composite membrane has been prepared from its monomers using a dual initiator system. The nonionic hydrophobic membrane so prepared has been chemically modified by a low temperature (50°C), single step reaction with chloroacetic acid. The carboxylated membrane has acid functional groups on its surface making it negatively charged and highly hydrophilic in nature. The membranes (unmodified and carboxylated) have been used for the separation of hazardous chromium (VI) salt solution where observed and intrinsic rejection has been studied as a function of pressure and concentration of the feed solution. The intrinsic rejection has been determined by calculating the concentration at the membrane surface (Cm) using Speigler-Kedam model and osmotic pressure model. The observed rejection for the chemically modified membrane decreases with increasing pressure but the intrinsic rejection is found to be more than 80% for all concentrations in the range of study. The experimental results have been fitted using Space-Charge model to obtain the membrane wall potential and the membrane surface concentration which are difficult to measure directly. The transport through the membrane capillaries has been described by the two dimensional model using Nernst-Planck equation for ion transport, Navier-Stokes equation and Poisson-Boltzmann equation for the radial distribution of potential. We have then presented a semianalytical series solution to the highly nonlinear Poisson-Boltzmann equation to reduce the computational time required to solve the set of coupled differential equations. The effective wall potential of the carboxylated membrane was found to be ,28.07 mV. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Removal of H2S and volatile organic sulfur compounds by silicone membrane extractionJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 1 2009I. Manconi Abstract BACKGROUND: This study explores an alternative process for the abatement and/or desulfurization of H2S and volatile organic sulfur compounds (VOSC) containing waste streams, which employs a silicone-based membrane to simultaneously remove H2S and VOSC. An extractive membrane reactor allows the selective withdrawal of VOSC and H2S simultaneously from the waste stream, while preventing direct contact between the waste stream and the absorbing solution and/or the biological treatment system. The influence of the sulfur compounds, membrane characteristics, extractant and pH was studied. RESULTS: Sulfide and the VOCS studied, i.e. methanethiol (MT), ethanethiol (ET) and dimethylsulfide (DMS) were removed from the synthetic wastewater using a silicone rubber membrane. Methanethiol showed the highest (8.72 × 10,6 m s,1) overall mass transfer coefficient (kov) and sulfide the lowest kov value (1.23 × 10,6 m s,1). Adsorption of the VOCS into the silicone membrane reduced the overall mass transfer coefficient. The kov when using Fe(III)EDTA, as extractant (5.81 × 10,7 m s,1) for sulfide extraction was one order of magnitude lower than with anaerobic water (2.54 × 10,6 m s,1). On the other hand, the sulfide removal efficiency with Fe(III)EDTA, was higher (84%) compared with anaerobic water (60%) as extractant. An additional mass transfer resistance was formed by elemental sulfur which remained attached to the membrane surface. CONCLUSIONS: Extraction of sulfide and VOCS from a synthetic wastewater solution through a silicone rubber membrane is a feasible process as alternative to the techniques developed to treat VOSC emissions. Optimizing the aqueous absorption liquid can increase the efficiency of extraction based processes. Copyright © 2008 Society of Chemical Industry [source] The membrane emulsification process,a reviewJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 3 2004C Charcosset Abstract Membrane emulsification has received increasing attention over the last 10 years, with potential applications in many fields. In the membrane emulsification process, a liquid phase is pressed through the membrane pores to form droplets at the permeate side of a membrane; the droplets are then carried away by a continuous phase flowing across the membrane surface. Under specific conditions, monodispersed emulsions can be produced using this technique. The purpose of the present paper is to provide a review on the membrane emulsification process including: principles of membrane emulsification, influence of process parameters and industrial applications. Small-scale applications such as drug delivery systems, food emulsions, and the production of monodispersed microspheres are also included. Compared with conventional techniques for emulsification, membrane processes offer advantages such as control of average droplet diameter by average membrane pore size and lower energy input. Copyright © 2004 Society of Chemical Industry [source] QUANTIFICATION OF FLUX DECLINE OF DEPECTINIZED MOSAMBI (CITRUS SINENSIS[L.] OSBECK) JUICE USING UNSTIRRED BATCH ULTRAFILTRATIONJOURNAL OF FOOD PROCESS ENGINEERING, Issue 4 2005P. RAI ABSTRACT Ultrafiltration of enzymatically treated mosambi (Citrus sinensis [L.] Osbeck) juice was performed in a batch, unstirred membrane cell. Thin film composite polyamide membrane of molecular weight cut-off 50,000 was used. The flux-decline mechanism was identified by the growth of a gel-type layer over the membrane surface. The flux decline, the gel resistance, the gel-layer thickness and various domains of resistances were calculated at a constant pressure difference in the range of 276,552 kPa. The conventional gel-filtration theory was employed to analyze the flux-decline behavior. The calculated permeate flux and gel-layer resistances were consistent with the experimental results. The calculated gel-layer thickness varied from 4.12 to 74.1 µm for different operating condition (pressure) and time. The time at which the gel resistance becomes equal to the membrane-hydraulic resistance ranged from 13 to 31 s for the pressure range studied herein. Thus, the deposited layer resistance to permeate flow was substantial, throughout the whole operation, except in the first few seconds. [source] Theoretical analysis of the effects of asymmetric membrane structure on fouling during microfiltrationAICHE JOURNAL, Issue 6 2009Weiyi Li Abstract There is a growing interest in the use of both asymmetric and composite membranes for microfiltration and ultrafiltration processes. This includes particle removal applications in the semiconductor industry and virus clearance in biopharmaceutical applications. Filter fouling plays an important role in these processes. Although flux decline models have been developed for homogeneous membranes, the effects of asymmetric membrane structure on flux decline behavior remain poorly understood on a fundamental level. Here, we develop a theoretical model to describe the effects of asymmetric membrane structure on flux decline. The asymmetric structure was described by the spatial variation in Darcy permeability in the directions normal to and parallel to the membrane surface. The velocity profile and flux decline because of pore blockage were described using Darcy's law and a pore blockage and cake filtration model. Flux decline data were obtained using pseudocomposite membranes with highly interconnected polyvinylidene fluoride membranes (PVDF) and straight through pore polycarbonate track-etched membranes (PCTE). Model composite membranes were formed by layering PCTE or PVDF membranes with different pore sizes on top of each other. Flux decline data for the composite membrane were in good agreement with model calculations. The results provide important insights into the effects of asymmetric membrane pore structures on flux decline. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Performance study of heptane reforming in the dense ceramic membrane reactorsAICHE JOURNAL, Issue 1 2008Wenliang Zhu Abstract Heptane reforming was investigated in three dense ceramic membrane reactors, where the membranes were modified differently with reforming catalyst. Each reactor displayed distinctive catalytic behavior. The reactor with a bare membrane showed low catalytic activity and low oxygen permeation flux (JO2), but gave stable performance. The left two membranes reactors modified with catalyst both displayed shift processes at the preliminary stage of membrane reaction, not only in JO2 but also in the selectivity of all products. Moreover, the membrane reactor with more catalyst gave higher performance in the case of JO2 and CO selectivity. The observed shift phenomena are due to the activation of catalyst on the membrane surface, and the different amounts of catalyst produce different impaction on the membrane reactions. On the basis of the results in three membrane reactors, a reaction pathway of hydrocarbon reforming in dense ceramic membrane reactor is proposed. Being some different from combustion and reforming mechanism (CRR), hydrocarbon reforming in dense ceramic membrane reactor has its own characteristics. © 2007 American Institute of Chemical Engineers AIChE J, 2007 [source] Hydrogen separation of methyltriethoxysilane templating silica membraneAICHE JOURNAL, Issue 12 2007Jong-Ho Moon Abstract Hydrogen separation on microporous methyltriethoxysilane-templating silica composite/,-alumina membranes (below MTES membrane) was studied using three binary gas mixtures: H2/N2, H2/CO2, and H2/CH4. The characteristics of unsteady and steady-state permeation/separation on the MTES membrane were compared to each other. Although permeation flux in the H2/N2 mixture was comparatively low, H2 selectivity was high (H2/N2 SF , 30,60). On the contrary, the H2/CO2 mixture showed high permeation flux but low H2 selectivity (H2/CO2 SF , 1.5,6.5). The H2/CH4 mixture showed a large difference between permselectivity (28,48) and separation factor (10,22). Results from this study revealed that it was difficult to predict the separation factor using the one-component permeation ratio (permselectivity) over the experimental range tested. These separation characteristics could be primarily ascribed to the molecular size and structure of each gas, which likely contributed to steric hindrance or molecular sieving within the membrane pore. In addition, the adsorption affinity of each molecule on the membrane surface acted as a key factor in separation performance because it significantly influenced surface diffusion. The generalized Maxwell-Stefan model incorporating the dust gas model, and the Langmuir model could successfully predict the transient and steady-state permeation/separation. © 2007 American Institute of Chemical Engineers AIChE J, 2007 [source] Ceramic membranes for ammonia recoveryAICHE JOURNAL, Issue 6 2006Olivier Camus Abstract An extensive screening program has been performed to find a suitable membrane configuration and operating conditions for the effective recovery of ammonia from the syngas loop. All the experiments have been performed at steady state. MFI zeolite membranes in tubular and multi-channel fiber configurations have been tested along with tubular silica membranes. At 80°C, a high ammonia permeance (2.1 × 10,7 mol.m,2.s,1.Pa,1), and a selectivity of about 10 were found with the tubular zeolite membrane, whereas for the silica membrane an even higher ammonia permeance was measured (7.6 x 10,7 mol.m,2.s,1.Pa,1) with a selectivity of about 7. For both silica and zeolite membranes, the selectivity was found to increase with increasing temperature up to 80°C. This is a combined effect of weaker adsorption of ammonia and increased diffusion at higher temperature. The results have been modeled using both the well-mixed reactor and the log mean pressure difference approaches. To overcome their limitations in addressing changes in feed concentration along the membrane surface, a segmental model has been used to obtain suitable operating conditions and membrane areas required for an industrial application. © 2006 American Institute of Chemical Engineers AIChE J, 2006 [source] Predictive membrane transport model for nanofiltration processes in water treatmentAICHE JOURNAL, Issue 6 2001Shih-Chieh Tu A membrane transport model was developed for prediction and simulation of membrane filtration (nanofiltration) dynamics with reference to permeate flux. It incorporates important phenomenological aspects of membrane transport, such as concentration polarization and gel layer formation, and illustrates the concentration of solutes as foulants in the mass-transfer boundary layer on the membrane surface. Membrane filtration tests using tannic acid as a model organic compound were designed for investigating permeate fluxes, as well as solute concentration profiles for permeates and concentrates. Membrane performance experiments were conducted under various operation conditions by varying several parameters including solute concentrations, transmembrane pressures, and reject flow rates. The tests showed that the NF-45 membrane composed of polypiperazine amide was more susceptible to organic fouling by tannic acid than the NF-70 membrane made of cross-linked aromatic polyamide. These observations were supported by surface-potential measurements that demonstrated higher negative surface charges and greater hydrophilicity for the NF-70 membrane in the presence of tannic acid. The predictive capability of the membrane transport model was evaluated using the results from membrane filtration tests. Model sensitivity studies were conducted to obtain information on effects of various input parameters pertaining to operating conditions and fluid-dynamic regimes. [source] Preparation of nitrocellulose (NC) immuno-affinity membrane for purification of rAPC antibodyJOURNAL OF SEPARATION SCIENCE, JSS, Issue 6-7 2008Haixiang Sun Abstract In this study, recombinant allophycocyanin (rAPC) with a purity of 98% was transferred from a gel to a nitrocellulose (NC) membrane to develop a simple and efficient immuno-affinity membrane. Atomic force microscopy (AFM) was used to investigate the surface topography of the affinity membrane and its characterization indicated that rAPC easily forms trimers or hexamers on the membrane surface on use of the given transfer method. The hydrodynamic radius (Rh) of the rAPC aggregation was equal to 103 nm or 365 nm according to dynamic light scattering (DLS), which was in agreement with the result obtained by AFM. Based on the specific immunological reaction of antigen and antibody, anti-APC antibodies were purified from rabbit polyclonal serum in a single step. The amount of absorbed antibody was 5.79 mg/g membrane according to analysis by ELISA methods. The purity of antibodies was up to 98% according to SDS-PAGE. The adsorption-desorption cycle of rAPC was repeated six times using the same immuno-affinity membrane, and there was no significant loss in adsorption capacity. The method provides a novel and efficient immunological affinity membrane for the purification of antibodies. [source] A New Method for the Treatment of Sperm Samples for Ultrastructural Study Based on the Use of Animal Tissues as Biological ContainersMICROSCOPY RESEARCH AND TECHNIQUE, Issue 9 2007Concepción Junquera Abstract The study of the ultrastructure of spematozoa by means of transmission electron microscopy often presents with problems of interpretation according to the method employed, depending on whether samples are either centrifuged previously to the fixation or immersed in viscous gels. The major problems of interpretation are: changes in the location of vesicles originated during the maturation process and modifications in the adsorption of seminal plasma proteins to the sperm membrane surface. The aim of our study is to communicate an original new method for the treatment of spermatozoa for ultrastructural study. Our method is based on the use of animal tissues as biological containers, inside which the spermatic suspensions are included. We developed this method using fresh sperm samples taken from mature Rasa aragonesa rams. As biological container, we used 2.5-cm long segments of the intestine of 1-week-old chickens (Gallus gallus) (diameter around 4 mm). To avoid any influence of digestive enzymes of the mucosa on the sperm surface, we put each intestine fragment inside out by means of microdissection forceps under bifocal optical microscope and cold light. One of the edges was tied with thin suture silk. The sperm suspension was injected in the optimal experimental condition and amount. Finally, the still open edge of the intestine segment was tied with silk in the same way as the other segment edge. By using this technique, we can perform a suitable morphological study at an ultrastructural level. In addition, the functional relationship of the ultrastructural components of the target cells is correctly preserved. Microsc. Res. Tech., 2007. © 2007 Wiley-Liss, Inc. [source] Quantitative microscopy reveals 3D organization and kinetics of endocytosis in rat hepatocytesMICROSCOPY RESEARCH AND TECHNIQUE, Issue 9 2006Permsin Marbet Abstract In order to demonstrate the power of quantitative microscopy, the endocytic apparatus of rat hepatocytes was reexamined using in situ liver and short term cultured hepatocyte couplets that were allowed to internalize endocytic markers for various time intervals. Correlative confocal light and electron microscopy demonstrate a tubulovesicular reticulum representing the endocytic apparatus. Volume and membrane area account for 2% of cell volume and 30% plasma membrane surface. Colocalization analysis demonstrated that pathway-specific ligands and fluid-phase markers enter EEA1-positive vesicles, the early endosomal compartment, immediately after internalization. These vesicles are translocated rapidly from basolateral to perinuclear and apical locations. Ligands are sorted within 5 min to their respective pathways. Sequential colocalization of an asialoglycoprotein-pulse with rab7 and lamp3 demonstrates that early endosomes change into or fuse with late endosomes and lysosomes. Alternatively, markers are sequestered into the common endosome consisting of rab11-positive, long tubules that originate from early endosomes and show an affinity for the transcytotic marker pIgA and its receptor. This compartment mediates transcytosis by delivering the receptor,ligand complex to the subapical compartment, a set of apical, rab11-positive vesicles, which are connected to the tubular reticulum. We conclude that vesicular traffic between preexisting compartments, maturation or fusion of endocytic organelles, and transport in tubules act in concert and together mediate transport between compartments of a tubulovesicular endocytic apparatus. In addition, we show that quantitative microscopy using high resolution data sets can detect and characterize kinetics of various parameters thus adding a dynamic component to 3D information. Microsc. Res. Tech., 2006. © 2006 Wiley-Liss, Inc. [source] Fluorescence Lifetimes Study of ,-Tocopherol and Biological Prenylquinols in Organic Solvents and Model MembranesPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 5 2006Jerzy Kruk ABSTRACT We have found that for biological prenyllipids, such as plastoquinol-9, ,-tocopherol quinol, and ,-tocopherol, the shortest fluorescence lifetimes were found in aprotic solvents (hexane, ethyl acetate) whereas the longest lifetimes were those of ubiquinonol-10 in these solvents. For all the investigated prenyllipids, fluorescence lifetime in alcohols increased along with an increase in solvent viscosity. In a concentrated hexane solution, the lifetimes of prenylquinols considerably decreased. This contrasts with methanol solutions, which is probably due to the self-association of these compounds in aprotic solvents. We have also found a correlation of the Stokes shift of prenyllipids fluorescence with the orientation polarizability of the solvents. Based on data obtained in organic solvents, measurements of the fluorescence lifetimes of prenyllipids in liposomes allowed an estimation of the relative distance of their fluorescent rings from the liposome membrane surface, and was found to be the shortest for ,-tocopherol quinol in egg yolk phosphatidyl-choline liposomes, and increased in the following order: ,-tocopherol in dipalmitoyl phosphatidylcholine liposomes < ,-tocopherol < plastoquinol-9 < ubiquinol-10 in egg-yolk phosphatidylcholine liposomes. [source] Surface Modification of Poly(propylene) Microporous Membrane to Improve Its Antifouling Characteristics in an SMBR: O2 Plasma TreatmentPLASMA PROCESSES AND POLYMERS, Issue 1 2008Hai-Yin Yu Abstract Fouling is the major obstacle in membrane processes applied in water and wastewater treatment. To improve the antifouling characteristics of PPHFMMs in an SMBR for wastewater treatment, the PPHFMMs were surface-modified by O2 low temperature plasma treatment. Structural and morphological changes on the membrane surface were characterized by XPS and FE-SEM. The change of surface wettability was monitored by contact angle measurements. Results of XPS clearly indicated that the plasma treatment introduced oxygen containing polar groups on the membrane surface. The static water contact angle of the modified membrane reduced obviously with the increase of plasma treatment time. The relative pure water flux for the modified membranes increased with plasma treatment time up to 1 min, then it decreased with further increase of plasma treatment time. Decreases in the tensile strength and the tensile elongation at break of the modified membranes were also observed. To assess the relation between the plasma treatment and the membrane fouling in an SMBR, filtration for activated sludge was carried out by using synthetic wastewater. After continuous operation in the SMBR for about 75 h, flux recovery were 8.7 and 12.3%, reduction of flux were 91.6 and 87.4% for the nascent and O2 plasma treated PPHFMM for 1 min, relative flux ratio for O2 plasma treated PPHFMM for 1 min was 49.9% higher than that of the nascent PPHFMM. [source] Interactive functional poly(vinylidene fluoride) membranes with modulated lysozyme affinity: a promising class of new interfaces for contactor crystallizersPOLYMER INTERNATIONAL, Issue 12 2009Annarosa Gugliuzza Abstract BACKGROUND: One of the challenges of current researches in biotechnological fields is the achievement of regular and increasingly smaller protein crystals for genomics and biocatalyst applications. The membrane contactor-based methodology appears to be a time-effective and economically competitive technology for accomplishing this target. RESULTS: A new class of interactive polymeric interfaces enabling the nucleation of very small protein crystals in a short time through controlling attractive interactions is discussed. Specifically, the role of attractive interfacial forces between a model lysozyme solution and modified poly(vinylidene fluoride) membranes is examined. The insertion of amphiphilic motifs in the fluorinated membranes allows quicker agglomeration of protein crystals at the membrane surface reducing significantly the induction time for protein nucleation. The chemical nature of the modifier permits the modulation of the membrane affinity to the lysozyme, involving polar and non-polar attractive interactions and preserving intrinsic structural features, transport properties and the hydrophobic character of the interfaces, according to the basics of membrane crystallization technology. The formation of critical nuclei is observed after 3 h and micro-sized crystals are formed in less than 24 h. CONCLUSION: The experimental evidence suggests these membranes as a promising class of interactive interfaces that may rapidly bring advances in genomics research. Copyright © 2009 Society of Chemical Industry [source] Plasma-induced grafting of hydroxyethyl methacrylate (HEMA) onto chitosan membranes by a swelling methodPOLYMER INTERNATIONAL, Issue 2 2003Yeping Li Abstract Hydroxyethyl methacrylate (HEMA) was grafted onto chitosan membranes by plasma-graft polymerization. Effects of monomer concentration, plasma power and plasma time on the amount of grafting were investigated. The results showed that there were two processes: grafting polymerization and etching of the membrane. The surface of the grafted membrane was evaluated by FTIR. Scanning electron microscopy indicated that the surface morphology of the grafted membrane could be adjusted through plasma power. Water contact angles of the chitosan surface decreased from 78.2° to 45.4° while the amount of grafting increased from 0 to 12.2%, indicating improved hydrophilicity of the membrane surface. Permeation coefficients through the original membrane, the membrane treated at 55,W for 15,min, and the membrane treated at 55,W for 30,min for creatinine were 9.12,×,10,7, 10.6,×,10,7 and 8.57,×,10,7,cm2,s,1, respectively. Thermogravimetry and mechanical testing showed that there were no significant changes on the bulk property of chitosan membrane after modification. © 2003 Society of Chemical Industry [source] PLAC1 (Placenta-specific 1): a novel, X-linked gene with roles in reproductive and cancer biologyPRENATAL DIAGNOSIS, Issue 6 2010Michael Fant Abstract Placenta-specific 1 (PLAC1) is a recently described X-linked gene with expression restricted primarily to cells derived from trophoblast lineage during embryonic development. PLAC1 localizes to a region of the X chromosome thought to be important in placental development although its role in this process has not been defined. This review summarizes our current understanding of its expression, regulation, and function. PLAC1 is expressed throughout human pregnancy by the differentiated trophoblast and localizes to membranous structures in the syncytiotrophoblast, including the microvillous plasma membrane surface. Recent studies have demonstrated that PLAC1 is also expressed by a wide variety of human cancers. Studies of the PLAC1 promoter regions indicate that its expression in both normal placenta and cancer cells is driven by specific interactions involving a combination of transcription factors. Although functional insight into PLAC1 in the normal trophoblast is lacking, preliminary studies suggest that cancer-derived PLAC1 has the potential to promote tumor growth and function. In addition, it also appears to elicit a specific immunologic response that may influence survival in some cancer patients, suggesting that it may provide a therapeutic target for the treatment of some cancers. We also discuss a potential role for PLAC1 as a biomarker predictive of specific pregnancy complications, such as preeclampsia. Copyright © 2010 John Wiley & Sons, Ltd. [source] Initial Deposition of Colloidal Particles on a Rough Nanofiltration MembraneTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2007Tania Rizwan Abstract The initial rate of colloid deposition onto semi-permeable membranes is largely controlled by the coupled influence of permeation drag and particle-membrane colloidal interactions. Recent studies show that the particle-membrane interactions are subject to immense local variations due to the inherent morphological heterogeneity (roughness) of reverse osmosis (RO) and nanofiltration (NF) membranes. This experimental investigation reports the effect of membrane roughness on the initial deposition of polystyrene latex particles on a rough NF membrane during cross flow membrane filtration under different operating pressures and solution chemistries. Atomic force microscopy was used to characterize the roughness of the membrane and observe the structure of particle deposits. At the initial stages of fouling, the AFM images show that more particles preferentially accumulate near the "peaks" than in the "valleys" of the rough NF membrane surface. Le taux initial de la déposition colloïdale sur des membranes semi-perméables est largement contrôlé par l'influence couplée entre la traînée de perméation et les interactions colloïdales membrane-particules. Des études récentes montrent que les interactions membranes-particules sont sujettes à d'immenses variations locales en raison de l'hétérogénéité morphologique inhérente (rugosité) des membranes d'osmose inverse (RO) et de nanofiltration (NF). Cette étude expérimentale décrit l'effet de la rugosité des membranes sur la déposition initiale de particules de latex de polystyrène sur une membrane NF rugueuse lors de la filtration des membranes en écoulement transversal pour différentes conditions opératoires et compositions chimiques des solutions. On a eu recours à la microscopie à force atomique pour caractériser la rugosité de la membrane et observer la structure des dépôts de particules. Aux stades initiaux du refoulement, les images AFM montrent que les particules s'accumulent préférentiellement près des «pics» plutôt que dans les «vallées» de la surface de membrane NF rugueuse. [source] Electrophysiological properties of BK channels in Xenopus motor nerve terminalsTHE JOURNAL OF PHYSIOLOGY, Issue 1 2004Xiao-Ping Sun Single channel properties of Ca2+ -activated K+ (BK or Maxi-K) channels have been investigated in presynaptic membranes in Xenopus motoneurone,muscle cell cultures. The occurrence and density of BK channels increased with maturation/synaptogenesis and was not uniform: highest at the release face of bouton-like synaptic varicosities in contact with muscle cells, and lowest in varicosities that did not contact muscle cells. The Ca2+ affinity of the channel (Kd= 7.7 ,m at a membrane potential of +20 mV) was lower than those of BK channels that have been characterized in other terminals. Hill coefficients varied between 1.5 and 2.8 at different potentials and open probability increased e-fold per 16 mV change in membrane potential over a range of [Ca2+]i from 1 ,m to 1 mm. The maximal activation rate of ensembled single BK channel currents was in the submillisecond range at ,+20 mV. The activation rate increased ,10-fold in response to a [Ca2+]i increase from 1 to 100 ,m, but increased only ,2-fold with a voltage change from +20 to +130 mV. The fastest activation kinetics of BK channels in cell-attached patches resembled that in inside-out patches with [Ca2+]i of 100 ,m or more, suggesting that many BK channels are located very close to calcium channels. Given the low Ca2+ affinity and rapid Ca2+ binding/unbinding properties, we conclude that BK channels in this preparation are adapted to play an important role in regulation of neurotransmitter release, and they are ideal reporters of local [Ca2+] at the inner membrane surface. [source] | |||||||||||||||||||||||||||||||||||||