Plain Membrane Research Articles

Membranes for direct methanol fuel cell based on modified heteropolyacids

Organic-inorganic membranes for direct methanol fuel cell (DMFC) application were prepared from sulfonated polyether ether ketone (SPEEK), containing heteropolyacids and an oxide phase either generated by hydrolysis ofamino-modified silanes or by dispersion of a surface-modified fumed silica. The heteropolyacid was based on lacunary divacant [γ-SiW10O36]−8 and contained epoxy groups which reacted with the ammo-groups in the oxide phase. The reaction provides a covalent bond between the heteropolyacid to the insoluble oxide phase, resulting in its fixation in the membrane. The organic-inorganic composites prepared in this way were more stable than the plain membrane, had lower methanol crossover and proton-conductivity in the same order of magnitude.

Affinity dye–ligand poly(hydroxyethyl methacrylate)/chitosan composite membrane for adsorption lysozyme and kinetic properties

A composite membrane from 2-hydroxyethyl methacrylate (HEMA) and poly(hydroxyethyl methacrylate)/chitosan (pHEMA/chitosan) was synthesized via UV initiated photo-polymerization in the presence of an initiator α,α′-azoisobutyronitrile (AIBN). Procion Brown MX 5BR was then covalently immobilized onto composite membrane as a dye–ligand. The binding characteristics of a model protein (i.e. lysozyme) to the dye–ligand immobilized affinity membrane have been investigated from aqueous solution using the plain composite membrane as a control system. The experimental data was analyzed using two adsorption kinetic models, the pseudo-first-order and the pseudo-second-order, to determine the best-fit equation for the adsorption of lysozyme onto affinity composite membrane. The second-order equation for the adsorption of lysozyme on the dye–ligand membrane systems is the most appropriate equation to predict the adsorption capacity for the affinity membrane. The reversible lysozyme adsorption on the affinity membrane obeyed the Freundlich isotherm. The lysozyme adsorption capacity of the plain membrane and the dye–ligand affinity membrane were 8.3 and 121.5 mg ml −1, respectively.

Model investigations of convective heat transfer and pressure loss in diagonal membrane heating surfaces

The paper presents the results of an investigation concerning heat transfer and pressure loss in air crossflow of diagonally shaped membrane heating surfaces. The heat and mass transfer analogy by means of naphthalene sublimation technique is used in order to evaluate mean Nusselt number values in such tube banks. The effect of tube bank arrangement on heat transfer coefficients and flow resistance is discussed. Convective heat transfer and pressure loss characteristics of diagonally shaped membrane tube banks, plain tube banks and ordinary membrane tube banks are compared.

Characterisation of a plasma membrane-associated phospholipase A 2 activity increased in response to cold acclimation

We here demonstrate the presence of a plasma membrane-associated phospholipase A(2) (EC 3.1.1.4; PLA(2)) activity in spinach (Spinacia oleracea) leaves. The pH profile of the spinach plasma membrane PLA(2) activity revealed two peaks, one at pH 4.4 and one at pH 5.5. The activity at pH 5.5 had an absolute requirement of Ca2+, with full enzyme activity at 10mumol/L Ca2+. The Ca2+-dependent PLA(2) activity was both heat sensitive and stimulated by diacylglycerol, whereas ATP completely inhibited the activity. Thus, the spinach plasma membrane contains a Ca2+-dependent PLA(2) activity, which has not previously been characterised in plants. Cold acclimation of spinach resulted in a 2.2-fold higher plasma membrane PLA(2) activity whereas the plasma membrane phospholipase D activity remained unaffected. Taken together, our data suggest a role of PLA(2) in cold acclimation in plants. (Less)

Multilayer capsules: a promising microencapsulation system for transplantation of pancreatic islets

In 1980, Lim and Sun introduced a microcapsule coated with an alginate/polylysine complex for encapsulation of pancreatic islets. Characteristic to this type of capsule is, that it consists of a plain membrane which is formed during a single procedural step. With such a simple process it is difficult to obtain instantly a membrane optimized with respect to all the properties requested for islet transplantation. To overcome these difficulties, it is recommended to build up the membrane in several consecutive steps, each optimized for a certain property. In this study, we have analysed such a multilayer microcapsule for the encapsulation of pancreatic islets. Therefore, empty and islet containing alginate beads were coated with alternating layers of polyethyleneimine, polyacrylacid or caboxymethylcellulose and alginate. By scanning electron microscopy the thickness of the covering multilayer-membrane was estimated to be less than 800 nm by comparison with an apparatus scale. Ellipsometric measurements showed that the membrane thickness is in the range of 145 nm. Neither the encapsulation procedure, nor the membrane-forming step did impede the stimulatory response of the islets. The encapsulation even lead to a significantly better stimulatory response of the encapsulated islets during week three and five of cell culture. Furthermore, the multilayer-membrane did not deteriorate the biocompatibility of the transplanted microcapsules, allowing an easy tuning of the molecular cut-off and the mechanical stability depending on the polycation–polyanion combination used. The multilayer membrane capsule has obvious advantages compared to a one-step encapsulation procedure. These beads guarantee a high biocompatibility, a precisely adjusted cut-off, an optimal insulin-response and high mechanical stability although the membrane is only 145 nm thick.

Impaired activation of cytosolic phospolipase A(2) in inflamed canine colonic circular muscle.

Arachidonic acid (AA) is a critical second messenger in several cell types. We examined whether cholinergic AA acts as a second messenger in contraction of colonic circular muscle cells and if this role is altered by inflammation. The experiments were performed on single dispersed cells. AA release was measured by high-performance liquid chromatography. Escherichia coli membranes labeled with (3)H-AA were used as a substrate for determining phospholipase A(2) (PLA(2)) activity, and Western immunoblotting for protein expression. Acetylcholine and the PLA(2) activator melittin induced cell contractions and AA release. Both effects were inhibited by the PLA(2) inhibitor ONO-RS-082. Cytosolic and membrane PLA(2) activities increased in response to acetylcholine. These were blocked by ONO-RS-082 and cytosolic PLA(2) 100-kilodalton antibody, but not by dithiothreitol, a secretory PLA(2) inhibitor. Acetylcholine- and melittin-stimulated release of AA and their contractile response were attenuated in inflamed cells. Immunoblotting indicated that the protein expression of cPLA(2) was suppressed during inflammation. AA acts as a second messenger in muscarinic receptor-activated contractions of colonic circular muscle cells. cPLA(2) is the primary enzyme that releases AA in these cells; its expression as well as activation are significantly attenuated by inflammation. The attenuated release of AA may partly account for the inhibition of colonic circular muscle tone and phasic contractions observed during inflammation.

Organotin — environmental fate and effects

Novel polysulfone (PSF) ultrafiltration membranes with pH and thermo sensitivity were prepared using the copolymer poly (N-vinylcaprolactam-co-acrylic acid) (poly (VCL-co-AA)) as an additive. The copolymer was synthesized by free radical solution polymerization, and directly blended in membrane casting solution to prepare the asymmetric membranes by phase inversion method. The presence of copolymer in blended membranes was confirmed by comparing IR spectra of plain PSF membrane and blended PSF membrane. The morphology and structure of the resulting membranes were observed by scanning electron microscope (SEM) and field emission scanning electron microscope (FESEM). The membranes were characterized in terms of pure water flux (PWF), hydraulic permeability and hydrophilicity. PWF increased from 1 to 18.8 L/m2h, when wt.% of copolymer increases from 0 to 2.5. Similarly, water contact angle decreased from 76° to 58°. The blended membranes showed evident of pH and thermo sensitivity. The stimuli responsive behaviour of membranes was also investigated in terms of pH and temperature. In addition, solution of bovine serum albumin (BSA) was used to study the permeation and antifouling performance of prepared membranes. A significant increase in BSA flux (from 0.061 L/m2h for plain membrane to 3.37 L/m2h for membrane with 6 wt.% of copolymer) and decrease in membrane fouling was observed.

Phospholipase A 2 and protein kinase C enzymatic activities and their interactions in Hydra vulgaris

Recent reports have assigned to activation of phospholipase A 2 (PLA 2), with subsequent production of arachidonic acid (AA) and its derivatives, and to stimulation of protein kinase C (PKC), a key role in the control of body pattern, tentacle regeneration, and bud formation in two Hydra species. Experiments conducted in vivo suggested also the occurrence of a bidirectional interaction between the two enzymes during these processes. Here we describe for the first time the simultaneous partial characterization of PLA 2 and PKC activities in a hydrozoan species, the freshwater Hydra vulgaris. PLA 2 activity was found to be associated with membrane fractions, dependent on pH and on millimolar Ca 2+ concentrations and counteracted by a specific inhibitor of mammalian membrane PLA 2, oleyloxyethyl-phosphoryl-choline (OOPC). A PKC-like enzyme with a molecular weight of about 70 kDa was partially purified from cytosolic extracts. Its activity was also found to depend on Ca 2+ as well as phosphatidylserine, but was not influenced by AA. Conversely, the PKC activator tetradecanoyl-phorbol-II-acetate (TPA) induced PLA 2 activation and AA liberation in H. vulgaris polyps in vivo. While PKC-PLA 2 interactions have been extensively investigated in mammals, the present study represents the first example of PKC-induced activation of an invertebrate PLA 2.

Down-regulation of protein kinase C attenuates the oxidant hydrogen peroxide-mediated activation of phospholipase A 2 in pulmonary vascular smooth muscle cells

Exposure of rabbit pulmonary vascular smooth muscle cells to H 2O 2 dose-dependently stimulates the cell membrane associated protein kinase C (PKC) activity, phospholipase A 2 (PLA 2) activity, phospholipase A 2 (PLA 2) activity, and arachidonic acid (AA0) release. Pretreatment of the cells with staurosporine (an inhibitor of PKC) prevents AA release and PLA 2 activity caused by H 2O 2. Treatment of the cells with 4β-PMA (an active phorbol ester), or 4α-PMA (an inactive phorbol ester) does not affect basal AA release. In contrast, 4β-PMA significantly stimulates the cell membrane associated PKC activity. Treatment of the cells with 4β-PMA for a short time (upregulation of PKC) augments PLA 2 activity and AA release caused by a sub-optimal dose of H 2O 2 (0.4 mM). Under this condition, staurosporine prevents the stimulatory effects of 4β-PMA on membrane PLA 2 activity, and AA release. In contrast to the up-regulation, pretreatment with 4β-PMA for a longer time (down-regulation of PKC) does not appreciably augment PLA 2 activity and AA release caused by 0.4 mM H 2O 2. Treatment of the cells with an intracellular Ca 2+ antagonist TBM-8 prevents H 2O 2 induced membrane PLA 2 activity and AA release without affecting membrane PKC activity. Treatment of the cells with TMB-8 before addition of 4β-PMA (up-regulation of PKC) followed by incubation with 0.4 mM H 2O 2 does not augment PLA 2 activity and AA release, although membrane PKC activity increases under this condition.

Synthesis of cell-impermeable inhibitor of phospholipase A 2

Phospholipase A 2 (PLA 2) in the cell surface membrane is considered a regulator of cellular secretion. The distinction between the role of the cell surface and the intracellular PLA 2 is not clear, since it has not been possible to differentiate unequivocally the activity of the enzymes in the various organelles. The use of an extracellular inhibitor of PLA 2 can greatly contribute to the understanding of cell surface PLA 2 function. In this paper, the preparation of a cell-impermeable inhibitor of PLA 2 is presented. This substance incorporates into lipid membranes and is capable of blocking the hydrolysis of membrane phospholipids by snake venom as well as by cell membrane PLA 2.