Modification of Membranes

The use of synthetic materials in biomedical applications has increased dramatically dining the past few decades. Surface properties of polymers are of fundamental importance in many branches of industrial applications (e.g., separation of gasses, liquid mixtures, bonding, coating, adhesion, etc.). Performances of membranes also depend on the properties of their surfaces, since membrane performance is strongly influenced by the surface phenomena. Hence, it is very natural that much attention has been paid to the membrane surface modification. Surface contamination which may lead to deterioration in membrane performance is also known to be governed by the membrane surface properties. Detailed methods for modification of synthetic membranes are discussed by Khulbe et al. [63] 

The blending or simple mixing of polymers is an easy and inexpensive method of modifying various properties of a polymer such as flexibility, heat distortion and process-ability. Property of polymer blend may be directly related to compatibility or miscibility of polymers forming a blend [64]. It was reported by Clark et al. [64] that the surface composition of homopolymer blend was governed by a combination of the homopolymer molecular weight and degree of crystallinity. 

To make the modified surface properties (hydrophilic/hydrophobic) more permanent, siuface-modifying macromolecules (SMMs) were developed. SMM has an amphi-phatic structure consisting theoretically of a main polyurethane chain terminated with two low polarity polymer chains (i.e., fluorine segments) [65]. 

It is known that, in a polymer blend, thermodynamic incompatibility between polymers usually causes demixing of polymers to occvir. If the polymer is equilibrated in air, the polymer with the lowest surface energy (hydrophobic polymer) will concentrate at the air interface and reduce the systems interfadal tension as a consequence. The preferential adsorption of a polymer of lower svirface tension at the svirface was confirmed by a number of researchers for miscible blend of two different polymers. Based on this concept, svuface modifying macromolecules (SMMs) as surface-active additives were synthesized and blended into polymer solutions of PES. Depending on the hydrophobic [66] or hydrophihc [67] nature of the SMM, the membrane svirface becomes either more hydrophobic or hydrophilic than the base polymeric material. 

The membrane surface can be modified by contacting the surface of one side of the polymeric (A) membrane with a solution of a different polymer (B). A thin layer of polymer (B) is left on top of the membrane of polymer (A) after solvent evaporation. Some post-treatment can also be applied. 

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Diffusion-mediated release of root exudates is likely to be affected by root zone temperature due to temperature-dependent changes in the speed of diffusion processes and modifications of membrane permeability (259,260). This might explain the stimulation of root exudation in tomato and clover at high temperatures, reported by Rovira (261), and also the increase in exudation of. sugars and amino acids in maize, cucumber, and strawberry exposed to low-temperature treatments (5-10°C), which was mainly attributed to a disturbance in membrane permeability (259,262). A decrease of exudation rates at low temperatures may be predicted for exudation processes that depend on metabolic energy. This assumption is supported by the continuous decrease of phytosiderophore release in Fe-deficient barley by decreasing the temperature from 30 to 5°C (67). 

Schnurr et al. [22] showed that rabbit 15-LOX oxidized beef heart submitochondrial particles to form phospholipid-bound hydroperoxy- and keto-polyenoic fatty acids and induced the oxidative modification of membrane proteins. It was also found that the total oxygen uptake significantly exceeded the formation of oxygenated polyenoic acids supposedly due to the formation of hydroxyl radicals by the reaction of ubiquinone with lipid 15-LOX-derived hydroperoxides. However, it is impossible to agree with this proposal because it is known for a long time [23] that quinones cannot catalyze the formation of hydroxyl radicals by the Fenton reaction. Oxidation of intracellular unsaturated acids (for example, linoleic and arachidonic acids) by lipoxygenases can be suppressed by fatty acid binding proteins [24]. 

Another approach to enhance separation performance of membrane for dehydration of isopropanol is the modification of PVA membranes in gaseous plasma [30], The modification of membrane properties in nitrogen plasma environment lead to increase in selectivity by about 1477 at 25 °C such increase in the selectivity is justified by an increase of cross-linking on membrane surface provoked by plasma treatment. 

The involvement of phenols and enzymes of the phenolase complex appears to be secondary to the induction of necrosis. The induction must involve a modification of membrane structure which leads to altered membrane permeability and loss of cell compart-mentalization. If this occurs, regulation of cellular metabolism is lost, enz3mies are activated, and these and their substrates that are normally separated by membranes would react together. 

Membrane permeability is one of the most important determinants of pharmacokinetics, not only for oral absorption, but also for renal re-absorption, biliary excretion, skin permeation, distribution to a specific organ and so on. In addition, modification of membrane permeability by formulation is rarely successful. Therefore, membrane permeability should be optimized during the structure optimization process in drug discovery. In this chapter, we give an overview of the physiology and chemistry of the membranes, in vitro permeability models and in silica predictions. This chapter focuses on progress in recent years in intestinal and blood-brain barrier (BBB) membrane permeation. There are a number of useful reviews summarizing earlier work [1-5]. 

Buchman III G. W., and Hansen, J. N. (1987). Modification of membrane sulfhydryl groups in bacteriostatic action of nitrite. Appl. Environ. Microbiol. 53, 79-82. 

The prenyl transferases are a class of enzymes that is involved in post-translational modification of membrane-associated proteins. These enzymes catalyze the transfer of a farnesyl (FTase, EC 2.5.1.58, for structural information see References 55-65) or geranyl-geranyl group (GGTase I, EC 2.5.1.59 GGTase n, EC 2.5.1.60, for structural information... 

This work concerns mainly the modification of commercial polymers bearing hydroxy fonctions as alcohol, hydroperoxide or carboxylic acid, by reactive gases or liquid volatil compounds capable to penetrate in the polymer matrix. The modifications of membranes properties as gas permeability or surface tension will also be reported. Few examples will also concern the reaction of double bond with 12 and HBr vapor as well as the oxidation of piperidine group by peracetic acid. 

Fig. 1 shows the increase of nitrite band near 780 cm- for various alcohol contents in ethylene-vinyl alcohol copolymers. The analysis of the hydroxyl region of the IR spectra (not shown) indicated that the reaction was not quantitative (residual OH band). The precise analysis of this band ( 34(X) 70 I / mol. cm) as w ell as the nitrite band (e780 639 I / mol. cm) allows to evaluate the reaction yield considering the total film thickness (Transmission 1R). The values decrease when the OH content increases (0.75 0.62 0.59 ans 0.59 for vinyl alcohol contents 2.6,4.9, 7.7 and 10.1% respectively). Complementary analysis by reflexion IR (HATR) showed that the first 5-8 pm (Germanium crystal) were fully transformed while the analysis of the first 20-25 pm (Zinc Selenide crystal) revealed a decrease of the yield from 1 to 0.5 when the alcohol content was increasing. Then, this treatment can be helpfull for surface modification of membranes. 

As it is thought that modifications of membranes are important in the cold stress response, a question which has not been addressed yet is the subcellular localisation of the cold-regulated gene products. No clear experimental data are available. However, from the cDNA sequences determined so far it can be deduced that the predicted proteins lack obvious signal sequences and are therefore very likely to be localised in the cytoplasm (Schaffer Fischer, 1988 Cattivelli Bartels, 1990 Kurkela Franck, 1990). These data are in agreement with comparisons of in vivo and in vitro synthesised protein patterns, because for many polypeptides no post-translational modifications were predicted from 2-dimensional electrophoresis analyses (Cattivelli Bartels, 1989). With the availability of cloned probes this problem can be analysed directly by the functional expression of the cDNA clones and the production of antibodies which can be used for immunolocalisation of the corresponding proteins. 

Schmidt, M. F. 1982. Acylation of proteins—a new type of modification of membrane glycoproteins. Trends Biochem. Sci. 7 322-324. 

Schmidt, M. F. 1983. Fatty acid binding a new kind of posttranslational modification of membrane proteins. Curr. Top. Microbiol. Immunol. 102 101-129. 

Fischer, M.A. and Black, H.S., Modification of membrane composition, eicosanoid metabolism, and immunoresponsiveness by dietary omega-3 and omega-6 fatty acid sources, modulators of ultraviolet-carcinogenesis, Photochem. Photobiol., 54, 381, 1991. 

Peschel, A., Jack, R., Otto, M., Collins, L., Staubitz, P., Nicholson, G., Kalbacher, H., Nieuwenhuizen, W., Jung, G., Tarkowski, A., van Kessel, K., van Strijp, J. Staphylococcus aureus resistance to human defensins and evasion of neutrophil killing via the novel virulence factor MprF is based on modification of membrane lipids with 1-lysine. J Exp Med 193 (2001) 1067-1076. 

An abundance of techniques is available for membrane labeling, e.g. biosynthetic incorporation of labeled amino acids absorption of labeled glycoproteins specific and nonspecific modification of membrane proteins using I-iodosulphanilic acid tritium laMed N-hydroxysuccinimide esters ethyl-1- C-acetimidate... 

Stubbs, C. D. and Smith, A. D. (1984). The modification of membrane polyunsaturated fatty acid composition in relation to membrane fluidity and function. Biochim. Biophys. Acta 779 89-137. 

Luminous chemical vapor deposition (LCVD) and luminous gas treatment (LGT), which does not yield the primary deposition, could be used in the preparation and modification of membrane and barrier [1]. The term primary deposition refers to the direct deposition of material from the luminous gas (LCVD) in contrast to secondary deposition that results from the deposition of ablated material in LGT. It should be emphasized, however, that both methods are nanofilm technologies and require the substrate membrane on which LCVD nanofilm is deposited or the surface is modified. Accordingly, their use should be limited to special cases where such a nanofilm could be incorporated into membrane or the LGT of surface is warranted. 

Type A plasma polymers (see Chapter 8), so far as the transport characteristics are concerned, could be viewed as nanoscale molecular sieves, which are not solution-diffusion membranes. Therefore, the increase of oc by reducing the transport rate of the denominator permeant with the minimal reduction in the transport rate of the numerator permeant is the main viable principle for LCVD and LGT modification of membranes. 

Imanidis G, Helbing-Strausak S, Imboden R, and Leuengberger H. Vehicle-dependent in situ modification of membrane-controlled drug release. J. Control. Rel. 1998 51 23-34. 

GoU Apparatus The goh apparatus of a cell is usually connected to an endoplasmic reticulum (ER) because it stores and then transports the proteins produced in tire ER. Further modification of membrane and export proteiirs. 

Peroxides can play a physiological role in the cell but also mediate processes leading to heart disease and carcinogenesis. Fatty acid peroxidation may also be related to free radical-mediated metabolic activation of carcinogens or drugs, which lead to the initiation of carcinogenesis or cytotoxicity. Modification of membrane function as a consequence of lipid peroxidation includes imcoupling of oxidative phosphorylation... 

Koncki, R. Hulanicki, A. Glab, S., Biochemical modifications of membrane ion-selective sensors, Trends Anal. Chem. 1997, 16, 528-536... 

Together with sorbic acid, benzoic acid also acts as a membrane perturbing agent (Hazan, Levine, and Abeliovich, 2004). Disruption of the OM by organic acids involves the action of dissociated as well as undissociated forms (Alakomi et al., 2000). High lipoid solubility and the ability to form membrane polar/hydrogen unions are responsible for benzoic interaction with cell membranes and the modification of membrane properties (Otero-Losada, 2003). 

Bodnar A, Jenei A, Bene L, Damjanovich S, Matko J. Modification of membrane cholesterol level affects expression and cinslering of class 1HLA molecules at the surface of JY human lymphoblasts. Immunol Lett 1996 54 221-226. 

Chow SC, Sisfontes L, Jondal M, Bjorkhem I. Modification of membrane phospholipid fatty acyl composition in a leukemic T cell hne effects on receptor mediated intracellular Ca increase. Biochim Biophys Acta 1991 1092 358-366. 

Jenski LJ, Sturdevant LK, Ehringer WD, Stillwell W. Omega-3 fatty acid modification of membrane structure and function 1. Dietary manipulation of tumor cell susceptibility to cell and complement-mediated lysis. Nutr Cancer 1993 19 135-146. 

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