Membrane additive solvents

Second, P-gp differs from other transporters in that it recognizes its substrates when dissolved in the lipid membrane [52], and not when dissolved in aqueous solution. The site of recognition and binding has been shown to be located in the membrane leaflet facing the cytosol [53, 54], This implies that the membrane concentration of the substrate, Csm, determines activation [57]. Since the nature of a molecular interaction is strongly influenced by the solvent, the lipid membrane must be taken into account as the solvent for the SAR analysis of P-gp. Under certain conditions, the effect of additional solvents or excipients (used to apply hydrophobic substrates or inhibitors) on the lipid membrane and/or on the transporter must also be considered. Lipophilicity of substrates has long been known to play an important role in P-gp-substrate interactions nevertheless, the correlation of the octanol/water partition coefficients with the concentration of half-maximum... 

As mentioned, the Peppas-Reinhart theory is valid in the case of highly swollen membranes. Additional work by Peppas and Moynihan [158] resulted in a theory for the case of moderately swollen networks. This theory was derived much like the Peppas-Reinhart theory with the exceptions that in a moderately swollen network, one may not assume that the diffusional jump length of the solute in the membrane, X2, i3, is equal to the diffusional jump length of the solute in pure solvent, X2, i and, also, one may not assume that the free volume of the polymer/solvent system is equal to the free volume of the solvent. The initial... 

The crude sample is injected or pumped onto the TE column. [Note Even a crude sample requires membrane filtration and/or centrifugation to prevent shortened column life of the trace enrichment column.] The TE column will attract the components of interest, depending on the nature bonded phase in the TE column, the solvent in which the sample is dissolved, and the solvent in which the TE column has been equilibrated. The TE column, most likely, will remove more than just the components of interest and, thus, might need an additional solvent wash sequence to remove other collected impurities. 

The mass-transfer efficiencies of various MHF contactors have been studied by many researchers. Dahuron and Cussler [AlChE 34(1), pp. 130-136 (1988)] developed a membrane mass-transfer coefficient model (k ) Yang and Cussler [AIChE /., 32(11), pp. 1910-1916 (1986)] developed a shell-side mass-transfer coefficient model (ks) for flow directed radially into the fibers and Prasad and Sirkar [AIChE /., 34(2), pp. 177-188 (1988)] developed a tube-side mass-transfer coefficient model (k,). Additional studies have been published by Prasad and Sirkar [ Membrane-Based Solvent Extraction, in Membrane Handbook, Ho and Sirkar, eds. (Chapman Hall, 1992)] by Reed, Semmens, and Cussler [ Membrane Contactors, Membrane Separations Technology Principle. and Applications, Noble and Stern, eds. (Elsevier, 1995)] by Qin and Cabral [MChE 43(8), pp. 1975-1988 (1997)] by Baudot, Floury, and Smorenburg [AIChE ]., 47(8), pp. 1780-1793 (2001)] by GonzSlez-Munoz et al. [/. Memhane Sci., 213(1-2), pp. 181-193 (2003) and J. Membrane Sci., 255(1-2), pp. 133-140 (2005)] by Saikia, Dutta, and Dass [/. Membrane Sci., 225(1-2), pp. 1-13 (2003)] by Bocquet et al. [AIChE... 

Electron-transfer Reactions - Light-induced electron transfer from a donor to a suitable acceptor has been described for numerous bimolecular systems. The reagents have been dispersed in a polar solvent,at microscopic or macroscopic interfaces, in latex dispersions, in nematic liquid crystals, in reverse micelles, in vesicles, and in lipid bilayer membranes. Additional studies have been concerned with electron transfer... 

Effects of additives. The results are summarized In Figure 2 in terms of water solubility of additive solvent and membrane performance evaluated with 0.2% ovalbumlne aqueous solution. The water flux rises very steeply from zero to 8.8xl0 ml/mln.m In correspondence with Increase In the water solubility of additive solvent from 1 to 4 g/dl. Contrary to the fact that the water flux curve has a plateau for the additive water solubility larger than 4 g/dl, the ovalbumlne permeation values for some water mis-slble additive solvents are undesirably higher than those for additive solvents, of which water solubility Is in the rang,e from 4 to 20 g/dl. 

Figure 3 Illustrates that membrane thickness Increases consistently with water solubility of additive solvents.

Figure 2. Relationship between membrane performance and water solubility of additive solvents (O, 0J solubility of additive solvents in water fA, ik) solubility of water in additive solvents. Water flux is normalized to the staridard value of 8.8 X 10 mL/min m and ovalubumine permeation is normalized to the standard...

Role of partially water soluble additive solvents. There have been published many studies on the membrane formation mechanism and the effects of solvents, additives (swelling agents or poreformers) and precipitants. Membrane performance and morphology are well correlated to polymer precipitation rate in nascent membrane (. Low precipitation rate generally produces membranes of finely pored sponge substrate structure with low solute permeation. Remarks on solvent-precipitant interaction by Frommer et al. (3) is helpful to speculation on membrane formation. In the following paragraphs is discussed the role of partially water soluble solvent as a plasticizer of nascent membrane matrix. 

For high accuracy, this measurement is repeated several times at varying solute concentrations, and the limiting value of Cjoiuie// as C,oiuie approaches zero is used in Eiq. 11.5-7. This procedure allows for the fact that Csoime is imperfectly known (since additional solvent passes through the membrane until equilibrium is established) and that the simplifications in Eq. 11.5-6 become exact and solvent nonidealities vanish as... 

In addition to carrier derlvatlzatlon, we attempted to Increase the solubility of the Fe(II) carriers through the addition of co-solvents to the liquid membrane. Addition of 50 (v v) propylene carbonate to benzonltrile resulted In six- to eightfold Increase in solubility without loss of stability towards dloxygen. 

Despite the viscosity and polarity being the main parameters to influence the flow of solvents in polymer membranes (the latter related to surface tension), in addition, there is an interaction between membrane and solvent, which influences the mechanism of mass transport that depends on the type of membrane material and of the specific properties of the solvents and is thus important in determining the flow of the solvent. However, this is another mechanism of mass transport... 

The most technologieally advaneed products are used for waterproofing and pipeline coatings. These products are also based on dispersion of asphalt in the above mentioned solvents but reinforced with addition of polymer. The addition of polymer modifies the plastie behavior of asphalt and renders it elastomeric. Additional solvents are usually added to improve the solubihty of polymerie eomponents. Reaetive polyurethanes are the most frequently used modifiers for waterproofing hquid membranes. Toluene and xylene are the... 

Another component of the polymer membrane of ion-selective electrodes is the plasticizer. It lowers the glass transition temperature of the polymer, serves as the solvent for the ionophore and other membrane additives, increases the polarity of the membrane, which facilitates the distribution of ions between two phases. The plasticizer content in the membrane is approx. 65% of weight. Due to the plasticizer, the membrane can be considered a liquid phase, since the diffusion coefficient of the dissolved, low-molecular-weight ionophores is approx. 10" - - 10 cmV [38]. Such membranes are often called liquid/polymer or solvent polymeric in the literature. 

Although ultrafiltration can easily control resist-bath conductivity, any small water-soluble molecule is allowed to pass through the membrane, including solvent, which constitutes an environmental/waste treatment problem. Many ED resists have been formulated to include water-soluble solvents, and maintaining bath solvent level therefore requires periodic analysis and addition of fresh solvents. (This is not the case with resists that have been ultrafiltered during manufacture to remove water-soluble solvent (section 2.4.10).)... 

Micellar structure has been a subject of much discussion [104]. Early proposals for spherical [159] and lamellar [160] micelles may both have merit. A schematic of a spherical micelle and a unilamellar vesicle is shown in Fig. Xni-11. In addition to the most common spherical micelles, scattering and microscopy experiments have shown the existence of rodlike [161, 162], disklike [163], threadlike [132] and even quadmple-helix [164] structures. Lattice models (see Fig. XIII-12) by Leermakers and Scheutjens have confirmed and characterized the properties of spherical and membrane like micelles [165]. Similar analyses exist for micelles formed by diblock copolymers in a selective solvent [166]. Other shapes proposed include ellipsoidal [167] and a sphere-to-cylinder transition [168]. Fluorescence depolarization and NMR studies both point to a rather fluid micellar core consistent with the disorder implied by Fig. Xm-12. 

---