Membrane,synthetic selective

The main effort as far as synthetic membranes are concerned is concentrated on the development of completely new membranes for processes such as pervap-oration, gas separation, membrane distillation, or as ion transferring separators in batteries, fuel cells or electrochemical production processes. Liquid membranes with selective carriers used today for the separation and concentration of heavy metal ions or certain organic compounds are being developed further to be used in gas separation. 

FIGURE 41.2 Basic principle of artificial cells Artificial cells are prepared to have some of the properties of biological cells. Like biological cells, artificial cells contain biologically active materials (I). The enclosed material (I) can be retained and separated from undesirable external materials, such as antibodies, leukocytes, and destructive substances. The large surface area and the ultra-thin membrane allow selected substrates (X) and products (Y) to permeate rapidly. Mass transfer across 100 mL of artificial cells can be 100 times higher than that for a standard hemodialysis machine. The synthetic membranes are usually made of ultrathin synthetic polymer membranes for this type of artificial cell. (From Chang, T.M.S., Artif. Cells Blood Substit. ImmobU. Biotechnol., 22(1), vii, 1994.)... 

Synthetic separation membranes are either nonporous or porous. For nonpor-ous membranes, permeability and selectivity are based on a solution-diffusion mechanism examples for technical membrane separations are gas separation, reverse osmosis, or pervaporation. For porous membranes, either diffusive or convective How can yield a selectivity based on size, for larger pore sizes typically according to a sieving mechanism examples for technical membrane separations are dialysis, ultrafiltration, or microfiltration. It is important to note that additional interactions between permeand and membrane, e.g., based on ion exchange or affinity, can change the membrane s selectivity completely membrane adsorbers with a pore structure of a microfiltration membrane are an example. 

Membrane material selection is dependent upon the mode of therapy employed. Convective therapies such as hemofiltration require a high hydraulic permeability and a large pore size, which might permit large molecules such as cytokines to pass through the fiber wall. Synthetic membranes are well suited for this role and are desired for most continuous, convective techniques (Jones, 1998). 

More recendy, two different types of nonglass pH electrodes have been described which have shown excellent pH-response behavior. In the neutral-carrier, ion-selective electrode type of potentiometric sensor, synthetic organic ionophores, selective for hydrogen ions, are immobilized in polymeric membranes (see Membrane technology) (9). These membranes are then used in more-or-less classical glass pH electrode configurations. 

A variety of containment strategies employ floating solid objects to control the rate of gaseous emissions from surface impoundments. These include synthetic membrane covers, rafts, and hollow plastic spheres. Synthetic membrane covers are feasible where the out-gassing of volatiles due to biological activity is not expected. Selection of the liner material must be... 

In this review, recent development of active transport of ions accross the liquid membranes using the synthetic ionophores such as crown ethers and other acyclic ligands, which selectively complex with cations based on the ion-dipole interaction, was surveyed,... 

The best known groups of the cyclic compounds concerned are the depsipep-tides (e.g., valinomycin), the macrotetrolides (e.g., nonactin and monactin) and the synthetic polyethers (crown ethers) they are used at concentrations of 10 4-10 7 M, e.g., in decane. Valinomycin membranes show a K+ selectivity of... 

I.S. Han, N. Ramamurthy, J.H. Yun, U. Schaffer, M.E. Meyerhoff, and V.C. Yang, Selective monitoring of peptidase activities with synthetic polypeptide substrates and polyion-sensitive membrane electrode detection. FASEB J. 10, 1621-1626 (1996). 

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