Membrane carriers

Barboiu, M., Luca, C., Popescu, G., Cot, L., Guizard, C., Hovnanian, N. and Barboiu, C. (1996) Facilitated transport of L-amino-adds II. Transport of L-phenylalanine by macrocydic fixed-site carrier membranes. Preliminary report. Roumaine Biotechnology Letters, 1 (2), 87-97. 

P.C. Meier, W.E. Morf, M. Laubli, and W. Simon, Evaluation of the optimum composition of neutral-carrier membrane electrodes with incorporated cation-exchanger sites. Anal. Chim. Acta 156,1—8 (1984). 

Secretory carrier membrane Ubiquitous integral membrane proteins of secretory and transport vesicles of unknown function, proteins (SCAMPs)... 

A double-carrier membrane system that mimics, in principle, the function of Na, K -ATPase in biological membranes was developed, although chemical compounds involved are completely different (Figure 35). The double-carrier system utilizes dicylohexyl-18-crown-6 (93) and trioctylamine (95) for enhanced transport of K ions from the feed to the receiving solution using picrate ion (pic ) as the pumping ion. The carrier 93 is for uphill transport of using a concentration... 

A double carrier membrane system for enhanced uphill transport of... 

Figure 36. Uphill transport of K ions as a function of time with (1) double carrier membrane system and (2) a symport system (reprinted with permission from Anal. Chem. 1988, 60, 2302. Copyright 1993 American Chemical Society).

Independent of the assumptions A to C the cation selectivity of the membranes in the equilibrium domain is therefore controlled by the ratio of the complex formation constants (6) and should therefore be identical for different types of neutral carrier membranes.18 Figure 2 indicates that there is indeed a close parallelism between the selectivities of solvent polymeric membranes (SPM) and bilayer lipid membranes (BLM) modified with valinomycin 1, nonactin 2, trinactin 5, and tetranac-tin 6 (see also Ref. 18). This is in good agreement with findings from Eisenman s45 and Lev s15 research groups. 

Within carrier membranes permselective for cations, the anions of low permeability can be treated as fixed charges/6-57... 

Fig. 4. Transport selectivity Kjj and potentiometric selectivity Kj j of a Na+-selective neutral carrier membrane using ligand 11. Experimental coefficients fCNaM obtained with (2) and (11) respectively given for different cations M. Membrane composition 32wt.% polyvinyl chloride, 65 wt.% dibutyl sebacate, 3wt.% carrier //. Thickness of membrane = 100 p.m. Current density approx. 0.1 p.Amm 2.

Obviously, the ion-selective transport behavior exhibited by neutral carrier membranes is based on the complexation specificity of the carrier ligands used. A comparison with (6) shows that (10) is equivalent to... 

Fig. 6. Transport selectivity and potentiometric selectivity of a Ca2 selective neutral carrier membrane (3 wt.% carrier 10, 65 wt.% o-nitrophenyl-octyl ether, 32wt.% polyvinyl chloride). Experimental selectivity coefficients KCaNa obtained with (16) and (18), respectively, as a function of the cationic concentration m (in moles/liter).

For thick carrier membranes we may usually apply the assumption of a thermodynamic equilibrium at the phase boundaries as a good approximation (see above). On the other hand, it should be considered that a positive flux of cationic complexes within the membrane (as induced by an applied voltage E< 0) leads to a certain accumulation of free carriers at x = d, respectively to a depletion at x = 0 (see Fig. 1). For practical purposes the carriers are confined to the membrane phase in the case of ideal bulk membranes (in contrast, a supply of carriers from the outside solutions is stipulated for transport studies on bilayers45,51). 

Fig. 7. Theoretical current-voltage characteristics of thick carrier membranes with different charge concentrations c = Z/CISn. The values for c are arbitrary and increase from curve A to D (for details see [55]).

We have some preliminary results indicating that reason 3 is the likely explanation for conventional carrier membranes. 

Lin AJ, Slack NL, Ahmad A et al (2003) Three-dimensional imaging of lipid gene-carriers membrane charge density controls universal transfection behavior in lamellar cationic liposome-DNA complexes. Biophys J 84 3307-3316... 

The prospects for facilitated transport membranes for gas separation are better because these membranes offer clear potential economic and technical advantages for a number of important separation problems. Nevertheless, the technical problems that must be solved to develop these membranes to an industrial scale are daunting. Industrial processes require high-performance membranes able to operate reliably without replacement for at least one and preferably several years. No current facilitated transport membrane approaches this target, although some of the solid polymer electrolyte and bound-carrier membranes show promise. 

The first representative of a potentiometric sensor was the pH-glass electrode invented in 1906 [35]. Decades of development resulted in the invention of many more ion-selective electrodes including more recently those based on neutral carrier membranes [36] and of the microelectronic fabricated ion selective field effect transistor (ISFET) [37]. 

Ion-exchange membrane and neutral carrier membrane electrodes... 

Abou-Rebeyeh, H., Korber, F., Schubert-Rehberg, K., Reusch, J., and Josic, D. (1991). Carrier membrane as a stationery phase for affinity chromatography and kinetic studies of membrane-bound enzymes.. Chromatogr. 566, 341-350. 

Photolithographic methods, which play a key part in the fabrication of semiconductors, are potential candidates for the photo-patterning of small enzyme-immobilized membranes on a FET at its wafer stage. Ion-sensing FET devices with neutral carrier membranes sensitive to alkaline and alkaline earth metal... 

Barboiu M, Luca C, Popescu G, Cot L, Guizard C, Hovnanian N, Barboiu C. Facilitated transport of L-amino-acids II. Transport of L-Phenylalanine by macrocyclic fixed-site carrier membranes. Preliminary report. Roum. Biotech. Lett. 1996 1 87-97. 

The biomimetic membranes represent a special group of carrier membranes. They are artificial membranes based on biomembrane mimicking, i.e., imitation of the essential features bio membranes use for separation. Nitrocellulose filters impregnated with fatty acids, their esters, and other lipid-like substances may be used— in other words, an imitation of many nonspecific barrier properties of biomembranes. The transport of gas through these membranes will essentially be according to facilitated transport (see Section 4.2). Biomimetic membranes for CO2 capture will transport the gas as HCO3. Development of these materials may be expected for selected applications. 

If the gas is cooled down, a C02-selective polymeric membrane may be used (cardopolymers and carrier membranes are especially interesting. Problem compression of exhaust gas may be needed see Section 4.3.1)... 

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