Pair Transport

For ion pair transport to take place, organic anions combine with organic cations to form a neutral complex, which is then transported through the membrane by passive diffusion. 

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It follows from the fermion commutation relations that the entries of a fe-matrix are related by a system of linear equalities. For example, consider the pair transport operator = 2 b a a b + h ala b ), which moves a spin-up, spin-down pair of electrons between sites p,v of A. If we define w o = ... 

Figure 18 (a) Mechanism of ion pair transport mediated by a cation carrier (b) plot of initial transport rates (V) of cation picrates as a function of the logarithm of the stability constants... 

Neubert, R., Ion-pair transport across membranes. Pharmaceutical Research 1989, 6, 743-747. 

To form the relatively undissociated water, 2 protons per electron pair, transported through complex IV, are removed from the mitochondrial matrix. An additional 2 protons per electron pair transported are extruded from the matrix by complex IV. The total number of protons lost by the mitochondrial matrix through the action of complexes I, III, and IV is thus 8-10 per electron pair, depending on the authority cited. The reason protons are extruded across the inner mitochondrial membrane is 2-fold complex IV apparently acts as a true proton pump with specific protein(s) of that complex acting as the transport particle(s). Complexes I and III, on the other hand, are associated with the so-called vectoral proton translocation process those enzymatic reactions that release protons (e.g., reoxidation of UQH2) take place at or near the intermembrane space surface on the inner mitochondrial membrane. This allows protons to be discharged into the intermembrane space rather than into the mitochondrial matrix. Overall, the pH differential between the cytosol and the mitochondrial matrix is about 1, or a 10-fold difference in [H+] (alkaline inside). 

P = Passive transport C = Convective transport A = Active transport F = Facilitated transport I = Ion pair transport E = Endocytosis. 

Experiments like the one depicted In Figure 8-19 have shown that four protons are translocated across the membrane per electron pair transported from C0QH2 through the CoQH2-cytochrome c reductase complex. Thus this complex transports two protons per electron transferred, whereas the cytochrome c oxidase complex transports only one proton per electron transferred. An evolutlonarlly conserved mechanism, called the Q cycle, accounts for the two-for-one transport of protons and electrons by the CoQH2-cytochrome c reductase complex. 

They explained this phenomenon in terms of ion pair transport. Lee et al. (M) studied copper extraction using two types of liquid membranes. More recently, Gokalp et al. (70) used liquid membranes containing polyethers to electrorefine silver and copper. They explored two geometries for the liquid membrane. They placed the membrane between the anode and cathode and also coated the cathode with the membrane in separate experiments. They were able to demonstrate the technical feasibility of this process. 

The simplest compounds known to form defined ion channels are the isophthalate derivative and the ion-pair transporter 11. Single channels were observed for both systems, although incoiporation and activity are somewhat erratic in both cases. 

Kim, J.I. and Stroeve, P. 1989. Selective and enhanced mass separation in hollow fiber membranes with facilitated ion-pair transport. 7. Membr. Sci. 45 99. 

Figure 9.23 Photovoltaic cell. Separation of photoelectrons and photoholes in the space-charge region of the TiOj electrode generates a photocurrent to the counter electrode, e.g., a transparent indium-tin-oxide covered glass plate. Within the cell an A/A" redox pair transports the current between the counter and semiconductor electrodes.

The number of moleeules of ATP generated as a result of the combined aetivities of the proton gradient and the CFoCF, eomplex is controversial. However, it seems unlikely that nc-p/p generates sufficient ATPs per NADI reduced (or per electron pair transported) to satisfy the demands of the Calvin cycle (which requires 1.5 ATPs per NADPH) md the other ATP-requiring proeesses of the chloroplast (e. g. synthesis of stareh, lipids, pigments, proteins, nucleic acids). It is probably for this reason that the evo-lutionarily more primitive process of cyclic photo-phosphorylation (c-p/p) persists in chloroplasts c-p/p generates only ATP and therefore assists nc-p/p in supplying the total ATP requirements of the chloroplast. 

Figure 26 (a) Ditopic ion pair transporter 73 (b) calix[4]pyrrole derivatives 74-76. 

Ion pair transport is also possible by incorporating the anion and cation transporters as independent components to the lipid bilayer, using a dual host approach. Using combinations or cocktails of different drugs is a commonly used strategy in biology. This approach has been demonstrated by using combinations of classical cation transporters such as valinomycin and calix[4]pyrrole derivatives such as 75. 

In BLM transport, the most common solvents are chlorinated hydrocarbons. These have low dielectric constants and, as a consequence, the transport is described by ion-pairs. Izatt et al. have extensively studied ion-pair transport through BLMs (18), In SLM transport, cyclohexyl phenyl ether is an important non-polar membrane solvent (19). The extraction equilibrium at the interface in a non-polar membrane... 

The efficiency of the redox reaction can be enhanced by the addition of an agent that serves as cocatalyst. The cocatalyst plays an important role in the generation of hydrogen and oxygen by reducing overpotential, improving electron-diole pair transport, and providing active sites for the reaction to occur [1,4],... 

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