Ion pair transport

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... 

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. 

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

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

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 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... 

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