Proton-driven cation transport through polyamic acid membranes incorporating crown ether moiety

Proton-driven cation transport against cation concentration gradient has been investigated using films of polyamic acid 18-crown-6 (1) and polyamide 18-crown-6 (3)/polyamic acid (5) mixtures as the polymeric membrane. Both membrane systems containing the crown ethers were found to act as efficient alkali metal ion pumps. The ion-transportability of the polyamic acid 18-crown-6 membrane decreased in the order K⁺ > Cs⁺ > Na⁺ > Li⁺, which is reflected in the cation-complexing ability of the 18-crown-6 moiety. The transport selectivity, however, was varied remarkably by the combined use of polyvinylpyrrolidone with (1) and, therefore, by the resulting increase in hydrophilicity of the membrane. The ion-selectivity in the transport through mixed membranes of (3) and (5) was also dependent on the membrane composition. For the proton-driven cation transport two mechanisms are proposed; in one of the transport mechanisms, the carboxylic group cooperates with the crown ether moiety and in the other the carboxylic group participates independently.