Control of Characteristics of Synthetic Bilayer Membranes via Specific Interactions with Ions

Abstract

Interactions of ions with polyamine and polyether ligands at the surface of the synthetic bilayer membranes were studied. The gel filtration experiments showed nearly 100% trapping of some sodium aromatic sulfonates by a polyether-type membrane (Fig.3). Fluorescence spectroscopic measurements suggested the interaction between sodium ion and the polyether ligands (Fig.4). Fig.5 shows a model for the interaction. As a result of the mixing between the double-chain ammonium membrane and the azobenzene membrane containing polyamine ligands, the absorption maximum of the azobenzene chromophore shifted from 320 to 355 nm (Fig.6). The rate of mixing was accelerated 30 times by addition of 10^-3 mol/l HCl. The acceleration effect was also observed upon addition of 10^-2 mol/l KCl. On the contrary, the rate decreased by Cu²⁺ ions. The results are shown in Table 1 and Fig.7. Fluorescence intensity of a biphenyl membrane which has polyamine ligands was enhanced by HC1 and quenched by Cu²⁺ ion (Table 2). In mixed membranes with a double-chain ammonium salt, the fluorescence intensity decreased due to phase separation induced by sulfate ions. Fig.9shows the experimental data and Fig.10 is a schematic illustration of the ion-induced phase separation.