AN ELECTROCHEMICAL STUDY OF ANTIBIOTIC IONOPHORES IN SELF-ASSEMBLED LIPID LAYERS AT PLATINUM

Self-assembled lipid layers (SALL) have been formed on a platinum elec trode surface from aqueous solutions of potassium oleate and lithium g amma-linolenate at 299 Ii in a pH 7.0 phosphate buffer. Cyclic voltamm etric measurements showed a significant decrease in the surface charge density due to oxide formation on the electrode surface in an aqueous solution in the presence of the lipids, A lipid barrier was formed th at was impermeable to the transport of water and azide ions to the ele ctrode surface. The antibiotic ionophores, nystatin, a polyene which t ransports primarily anions across membranes, and alamethicin, an antib iotic peptide which transports anions and excludes cations, were intro duced into the SALL in separate experiments. The surface charge densit y increased in the presence of these ionophores as a result of diffusi on of water to the electrode surface through the apparent ionophore po res. Azide ions diffused through the ionophore-incorporated SALL and w ere detected and measured electrochemically by a decrease in surface c harge density from oxide due to the blocking of the electrode surface by the adsorbed azide ions. The electrode surface coverage was determi ned to be 16.4 +/- 0.4 water molecules or 15.6 +/- 1.8 azide ions per nystatin pore and 57.2 +/- 1.1 water molecules or 56.6 +/- 3.8 azide i ons per alamethicin pore, These results agree with calculations for mo nolayer coverage based on geometrical dimensions of the molecules.