ELECTROCHEMICAL STUDIES OF THALLIUM(I) TRANSPORT ACROSS GRAMICIDIN MODIFIED ELECTRODE-ADSORBED PHOSPHOLIPID MONOLAYERS

Gramicidin A channels have been incorporated into di-O-PC monolayers adsorbed on mercury electrodes. The transport of Tl(I through the channels was studied by cyclic voltammetry under varying conditions of electrolyte composition and gramicidin coverage. In the voltammograms, the reduction of Tl(I) has the appearance of a kinetic type wave. It was found that the channels are selectively permeable to Tl(I) as opposed to Cd(II). There is no evidence of any binding of Tl(I) in the channel and the ion diffuses through in its aqueous form. It is also shown that the surface concentration of conducting gramicidin channels is low. The reduction current of Tl(I) measured at high scan rates is enhanced in Mg(II) electrolytes compared to that in K(I) electrolytes and the rate constant is decreased in chloride as opposed to nitrate electrolyte. In the presence of significant concentrations of Tl(I) complexing agents in solution the channel rate constant is suppressed.