An ion-gate response of the glutathione monolayer assembly formed on a gold electrode. Part 1. The effect of pH, K⁺ and Ca²⁺

The electrochemical behavior of the self-assembled glutathione (GSH) monolayer formed on a gold electrode was studied in aqueous Fe(CN)₆^3- solution in order to characterize the ion permeation properties of this monolayer assembly. It was found that the GSH monolayer showed ion-gate behavior for the permeation of Fe(CN)₆^3- probe ion. At pH 5.3, the monolayer assembly strongly hindered the electron transfer between the gold surface and the Fe(CN)₆^3- ion in solution. In contrast, the electron transfer was drastically improved at pH 2.9. The electron transfer was also found to improve with increasing Ca²⁺ concentration. The rate constant of Fe(CN)₆^3- reduction increased linearly with Ca²⁺ concentration. The ion-gate behavior of the GSH monolayer is discussed in terms of the conformational change in GSH caused by the coordination with Ca²⁺ and the electrostatic interaction between GSH and Fe(CN)₆^3-.