The electrochemical behavior of the self-assembled glutathione (GSH) monolayer formed on a gold electrode was studied in aqueous Fe(CN)63- 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)63- probe ion. At pH 5.3, the monolayer assembly strongly hindered the electron transfer between the gold surface and the Fe(CN)63- 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)63- 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)63-.
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