Potential-Dependent Rectified Electron Transfer at a Meldola′s Blue Incorporated Decanethiol-Modified Electrode as a Model of Biological Membrane

Meldola′s blue was immobilized into a self-assembled decanethiol monolayer modified on a gold electrode to provide a biological membrane model for electron transport having a molecular gate. Cyclic voltammograms of ferricyanide at this modified electrode showed only its reduction current at potentials where Meldola′s blue was reduced, but not at the redox potential of ferricyanide itself and no reaction was observed for ferrocyanide, indicating the direction of electron flow was controlled through the functionalized monolayer. Similar electrochemical responses were also observed for both octacyanotungustate and octacyanomolybdate. The cathodic peak currents observed in metal cyanide solutions at the modified electrode decreased in the order of Fe(CN)₆³⁻ > W(CN)₈³⁻ > Mo(CN)₈³⁻ at a given pH. From the analysis of the voltammograms using the microelectrode assembly model, the potential-dependent rectified electron flow was explained in terms of a gate function of Meldola′s blue in the monolayer, and the apparent electron transfer rate constant, k⁰_app, and the apparent diffusion coefficient, D_app, of metal cyanide ions in the monolayer were also estimated.