Electron transfer of some redox systems through physisorbed 4-methylesculetin: A catalytic behavior toward oxidation of catechols

Abstract

Glassy carbon electrode shows the adsorption of 4-methylesculetin in aqueous solution. Homogeneous and heterogeneous electron transfer through spontaneously physisorbed 4-methylesculetin were examined on glassy carbon electrode for some electron transfer systems in aqueous solutions. The various redox couples such as catechol, 4-methylcatechol, 4-tert-buthylecatechol, 3,5-di-tert-butylcatechol and Fe(CN)64- were examined for the evaluation of their electron transfer via physisorbed layer of 4-methylesculetin on the glassy carbon electrode. These redox systems were categorized according to their kinetic sensitivity to surface modification. Adsorption of catechol and its direct electron transfer was profoundly inhibited by an adsorbed layer of 4-methylesculetin. Under these conditions, catechol participates in catalytic electron transfer with 4-methylesculetin. The magnitude of inhibition of direct electron transfer of catechol was affected by 4-methylesculetin/catechol ratio bulk concentration, pH and electrolyte concentration. On the other hand catechol derivatives such as 3,5-di-tert-butylcatechol competes for adsorption on glassy carbon electrode with 4-methylesculetin. Fe(CN)64- is insensitive to the surface modification and considered as electron tunneling through the adsorbed 4-methylesculetin layer(s).