Molecular and Biological Catalysts Coimmobilization on Electrode by Combining Diazonium Electrografting and Sequential Click Chemistry

A generic approach has been developed for sequential heterogeneous surface modification of electrodes. The strategy, which is applicable for a wide range of functional groups, involves two main steps. In the first one, azide-alkene bifunctionalized electrodes are obtained by electrochemical reduction of a mixture of diazonium salts generated in situ from the corresponding 4-azidoaniline and 4-vinylaniline. In that way, we provide reactive sites that are available for further selective functionalization in a sequential process based on 'click reactions', in which subsequent immobilization of the targeted molecules is achieved by the azide-alkyne cycloaddition Huisgen reaction and alkene-thiol coupling. Feasibility of the method has been first demonstrated for the coimmobilization of two distinct redox moieties (cobaltocenium and ferrocene) as evidenced by cyclic voltammetry and X-ray photoelectron spectroscopy measurements. The versatility of the sequential method has then been exploited for the coimmobilization of a molecular electrocatalyst [Cp*Rh(bpy) Cl](+) and a biological catalyst, a NAD-dependent dehydrogenase, that were proved to act in cascade in the electroenzymatic reduction of D-fructose to D-sorbitol. Such simple combination of diazonium chemistry and robust chemical reactions ('click chemistry') is promising for the environmentally friendly heterogeneous modification of electrodes with multiple chemical and biological catalysts.