A functional model related to cytochrome c oxidase and its electrocatalytic four-electron reduction of O2.

A cytochrome c oxidase model that consists of a cobalt(II) porphyrin with a copper(I) triazacyclononane macrocycle fastened on the distal face and an imidazole covalently attached to the proximal face has been synthesized and characterized. Redox titrations with molecular oxygen (O2) and cobaltocene were carried out, and O2 was found to bind irreversibly in a 1:1 ratio to the model compound. This O2 adduct (a bridged peroxide) can be fully reduced to the deoxygenated form with four equivalents of cobaltocene. The model compound was adsorbed on an edge-plane graphite electrode, and rotating ring-disk voltammetry was used to monitor the electrocatalytic reduction of O2. Four-electron reduction of O2 was observed at physiological pH.