Electrochemical simulation of function of cytochrome oxidase using synthetic porphyrins.

Abstract

In order to mimic the function of cytochrome oxidase and inversely to get insight into its function and structure and furthermore their correlation, electrocatalytic reduction of molecular oxygen was examined using water-soluble and immobilized iron and cobalt porphyrins and phthalocyanines. In the presence of iron porphyrins, oxygen was reduced via hydrogen peroxide to water quantitatively by an electrogenerated penta-coordinated high-spin iron (II) form of the porphyrins at potentials closely correlated with iron (III) to iron (II) reduction potentials. The rate constant of oxygen reduction in natural enzyme system was attained only by the use of porphyrins containing a lot of amino groups, suggesting inversely one of the causes of high composition ratio of basic amino acids in this enzyme. By the use of iron phthalocyanines also, oxygen was reduced via hydrogen peroxide to water at potentials correlated with iron (II) to iron (I) reduction potentials. Howerver when mononuclear cobalt complexes were employed, hydrogen peroxide was produced almost quantitatively as the final product.