Iron porphyrins as models of cytochrome c oxidase

A series of iron porphyrins has been synthesized as models of cytochrome c oxidase; their activity as 4e catalysts in the reduction of dioxygen has be en studied at pH 7 . These compounds have been obtained by grafting very di fferent residues onto the same iron complex, namely tripodal tetraamines, p ickets, and straps. in order to change the environment of the metal center. In the case of porphyrins bearing a tripodal cap. the secondary amines hav e been alkylated with different substituents so as to modify the electronic environment of the distal pocket, Surprisingly. when the iron porphyrin is functionalized with four identical acryl-amido pickets, the resulting comp lex exhibits biomimetic activity in that it catalyzes oxygen reduction with almost no production of hydrogen peroxide. The crystal structure of the re dox-inactive zinc(ii) analogue is reported, this shows how the metal influe nces the spatial arrangement of the four pickets through axial coordination and hydrogen bonding. Even a bis-strapped iron porphyrin, for which no dim erization or self-aggregation can occur at the electrode surface. acts as a 4e(-) catalyst for O-2 reduction. It is thus demonstrated that at pH close to physiological values. the iron porphyrin is an intrinsically efficient catalyst for the reduction of oxygen to water.