Iron Porphyrins as Models of Cytochrome c Oxidase

摘要

A series of iron porphyrins has been synthesized as models of cyto-chrome c oxidase;their activity as 4e~- catalysts in the reduction of dioxygen has been studied at pH7. These compounds have been obtained by grafting very different residues onto the same iron complex,namely tripodal tetraa-mines,pickets,and straps in order to change the environment of the metal center.In the case of porphyrins bearing a tripodal cap,the secondary amines have been alkylated with different sub-stituents so as to modify the electronic environment of the destal pocket.Sur-prisingly,when the iron porphyrin is functionalized with four identical acryl-amido pickets,the resulting comlpex exhibits biomimetic activity in that it catalyzes oxygen reduction with almost no production of hydrogen peroxide.The crystal structure of the redox-inac-tive zinc(II) analogue is reported;this shows how the metal influences the spatial arrangement of the four pickets through axial coordination and hydro-gen bonding.Even a bis-strapped iron porphyrin,for which no dimerization or self-aggregation can occur at the elec-trode surface,acts as 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.