Formation of superoxide-metal ion complexes and the electron transfer catalysis

The formation of a variety of superoxide-metal complexes and their catalytic functions have been reviewed. The g(zz)-values of the EPR spectra of superoxide-metal ion complexes vary significantly depending on the type of metal ions. From the deviation of the g(zz)-value from the free spin value are determined the energy splitting values (DeltaE) of pi(g) levels due to complex formation. The DeltaE values correlate well with the catalytic reactivities of the metal ions in the electron transfer reduction of oxygen. Such a complex formation between superoxide ion and metal ions has been shown to play an essential role in the enzymatic function of superoxide dismutase, formation of active oxygen-copper complexes and the novel catalytic effect of O-2 in back electron transfer of zinc porphyrin-fullerene linked molecules. (C) 2002 Elsevier Science B.V. All rights reserved.