CATALASE MODELING WITH METALLOPORPHYRIN COMPLEXES HAVING AN OXYGEN LIGAND IN A PROXIMAL POSITION - COMPARISON WITH COMPLEXES CONTAINING A PROXIMAL NITROGEN

Models of catalase having a proximal oxygen ligand are described. Their ability to catalyze the dismutation of hydrogen peroxide or the oxygenation of an olefin are reported and compared to similar catalysts having a proximal nitrogen ligand. Manganese complexes are always more efficient for both oxygenase and dismutase activities than the corresponding iron derivatives. Whereas molecules having a proximal nitrogen ligand catalyzed both reactions, dismutation and oxygenation, complexes having a proximal oxygen ligand catalyze mainly the dismutation reaction in the case of manganese derivatives and only this reaction in the case of iron complexes, the "true models" of catalase. These data suggest that, among other factors, one of the possible roles of the tyrosinato ligand in catalase is to inhibit any possible oxygen transfer reaction from the compound I species, in order to avoid an oxidative degradation of the protein.