Disproportionation of H2O2 Mediated by Diiron-Peroxo Complexes as Catalase Mimics

Heme iron and nonheme dimanganese catalases protect biological systems against oxidative damage caused by hydrogen peroxide. Rubrerythrins are ferritine-like nonheme diiron proteins, which are structurally and mechanistically distinct from the heme-type catalase but similar to a dimanganese KatB enzyme. In order to gain more insight into the mechanism of this curious enzyme reaction, non-heme structural and functional models were carried out by the use of mononuclear [Fe-II(L1-4)(solvent)(3)](ClO4)(2) (1-4) (L-1 = 1,3-bis(2-pyridyl-imino)isoindoline, L-2 = 1,3-bis(4 '-methyl-2-pyridyl-imino)isoindoline, L-3 = 1,3-bis(4 '-Chloro-2-pyridyl-imino)isoindoline, L-4 = 1,3-bis(5 '-chloro-2-pyridyl-imino)isoindoline) complexes as catalysts, where the possible reactive intermediates, diiron-perroxo [Fe-2(III)(mu-O)(mu-1,2-O-2)(L-1-L-4)(2)(Solv)(2)](2+) (5-8) complexes are known and well-characterized. All the complexes displayed catalase-like activity, which provided clear evidence for the formation of diiron-peroxo species during the catalytic cycle. We also found that the fine-tuning of iron redox states is a critical issue, both the formation rate and the reactivity of the diiron-peroxo species showed linear correlation with the Fe-III/Fe-II redox potentials. Their stability and reactivity towards H2O2 was also investigated and based on kinetic and mechanistic studies a plausible mechanism, including a rate-determining hydrogen atom transfer between the H2O2 and diiron-peroxo species, was proposed. The present results provide one of the first examples of a nonheme diiron-peroxo complex, which shows a catalase-like reaction.

Automated summary

The study demonstrates that a nonheme diiron-peroxo complex exhibits catalase-like activity and displays properties related to iron redox states. By investigating nonheme structural and functional models, a potential catalytic cycle mechanism was proposed.