Biomimetic Oxygen Reduction Reaction Catalyzed by Microperoxidase-11 at Liquid/Liquid Interfaces

An investigation of oxygen reduction reaction (ORR) catalyzed by microperoxidase-11 (MP-11) at the polarized water/1,2-dichloroethane (DCE) interface is reported. MP-11 contains a heme group covalently bonded to an undecapeptide chain via two thioether bonds of cysteine residues, as in cytochrome c oxidases (CcOs), and has been widely studied as a biomimetic model of CcOs. Herein we demonstrated that MP-11 can adsorb at the water/DCE interface and catalyze the O2 reduction by lipophilic electron donors, namely tetrathiafulvalene (TTF) and 1,1′-dimethylferrocene (DFc). The overall catalytic ORR corresponds to a proton coupled electron transfer (PCET) reaction and is kinetically controlled by the heterogeneous conversion of MP-11 from ferric (FeIII-MP-11) to ferrous state (FeII-MP-11). Given that a significant amount of H2O2 was produced for both electron donors, it indicates that MP-11 has a remarkable impact on the ORR pathway and that MP-11, similar to other mononuclear macrocyclic compounds, cannot selectively catalyze the 4e–/4H+ reduction of O2 to H2O. The results also suggest that one should carefully considers the role of Cu site in CcOs and the reaction environment to understand respiratory ORR and to develop more selective catalysts for practical applications (e.g., fuel cells).