EPR spin trapping studies of H2O2 activation in metaloporphyrin catalyzed oxygenation reactions: Insights on the biomimetic mechanism

Abstract Oxygen radicals have been proposed to have a role in the metaloporphyrin based biomimetic mechanisms as they can be formed from metal-oxo or metal-hydroperoxy species. Herein EPR studies of biomimetic oxygenation reactions using BMPO as a spin trap are used to investigate the production of reactive oxygen species during the catalytic activation of H 2 O 2 by Fe III and Mn III porphyrins. Firstly, reactions in control conditions were studied and the formation of BMPO-OH • adducts was observed. These provided a baseline system for further comparative evaluation of the effect of different components of the catalytic reactions, including metaloporphyrins, solvents, co-catalysts and substrates on ROS production and H 2 O 2 consumption. In the absence of co-catalyst or using ammonium acetate as co-catalyst, the metaloporphyrin centered pathways do not generate additional hydroxyl or superoxide radicals. In contrast, in the presence of sodium hydroxide, the production of additional hydroxyl radicals by a metaloporphyrin-mediated process is observed. The EPR results also differentiate the action of intermediates ascribed to metaloporphyrin-H 2 O 2 adducts and high-valent oxo-species by their relative rates of H 2 O 2 consumption and their effect on the production of BMPO-OH • .