Generation of Superoxide in a Water-Soluble Model System with FeTMPyP

In a model system of a water-soluble hemin, tetrakis(4-methylpyridyl)porphinatoiron(III) pentachloride (FeTMPyPCl5), with 3-methyl-2-benzothiazolinone hydrazone (MBTH), superoxide anion radical (O2•-), hydrogen peroxide, and then hydroxyl radical were generated in a phosphate buffer solution (pH 6.0–7.5) under aerobic conditions. The hemin was degraded in this system. The reactive oxygen species were deduced from inhibition of the degradation by adding SOD and catalase, and one of them was trapped by 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as a DMPO–hydroxyl radical adduct, which was detected by ESR. The mechanism for activating dioxygen and the degradation of hemin was examined, and it was proposed to be the initial one-electron reduction of hemin by MBTH forming a dioxygen complex and liberating superoxide as one of the routes during the reduction–autoxidation cycle in aqueous media.