Efficient oxygen consumption by hydroxo(protoporphyrinato)iron(III) adsorbed on magnesium oxide powder in the presence of cysteine

Article abstract of DOI:10.1246/bcsj.72.2463

The oxygen reduction ability of hydroxo(protoporphyrinato)iron(III) (HEM) adsorbed on powdery supports in the presence of cysteine was investigated using a Clark-type oxygen electrode. All of the oxygen consumption rates for HEM adsorbed on powdery supports having different surface basicity values (CaO > MgO > TiO₂) were larger than the cases of HEM in aqueous solution and of MgO suspension without HEM in the presence of cysteine. Maximum oxygen consumption rate was obtained in the case of the HEM/MgO system. This result suggests that the optimum surface basicity of powdery support is necessary to achieve efficient oxygen consumption. From the measurements for ESR and Raman spectra of the HEM/MgO system, we confirmed the change for the iron valence of HEM from III to II in the presence of cysteine. The production of cystine through the dimerization of cysteinyl radicals in the reaction mixture was also confirmed by the measurements of ESR spectra and capillary electrophoresis (CE). A possible mechanism for accelerating the oxygen consumption rate of the HEM/MgO system in the presence of cysteine is discussed, concerning the effect of the catalytic ability of MgO on the turnovers of iron valence.