The overall six-electron oxidation of water soluble porphyrin Fe IIITPPS by hydrogen peroxide and peroxomonosulfate ion was studied by the stopped-flow method with UV-vis detection. A three-step consecutive reaction was observed with two intermediates: FeIIITPPS → Int1 → Int2 → products. The products were identified as the iron(iii) complex of the biliverdin analog formed from TPPS and 4-sulfobenzoic acid. All the rate constants with both oxidizing agents were determined. Intermediate Int1 is proposed to be the species (TPPS+)FeIVO. Although no unambiguous proposal for the structure of Int2 can be made, it is most probably the product of the four-electron oxidation of the original FeIIITPPS, contains an iron-oxo center and has a dissociable proton with a pK of around 3.1. In spite of the protolytic equilibria occuring in the pH region 2-4, the kinetic observations do not show pH dependence.
ASJC Scopus subject areas
- Inorganic Chemistry