Spectral and kinetic investigation on oxidation and reduction of water soluble porphyrin–manganese(III) complex

In this work the oxidation and reduction reactions of MnIII–Coproporphyrin-I (MnIII-CPI) have been studied and four forms of manganese–CPI complexes have been characterized. This complex was observed to be highly reactive (at basic pH) towards Mn(II), hypochlorite, hydrogen peroxide and oxone, forming [MnIV(O)CPI(OH)]− that was unstable and, after a short time, formed again [MnIIICPI(OH)2]−. With an excess of NaClO, a further oxidation of the complex [MnIV(O)CPI(OH)]−, provoked a significant spectral change for the [MnV(O)CPI(OH)] formation that showed, in the time, a partial polymerization. [MnIIICPI(OH)2]− was reduced by sodium dithionite to form the very unstable complex of [MnIICPI(OH)]− that successively degraded with Mn(II) release.

Graphical abstractA spectroscopic and kinetic study of the formation, oxidation and reduction of the MnIII–Coproporphyrin-I complex was performed. The nature and composition of the reaction products obtained depended on the characteristic of the reactive used. The experimental conditions in the formation of complexes with Mn in all oxidation states (2,3,4,5) have been performed.Figure optionsDownload full-size imageDownload as PowerPoint slide