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

In this work the oxidation and reduction reactions of Mn^III-Coproporphyrin-I (Mn^III-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 [Mn^IV(O)CPI(OH)]⁻ that was unstable and, after a short time, formed again [Mn^IIICPI(OH)₂]⁻. With an excess of NaClO, a further oxidation of the complex [Mn^IV(O)CPI(OH)]⁻, provoked a significant spectral change for the [Mn^V(O)CPI(OH)] formation that showed, in the time, a partial polymerization. [Mn^IIICPI(OH)₂]⁻ was reduced by sodium dithionite to form the very unstable complex of [Mn^IICPI(OH)]⁻ that successively degraded with Mn(II) release.