Zinc porphyrin π-radical cations in aqueous solution. Formation, spectra and decay kinetics

Publisher Website
Google Scholar
Abstract
Zinc porphyrins are oxidised readily to the π-radical cation by certain inorganic and organic radicals in aqueous solution under pulse-radiolytic conditions. Bimolecular rate constants for the oxidation process depend upon thermodynamic driving forces and Colulombic interactions between the reactants and lie within the range 107–1010 dm3 mol–1 s–1. The resultant π-radical cations exist in aqueous solution in equilibrium with any anions or complexing agents (e.g. pyridine) present in the solution. This complexation affects both the absorption spectrum of the π-radical cation and its rate of decay. With zinc tetrakis(4-sulphonatophenyl)porphyrin the π-radical cation is quite persistent (t1/2≈ 6 s) but its rate of decay increases when SCN– ions are present. Positively charged zinc porphyrins form shorter-lived π-radical cations that decay on the microsecond timescale. Under some conditions this decay leads to the formation of a relatively long-lived intermediate which is either a π-radical dimer or an isoporphyrin derivative.

This publication has 1 reference indexed in Scilit: