One-Electron Oxidation of Chlorophyll a by a Variety of Metallo-meso-Tetraphenylporphyrin Cation Radicals in Carbon Tetrachloride: A Pulse Radiolytic Study
Chambers, James H., Jr.
MetadataShow full item record
Previous studies have shown that the more labile metalloporphyrins are demetallated in irradiated solutions of dichloroethane due to the radiolytic production of HCl. In these experiments, pyridine was required to neutralize the acid, but pyridine complexes easily to the central metal of the porphyrin. In similar experiments in pure CC14, demetallation does not occur upon irradiation and the one-electron oxidation of neutral, noncomplexed metalloporphyrins can be carried out using the pulse radiolysis technique. Oxidation of the metalloporphyrins in CC14 was found to have second order rate constants of 5 x 107-1 x 109 M-1s-1. One-electron transfers from Chlorophyll a to various metalloporphyrins gave second order rate constants Al106-107 M-1s-1 . Complications arising from fragmentation of CC14 solvent molecules caused some ambiguities in the characterization of the oxidation processes. Also, the rate constants for the electron transfer reactions were 103-104 M-1s-1 lower than the expected diffusion controlled rate constants.