ELECTROCATALYSIS OF METALLOPORPHYRINS .10. ELECTROCHEMICAL OXIDATION AND REDUCTION OF WATER-SOLUBLE COBALT(III)-TETRAKIS(4-TRIMETHYL-AMMONIUMPHENYL)PORPHYRIN

The aggregation of cobalt(III)-tetrakis(4-trimethylammoniumphenyl)porphyrin (CoTMAP) in acidic and neutral media has been investigated. CoTMAP obeys Beer's law in the concentration range 10(-6)-5x10(-5) M at pH 1 (0.05 M H2SO4 +0.25 M Na2SO4) and in the concentration range 10(-6)-10(-4) M at pH 7 (0.1 M phosphate buffer). In view of the aggregation of COTMAP, its electro-oxidation and electroreduction have been studied by means of cyclic voltammetry, the rotating ring disk electrode technique, computerized potential-step chronocoulometry on a rotating disk electrode and the in-situ UV-Vis spectroelectrochemical method. In the presence of aggregating CoTMAP in aqueous solutions, its products generated during electro-oxidation will adsorb cumulatively on glassy carbon electrodes. The reduced Co(I) state product will also adsorb cumulatively on the electrodes in both the presence and the absence of aggregation. Reaction mechanisms for the electro-oxidation and electroreduction of CoTMAP in aqueous solutions in both the absence and the presence of aggregation are proposed.