The electrocatalytic effects of heat-treated Co(II) tetramethoxyphenylporphyrin adsorbed on graphite electrode ((Co-TMPP)/graphite) on the cathodic reduction of cystine were investigated in solns. of various pH using cyclic voltammetry and rotating ring-disk electrode techniques. The current efficiency of such relations on thin layer Co-TMPP/graphite electrodes is about 80-90%. The standard rate constants (k0) of cystine reduction in solns. of various pH were calculated and the effects of pH value on the reaction mechanism and kinetics of cystine reduction catalyzed by Co-TMPP/graphite are discussed.

Key words: PORPHINE P, CYSTINE, REACTION MECHANISM, METAL CATALYST, REACTION KINETICS, ELECTROLYSIS, COBALT COMPLEX, REDUCTION REACTION, TRANSITION METAL COMPLEX, ELECTROCHEMICAL REACTION