FIRST DIRECT INTERFACIAL ELECTRON-TRANSFER BETWEEN A BIOMOLECULE AND A SOLID ELECTRODE IN NONAQUEOUS MEDIA - DIRECT ELECTROCHEMISTRY OF MICROPEROXIDASE-11 AT GLASSY-CARBON IN DIMETHYL-SULFOXIDE SOLUTION

The direct heterogeneous electron transfer between the imidazole compl ex of microperoxidase-11 (im-MP-11) and naked glassy carbon electrodes in dimethyl sulfoxide (1-3.6% H2O) containing 0.1 M tetra-n-butylammo nium perchlorate has been accomplished using cyclic voltammetry. Homog eneous solutions of im-MP-11 in dimethyl sulfoxide were prepared by we ak complexation with 18-crown-6. Heterogeneous electron transfer betwe en im-MP-11 and glassy carbon has been shown to be persistent and at l east quasi-reversible in dimethyl sulfoxide solution. The redox potent ial for im-MP-11 in dimethyl sulfoxide has been found to be - 274 +/- 5 mV vs. Ag/AgCl - significantly less negative than the potential (- 3 89 mV vs. Ag/AgCl) for this same complex in aqueous 75 mM phosphate bu ffer, pH 7.0, containing 0.1 M NaClO4. The calculated diffusion coeffi cient (1.8 X 10(-7) cm(2) s(-1)) and the rate of electron transfer in dimethyl sulfoxide (2.7 +/- 0.3 X 10(-4) cm s(-1)) are approximately o ne order of magnitude lower than that for the same complex in 0.02 M a queous phosphate buffer, pH 7.0.