First direct interfacial electron transfer between a biomolecule and a solid electrode in non-aqueous media: Direct electrochemistry of microperoxidase-11 at glassy carbon in dimethyl sulfoxide solution

The direct heterogeneous electron transfer between the imidazole complex of microperoxidase-11 (im-MP-11) and naked glassy carbon electrodes in dimethyl sulfoxide (1–3.6% H2O) containing 0.1 M tetra-n-butylammonium perchlorate has been accomplished using cyclic voltammetry. Homogeneous solutions of im-MP-11 in dimethyl sulfoxide were prepared by weak complexation with 18-crown-6. Heterogeneous electron transfer between im-MP-11 and glassy carbon has been shown to be persistent and at least quasi-reversible in dimethyl sulfoxide solution. The redox potential for im-MP-11 in dimethyl sulfoxide has been found to be −274 ± 5 mV vs. Ag/AgCl — significantly less negative than the potential (−389 mV vs. Ag/AgCl) for this same complex in aqueous 75 mM phosphate buffer, pH 7.0, containing 0.1 M NaClO4. The calculated diffusion coefficient (1.8 × 10−7 cm2 s−1) and the rate of electron transfer in dimethyl sulfoxide (2.7 ± 0.3 × 10−4 cm s−1) are approximately one order of magnitude lower than that for the same complex in 0.02 M aqueous phosphate buffer, pH 7.0.