EFFECTS OF AXIAL LIGAND REPLACEMENT ON THE REDOX POTENTIAL OF CYTOCHROME-C

The formal potentials (E(0)') and electron transfer numbers (n) of imidazole (Im), 1-methylimidazole (1-MeIm), and 1-ethylimidazole (1-EtIm) complexes of cytochrome c have been determined for the first time using optically transparent thin-layer spectroelectrochemistry. In comparing these results with the E(0)' value of the cytochrome c, their potentials at infinite dilution have been calculated, which indicate that axial replacement of methionine-80 by Im, 1-MeIm, and 1-EtIm gives rise to 426, 359, and 327 mV negative shifts-relative to that of native cytochrome c, respectively. Thereby, the origins of the effects of axial substitution on redox potential are discussed.