Abstract: | F430M, the pentamethyl ester of coenzyme F430, can be oxidized reversibly by one electron. The oxidation potential has been determined, and the electrolytically prepared oxidation product was characterized by its UV/VIS and ESR spectrum. The strongly anisotropic and nearly axial ESR spectrum is consistent with a S = ½ species with the unpaired-electron spin density predominantly in a d -type orbital of the central nickel ion. The properties of Ni(III)F430M are discussed in the context of two hypothetical mechanisms for the catalytic role of coenzyme F430 in methyl coenzyme M reductase, which catalyses the last step of methane formation in methanogenic bacteria. |