RATES OF ELECTRON-TRANSFER REACTIONS OF SOME COPPER(II)-PHENANTHROLINE COMPLEXES WITH CYTOCHROME-C(II) AND TRIS(PHENANTHROLINE)COBALT(II) ION

Rate constants for the one-electron oxidation of horse heart cytochrome c(II) (ferrocytochrome c) by aquated bis-(1, 10-phenanthroline)copper(II) ion, bis(2, 9-dimethyl-1, 10-phenanthroline)copper(II) ion, and bis(5-nitro-1, 10-phenanthroline)copper(II) ion were found to be [FORMULA OMMITED] respectively, in aqueous solution at pH 6.1, at 25°C, and at an ionic strength of 0.1 M. Activation enthalpies, [FORMULA OMMITED] were also measured for the same reactions. The rate constant and activation parameters for the one-electron oxidation of tris(1, 10-phenanthroline)cobalt(II) ion by bis(2, 9-dimethyl-1, 10-phenanthroline)copper(II) ion were found to be [FORMULA OMMITED] under the same conditions. These results are discussed in terms of a “structural barrier” to electron transfer, which is a consequence of the difference in coordination number and stereochemistry between the copper(II) reactants and the copper(I) products. © 1979, American Chemical Society. All rights reserved.