Dinuclear site Electrochemical

Cyclic voltammetry has been also used for estimation of the rate constants for oxidation of water-soluble ferrocenes in the presence of HRP (131). There is a perfect match between the data obtained spectrophotometrically and electrochemically (Table IV), which proves that the cyclic voltammetry reveals information on the oxidation of ferrocenes by Compound II. It is interesting to note that an enzyme similar to HRP, viz. cytochrome c peroxidase, which catalyzes the reduction of H202 to water using two equivalents of ferrocytochrome c (133-136), is ca. 100 times more reactive than HRP (131,137). The second-order rate constant equals 1.4 x 106 M-1 s 1 for HOOCFc at pH 6.5 (131). There is no such rate difference in oxidation of [Fe(CN)e]4- by cytochrome c peroxidase and HRP (8). These comparisons should not however create an impression that the enzymatic oxidation of ferrocenes is always fast. The active-R2 subunit of Escherichia coli ribonucleotide reductase, which has dinuclear nonheme iron center in the active site, oxidizes ferrocene carboxylic acid and other water-soluble ferrocenes with a rate constant of... 

Molecular hysteresis results when the interconversion between the states does not follow the same pathway on sweeping the external stimulus or field in one or the opposite directions [8.240a, 8.241]. A hysteresis loop has, for instance, been described for the electrochemical interconversion of redox states in a dinuclear metal complex it involves the switching between two different binding sites [8.240b]. Spin... 

In addition, the authors were able to analyze the carbonyl infrared spectral shifts for the range of closely related dinuclear systems in terms of a charge distribution parameter, Ap, which was found to correlate Knearly with the separation potentials of the successive one-electron oxidations of the dinuclear systems. Overall, the authors clearly showed the power of electrochemistry and in situ spectro-electrochemical techniques with respect to probing site-to-site interactions in homodinuclear complexes. Further studies of inorganic systems are described in Volume 7 of the Encyclopedia. 

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