Journal
ELECTROCHEMISTRY COMMUNICATIONS
Volume 4, Issue 2, Pages 177-181Publisher
ELSEVIER SCIENCE INC
DOI: 10.1016/S1388-2481(01)00299-5
Keywords
cytochrome c monolayers; indium/tin oxide; redox-linked conformational changes; interfacial electron transfer kinetics; unusual quasireversibility
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The adsorptive immobilization and electrochemistry of horse and yeast cytochrome c on indium/tin oxide (ITO) electrodes is reported. Near-monolayer coverage was achieved in pH 7 phosphate buffers of ionic strength equal to 10 and 50 mM, respectively, for the horse and yeast species. The layers exhibit very well-behaved voltammetry and are stable on the timescale of hours to days. Cyclic voltammetry revealed quasireversible behavior that is a product of both electron transfer (ET) kinetics and ET-induced conformational changes. A square scheme mechanism linking the redox states and the conformational states is proposed. Using a simple ET kinetic model that adequately describes the voltammetry at higher scan rates, a standard ET rate constant of 18 s(-1) was determined for adsorbed horse cytochrome c. With decreasing scan rate, we observed a limiting peak separation of approximately 10 mV, an example of unusual quasireversibility (UQR) that we attribute to the effect of conformational changes. Finally we note that the intrinsic cytochrome c ET rate on ITO is some 6 orders of magnitude less than for gold. (C) 2002 Published by Elsevier Science B.V.
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