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Published November 1985 | public
Journal Article

Kinetics and mechanisms of electron transfer between blue copper proteins and electronically excited chromium and ruthenium polypyridine complexes


The kinetics of the quenching of the long-lived excited states of CrL_3^(3+) and RuL_3^(2+) complexes (L is 1,10-phenanthroline and 2,2'-bipyridine or substituted derivatives) by the copper proteins plastocyanin, azurin, and stellacyanin have been studied in aqueous solution. The rate constants for quenching by the Cu(I) proteins approach a limiting value of ~10^(6) s^(-1) at high protein concentration. The kinetic behavior for plastocyanin is discussed in terms of a model in which the metal complex binds at a remote site 10-12 Å from the copper center. The model allows for electron transfer both from this remote site and by attack of the metal complex adjacent to the copper center. The results show that at low protein concentration the adjacent pathway is about 10 times faster than the remote pathway. The rate constant for the intramolecular electron transfer from the remote site is consistent with the value expected on the basis of theoretical calculations.

Additional Information

© 1985 American Chemical Society. Received January 28, 1985. Publication Date: November 1985. Research at the California Institute of Technology was supported by National Institutes of Health Grant AM19038, and research at Brookhaven National Laboratory was carried out under contract DE-AC02-76CH00016 with the U.S. Department of Energy and supported by its Division of Chemical Sciences and Office of Basic Energy Sciences. A.M.E. acknowledges a postdoctoral fellowship from the NSERC (1980-1981). S.L.M. thanks AT&T Bell Laboratories for a predoctoral fellowship (1983-present). We wish to acknowledge helpful discussions with Dr. C. Creutz and the assistance of J. Horwitz of the University of California at Santa Cruz and Dr. R. Humphry-Baker of L'Ecole Polytechnique Fiderale de Lausanne during the early stages of this work.

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