Electron transfer in ruthenium-modified proteins |
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Authors: | Morten J. Bjerrum Danilo R. Casimiro I. -Jy. Chang Angel J. Di Bilio Harry B. Gray Michael G. Hill Ralf Langen Gary A. Mines Lars K. Skov Jay R. Winkler Deborah S. Wuttke |
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Affiliation: | (1) Contribution from the Beckman Institute, California Institute of Technology, 91125 Pasadena, California |
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Abstract: | Photochemical techniques have been used to measure the kinetics of intramolecular electron transfer in Ru(bpy)2(im)(His)2+-modified (bpy = 2,2-bipyridine; im = imidazole) cytochromec and azurin. A driving-force study with the His33 derivatives of cytochromec indicates that the reorganization energy () for Fe2+Ru3+ ET reactions is 0.8 eV. Reductions of the ferriheme by either an excited complex,*Ru2+, or a reduced complex, Ru+, are anomalously fast and may involve formation of an electronically excited ferroheme. The distance dependence of Fe2+Ru3+ and Cu+Ru3+ electron transfer in 12 different Ru-modified cytochromes and azurins has been analyzed using a tunneling-pathway model. The ET rates in 10 of the 12 systems exhibit an exponential dependence on metal-metal separation (decay constant of 1.06 å–1) that is consistent with predictions of the pathway model. |
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Keywords: | Electron transfer cytochromec azurin ruthenium electronic coupling driving-force dependence |
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