Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published January 20, 1988 | Published
Journal Article Open

Distance dependence of photoinduced long-range electron transfer in zinc/ruthenium-modified myoglobins


An experimental investigation of the distance dependence of long-range electron transfer in zinc/ruthenium-modified myoglobins has been performed. The modified proteins were prepared by substitution of zinc mesoporphyrin IX diacid (ZnP) for the heme in each of four previously characterized pentaammineruthenium(III) (a_5Ru;a = NH_3) derivatives of sperm whale myoglobin (Mb): a_5Ru(His-48)Mb, a_5Ru(His-12)Mb, a_5Ru(His-116)Mb, a_5Ru(His-81)Mb. Electron transfer from the ZnP triplet excited state (^3ZnP*) to Ru^3+, ^3ZnP*-Ru^3+ → ZnP^+-Ru^2+ (ΔE° ~ 0.8V) was measured by time-resolved transient absorption spectroscopy: rate constants (k_f) are 7.0 × 10^4 (His-48), 1.0 × 10^2 (His-12), 8.9 × 10^1 (His-116), and 8.5 × 10^1 (His-81) s^-1 at 25 °C. Activation enthalpies calculated from the temperature dependences of the electron-transfer rates over the range 5-40 °C are 1.7 ± 1.6 (His-48), 4.7 ± 0.9 (His-12), 5.4 ± 0.4 (His-116), and 5.6 ± 2.5 (His-81) kcal mol^-1. Electron-transfer distances (d = closest ZnP edge to a_5Ru(His) edge; angstroms) were calculated to fall in the following ranges: His-48, 11.8-16.6; His-12, 21.5-22.3; His-116, 19.8-20.4; His-81, 18.8-19.3. The rate-distance equation is k_f = 7.8 × 10^8 exp[-0.9l(d - 3)] s^-1 . The data indicate that the ^3ZnP*-Ru(His-12)^3+ electronic coupling may be enhanced by an intervening tryptophan (Trp-14).

Additional Information

© 1988 American Chemical Society. Received May 8, 1987. Publication Date: January 1988. Contribution No. 7588 from the Arthur Amos Noyes Laboratory, California Institute of Technology, Pasadena, California 91125. We thank Charlie Lieber, Jenny Karas, Walther Ellis, Lome Reid, Jose Onuchic, David Beratan, A. Kuki, Harvey Schugar, R. A. Marcus, and Jay Winkler for helpful discussions. A.W.A. acknowledges a fellowship from the Fannie and John Hertz Foundation. S.L.M. acknowledges a fellowship from AT&T Bell Laboratories. This research was supported by National Science Foundation Grants CHE85-18793 and CHE85-09637.

Attached Files

Published - Axup_1988_J_Am_Chem_Soc_Distance_dependence_of_photoinduced_long-range.pdf


Files (667.6 kB)

Additional details

August 19, 2023
October 23, 2023