Rates of DNA-Mediated Electron Transfer Between Metallointercalators
Ultrafast emission and absorption spectroscopies were used to measure the kinetics of DNA-mediated electron transfer reactions between metal complexes intercalated into DNA. In the presence of rhodium(III) acceptor, a substantial fraction of photoexcited donor exhibits fast oxidative quenching (>3 × 10^(10) per second). Transient-absorption experiments indicate that, for a series of donors, the majority of back electron transfer is also very fast (∼10^(10) per second). This rate is independent of the loading of acceptors on the helix, but is sensitive to sequence and π stacking. The cooperative binding of donor and acceptor is considered unlikely on the basis of structural models and DNA photocleavage studies of binding. These data show that the DNA double helix differs significantly from proteins as a bridge for electron transfer.
© 1996 American Association for the Advancement of Science. 22 November 1995; Accepted 6 May 1996. We are grateful to NIH (GM49216 to J.K.B.) and NSF (CHE-9304373 to P.F.B.) for financial support. We also thank NSF for predoctoral support of M.R.A. and R.E.H., and the American Cancer Society for postdoctoral support of E.D.A.S. We are also grateful to N. J. Turro for helpful discussions and to the reviewers for thoughtful comments.