Long-range photoinduced electron transfer through a DNA helix
Rapid photoinduced electron transfer is demonstrated over a distance of greater than 40 angstroms between metallointercalators that are tethered to the 5' termini of a 15-base pair DNA duplex. An oligomeric assembly was synthesized in which the donor is Ru(phen)_2dppz^(2+) (phen, phenanthroline, and dppz, dipyridophenazine) and the acceptor is Rh(phi)_2phen^(3+) (phi, phenanthrenequinone diimine). These metal complexes are intercalated either one or two base steps in from the helix termini. Although the ruthenium-modified oligonucleotide hybridized to an unmodified complement luminesces intensely, the ruthenium-modified oligomer hybridized to the rhodium-modified oligomer shows no detectable luminescence. Time-resolved studies point to a lower limit of 10^9 per second for the quenching rate. No quenching was observed upon metallation of two complementary octamers by Ru(phen)_3^(2+) and Rh(phen)_3^(3+) under conditions where the phen complexes do not intercalate. The stacked aromatic heterocycles of the DNA duplex therefore serve as an efficient medium for coupling electron donors and acceptors over very long distances.
© 1993 American Association for the Advancement of Science. 4 June 1993; Accepted 29 September 1993. We are grateful to C. V. Kumar for helpful discussions and to J. Winkler for expert technical assistance. In addition, J.K.B. thanks the National Institutes of Health (GM49216) and the National Foundation for Cancer Research for their financial support. N.J.T. thanks the National Science Foundation and Air Force Office of Scientific Research for their financial support. We are also grateful to the National Science Foundation for postdoctoral (C.J.M.) and predoctoral (M.R.A.) fellowships as well as the Deutsche Forschungsgemeinschaft (S.H.B.) and the Parsons Foundation (Y.J.). We also thank A. Harriman and S. Atherton of the Center for Fast Kinetic Research, which is supported jointly by NIH and the University of Texas at Austin, for assistance in the single-photon counting measurements.