Long-Range Photoinduced Electron Transfer Through a DNA Helix

TLDR

The stacked aromatic heterocycles of the DNA duplex serve as an efficient medium for coupling electron donors and acceptors over very long distances. The authors synthesized an oligomeric assembly with a Ru(phen)₂dppz²⁺ donor and a Rh(φ)₂phen³⁺ acceptor intercalated one or two base steps from the helix termini. Rapid photoinduced electron transfer over >40 Å was observed between Ru‑ and Rh‑modified DNA duplexes, with a quenching rate exceeding 10⁹ s⁻¹ and no luminescence detected when the donor and acceptor were hybridized, while no transfer occurred when the complexes failed to intercalate.

Abstract

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) 2 dppz 2+ (phen, phenanthroline, and dppz, dipyridophenazine) and the acceptor is Rh(phi) 2 phen 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.