Intramolecular photoinduced electron transfer to anthraquinones linked to duplex DNA: The effect of gaps and traps on long-range radical cation migration

A series of duplex DNA structures was prepared that incorporate an anthraquinone group linked covalently to the 5'-terminus of one strand and two GG steps separated by three base pairs in the complementary strand. Physical, chemical, and spectroscopic methods indicate that the quinone is associated with the DNA by end-capping rather than by intercalation. Irradiation of the linked anthraquinone leads to piperidine-requiring strand cleavage predominantly at the 5'-G of the GG steps. The 5'-G of the distal GG step is more than 40 Angstrom from the anthraquinone group. This long-range DNA damage is attributed to migration of a radical cation (hole) through the duplex DNA from its point of generation near the anthraquinone to its point of reaction at the GG step. This migration is not interrupted by imposition of a gap caused by an abasic site. However, the incorporation of 8-OxoG into the DNA duplex blocks migration by introducing a deep, reactive trap for the radical cation.