Intercalative binding and photoredox behavior of [Cr(phen)2(dppz)]3+ with B-DNA

Dramatically increased binding to calf thymus B-DNA is reported for the complex Cr(phen)2(dppz)3+ (where dppz is dipyridophenazine) relative to that observed for Cr(phen)3 3+. UV–Vis absorption, viscosity, and equilibrium dialysis data provide convincing evidence that this enhanced binding by Cr(phen)2(dppz)3+ is associated with intercalation by the dppz ligand. In aqueous buffer solution (pH 7.4), the 2Eg→4A2g phosphorescence signal of Cr(phen)2(dppz)3+ centered at 730 nm is quenched in the presence of calf thymus DNA or the mononucleotides deoxyguanosine-5′-monophosphate (dGMP) and deoxyadenosine-5′-monophosphate (dAMP). Stern–Volmer lifetime plots for calf thymus DNA, dGMP, and dAMP yield bimolecular quenching rate constants of 3.0×107, 2.4×109, and 1.8×107 M−1 s−1, respectively. The study demonstrates that Cr(phen)2(dppz)3+ is a stronger photooxidant than Cr(phen)3 3+ and Cr(bpy)3 3+ (and markedly stronger than Ru(phen)2(dppz)2+), and is capable of both guanine and adenine nucleobase oxidation.