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 E-2(g) --> (4)A(2g) 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 x 10(7), 2.4 x 10(9), and 1.8 x 10(7) 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. (C) 2001 Elsevier Science B.V. All rights reserved.