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

• Published in: Inorganica Chimica Acta 2001-10, Vol.322 (1), p.74-78
• Main Authors: Barker, Kylie D, Benoit, Bethany R, Bordelon, Jason A, Davis, Robert J, Delmas, Andrew S, Mytykh, Olga V, Petty, Jeffrey T, Wheeler, John F, Kane-Maguire, Noel A.P
• Format: Article
• Language: English
• Subjects: Chromium(III) complexes; DPPZ ligand; Intercalative binding; Polypridyl complexes
• ISSN: 0020-1693; 1873-3255
• DOI: 10.1016/S0020-1693(01)00555-2

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 2E g→ 4A 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 3.0×10 7, 2.4×10 9, and 1.8×10 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. UV–Vis absorption, viscosity, and equilibrium dialysis data provide convincing evidence that the enhanced binding of the complex Cr(phen) 2(dppz) 3+ to duplex calf thymus DNA is associated with intercalation by the dppz ligand, while emission quenching studies establish the complex as a potent excited state oxidant capable of both guanine and to a lesser extent adenine nucleobase oxidation.