Direct DNA photocleavage by a new intercalating dirhodium(II/II) complex:: Comparison to Rh2(μ-O2CCH3)4

Transition metal complexes possessing the intercalating dppz ligand (dppz = dipyrido[3,2-a:2',3'-c]phenazine) typically bind ds-DNA through intercalation (K-b similar to 10(5)-10(6) M-1), and DNA photocleavage by these complexes with visible light proceeds through the generation of a reactive oxygen species. The DNA binding and photocleavage by [Rh-2(mu-O2CCH3)(2)(eta(1)-O2CCH3)(CH3OH)(dppz)](+) (2) is reported and compared to that of Rh-2(mu-O2CCH3)(4) (1). Spectral changes and an increase in viscosity provide evidence for the intercalation of 2 to double stranded DNA with K-b = 1.8 x 101 M-1. DNA photocleavage by 2 is observed upon irradiation with lambda(irr) > 395 nm both in air and deoxygenated solution. DNA photocleavage is not observed for 1 or free dppz ligand under these irradiation conditions. The coupling of a single dppz ligand to a dirhodium(II/II) bimetallic core in 2 provides a means to access oxygen-independent DNA photocleavage with visible light.