Redox, Spectroscopic, and Photophysical Properties of Ru-Pt Mixed-Metal Complexes Incorporating 4,7-Diphenyl-1,10-phenanthroline as Efficient DNA Binding and Photocleaving Agents

The redox, spectroscopic, and photophysical properties as well as DNA interactions of the new bimetallic complexes [(Ph(2)phen)(2)Ru(BL)PtCl2](2+) (Ph(2)phen = 4,7-diphenyl-1,10-phenanthroline, and BL (bridging ligand) = dpp = 2,3-bis(2-pyridyl)pyrazine, or dpq = 2,3-bis(2-pyridyl)quinoxaline) were investigated. These Ru-polyazine chromophores with Ph2phen TLs (terminal ligands) and polyazine BLs are efficient light absorbers. The [(Ph(2)phen)(2)Ru(BL)PtCl2](2+) complexes display reversible Ru-II/III oxidations at 1.57 (dpp) and 1.58 (dpq) V vs SCE (saturated calomel electrode) with an irreversible Pt-II/IV oxidation occurring prior at 1.47 V vs SCE. Four, reversible ligand reductions occur at -0.50 dpp(0/-), -1.06 dpp(-/2-), -1.37 Ph(2)phen(0/-), and 1.56 V vs SCE Ph(2)phen(0/-). For the [(Ph(2)phen)(2)Ru(dpq)PtCl2](2+) complex, the first two reductions shift to more positive potentials at 0.23 and 0.96 V vs SCE. The electronic absorption spactroscopy is dominated in the UV region by pi ->pi* ligand transitions and in the visible region by metal-to-ligand charge transfer (MLCT) transitions at 517 nm for [(Ph(2)phen)(2)Ru(dpp)PtCl2](2+) and 600 nm for [(Ph(2)phen)(2)Ru(dpq)PtCl2](2+). Emission spectroscopy shows that upon attaching Pt to the Ru monometallic precursor the lambda(em)(max) shifts from 664 nm for [(Ph(2)phen)(2)Ru(dpp)](2+) to 740 nm for [(Ph(2)phen)(2)Ru(dpp)PtCl2](2+). The cis-(PtCl2)-Cl-II bioactive site offers tie potential of targeting DNA by covalently binding the mixed-metal complex to DNA bases. The multifunctional interactions with DNA were assayed using both linear and circular plasmid pUC18 DNA gel shift assays. Both title complexes can bind to and photocleave DNA with dramatically enhanced efficiency relative to previously reported systems. The impact of the Ph(2)phen TL on photophysics and bioreactivity is somewhat surprising given the Ru-BL charge transfer (CT) nature of the photoreactive state in the complexes.