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

摘要

The redox, spectroscopic, and photophysical properties as well as DNA interactions of the new bimetallic complexes [(Ph_2phen) _2Ru(BL)PtCl_2]~(2+) (Ph_2phen = 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 Ph_2phen TLs (terminal ligands) and polyazine BLs are efficient light absorbers. The [(Ph_2phen)_2Ru(BL)PtCl_2]~(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 PtII/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 _2phen~(0/-), and -1.56 V vs SCE Ph_2phen ~(0/-). For the [(Ph_2phen)_2Ru(dpq)PtCl _2]~(2+) complex, the first two reductions shift to more positive potentials at -0.23 and -0.96 V vs SCE. The electronic absorption spectroscopy is dominated in the UV region by ππ* ligand transitions and in the visible region by metal-to-ligand charge transfer (MLCT) transitions at 517 nm for [(Ph_2phen)_2Ru(dpp)PtCl_2] ~(2+) and 600 nm for [(Ph_2phen)_2Ru(dpq)PtCl _2]~(2+). Emission spectroscopy shows that upon attaching Pt to the Ru monometallic precursor the _(max)~(em) shifts from 664 nm for [(Ph_2phen)_2Ru(dpp)]~(2+) to 740 nm for [(Ph_2phen)_2Ru(dpp)PtCl_2]~(2+). The cis-Pt~(II)Cl_2 bioactive site offers the 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 Ph2phen TL on photophysics and bioreactivity is somewhat surprising given the RuBL charge transfer (CT) nature of the photoreactive state in the complexes.