Synthesis, Characterization, and DNA Binding Properties of a Series of Ru, Pt Mixed-Metal Complexes

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Abstract
A series of mixed-metal complexes coupling ruthenium light absorbers to platinum reactive metal sites through polyazine bridging ligands have been prepared of the form [(tpy)RuCl(BL)PtCl2](PF6) (BL = 2,3-bis(2-pyridyl)pyrazine (dpp), 2,3-bis(2-pyridyl)quinoxaline (dpq), 2,3-bis(2-pyridyl)benzoquinoxaline (dpb); tpy = 2,2‘:6‘,2‘ ‘-terpyridine). These systems possess electron-rich Ru metal centers bound to five polyazine nitrogens and one chloride ligand. This leads to complexes with low-energy Ru → BL charge-transfer bands that are tunable with BL variation occurring at 544, 632, and 682 nm for dpp, dpq, and dpb, respectively. This tuning of the charge-transfer energy results from a stabilization of the BL(π*) orbitals in this series as evidenced by the cathodic shift in the first reduction of these complexes occurring at −0.50, −0.32, and −0.20 V vs Ag/AgCl, for dpp, dpq, and dpb, respectively. The chlorides bound to the PtII center are substitutionally labile giving these complexes the ability to covalently bind to DNA. All three title bimetallics, [(tpy)RuCl(BL)PtCl2](PF6), avidly bind double-stranded DNA with t1/2 = 1−2 min, substantially reducing the migration of DNA through an agarose gel. Details of the synthetic methods, FAB MS data, spectroscopic and electrochemical properties, and DNA binding studies are presented.

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