Multifunctional DNA Interactions of Ru-Pt Mixed Metal Supramolecular Complexes with Substituted Terpyridine Ligands

The coupling of a light absorbing unit to a bioactive site allows for the development of supramolecules with multifunctional interactions with DNA. A series of mixed metal supramolecular complexes that couple a DNA-binding CiS-(PtCl2)-Cl-II center to a ruthenium chromophore via a polyazine bridging ligand have been prepared, and their DNA interactions have been studied, [(TL)RuCl(dpp)PtCl2](PF6) (TL = tpy (2,2':6',2 ''-terpyridine), MePhtpy (4'-(4-methylphenyl)-2,2':6',2 ''-terpyridine), or (t)Bu(3)tpy (4,4',4 ''-tri-tert-butyl-2,2':6',2 ''-terpyridine and dpp = 2,3-bis(2-pyridyl)pyrazine). This series provides for unique tridentate coordinated Ru(II) systems to photocleave DNA with preassociation with the DNA target via coordination of the Pt(II) center. Electronic absorption spectroscopy of the complexes displays intense ligand-based pi ->pi* transitions in the UV region and metal to ligand charge transfer (MLCT) transitions in the visible region. The Ru(d pi)-> dpp(pi*) MLCT transitions occur at 545 nm, red-shifted relative to the 520 nm maxima for the monometallic synthons, [(TL)RuCl(dpp)](PF6). The title RuPt complexes display reversible Ru-II/III oxidative couples at 1.10, 1.10, and 1.01 V vs Ag/AgCl for TL = tpy, MePhtpy, and (t)Bu(3)tpy, respectively. The TL0/- reduction occurred at -1.43, -1.44, and -1.59 V vs Ag/AgCl for TL = tpy, MePhtpy, and (t)Bu(3)tpy, respectively. These complexes display a dpp(0/-) couple (-0.50 -0.55, and -0.59 V) significantly shifted to positive potential relative to their monometallic synthons (-1.15, -1.16, and -1.22 V), consistent with the bridging coordination of the dpp ligand. Coupling of (TL)(RuCl)-Cl-II(BL) subunit to a cis-(PtCl2)-Cl-II site provides for the application of photochemically inactive Ru-II(tpy)-based chromophores in DNA photocleavage applications. The [(TL)RuCl(dpp)PtCl2](+) complexes display covalent binding to DNA and photocleavage upon irradiation with visible light modulated by TL identity. The redox, spectroscopic, DNA-binding, and photocleavage properties of a series of supramolecular complexes are presented.