A Multifunctional Tetrametallic Ru−Pt Supramolecular Complex Exhibiting Both DNA Binding and Photocleavage

A new tetrametallic supramolecular complex, [{(bpy)2Ru(dpp)}2Ru(dpp)PtCl2](PF6)6 (bpy = 2,2‘-bipyridine, dpp = 2,3-bis(2-pyridyl)pyrazine), has been prepared and characterized. This supramolecular assembly is multifunctional, forming coordinate covalent bonds to DNA through its cis-PtCl2 moiety and photocleaving DNA through its Ru polypyridine chromophores. Electronic absorption spectroscopy shows ligand-based π→π* transitions in the UV with Ru-based metal-to-ligand charge transfer transitions throughout much of the visible. The Ru→dpp CT transitions center at 542 nm (e = 35 000 M-1 cm-1). This complex has a HOMO localized on peripheral Ru with E1/2oxd = 1.58 V vs Ag/AgCl, and a LUMO based on the μ-dpp connecting Ru and Pt, E1/2red = −0.40 V. Gel electrophoresis analysis shows the tetrametallic coordinates to pUC18 DNA and, when excited with visible light, cleaves DNA through an oxygen-mediated pathway.