A multifunctional tetrametallic Ru-Pt supramolecular complex exhibiting both DNA binding and photocleavage

A new tetrametallic supramolecular complex,[{(bpy)(2)Ru(dpp)}(2)Ru(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 pi ->pi* 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 (epsilon = 35 000 M-1 cm(-1)). This complex has a HOMO localized on peripheral Ru with E-1/2(oxd) = 1.58 V vs Ag/AgCl, and a LUMO based on the mu-dpp connecting Ru and Pt, E-1/2(red) = -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.