A tris(2,2′-bipyridine)ruthenium( ii ) derivative tethered to a cis-PtCl ₂ (amine) ₂ moiety: syntheses, spectroscopic properties, and visible-light-induced scission of DNA

A tris(2,2'-bipyridine)ruthenium(II) derivative having two N-(3-ammoniopropyl)carbamoyl pendant units has been prepared and reacted with cis-PtCl2(DMSO)2 (DMSO = dimethyl sulfoxide) to give a heteronuclear Ru(II)Pt(II) dimer having a cis-Pt(II)Cl2(aliphatic amine)2 unit, [Ru(bpy)2(mu-bridge)PtCl2](PF6)2 (bpy = 2,2'-bipyridine, bridge = 4,4'-bis(N-(3-aminopropyl)carbamoyl)-2,2'-bipyridine). The ESI-TOF mass spectrum of the Ru(II)Pt(II) dimer shows a set of signals corresponding to {[Ru(bpy)2(mu-bridge)PtCl2](PF6)}(+) (m/z 1181.1). The MLCT (metal-to-ligand charge transfer) luminescence intensity is enhanced upon the platination of two amine units, presumably due to the formation of a relatively rigid metallocycle. More interestingly, the luminescence intensity is further enhanced by the complexation of the Ru(II)Pt(II) dimer with either 5'-GMP (guanosine 5'-monophosphate disodium salt) or calf thymus DNA. Visible-light-induced scission of supercoiled pBR322 DNA is found to be efficiently enhanced in the presence of the title Ru(II)Pt(II) dimer.