DNA-binding properties of flexible diamine bridged dinuclear ruthenium(II)-2,2′-bipyridine complexes

A series of new flexible diamine bridged dinuclear ruthenium(II) complexes, [{RuCl(bpy)2}2(μ-BL)]2+ (bpy = 2,2′-bipyridine; BL = H2N(CH2)nNH2 (n = 4 (bn), 8 (on), 12 (don))), were prepared ([Ru2-bn]2+, [Ru2-on]2+, [Ru2-don]2+). Time-course spectroscopic experiments revealed that these ruthenium(II) complexes selectively bind to guanine bases in CT-DNA and the degree of binding of [Ru2-on]2+ or [Ru2-don]2+ to CT-DNA relative to [Ru2-bn]2+ is high, which may be explained by the length of bridging ligand BL. The site of ruthenation in double-stranded plasmid pBR322 DNA derives from intrastranded cross-links between two deoxyguanosines by measuring the inhibition of the restriction enzyme Nhe I.