Synthesis and DNA binding of μ-[2,9-bis(2-imidazo[4,5-f][1,10]phenanthroline)-1,10-phenanthroline]bis[1,10-phenanthrolinecopper(II)]

A binuclear complex [(phen)Cu(μ-bipp)Cu(phen)](ClO4)4, where phen = 1,10-phenanthroline and bipp = 2,9-bis(2-imidazo[4,5-f][1,10]phenanthroline)-1,10-phenanthroline, has been synthesized and its interaction with calf-thymus DNA in the buffer containing 5 mM Tris and 50 mM NaCl has been studied by means of electronic absorption titration, luminescence titration and viscometric measurements. The absorbance of the complex in the range of 320–400 nm, which is mainly based on bipp showed no obvious change upon addition of DNA, while the peak at 270 nm, which is determined by both phen and bipp decreased by up to 18%. The emission band of the complex around 360 nm decreased remarkably in presence of DNA. The emission quenching of this complex by [Fe(CN)6]4− was depressed greatly when bound to DNA. The relative viscosity of DNA was increased by this complex more significantly than a bipp directed intercalating reagent. These results suggest that this complex binds to calf thymus DNA by intercalation of the two phenanthrolinecopper terminals. The apparent intrinsic binding constant of the complexes with DNA was 1.6 × 104 M−1 as determined by UV–visible titration.