Synthesis of ruthenium polypyridyl complexes and the steric influence of the intercalated ligand on DNA-binding

Two structurally related ligands dmtatp (2, 3-dimethyl-1, 4, 8, 9-tetraazatriphenylene), dptatap(2, 3-diphenyl-1,4,8, 9-tetraazatriphenylene) and their ruthenium(I) complexes [Ru(bpy)(2)dmtatp](2+) (1) and [Ru(bpy)(2)dptatp](2+) (2) were synthesized and characterized. Combined with the previous study data of [Ru(bpy)(2)tatp](2+) (3, tatp = 1,4,8,9-tetraazatriphenylene) the steric influence of the intercalated ligand of these complexes on DNA-binding were investigated by electronic absorption, steady-state luminescence, CD spectra and viscosity measurement. All the data suggested that the complexes bind with DNA by intercalation and the order of binding affinities is 3>2>1, consistent with the reduced steric effect of the intercalated ligand.