Spectral characteristics, DNA-binding and cytotoxicity of two functional Ru(II) mixed-ligand complexes

Two functional Ru(II) mixed-ligand complexes, Ru(phen)(2)(ttbd)](2+) (1) (ttbd = 4-(6-propenyl-pyrido3,2-a]phenzain-10-yl-benzene-1,2-diamine, phen = 1,10-phenanthroline) and Ru(bpy)(2)(ttbd)](2+) (2) (bpy = 2,2'-bipyridine), have been synthesized and characterized. The spectral characteristics of complexes 1 and 2 were investigated using fluorescence spectroscopy and revealed that both complexes were very sensitive to solvent polarity and oxygen molecules in nonaqueous solvents. The binding properties of the two complexes towards calf thymus DNA (CT-DNA) were investigated with different spectrophotometric methods, viscosity measurements and quantum chemistry calculations, indicating that both complexes could enantioselectively bind to CT-DNA by means of intercalation, but with different binding strengths and discrimination. On the other hand, the cytotoxicity of both complexes have been evaluated by MTT assays and Giemsa staining experiments. The main results reveal that the hydrophobicity and surface area of the ancillary ligands have a significant effect on their DNA binding behavior and both complexes are likely to be useful for optically probing nonaqueous and oxygen-free environments.