Aliphatic polyamine ruthenium(II) complexes: crystal structure, DNA-binding, photocleavage, cytotoxicity, and antioxidation

The DNA-binding behaviors of two aliphatic polyamine Ru(II) complexes, [Ru(dppt)(dien)](ClO₄)₂ (1) and [Ru(pta)(dien)](ClO₄)₂ (2) (dppt, pta, and dien standing for 3-(1,10-phenanthrolin-2-yl)-5,6-diphenyl-as-triazine, 3-(1,10-phenanthrolin-2-yl)-5,6-diphenyl-as-triazino[5,6-f]-acenaphthylene, and diethylenetriamine, respectively), were studied through absorption titration, thermal denaturation, and viscosity measurements. The results indicate that the DNA-binding affinity of 2 is much greater than that of 1; 2 binds to CT-DNA in an intercalative mode but 1 binds to CT-DNA through partial intercalation. In addition, the complexes react with DNA in an energy-driven process with a decrease in entropy. The photocleavage of plasmid pBR322 can be triggered by 1 and 2 and strengthened with an increased concentration of both complexes. The scavenging activity of 1 against hydroxyl radical (˙OH) is slightly better than that of 2 according to the antioxidation experiment. The standard cytotoxicity experiments were carried out with MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide); the results indicate that the proliferation of Hela, A549, and 7402 cells is inhibited by these two compounds in a dose-dependent manner. The X-ray crystal structure of 1 and some results of DFT (the density functional theory) calculations were analyzed to further understand the differences in DNA-binding strength of the complexes.