Studies on DNA Interactions and Biological Activities of Lanthanum(III) Complexes with 4-Quinoline Terpyridine and 1,10-Phenanthroline

A series of lanthanum(III) complexes [La(4-qtpy)2(NO3)2](NO3) (1), [La(4-qtpy)3(NO3)](NO3)2 (2), [La(4-qtpy)(phen)(NO3)2](NO3) (3) and [La(4-qtpy)(phen)2(NO3)2](NO3) (4) (4-qtpy = 4′-[(4-quinoline)-2,2′;6′,2′′-terpyridine]) were synthesized and characterized. The cyclic voltammetric studies revealed that the complexes 1 and 3 are redox active. UV-visible absorption spectral studies and viscosity measurements revealed that complexes bind to DNA through intercalation. Complexes 1 and 3 have shown the highest binding propensity (Kb = 4.241 + 0.2 × 106 for 1 and 1.492 + 0.2 × 106 for 3). The results of chemical nuclease studies revealed that the complexes 3 and 4 have shown maximum chemical nuclease activity in the presence of H2O2 and the mechanism involves hydroxyl radicals. The antibacterial activities of the complexes 1 to 4 were tested against Gram positive and Gram negative bacteria in which complex 3 shows comparable results with the standard antibiotic tetracycline. The cytotoxic activities of 4-qtpy and complex 4 were done by MTT assay against HeLa cell lines.

Importance of Binding Affinity for the Activity of a Metallodendritic Chemical Nuclease

A family of bis(2-pyridyl)amino-modified poly(amidoamine) dendrimer Cu complexes was prepared, and their chemical nuclease activities and binding affinity (Kb) levels for DNA plasmid were investigated. The Kb values of the G2 to G6 apodendrimers for DNA plasmid were found to be 7.4, 23, 48, 70, and 280 µM−1, respectively, using ethidium bromide (EtBr) displacement experiments. The chemical nuclease activities of the corresponding complexes were determined by gel electrophoresis, and a clear positive dendritic effect was observed. Further analysis indicated a linear correlation between the Kb values of the G2 to G5 apodendrimers and the nuclease activity of the corresponding complexes. This observation indicated the importance of substrate binding affinity for macromolecular nuclease activity. In addition, an experiment using 3′-(p-hydroxyphenyl) fluorescein suggested that hydroxyl radicals formed under the tested conditions. Subsequently performed inhibition studies indicated that the hydroxyl radical was the active species responsible for the plasmid cleavage.

Hetero-Binuclear Complexes of Lanthanum (III) Using Bridging N,N′-Bis(2-Pyridylmethyl)Oxamide and Terminal 1,10-Phenanthroline: Synthesis, Characterization and Biological Evaluation

In the present study, hetero-binuclear La(III) complexes were newly synthesized using well known bridging ligand N,N′-bis(2-pyridylmethyl)oxamide (2PMO, 1) and “complexes as ligands” [Cu(2PMO)] (2) and [Ni(2PMO)] (3). The newly synthesized mononuclear (4) as well as hetero-binuclear complexes (5 and 6) were characterized by analytical and spectroscopic techniques. The newly synthesized complexes were tested for their binding ability towards CT-DNA and chemical nuclease property towards SC pUC 19 DNA. The complexes were tested for antibacterial activities against Gram negative bacteria (E. coli and K. pneumonia) and Gram positive bacteria (B. subtilis and S. aureus), antioxidant activities by DPPH radical scavenging and ferrous-ion chelation methods and cytotoxicity against MCF-7 cell lines by MTT assay. The structure-activity relationship revealed that the newly synthesized hetero-binuclear complexes show potent DNA binding and chemical nuclease activities, antibacterial, antioxidant and cytotoxic activities.