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.
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.
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