copper(I) complexes [Cu(4MTU) 2 Cl] (2), [Cu(4MTU) (B)Cl] (3), [Cu(6MTU) 2 Cl] (5) and [Cu(6MTU) (B)Cl] ( 6) where 4MTU ¼ 1-Benzyl-3-(4-methyl-pyridin-2-yl)-thiourea (1) and 6MTU ¼ 1-Benzyl-3-(6-methylpyridin-2-yl)-thiourea (4), B is a N,N-donor heterocyclic base, viz. 1,10-phenanthroline (phen 3, 6), were synthesized, characterized by various physico-chemical and spectroscopic techniques. The elemental analysis suggests that the stoichiometry to be 1:2 (metal:ligand) for 2, 5 1:1:1 (metal:ligand:B) for 3, 6. Xray powder diffraction illustrates that the complexes have crystalline nature. IR data coupled with electronic spectra and molar conductance values suggest that the complex 2, 5 show the presence of a trigonal planar geometry and the complex 3, 6 show the presence of a tetrahedral geometry about the Cu(I) centre. The binding affinity towards calf thymus (CT) DNA was determined using UV-Vis, fluorescence spectroscopic titrations and viscosity studies. These studies showed that the tested phen complexes 3, 6 bind moderately (in the order of 10 5 M À1 ) to CT DNA. The complex 2, 5 does not show any apparent binding to the DNA and hence poor cleavage efficiency. Complex 3, 6 shows efficient oxidative cleavage of plasmid DNA in the presence of H 2 O 2 involving hydroxyl radical species as evidenced from the control data showing inhibition of DNA cleavage in the presence of DMSO and KI. The in vitro antibacterial assay indicates that these complexes are good antimicrobial agents against various pathogens. Anti-bacterial activity is higher when thiourea coordinates to metal ion than the thiourea alone.

Three new Ni(II) square planar complexes of 4-methoxy-3-benzyloxybenzaldehyde thiosemicarbazide(4m3BTSC) having polypyridyl bases of general formulation [ML2] (1) and [MLB] (2, 3), where L = 4m3BTSC and B is N,N-donor heterocyclic bases, namely, 1,10-phenanthroline (phen, 2), 2,2′-bipyridine (bpy, 3), are synthesized and characterized. The free radical scavenging assay results showed that complex 1 possesses significant activity when compared to complexes 2 and 3. The biological studies showed that the ligand and its complexes exhibited significant and different biological activities and also the prepared compounds are nonmutagenic. They may be potential commercial antioxidants because of their nonmutagenic and nontoxic nature. The DNA interaction of the new complexes is evaluated by absorption, emission, and melting temperature methods, and the results suggested that the binding affinity of the complexes increases with the presence of planar ligand in the molecule. The nickel (II) complexes with planar phenanthroline bases show moderate DNA binding and cleavage ability.

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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.