Six ternary a-amino acid copper(II) complexes of the general formula [Cu(AA)(B)(H 2 O)](X) (1-6), where AA is L-leu = L-leucine (1-3) or L-ile = L-isoleucine (4-6), B is a N,N-donor heterocyclic base, viz. 2,2 0 -bipyridine (bpy, 1, 4), 1,10-phenanthroline (phen, 2, 5) and dipyrido[3,2:2 0 ,3 0 -f]quinoxaline (dpq, 3, 6) and X ¼ ClO 4 À =NO 3 À have been synthesized, characterized, and their DNA binding and cleavage activity studied. The bpy and dpq complexes of L-ile (4, 6) have been structurally characterized by X-ray crystallography. The complexes show a distorted square-pyramidal (4 + 1) CuN 3 O 2 coordination geometry. The one-electron paramagnetic complexes display a d-d band near 600 nm in water and show a cyclic voltammetric response due to a Cu(II)/Cu(I) couple near À0.1 V (vs. SCE) in DMF-0.1 M TBAP. All complexes are 1:1 electrolytes. Binding interactions of the complexes with calf thymus DNA (CT-DNA) have been investigated by absorption, emission, viscosity and DNA melting studies. The phen and dpq complexes are avid binders to the calf thymus DNA, giving an order: (3, 6) (dpq) > (2, 5) (phen) ) (1, 4) (bpy). The bpy complexes do not show any apparent binding to the DNA and hence show poor DNA cleavage activity. The phen and dpq complexes (2,3,5, 6) show efficient oxidative cleavage of pUC19 supercoiled DNA (SC-DNA) in the presence of the reducing agent 3-mercaptopropionic acid (MPA) involving hydroxyl radical ( Å OH) species, as evidenced from the control data showing inhibition of DNA cleavage in the presence of Å OH radical quenchers, viz. DMSO, mannitol, KI and catalase.

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Crystal structure DNA binding Chemical nuclease activity Hydroxyl radical a b s t r a c t

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.

a b s t r a c tNew ternary copper (II) complexes, [Cu(L-orn)(B)(Cl)](ClÁ2H 2 O) (1-2) where L-orn is L-ornithine, B is an N,N-donor heterocyclic base, viz. 2,2 0 -bipyridine (bpy, 1) and 1,10-phenanthroline (phen, 2), were synthesized and characterized by various spectroscopic techniques. Complex 2 is characterized by the X-ray single crystallographic method. The complex shows a distorted square-pyramidal (4 + 1) CuN 3 OCl coordination sphere. Binding interactions of the complexes with calf thymus DNA (CT-DNA) were investigated by UV-Vis absorption titration, ethidium bromide displacement assay, viscometric titration experiment and DNA melting studies. Complex 2 shows appreciable chemical nuclease activity in the presence of 3-mercaptopropionic acid (MPA). The complexes were subjected to in vitro cytotoxicity studies against carcinomic human alveolar basal epithelial cells (A-549) and human epithelial (HEp-2) cells. The IC 50 values of 1 and 2 are less than that of cisplatin against HEp-2 cell lines. MIC values for 1 against the bacterial strains Streptococcus mutans and Pseudomonas aeruginosa are 0.5 mM.