The variable chelating behavior of 3-methoxysalicylaldehyde-4(N)-substituted thiosemicarbazones was observed in equimolar reactions with [PdCl(2)(PPh(3))(2)]. The new complexes were characterized by various analytical, spectroscopic techniques (mass, (1)H-NMR, absorption, IR). All the new complexes were structurally characterized by single crystal X-ray diffraction. Crystallographic results showed that the ligands H(2)L(1) and H(2)L(4) are coordinated as binegative tridentate ONS donor ligands in the complexes 1 and 4 by forming six and five member rings. However, the ligands H(2)L(2) and H(2)L(3) bound to palladium in 2 and 3 as uninegative bidentate NS donors by forming a five member chelate ring. From this study, it was found that the substitution on terminal 4(N)-nitrogen may have an influence on the chelating ability of thiosemicarbazone. The presence of hydrogen bonding in 2 and 3 might be responsible for preventing the coordination of phenolic oxygen to the metal ion. The interaction of the complexes with calf-thymus DNA (CT-DNA) has been explored by absorption and emission titration methods. Based on the observations, an electrostatic binding mode of DNA has been proposed. The protein binding studies were monitored by quenching of tryptophan and tyrosine residues in the presence of complexes using Lysozyme as model protein. Antibacterial activity studies of the complexes have been screened against pathogenic bacteria such as Enterococcus faecalis, Staphylococcus aureus, Escherichia coli, Klebsiella pneumonia and Pseudomonas aeruginosa. MIC50 values of the complexes showed that they exhibited significant activity against the pathogens and among them, 3 exhibited higher activity. Further, anticancer activity of the complexes on the lung cancer cell line A549 has also been studied.

The reaction of salicylaldehydethiosemicarbazone, [H 2 -(Sal-tsc)], with an equimolar amount of [RuHCl(CO)(PPh 3 ) 3 ] has afforded two complexes, namely [Ru(H-Sal-tsc)(CO)Cl-(PPh 3 ) 2 ] (1) and [Ru(Sal-tsc)(CO)(PPh 3 ) 2 ] (2), in one pot. The new complexes were separated and characterized by elemental analyses, various spectroscopic techniques (NMR, UV−vis, IR), Xray crystallography, and cyclic voltammetry. In complex 1, the ligand coordinated in a bidentate monobasic fashion by forming an unusual strained NS four-membered ring in 32% yield. However, in 2, the ligand coordinated in a tridentate dibasic fashion by forming ONS fiveand six-membered rings in 51% yield. Comparative biological studies such as DNA binding, cytotoxicity (MTT, LDH, and NO), and cellular uptake studies have been carried out for new ruthenium(II) complexes (1 and 2). From the DNA binding studies, it is inferred that the complex 1 exhibited electrostatic binding and 2 exhibited intercalative binding modes. On comparison of the cytotoxicity of the complexes in human lung cancer cells (A549) and liver cancer cells (HepG2), complex 2 exhibited better activity than 1; this may be due to the strong chelation and subsequent electron delocalization in 2 increasing the lipophilic character of the metal ion into cells.

The coordination propensities of 4(N,N')-diethylaminosalicylaldehyde-4(N)-substituted thiosemicarbazones (H(2)L(1-4)) were investigated by reacting with an equimolar amount of [PdCl(2)(PPh(3))(2)]. The new complexes were characterized by various spectroscopic techniques. The structure determination of the complexes [Pd(DeaSal-tsc)(PPh(3))] (1), [Pd(DeaSal-mtsc)(PPh(3))] (2) and [Pd(DeaSal-etsc)(PPh(3))] (3) by X-ray crystallography showed that ligands are coordinated in a dibasic tridentate ONS donor fashion forming stable five and six membered chelate rings. The binding ability of complexes (1-4) to calf-thymus DNA (CT DNA) has been explored by absorption and emission titration methods. Based on the observations, an electrostatic and an intercalative binding mode have been proposed. The protein binding studies have been monitored by quenching of tryptophan and tyrosine residues in the presence of complexes using lysozyme as a model protein. As determined by MTT assays, complex 3 exhibited a higher cytotoxic effect towards human lung cancer cell line (A549) and liver cancer cells (HepG2). LDH, NO assay and cellular uptake of the complexes have been studied. Further, antibacterial activity studies of the complexes have been screened against the pathogenic bacteria such as Enterococcus faecalis, Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa, MIC50 values of the complexes showed that the complexes exhibited significant activity against the pathogens and among the complexes, 3 exhibited higher activity.

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One pot synthesis of three structurally different Ni(II) thiosemicarbazone complexes 1, 2 and 3 were obtained from the reaction between [NiCl(2)(PPh(3))(2)], 1,2-bis(diphenylphosphino)ethane, and [H(2)-(Sal-tsc)]. The obtained products were characterized by various spectral and analytical techniques. From the X-ray crystallographic analysis, an unexpected N-arylation on the coordinated salicylaldehydethiosemicarbazone was found in complex 2. The comparative biological evolutions such as DNA/protein binding, antioxidant, cytotoxicity (MTT, LDH, and NO) and cellular uptake studies have been examined for [Ni(Sal-tsc)(PPh(3))] (1) and [(Ni(Sal-tsc))(2)(μ-dppe)] (3). When comparing the cytotoxicity of the complexes, 1 exhibited higher activity than 2 and 3 and by comparing with standard cis-platin, both of them were found to exhibit better activity under identical conditions.