Polynuclear zinc(II) complexes of thiosemicarbazone: Synthesis, X-ray structure and biological evaluation

Abstract

Two new dimeric Zn(II) ([{ZnL1(DMSO2)}(2)]center dot DMSO (1), [{(ZnLCl)-Cl-2}(2)] (2)) and a novel tetrameric Zn(II) complex ([(Zn2L3)(2)(mu-OAc)(2)(mu(3)-O)(2)] (3)), where H2L1 = 4-(p-methoxyphenyl) thiosemicarbazone of o-hydroxynapthaldehyde, HL2 = 4-(p-methoxyphenyl)thiosemicarbazone of benzoyl pyridine and H2L3 = 4-(p-chlorophenyl)thiosemicarbazone of o-vanillin are reported. Ligands and their complexes were characterized by spectroscopic and single crystal X-ray diffraction techniques. In addition, the complexes exhibited good binding affinity towards HSA (10(12)M(-1)), which is supported by their ability to quench the tryptophan fluorescence emission spectra of HSA. The complexes were also screened for their DNA binding propensity through UV-vis absorption titration, circular dichroism and fluorescence spectral studies. Results show that they effectively interact with CT-DNA through an intercalative mode of binding, with binding constants ranging from 10(3) to 10(4) M-1. Among the three complexes 1 has the highest binding affinity towards CT-DNA. Further, the phosphatase activity was evaluated using bis(2,4-dinitrophenyl)phosphate (BDNPP) as substrate, however, the complexes did not yield any measurable catalytic activity. Nevertheless the complexes showed significant cytotoxic potential against HeLa and HT-29 cancer cell lines that was assessed through MTT assay and DAPI staining. Remarkably, complex 1 showed better activity than cisplatin against HT-29 cell line.