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

Abstract Two new dimeric Zn(II) ([{ZnL1(DMSO2)}2]·DMSO (1), [{ZnL2Cl}2] (2)) and a novel tetrameric Zn(II) complex ([(Zn2L3)2(μ–OAc)2(μ3–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 (1012 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 103 to 104 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.