Evaluation of DNA binding and DNA cleavage of nickel(II) complexes with tridentate α-N-heterocyclic thiosemicarbazones ligands

Two mononuclear thiosemicarbazones nickel(II) complexes of the type [Ni(L1)(2)] (1) and [Ni(HL2)(L2)] (2), where HL1 = (E)-N-methyl-2-(quinolin-2-ylmethylene)hydrazinecarbothioamide and HL2 = (E)-N, N-dimethyl-2-(quinolin-2-ylmethylene)hydrazinecarbothioamidehave been synthesized and characterized by X-ray crystallography, infrared spectroscopy, elemental analysis and DFT calculations. Single-crystal diffraction analysis revealed that the HL1 ligands in 1 are predominantly in the thiolato resonance forms, while the HL2 ligands in 2 coordinate in thiolato and thione forms simultaneously. The interactions of both nickel(II) complexes with calf thymus DNA (CT-DNA) and supercoiled pBR322 plasmid DNA were investigated by fluorescence and UV-visible spectra, viscosity measurement, as well as agarose gel electrophoresis. The results of binding experiments displayed that both nickel(II) complexes were able to interact with CT-DNA via intercalative mode with a moderate binding affinity in the order 2 > 1. Gel electrophoresis assay revealed that the complexes could cleave the pBR322 plasmid DNA in a dose-dependent manner. (C) 2017 Elsevier B.V. All rights reserved.