Synthesis, characterization, structural analysis and DNA binding studies of nickel(II)–triphenylphosphine complex of ONS donor ligand – Multisubstituted thiosemicarbazone as highly selective sensor for fluoride ion

Abstract

A new kind of Ni(II) complex of the type, [Ni(PPh3)(L)](1), {where L=chemosensor thiosemicarbazone=2-(3-bromo-5-chloro-2-hydroxybenzylidene)-N-phenyhydrazine-carbothioamide} have been synthesized and characterized by NMR, IR, UV–Vis spectroscopic methods and single crystal X-ray studies. Based on spectroscopic and X-ray crystallographic studies, a square planar structure has been proposed for the Ni(II) complex. The interaction between Ni(II) complex and CT-DNA has been investigated using UV–Vis, circular dichroism studies and gel electrophoresis. In UV studies, the observed strong hypochromism in absorption intensities and binding constant value (Kb=1.8×105) indicates significant interaction between the electronic states of the Ni(II) complex chromophore with that of DNA bases. With increasing concentration of Ni(II) complex, the peaks at 275 and 245nm of CT-DNA are shifted to 1–2nm without any change in the zero-cross over at 259nm in circular dichroism studies. These observations suggest that the complex bind to DNA through a non-intercalative mode due to the waggling of three phenyl rings of triphenyl phosphine group. The Ni(II) complex display significant hydrolytic cleavage of circular plasmid pUC18 DNA. At high concentration, the Ni(II) complex almost promotes the maximum conversion of DNA from form I to form II along with the appearance of form III. The newly synthesized thiosemicarbazone compound is a promising system for the development of new colorimetric probes for the detection of anions. Anion sensing ability of the receptor (L) with halide ions (F−, Cl−, Br− and I−) have been carried out in different solvents. The receptor shows a remarkable color change from colorless to dark orange in CH3CN solution on selective binding with fluoride ion. The anion recognition property of the receptor via hydrogen bonding interactions is monitored by UV–Vis titration and 1H NMR spectroscopy.