Synthesis, X-ray structure and cytotoxic effect of nickel(II) complexes with pyrazole ligands

Here we present the synthesis of the new Ni(II) complexes with chelating ligands 1-benzothiazol-2-yl-3,5-dimethyl-1H-pyrazole (a), 5-(2-hydroxyphenyl)-3-methyl-1-(2-pyridylo)-1H-pyrazole-4-carboxylic acid methyl ester (b) and 1-benzothiazol-2-yl-5-(2-hydroxyphenyl)-3-methyl-1H-pyrazole-4-carboxylic acid methyl ester (c). These ligands a–c create solid complexes with Ni(II). The crystal and molecular structures of two complexes were determined by X-ray diffraction method. Thermal stability of two complexes with ligand c by TG/DTG and DSC methods were also shown. Cytotoxic activity of all the complexes against three tumour cell lines and to normal endothelial cells (HUVEC) was also estimated. Complexes with ligand c exhibited relatively high cytotoxic activity towards HL-60 and NALM-6 leukaemia cells and WM-115 melanoma cells. Cytotoxic effectiveness of one of these complexes against melanoma WM-115 cells was two times higher than that of cisplatin. The protonation constant log K = 9.63 of ligand b corresponding to the phenol 2-hydroxy group has been determined in 10% (v/v) DMSO/water solution (25 °C). The coordination modes (formation of two monomeric species: NiL and NiL2) in the complexes with Ni(II) are discussed for b on the basis of the potentiometric and UV/Vis data.

New Ni(II) complexes with chelating ligands: 1-benzothiazol-2-yl-3,5-dimethyl-1H-pyrazole (a), 5-(2-hydroxybenzo-2-yl)-3-methyl-1-(2-pyridinyl)pyrazol-4-carboxylic acid methyl ester (b) and 1-(2-benzothiazo-2-yl)-5-(2-hydroxyphenyl)-3-methyl-1H-pyrazol-4-carboxylic acid methyl ester (c) have been synthesized and characterized. Cytotoxic activity of their complexes 1a–c, 2a–c and 3c on tumour and normal cells are also shown.Figure optionsDownload as PowerPoint slideHighlights
► X-ray crystal structures of Ni(II) complexes pyrazole-derived ligand.
► The complexing properties of pyrazole ligand b with Ni(II) in solution were examined.
► Cytotoxic effect of Ni(II) complexes against tumour and normal cells.
► Complex 1c showed higher cytotoxicity than cisplatin against melanoma WM-115 cells.