Synthesis and characterization of some water soluble Zn(II) complexes with (E)-N-(pyridin-2-ylmethylene)arylamines that regulate tumour cell death by interacting with DNA

The synthesis and spectroscopic properties of nine water soluble zinc(II) complexes of (E)-N-(pyridin-2-ylmethylene)arylamines (Ln) with the general formula [Zn(X)2(Ln)] (X = Cl−, Br−, I−; (1–8)) and [Zn(μ-N3)(N3)(L3)]2 (9) are reported. The complexes were characterized by elemental analysis and their spectroscopic properties were studied using UV-Visible, fluorescence, IR and 1H NMR spectroscopies. The solid state structures of zinc(II) complexes 2–4 and 6–9 were established by single crystal X-ray crystallography. The majority of the structures are mononuclear with tetra-coordinate zinc centres (2–4, 6 and 7) except where L carries an additional donor atom capable of coordinating zinc (8), in which case the zinc atom has a distorted square pyramidal geometry. The centrosymmetric molecule of [Zn(μ-N3)(N3)(L3)]2 (9) is binuclear with the zinc atoms in a trigonal bipyramidal coordination environment. In general, the dichlorozinc derivatives 1, 3–5 and 8 exhibited moderately elevated in vitro cytotoxic potency towards the human epithelial cervical carcinoma (HeLa) cell line, with 4 as the best performer (IC50 value of 18 μM). Apoptosis-inducing activity, assessed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, showed that the zinc complexes interacted with DNA and thereby interfered the DNA binding of several transcription factors to its promoter sites, thus inhibiting gene transcription required for the biological activity of cells.