Development of new cobalt, copper, and zinc complexes of Schiff-base ligands as prospective chemotherapeutic agents

Fluorobenzaldehyde was converted into new, bidentate Schiff-base ligands with nitrogen and sulphur donor sites in two steps. The first step proceeds via Knoevenagel condensation; the product obtained was treated with thiosemicarbazide to yield the ligand L1. The Schiff-base ligand, L2, was synthesized by treating L1 with 4-chlorobenzylchloride in a basic medium. Co (II), Cu (II), and Zn (II) complexes were synthesized with the ligands L1 and L2. All these complexes were characterized by FTIR, UV–Vis, NMR spectroscopy, ESI-mass spectral analysis, magnetic moment, molar conductance, thermal, powder XRD, and electrochemical studies. From these studies, the molecular formulae of the complexes were found to be [M(L)2Cl2], where M = Co (II), Cu (II) and Zn (II) and L = L1 or L2 based on the ligand used in the synthesis. The synthesized complexes were observed to have a high spin and distorted octahedral geometry and were non-electrolytic. The UV absorption titrimetric analysis confirmed that these complexes would bind strongly to CT-DNA through the intercalative mode. The electrophorograms supported the statement that Cu (II) complexes could effectively catalyze the hydrolytic cleavage of CT-DNA and can be considered potent metallonuclease agents. The DPPH assay determined the antioxidant properties of these complexes, and the cupric complexes were observed to possess better antioxidant properties than the standard used ascorbic acid. The cell viability analysis of these complexes showed an elevated control of proliferation against a human breast adenocarcinoma (MCF-7) cancer cell line compared to a human cervical carcinoma (HeLa) cell line. The results exhibited by these compounds were compared with the standard drug, cisplatin. The binding affinity of the Cu (II) metal ion complex towards CT-DNA was high when compared to Co (II) and Zn (II) metal ions. These results are in line with the cytotoxicity studies. Molecular docking studies also hold up the experimental data. Cu (II) complexes using ligand L2 show higher efficiency than those with ligand L1 in all biological assays and can be considered a potent DNA-targeting drug.