Unpredicted formation of copper(ii) complexes containing 2-thiophen-2-yl-1-thiophen-2-ylmethyl-1H-benzoimidazole and their most promising in vitro cytotoxicity in MCF-7 and HeLa cell lines over cisplatin†
An in situ reaction of CuCl2·2H2O, o-phenylenediamine, thiophene-2-carbaldehyde and sodium azide in methanol afforded complex 1a. Originally, it was expected to form a binuclear copper(II) complex containing N,N′-bis-thiophene-2-ylmethylene-benzene-1,2-diamine. However, the reaction afforded a binuclear complex 1a bis-(μ-azido)-2-thiophene-2-yl-1-thiophen-2-ylmethyl-1(H)-benzoimidazole copper(II) in decent yield. The same reaction carried out in the absence of sodium azide afforded complex 1b. The new complexes were characterized by various spectroscopic (IR, UV-Vis and EPR) techniques and the structure of the complexes is confirmed by X-ray crystallography. Computational details of theoretical calculations (DFT) have been discussed for complex 1a. The interaction of the ligand and complexes with calf thymus (CT-DNA) has been examined by photophysical studies, which revealed that the complexes bound to DNA through an electrostatic mode. Albumin (Bovine Serum Albumin) binding studies of the complexes (1a and 1b) confirmed their effect on altering the albumin structure by quenching the tryptophan and tyrosine residues. Antioxidant studies showed that the Cu(II) complexes exhibited significant antioxidant activity. Cell proliferation MTT assays were performed for all the compounds in breast cancer (MCF-7) and cervical cancer (HeLa) cell lines. The ligand and new complexes overcame cisplatin resistance in the MCF-7 and HeLa cell lines. Further, their nontoxic nature was confirmed when they were tested against human normal Embryonic kidney cells (HEK). Among the two complexes, complex 1a was the most effective against MCF-7 (IC50 value of 3.417 μM) and HeLa (0.6 μM) compared with complex 1b (10.2 μM; 11.7 μM).