Synthesis, interaction with DNA and antiproliferative activities of two novel Cu(II) complexes with Schiff base of benzimidazole

•Two novel Cu(II) complexes of benzimidazole Schiff base have been synthesized.•Complex (1) structure was determined by X-ray diffraction.•The complexes and ligands bound DNA moderately via partial intercalation modes.•Complex (1) could cleave pBR322 plasmid DNA via radical mechanism.•Complex (1) has strongest activity against two tested cancer cell lines.

Two novel copper(II) complexes with Schiff base of benzimidazole [Cu(L)Cl]2·CH3OH have been synthesized. HL1 (N-(benzimidazol-2-ymethyl)-5-chlorosalicylideneimine, C15H11ClN3O) and HL2 (N-(benzimidazol-2-ymethyl)-salicylideneimine, C15H12N3O) are ligands of complex (1) and complex (2), respectively. The complexes were characterized by elemental analysis, IR, UV–Vis, TGA and X-ray diffraction. Within the complexes, Cu(II) ions were four coordinated by two nitrogen atom of azomethine and imine, one phenolic oxygen atom from HL and one chloride atom. A distorted quadrilateral structure was formed. Complex (1) crystallized in the triclinic crystal system. Results showed that π–π stacking effect occurred due to the existence of aromatic ring from Schiff base and hydrogen bonding between methanol and adjacent atoms. The DNA binding properties of the complexes were investigated by electronic absorption spectra, fluorescence spectra and viscosity measurements. Results indicated that complexes bound to DNA via partial intercalation mode. The DNA binding constants Kb/(L mol−1) were 1.81 × 104 (1), 1.37 × 104 (2), 6.27 × 103 (HL1) and 3.14 × 103 (HL2) at 298 K. The title complexes could quench the emission intensities of EB-DNA system significantly. The results of agarose gel electrophoresis indicated complex (1) could cleave supercoiled DNA through the oxidative mechanism. The inhibition ratios revealed that complex (1) and HL1 had strong antiproliferative activities against human breast cancer cells (MCF-7) lines and human colorectal cancer cells (COLO205) lines in vitro. The antiproliferative activities of complex (1) against MCF-7 lines (IC50 = 16.9 ± 1.5 μmol L−1) and against COLO205 lines (IC50 = 16.5 ± 3.4 μmol L−1) is much stronger than that of HL1, which had the potential to develop anti-cancer drug.

Graphical abstractTwo novel copper(II) complexes [Cu(L)Cl]2·CH3OH (HL1 = N-(benzimidazol-2-ymethyl)-5-chlorosalicylideneimine, C15H11ClN3O; HL2 = N-(benzimidazol-2-ymethyl)-salicylideneimine, C15H12N3O) have been synthesized and characterized. The interactions between the complexes and DNA have been investigates by means of fluorescence spectra, viscosity and agarose gel electrophoresis. The inhibition ratios of complex (1) and HL against human breast cancer cells (MCF-7) and human colorectal cancer cells (COLO205) were tested in vitro.Figure optionsDownload full-size imageDownload as PowerPoint slide