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

Two novel copper(II) complexes with Schiff base of benzimidazole [Cu(L)Cl](2)center dot CH3OH have been synthesized. HL1 (N-(benzimidazol-2-ymethyl)-5-chlorosalicylideneimine, C15H11ClN3O) and HL2 (N-(benzimidazol-2-ymethyl)-salicylideneimine, C15H12N3O) are ligands of complex (I) 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 pi-pi 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 K-b/(L mol(-1)) were 1.81 x 10(4) (1), 1.37 x 10(4) (2), 6.27 x 10(3) (HL1) and 3.14 x 10(3) (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 mu mol L-1) and against COLO205 lines (IC50 = 16.5 +/- 3.4 mu mol L-1) is much stronger than that of HL1, which had the potential to develop anticancer drug. (C) 2013 Elsevier B.V. All rights reserved.