Synthesis, spectral characterization, protein binding and cytotoxic evaluation of new cobalt(II) and cobalt(III) complexes containing benzimidazolylterpyridine as ligand

Abstract

Two new six-coordinate cobalt(II) [Co(bitpy)2]Cl2 (1) and cobalt(III) [Co(bitpy)2](ClO4)3 (2) complexes containing benzimidazolylterpyridine (bitpy) ligand have been synthesized and characterized using spectroscopic and electrochemical techniques. The g ‖ and g ⊥ values in the EPR spectrum for 1 were 2.215 and 2.012, respectively, and clearly authenticated the formation of stable octahedral low spin Co(II) meridional isomer complex. Similarly, 1H NMR spectrum of 2 revealed low spin and its diamagnetic nature. The interaction of the complexes with bovine serum albumin (BSA) has been investigated and revealed that the cobalt complexes quenched the intrinsic fluorescence by following the static quenching mechanism. MTT assay was used to check the anticancer potential of 2 against human breast cancer cells (MCF-7) and human cervical cancer cells (HeLa). The IC50 values of 2 were lower than 7 µM in both the cancer cells and higher than 100 µM for non-cancerous cells (human embryonic kidney cells), indicating the specificity of the complex toward cancer cells. Furthermore, the morphological changes induced by 2 on the tested cell lines were monitored by AO-EB (acridine orange-ethidium bromide) and DAPI (4′,6-diamidino-2-phenylindole) staining methods.