Synthesis, characterization, DNA binding and cytotoxicity studies of two novel Cu(II)-2-(2′-pyridyl) quinoxaline complexes

Abstract

Two novel copper (II) complexes, namely [Cu(2,2′-pq)(NO3)](NO3) (1) and [Cu(2,2′-pq)2(NO3)](NO3)·6H2O(2) where 2,2′-pq is 2-(2′-pyridyl quinoxaline) were synthesized and characterized by various spectral methods. Complex 2 characterized by single crystal X-ray diffraction showed a distorted trigonal bipyramidal geometry and crystallized together with an hexamer, (H2O)6 cluster, with R66(12) topology and chair conformation. The interaction of Calf Thymus DNA (CT-DNA) with 1 and 2 was investigated by UV–Visible absorption spectra, Viscosity, Cyclic Voltammetry, Fluorescence and Circular Dichroism (CD), indicating that both complexes can bind to DNA both by means of intercalation and groove binding. Their DNA interaction mode depends on their concentrations and the differences between their structures. Cleavage experiments were performed by agarose gel electrophoresis using pBR322 DNA both in dark and after illumination. Furthermore, the cytotoxicity of both complexes was evaluated against MCF-7 and healthy cells (HEK-293) by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assays; moreover their cell uptake against MCF-7 tumor cells and HEK-293 normal cells was revealed by using confocal laser scanning. Both complexes have the potential to act as effective anticancer drugs with 2 to present an IC50 smaller than that of cis-platin and also to be useful for optically probing tumor cells since it fluoresces at blue and green when is treated with MCF-7 cells.