Synthesis, characterization, DNA/protein-binding study and anticancer activity of novel tricarbonyl Re(i) complexes with an ONS donor azo-thioether pincer ligand

Two new rhenium(I) tricarbonyl complexes of general formula [Re(CO)3(L1/L2)] (1/2) were fabricated and thoroughly characterized by diverse spectroscopic techniques. The crystal structures of the complexes were confirmed by single crystal X-ray diffraction, which disclosed distorted octahedral geometry around the central metal. A theoretical calculations by DFT and TDDFT were carried out to support experimental observations. The DNA-binding ability of complexes with calf thymus DNA was investigated by UV-Vis absorption and fluorescence spectroscopy. Viscosity studies suggested an intercalative mode of binding of the complexes with CT-DNA. BSA protein-binding studies revealed quenching of tryptophan and tyrosine residues in the presence of complexes, and the quenching mechanism was shown to be static. Changes in the microenvironmental and structural properties of BSA were scrutinised by circular dichroism, synchronous and 3D fluorescence studies. The in vitro toxicity of the complexes against a human-breast epithelial adenocarcinoma cell line (MCF-7) and human-breast epithelial cell line (used as normal cell line; MCF-10A) was explored using the MTT assay.