Spectroscopic and Molecular Docking Studies of Co(III) Carboxamide Complexes with HAS

The binding of small molecules to Human Serum Albumin (HSA) has been investigated for many yearsthrough different spectroscopic techniques to illustrate details of the protein structure and bindingmechanism. The carboxamide [–C(O)NH–] group, ubiquitous throughout nature in the primary structure ofproteins, is an important ligand construction unit for coordination chemists. Metal complexes of carboxamideligands have paid special attention in biological systems and DNA cleavage. We report here the synthesis,spectroscopic characterization and molecular docking studies of [Co(bpb)(Br)(H۲O)], (۱) and[Co(bpb)(N۳)(H۲O)], (۲) complexes where bpb۲-= N,N'-bis(pyridine-۲-carboxamido) benzenedianion. The interaction of ۱ and ۲ with HSA was investigated under physiological conditions, usingfluorescence and circular dichroism techniques. The interaction between the complexes and HSAresulted to fluorescence quenching with a blue shift at λmax of ۳۴۳ nm. The magnitude of the Kqvalue for both ۱ and ۲ complexes (~ ۱۰۱۱ M-۱s-۱) indicates the static mecnanism for the interaction type.Furthermore, molecular docking analysis by using Vina was done to obtain more information regarding thebinding sites between the HSA and complexes. The results demonstrated the presence of strong HSAcomplexinteractions with the binding affinities of -۹.۷ kcal/mol and -۹.۳ kcal/mol for ۱ and ۲, respectively.However, the H-bonding interactions between H atoms of the axially coordinated water molecule and theoxygen atoms of proline (Pro-۴۴۷B) and cysteine (Cys-۴۴۸B) residues, led to the changes in the secondarystructure of the protein.