Interaction of a Biologically Active Zn²⁺ Complex with Human Serum Albumin: Experimental and Theoretical Insights

We report the synthesis and characterization of a novel Zn²⁺ complex derived from a coumarin-based azo dye ligand. The complex was confirmed by ¹H NMR and ESI-MS analyses and further examined for its biological activity. Antibacterial assays revealed significant inhibition against Escherichia coli (DH5 α ), while cytotoxicity tests on the human breast cancer cell line MDA-MB-468 indicated moderate dose-dependent effects. Protein-binding studies using UV–Vis, fluorescence, circular dichroism, and time-resolved fluorescence spectroscopy demonstrated that the complex interacts with human serum albumin (HSA) through a static quenching mechanism, accompanied by conformational changes and a reduction in esterase-like activity. Thermodynamic analysis indicated spontaneous binding driven primarily by hydrogen bonding and van der Waals interactions, which were consistent with molecular docking results showing preferential localization of the ligand at subdomain IB of HSA. Together, these findings highlight the dual biological activity and protein-binding capability of the Zn²⁺ complex, suggesting its promise as a scaffold for the design of new metal-based therapeutic agents.