Spectroscopic and Physicochemical Analysis of Bioactive Cobalt(II) β-Diketo Ester Complexes: Insights into DNA and BSA Binding Mechanisms

The urgent need for effective therapies against cancer and antimicrobial-resistant pathogens motivates the development of novel metal-based complexes. Herein, we report the synthesis and characterization of four novel cobalt(II) complexes with biologically relevant β-diketo ester ligands. The complexes were characterized via UV-Vis, FTIR, mass spectrometry, and elemental analysis. Their biological activities were evaluated through antimicrobial and cytotoxic assays. Complex B1 exhibited the strongest antimicrobial activity, with minimum inhibitory concentrations (MICs) of 0.23 mg/mL against Staphylococcus aureus and Proteus mirabilis, and 0.01 mg/mL against Mucor mucedo, exceeding the performance of ketoconazole. Cytotoxicity studies on SW480 colorectal cancer cells and HaCaT normal keratinocytes identified B3 as the most potent anticancer agent (IC50 = 11.49 µM), selectively targeting tumor cells. Morphological analysis indicated apoptosis as the primary mode of cell death. Mechanistic studies were performed to elucidate interactions with biomolecules. UV-Vis and fluorescence spectroscopy, viscosity measurements, and molecular docking revealed that B3 binds strongly to calf thymus DNA via hydrophobic interactions and groove binding, and exhibits selective binding to bovine serum albumin (site II, subdomain IIIA). These results highlight the potential of cobalt(II) complexes as multifunctional agents with significant antimicrobial and antitumor activities and provide detailed insight into their molecular interactions with DNA and serum proteins.