Structural, electronic and antioxidant properties of curcuminato chelates with group IV oxo cations using density functional theory

Curcumin, the principal bioactive polyphenol of turmeric, forms stable chelate complexes with oxo-metal(IV) ions, yet the influence of metal identity and ligand configuration on the resulting structural, electronic, and antioxidant properties remains poorly understood. Here, density functional theory (DFT) calculations are employed to provide a comprehensive characterization of TiO 2+ , ZrO 2+ , and HfO 2+ −curcumin chelates with the A1, B1(m), B1(r), and C1 configurations at the M06-2X-GD3/6-31++G**//LANL2DZ level of theory in both gas and solution phases. The electronic structures were analyzed via NBO, ESP, and RDG. The binding energies of the A1, B1(m), B1(r), and C1 configurations are -647.02, -644.38, -645.61 and -641.37 kcal mol-1 for TiO 2+ complexes, -619.03, -616.94, -617.89 and -613.32 kcal mol-1 for ZrO 2⁺ complexes and -650.08, -647.94, -648.74, and -644.61 kcal mol-1 for HfO 2⁺ complexes. The A1 configuration significantly affords the highest binding energy across all three metal oxo complexes, following the stability order HfO 2+ > TiO 2+ > ZrO 2+ . The findings demonstrate that while complexation marginally increases O–H bond dissociation energy, it significantly decreases O–H proton dissociation energy, thereby enhancing proton-coupled electron transfer (PCET) and superoxide scavenging efficiency. TD-DFT calculations confirm a hypsochromic shift in the UV–vis absorption spectra for ZrO 2 ⁺ complexes, aligning with experimental observations. This configuration-resolved study provides a comprehensive rational framework for the design of next-generation metal-curcumin therapeutics with tunable antioxidant profiles.