Quantum chemistry elucidation of deep eutectic solvent-curcumin interactions: From extraction efficiency to molecular mechanisms.

The molecular mechanism of the deep eutectic solvent (DES)-mediated efficient extraction of curcumin (Cur) was investigated. Quantum chemical calculations were employed to elucidate the interaction within the hydrogen bond acceptor-hydrogen bond donor-Cur ternary system for the first time. The density functional theory computations, along with analyses of electrostatic potential, molecular polarity index, independent gradient model based on Hirshfeld partition, and atom-in-molecules theory, revealed that L-proline/Betaine (L-Pro/ACA) achieves optimal electrostatic complementarity and polarity alignment with Cur. The L-Pro/ACA (2:3)-Cur complex features a predominant H-bonding of N3⋯H42O. The interaction of this complex exhibited the highest electron density (0.0693 a.u.) at its bond critical point and the most negative bond energy (-24.0810 kcal/mol) among all the examined DESs, indicating superior H-bonding strength and enhanced complex stability. The incorporation of Cur perturbs the preexisting H-bonding network and redistributes the electron density of the original N⋯HO interaction region in the DES.