Abstract:
Three deep eutectic solvents (DESs) were prepared by mixing caprylic acid (C8) with decanoic acid (C10), lauric acid (C12) and myristic acid (C14) at a molar ratio of
n(C8):
n(C10) = 2:1,
n(C8):
n(C12) = 5:1 and
n(C8):
n(C14) = 6:1, respectively. The melting points of the DES mixtures were lower than those of the individual fatty acid components and other prepared DES mixtures with different molar ratios. Using the absorbance-concentration standard curve, the solubility of curcumin in the C8-C10, C8-C12 and C8-C14 DES was determined to be 1.11, 1.24 and 1.44 mmol/L, respectively, which were 29, 32 and 38 times higher than those of curcumin in water. Gaussian simulation was used to calculate the Gibbs free energies of the molecular complexes formed by curcumin and the C8, C10, C12 and C14 fatty acid, and the values were determined to be −48.49, −64.27, −91.26、 −120.59 kJ/mol, respectively. According to the electrostatic density diagram drawn by Multiwfn and VMD, the association manner between curcumin and the fatty acids was obtained. Curcumin and C14 with the longest alkyl chain formed a "sandwich" typed complex, in which curcumin and C14 had strong hydrogen bonding and hydrophobic interactions. making curcumin show the highest solubility ability, the strongest UV-Vis absorption and fluorescence emission intensities in the C8-C14 DES. The stability and DPPH free radical scavenging ability of curcumin dissolved in DESs were found to be much better than in water.