Comprehensive understanding on solubility and solvation performance of curcumin (form I) in aqueous co-solvent blends

The intermolecular interactions and overall charge distribution of curcumin were respectively investigated by using Hirshfeld surface analysis and molecular electrostatic potential surface. The mole fraction solubility magnitudes of curcumin (I) in aprotic co-solvent blends of DMSO + water, acetone + water and acetonitrile + water ranging from 278.15 to 318.15 (333.15) K under 101.1 kPa was obtained by means of shake-flask method. Under the same conditions, e.g. identical temperature and mass fraction of DMSO (acetone or acetonitrile), the equilibrium solubility of curcumin was greater in DMSO + water blends than in acetone/acetonitrile + water blends. The lowest solubility magnitude was found in neat water at 278.15 K; and the highest one, in acetone/acetonitrile at temperature of T  = 318.15 K (aqueous solutions of acetone or acetonitrile) or 333.15 K (aqueous solutions of DMSO). No crystal   transition and solvate formation occurred in experimental processes as documented through X-ray power diffraction analysis. The acquired data were correlated by means of the Jouyban-Acree model, Apelblat model and modified van’t Hoff-Jouyban–Acree model. The preferential solvation at 298.15 K was investigated by the approach of inverse Kirkwood–Buff integrals. The parameters of preferential solvation for DMSO, acetone or acetonitrile were positive in the above three blends with middle and DMSO/acetone/acetonitrile-rich composition ranges, which specified that preferential solvation of curcumin was made by co-solvent. The extended Hildebrand solubility approach was further employed to describe the mole fraction solubility at 298.15 K in DMSO/acetone/acetonitrile + water blends studied in the current work and in ethanol/ n -propanol/isopropanol/PG + water blends reported previous by us, obtaining average relative deviations < 5.21%.