Measurement, correlation, and thermodynamic properties for solubilities of bioactive compound (−)-epicatechin in different pure solvents at 298.15 K to 338.15 K

The solubility of a bioactive compound is an important phenomenon in chemical and food processing industries. Many pharmaceutical and food industries are focused on solubilization and formulation development of bioactive compounds. The solubility of the (−)-epicatechin in 75% ethanol, methanol, acetone, and water was investigated as a function of temperature (298.15 to 338.15 K) at 0.1 MPa atmospheric pressure and correlated with calculated solubility. The experimental solubility of (−)-epicatechin was also evaluated based on the thermodynamic principles of the modified Apelblat model. The experimental solubility of (−)-epicatechin in pure solvents increased with increasing temperature from 298.15 to 338.15 K. The highest (0.2 ± 0.1 × 10−2) and lowest (0.7 ± 0.2 × 10−4) solubilities of (−)-epicatechin were observed in pure water at 338.15 and 298.15 K, respectively. The experimental solubilities were correlated with isothermal models (Apelblat and ideal equations) at each studied temperature, and a modified Apelblat model was used to evaluate experimental solubility of (−)-epicatechin based on the thermodynamic principles. The results showed good root-mean-square deviations (RMSD) and average relative deviations (ARD) as 0.1 to 0.9 and − 0.6 to 0.02, respectively, for the Apelblat model. For the ideal equation, RMSD and ARD were obtained as 0.1 to 0.9 and − 0.01 to −0.3, respectively. Changes in enthalpies (∆H°) and entropies (∆S°) for (−)-epicatechin dissolution occurred in the ranges of −64 ± 4 to 201 ± 4 kJ mol−1 and -216 ± 14 to 595 ± 2 J mol−1 K−1, respectively. These thermodynamic analyses indicated that the process was endothermic, entropy-driven, and favorable at studied temperatures in pure solvents. The results suggested that the (−)-epicatechin could solubilize in the solvents, especially in 75% ethanol and acetone, and therefore useful to pharmaceutical industries for bioactive product formulation.