Solid-liquid equilibrium of abscisic acid in twelve pure solvents: Experiments, modeling, and molecular simulation

Abscisic acid (ABA) is one of the five natural growth regulators for plants and crystallization technology is used in the manufacturing of it. The thermodynamic behavior of it plays an important role in the development and design of crystallization processes. In this study, the solubility of ABA in twelve pure solvents was gravimetrically investigated over the temperature range of 278.15 K to 313.15 K. It was found that the solubility of ABA increased steadily with the rise of temperature. Four thermodynamic models (the modified Apelblat equation, van't Hoff equation, lambda h model and NRTL model) were applied to correlate the experimental solubility data, and the modified Apelblat equation model showed better fitting performance. The mixed thermodynamic properties of ABA in various pure solvents were also calculated, indicating that the mixed process is spontaneous and entropy-driven. Furthermore, to further explore the solid-liquid equilibrium behavior, Hirshfeld surface of ABA crystal was calculated and molecular dynamics simulations of different systems were performed. Based on equilibrium configurations of different systems, solute-solvent interaction energy was calculated, providing a reasonable explanation for the solubility of ABA. Meanwhile, the radial distribution function (RDF) plots were also employed to analyze the hydrogen bonding interactions between ABA molecules and solvent molecules.