Organic solvent effects on solid-liquid phase equilibrium of d-mannitol and aqueous binary solvents: An experimental and computational study

Solubility behavior of d-mannitol (d-man) in pure water and four water-organic solvents from 288.15 K to 318.15 K at atmospheric pressure was studied by both phase equilibria and molecular modelling methods. A dynamic method was employed to determine the data on equilibrium, both molecular dynamic (MD) simulations and density functional theory (DFT) calculations were carried out to uncover the relationship between intermolecular interactions and solubility behavior. The MD results illustrate that the strength in hydrogen bond of solute-organic solvent captures the solubility ranking of d-man in corresponding mixed solvents, and the radial distribution function (RDF) plots indicate that organic solvents have enhancement effect on the water aggregation in solution which weakened the strong interaction between d-man and water molecules. Both of them suggest that solubility behavior not only depends on solute-solvent interaction, the solvent-solvent interaction also plays a key role in determining it. The solubility was further fitted by the modified Apelblat model, λh model, NRTL model and finally, mixing properties (enthalpy, Gibbs energy and entropy) were discussed, indicating the dissolution process is governed by both enthalpy and entropy of solution.