Uncovering the solubility behavior of vitamin B6 hydrochloride in three aqueous binary solvents by thermodynamic analysis and molecular dynamic simulation

Solubility of vitamin B6 hydrochloride (VB6H) in three water-organic binary mixed solvents from 278.15 K to 313.15 K at atmospheric pressure was investigated by experiments and molecular simulations. The solvation free energy suggests that the solubility of VB6H increases with solute-solvent interaction strength increasing and there exists the strongest interaction energy at co-solvency composition in binary solvents. Radial distribution function (RDF) shows the tendency to aggregation of two solvent molecules as the molar fraction of organic solvent in mixtures increases, which suggests, to some extent, the interaction between solute and solvent molecules would be weaken and the solubility of VB6H decreases. It could be concluded that the solubility behavior of VB6H is a result from both solute-solvent and solvent-solvent interactions. Then the experimental data were correlated by the modified Apelblat model, the λh model, the CNIBS/R–K model and the NRTL model, respectively. And all of the models present a good consistency with the data. Furthermore, the calculations of mixing thermodynamic properties show that the mixing process of VB6H in the investigated solvents is exothermic and spontaneous. The experimental data can be used as basic data in the industrial production and scientific research of VB6H, a high value-added product. MD simulations and correlation models herein are helpful to understanding of solid-liquid equilibrium of compounds in binary solvent systems, then prediction of solubility which is the target of considerable researches.