Solid-liquid phase equilibrium of praziquantel in eleven pure solvents: Determination, model correlation, solvent effect, molecular simulation and thermodynamic analysis

Abstract

The equilibrium solubility and thermodynamic properties of praziquantel (PZQ) in eleven organic mono-solvents were reported. Solubility determinations were performed through the laser monitoring method at T = (278.15–323.15) K and p = 101.3 kPa. It is found that the mole fraction solubility of PZQ increases apparently with the augmented experimental temperature. The solubility of PZQ in mono-solvents exhibits the following order from maximum to minimal at 298.15 K: DMA (0.04891) > DMF (0.04191) > 2-butoxyethanol (0.03351) > 2-propoxyethanol (0.03137) > 2-ethoxyethanol (0.02931) > n-butanol (0.02008) > n-propanol (0.01834) > ethanol (0.01735) > n-propyl acetate (0.01446) > n-butyl acetate (0.01183) > ethanediol (0.002505). The highest value in PZQ solubility profile is related to DMA at 323.15 K (x1 = 0.1026) and the lowest one is obtained for ethanediol (9.430e-4, T = 278.15 K). The results of using the KAT-LSER model to study the solvent effect of PZQ solubility show that the solute-solvent interactions are principally attributed to the hydrogen bonding basicity and solvent’s self-cohesiveness. Then, the analysis of solute-solvent interaction using MD simulation shows that the interaction between solute and solvent molecules has a great influence on the solubility of PZQ in selected solvents. In addition, all recorded solubility of PZQ was regressed by λh model, modified Apleblat model, Two-Suffix Margules model, NRTL model and UNIQUAC model. By calculating the deviation between the experimental data and the regression data, it shows that the modified Apelblat model and λh model can provide more accurate correlation results for the solubility of PZQ in all the solvents studied. Furthermore, apparent thermodynamic properties of PZQ in all mono-solvents studied were calculated and investigated according to Van’t Hoff equation, and it turns out that the dissolution process is an endothermic, non-spontaneous process driven by entropy.