Toward understanding the solid-liquid equilibrium behavior of dinotefuran by thermodynamic analysis and molecular dynamic simulation

Dinotefuran is a third-generation nicotinic insecticide with a wide insecticidal spectrum and low toxicity to humans and other mammals, which has a huge potential market. The insight into the solid–liquid equilibrium behavior of dinotefuran in various solvents could further guide the design, development, and refinement of the further crystallization process. However, the complexity and variability of the dissolution process make it very challenging to study. In this research, the solid–liquid equilibrium of dinotefuran in both mono-solvents and mixed solvents was systematically investigated through a combined approach of the experimentation and molecular dynamics simulation. Firstly, the solubility of dinotefuran in a range of solvents was ascertained using the laser dynamic monitoring method over spanning temperatures from 278.15 to 318.15 K. The results showed that the solubility of dinotefuran in mono-solvents increase with the temperature increasing, while the solubility in mixed solvents exhibited an initial increase followed by a decrease with the organic solvent molar fraction increasing. Then the experimental data were fitted using five thermodynamic models. The NRTL model has the lowest 10²ARD and 10⁴RMSD values, indicating the best correlation, validity and fit. The dissolution behavior of dinotefuran was explored by calculating the thermodynamic properties. The results indicated that dinotefuran dissolution was a spontaneous, disorder degree increase process, and dissolution an exothermic process except the isopropanol + water mixed solvents. Additionally, the influence of the physicochemical properties of the solvent on the dinotefuran dissolution process was investigated, with a particular focus on the critical role of solvent polarity. Hansen solubility and the preferred solvation parameters of dinotefuran in the solvents were also further calculated to analyze the dissolution process. For the studied mixed solvents, when the ratios of methanol, ethanol, isopropanol, and acetone reached 0.85, 0.75, 0.50, and 0.70, respectively, dinotefuran molecules turned to be preferentially solvated by the water molecules. Finally, molecular dynamics simulation was performed to reveal the mechanisms of dinotefuran dissolution, suggesting the greater solute–solvent interaction, the easier dissolution. The solid–liquid equilibrium data might provide a guidance for the development of environment-friendly and efficient formulation.