Equilibrium solubility investigation and thermodynamic aspects of biologically active gimeracil (form P) dissolved in aqueous co-solvent mixtures of isopropanol, N,N-dimethylformamide, ethylene glycol and dimethylsulfoxide

Abstract

Solubilities of gimeracil (form P) in aqueous co-solvent mixtures of isopropanol, N,N-dimethylformamide (DMF), ethylene glycol (EG) and dimethylsulfoxide (DMSO) were investigated via the isothermal dissolution equilibrium method at (283.15–328.15) K under ambient pressure p = 101.2 kPa. Experimental solubility was increased with increasing temperature and mass fraction of each co-solvent. The largest solubility was found in neat co-solvents. The solids equilibrated with liquid phase were characterized by X-ray power diffraction, indicating no polymorphic transformation, solvate formation or crystal transition according to the spectral data. The Jouyban-Acree model was adopted to correlate the obtained solubility. The highest RAD and RMSD values were, respectively, 2.61 × 10−2 and 14.96 × 10−4. Quantitative values for the local mole fraction of DMF (EG, DMSO or isopropanol) and water around gimeracil (form P) were acquired by using the Inverse Kirkwood–Buff integrals method. The preferential solvation parameters for isopropanol were positive in the isopropanol mixtures in intermediate and isopropanol-rich compositions, which indicated that gimeracil (form P) was preferentially solvated by isopropanol. Gimeracil (form P) could act mainly as a Lewis acid interacting with proton-acceptor functional group of isopropanol. Within the same region, gimeracil (form P) was not preferentially solvated by DMF, EG and DMSO. Furthermore, the method of linear solvation energy relationships was performed with a suitable combination of solvent polarity descriptors to explain the nature of intermolecular interactions resulting in the solubility variation in the co-solvent mixtures.