Abstract
The Hirshfeld surface, molecular surface electrostatic potential together with molecular surface average local ionization energy, were employed in this work to analyze the electrostatic characteristics of acidity and basicity of doxofylline at a microscopic level. H···H and O···H contacts present predomination among all contact interactions and doxofylline molecule can behave as a hydrogen-bonding donor with powerful ability. The nitrogen of -N = group and oxygen of >C=O group of doxofylline molecule are primary sites of electrophilic attack. The mole-fraction solubility of doxofylline in four blends of isopropanol + water, ethanol + water, acetone + water and methanol + water covering the temperature from 278.15 to 323.15 K was acquired by the use of saturation shake-flask method under atmospheric pressure of 101.2 kPa. For each aqueous solution, the solubility data firstly presented a peak at isopropanol (ethanol, acetone or methanol) composition of 0.7 and then decreased with the increasing mass fraction of organic solvents at a fixed temperature. No existence of crystaltransition and solvation was recorded in all experiments as indicated by X-ray power diffraction patterns. Solubility data were mathematically correlated by Jouyban-Acree, modified Wilson model, Apelblat and modified van’t Hoff-Jouyban–Acree models. Investigation on preferential solvation of crystalline doxofylline was performed by the inverse Kirkwood–Buff integrals over temperatures from 293.15 to 313.15 K. The preferential solvation parameters of isopropanol, acetone or acetonitrile presented positive values in blends with middle isopropanol/acetone/acetonitrile composition regions, demonstrating the preferential solvation of doxofylline by isopropanol/acetone/acetonitrile. In addition, the extended Hildebrand solubility approach was employed to quantitatively describe the solubility behavior at 298.15 K in isopropanol/ethanol/acetone/methanol + water blends studied in this paper and in acetonitrile + water blends previously reported, attaining the average relative deviations of < 7.80 %.
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