Measurement and correlation of solubility and thermodynamic properties of N-acetyl-l-glutamine in some pure solvents and binary solvents at various temperatures

The solubility data of N-acetyl-l-glutamine in aqueous solution with different proportions of methanol and ethanol were determined with a static analytical method from 293.15 to 318.15 K. The data were then correlated by five models including the modified Apelblat equation, Van't Hoff equation, local composition model (NRTL model), CNIBS/Redlich-Kister model, and Jouyban-Acree model. The results show that Van't Hoff equation agrees well with the experimental data. When the ratio of methanol or ethanol in aqueous solution is in the range of 0.2-0.4, the solubility of N-acetyl-l-glutamine reaches its maximum. Besides, the melting temperature and fusion enthalpy of N-acetyl-l-glutamine were measured by the differential scanning calorimetry (DSC) and no polymorphism was found in the systems studied. The thermodynamic properties including enthalpy, entropy and Gibbs free energy during dissolution were calculated accordingly in this work.