Solubility of Four DL-Amino Acids at Nine Equidistant Temperatures in Aqueous Mixtures of Dipolar Aprotic N,N-Dimethylformamide and the Solution Thermodynamics

Abstract

The solubilities of the α-amino acids; DL-Tyrosine, DL-Leucine, DL-Isoleucine and DL-Threonine in six compositions of the binary mixture of pure water and dipolar aprotic N,N-dimethylformamide are evaluated by applying ‘analytical gravimetric’ method at nine equidistant temperatures in the range of 278.15 K to 318.15 K under 0.1 MPa pressure. Powder X-Ray diffraction and thermogravimetric analysis are performed to investigate solvate formation in saturated solutions. The equilibrium solubility values are compared with other literature and discussed. The variation of experimental solubility values in all compositions of such binary solvent mixtures at the experimental nine different temperatures are analysed in the light of chemical interactions involved. The standard molar dissolution Gibbs free energy, enthalpy and entropy are computed using the van’t Hoff analysis. The computed values of the same indicate that the process is endothermic. The standard molar Gibbs free energy as controlled by chemical, hydrophilic and hydrophobic interactions, imparts dissolution of the amino acids in the order, DL-Thr > DL-Ile > DL-Leu > DL-Tyr, as induced by the significant roles of side chains of such amino acids.