Water-DMF-L-α-alanine and water-carbamide-L-α-alanine systems. Thermodynamic properties, solvation, and interspecies interactions at 273–333 K

Abstract

Thermal effects of dissolution of L-α-alanine in water-N,N-dimethylformamide mixtures (0–0.1 molar parts of DMF) at 283–318 K were measured calorimetrically. Standard enthalpies and heat capacities of dissolution of the amino acid and also thermal variations in entropies and free energies were calculated. The comparison with previously obtained data on the thermodynamics of dissolution of L-α-alamine in the carbamide water solution was performed. Temperature variations in the reduced Gibbs energy in the course of dissolution of L-α-alanine in water-DMF and water-carbamide mixtures have negative values originating from the prevalence of the entropy component. At the increase in temperature both mixtures become less structured. The interaction of L-α-alanine with hydrophilic and hydrophobic amides differs fundamentally: In the first case it is enthalpy-attractive and does not depend on temperature, while in the second case it is repulsive and decreases with the increase in temperature.