Physicochemical study of solute-solute and solute-solvent interactions of aqueous binary mixtures of l -alanine methyl ester hydrochloride and l -valine methyl ester hydrochloride at different temperatures: Volumetric and compressional studies

Amino acids are the building blocks of proteins and their study provides important information, which can be related to the behavior of larger biomolecules such as proteins. The present article reports experimental values of density (ρ) and speed of sound (u) of aqueous binary mixtures of biologically important amino acid derivatives, namely, l -alanine methyl ester hydrochloride and l -valine methyl ester hydrochloride at different temperatures i.e. T = (278.15, 288.15 and 298.15) K within the concentration range of (0–0.16) mol·kg−1. The obtained data of densities and speeds of sound of solutions were processed to obtain different derived parameters, such as apparent molar volume of solute (Vϕ), isentropic compressibility of solution (κs) and apparent molar isentropic compressibility of solute (κϕ). The limiting values of apparent molar volume of solute ( V ϕ 0 ) , apparent molar isentropic compressibility of solute ( κ ϕ 0 ) , apparent molar expansivity ( E ϕ 0 ) of solute, coefficient of thermal expansion ( α ∗ ) , hydration number ( n H ) and second derivative of limiting apparent molar volume ( ∂ 2 V ϕ 0 / ∂ T 2 ) have also been computed. The results have been interpreted in terms of various interactions occurring among solute and solvent molecules and structure making and structure breaking tendencies of the solute in these aqueous binary systems.