Exploration of the Thermodynamic Parameters of Glycine, Alanine, and Their Dipeptides as a Function of Temperature (278.15–323.15 K)

This study investigates the thermodynamic behavior of amino acids (glycine, alanine) and peptides (glycylglycine, alanine-alanine) in aqueous solutions over a temperature range of 278.15–323.15 K. Densities and speeds of sound were measured for three concentrations (0.01, 0.05, and 0.1 mol/kg) at 1 K intervals. From the density and speed of sound data, key parameters, such as apparent molar volume and apparent molar adiabatic compressibility, have been derived. These parameters were analyzed to elucidate ion–ion and ion–solvent interactions within the solutions. Least squares fitting was employed to determine coefficients for density, speed of sound, thermal expansion, apparent molar volume, isentropic compressibility, and apparent molar isentropic compressibility. The thermal expansion coefficient (α), reflecting the temperature dependence of densities, was evaluated and analyzed alongside apparent molar expansibility (VE). Trends in α and VE highlight the significant influence of the solute’s structural formulas, with hydrophobic interactions playing a crucial role in altering the solvent structure around the solutes. These findings provide insight into the temperature-dependent thermodynamic properties of amino acids and peptides in aqueous environments.