Thermodynamics Research Center / ThermoML | International Journal of Thermophysics

ABSTRACT

Density (n) and ultrasonic velocity (u) values of amino acids l-alanine, l-proline, l-valine, and l-leucine in 2M aqueous KCl and 2M aqueous KNO3 solutions have been measured as a function of amino acid concentration at different temperatures (298.15 K, 303.15 K, 308.15 K, 313.15 K, 318.15 K, and 323.15 K). Using the n and u data, partial molal volume (oo v ) and partial molal isentropic compressibility (oo k ) values have been computed. The increase in partial molal volume with temperature has been attributed to the volume expansion of hydrated zwitterions. The oo v and oo k values of l-alanine, l-proline, l-valine, and l-leucine in 2M aqueous KCl and KNO3 solutions have been found to be larger than the corresponding values in water. The larger partialmolal volumes of l-alanine, l-proline, l-valine, and l-leucine in 2Maqueous KCl and KNO3 solutions have been ascribed to the formation of zwitterion- K+/Cl./NO3. and K+/Cl./NO3. water dipole aggregates in solutions. The formation of these entities in solutions causes the release of water associated with zwitterions to the bulk water. The larger partial molal compressibilities of l-alanine-/ l-proline-/l-valine-/l-leucine 2M aqueous KCl/KNO3 solutions than the corresponding values in water have been attributed to the formation of zwitterion ion and ion water dipole incompressible entities in solutions.