Thermodynamics of the Interaction of a Homologous Series of Amino Acids with Sorbitol

Abstract

The apparent molar volumes V2,φ, apparent molar isentropic compressibilities KS,2,φ, and enthalpies of dilution of aqueous glycine, alanine, α-amino butyric acid, valine, and leucine have been determined in aqueous 1.0 and 2.0 mol·dm −3 sorbitol solutions at 298.15 K. These data have been used to calculate the infinite dilution standard partial molar volumes V 0 2,m, partial molar isentropic compressibilities K 0 S,2,m, and enthalpies of dilution � dilH 0 of the amino acids in aqueous sorbitol, along with the standard partial molar quanti- ties of transfer of the amino acids from water to aqueous sorbitol. The linear correlation of V 0 2,m for this homologous series of amino acids has been utilized to calculate the contribution to V 0 2 of the charged end groups (NH + 3 ,C OO − ) ,t he CH 2 group, and other alkyl chains of the amino acids. The results for the standard partial molar volumes of transfer, compressibilites and enthalpies of dilution from water to aqueous sorbitol solutions have been correlated and interpreted in terms of ion-polar, ion-hydrophobic, and hydrophobic-hydrophobic group interactions. A comparison of these thermodynamic properties of transfer suggest that an enhancement of the hydrophilic/polar group interactions is operating in ternary systems of amino acid, sorbitol, and water.