SOME THERMODYNAMIC PROPERTIES OF AQUEOUS AMINO-ACID SYSTEMS AT 288.15-K, 298.15-K, 313.15-K AND 328.15-K - GROUP ADDITIVITY ANALYSES OF STANDARD-STATE VOLUMES AND HEAT-CAPACITIES

Densities and heat capacities have been measured for aqueous solutions of L-aspartic acid, L-glutamic acid and alpha-aminobutyric acid at 288.15, 298.15, 313.15 and 328.15 K. These data have been used to calculate apparent molar volumes, V(2,phi), and apparent molar heat capacities, C(p,2,phi), which in turn have been used to calculate standard-state volumes, V2-degreesBAR and standard-state heat capacities, C(p,2)degreesBAR. Helgeson, Kirkham and Flowers equations, for neutral organic species in water, have been used to model the calculated standard-state volumes and heat capacities of the amino acids as a function of temperature at constant pressure. These data, and data previously reported for amino acid systems, have been used as input for a group additivity type analysis. The merits of the additivity scheme are discussed, and attempts are made to interpret the predicted trends in the group contributions as a function of temperature.