Some thermodynamic properties of aqueous amino acid systems at 288.15, 298.15, 313.15 and 328.15 K: group additivity analyses of standard-state volumes and heat capacities

Abstract

Densities and heat capacities have been measured for aqueous solutions of L-aspartic acid, L-glutamic acid and α-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, ϕ}, and apparent molar heat capacities, C_{p, 2, ϕ}, which in turn have been used to calculate standard-state volumes, V°₂, and standard-state heat capacities, C°_{p, 2}. 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.