CALORIMETRIC INVESTIGATIONS OF AQUEOUS AMINO-ACID AND DIPEPTIDE SYSTEMS FROM 288.15 TO 328.15 K

Densities and heat capacities have been measured for aqueous solutions of L-asparagine, L-glutamine, glycylglycine, glycyl-L-valine, glycyl- L-asparagine, and glycyl-DL-leucine at 288.15, 298.15, 313.15, and 328 .15 K. These data have been used to calculate apparent molar volumes, V-2,V-phi and apparent molar heat capacities, C-p,C-2,C-phi which in t urn have been used to obtain standard state volumes, <(V)(0)over bar>( 2), and heat capacities, <(C)(0)over bar>(p,2). The semi-empirical mod elling procedures of Helgeson, Kirkham, and Flowers have been used to subdivide the calculated standard state volume and heat capacity data into solvation and nonsolvation contributions. The nonsolvation compon ents of the standard state properties are used in group additivity ana lyses. These analyses yield structural contributions to standard state volumes and heat capacities for the CH(NH2)CO2H, CH2, OH, COOH, CH, C ONH2, and CONH groups. The temperature dependences of these contributi ons are discussed. Some comments are reported concerning the practical ity of using the thermodynamic properties of aqueous amino acid and pe ptide systems as the basis for modelling standard state thermodynamic properties of aqueous protein systems.