Thermochemical investigation of acid-base interactions in peptide solutions

Heat effects of interaction of D,L-alpha-alanyl-D,L-alpha-alanine, glycil-gamma-aminobutyric acid, glycil-L-asparagine and D,L-alpha-alanyl-D,L-asparagine with KOH, LiOH and HNO3 solutions were measured by the direct calorimetry method at 288.15, 298.15, 308.15, 318.15 K and at several values of the ionic strength created by adding KNO3 and LiNO3. The standard dissociation enthalpies of the investigated ligands were obtained by the extrapolation to zero ionic strength. The standard thermodynamic characteristics (Delta G(0), Delta H-0, Delta S-0 , Delta C-p(0)) of the processes of acid-base interaction in dipeptide solutions were calculated. Several peculiarities of acid-base interaction reactions in the solutions of biologically important ligands were found. The correlations between the thermodynamic characteristics of the protolytic equilibria in the dipeptide and aminoacids solutions and the structure of these compounds were determined.