THERMODYNAMIC CHARACTERISTICS OF PROTOLYTIC EQUILIBRIA INVOLVING TYROSYL-PROLINE

The enthalpies of interaction of Tyr-Pro hydrochloride solution with HCl at 298.15 K and ionic strength values of 0.25 M, 0.5 M and 0.75 M (background electrolyte KCl) were measured by calorimetric method. The step dissociation constants of Tyr-Pro were determined by the potentiometric method at a temperature of 298.15 K and a solution ionic strength value of 0.2 M (background electrolyte KCl). The following values of pK = 2.87 ± 0.05, pK = 7.51 ± 0.05 and pK = 9.79 ± 0.05 were obtained. The enthalpies of stepwise dissociation of the dipeptide were calculated using the universal HEAT program. Standard thermodynamic characteristics (ΔH, ΔG, ΔS) of acid-base interaction reactions in aqueous solutions of Tyr-Pro were calculated. The influence of the background electrolyte concentration on the enthalpies of peptide dissociation is considered.