Thermodynamic Characteristics of Protolytic Equilibriums Involving Tyrosyl-Proline

The enthalpies of interaction of a solution of Tyr-Pro hydrochloride with HCl at a temperature of 298.15 K and ionic strength values of 0.25, 0.5, and 0.75 M (background electrolyte KCl) were measured using a calorimetric method. The stepwise dissociation constants of Tyr-Pro were determined using a potentiometric method at a temperature of 298.15 K and a solution ionic strength of 0.2 M (background electrolyte KCl). The following values were obtained pK1 = 2.87 ± 0.05, pK2 = 7.51 ± 0.05, and pK3 = 9.79 ± 0.05. The enthalpies of stepwise dissociation of the dipeptide were calculated using the universal program HEAT. Standard thermodynamic characteristics have been calculated (ΔrH°, ΔrG°, ΔrS°) acid-base reactions in aqueous solutions of Tyr-Pro. The influence of the background electrolyte concentration on the peptide dissociation enthalpy is considered.