Thermodynamics of the Stepped Dissociation of D,L-Alanil–D,L-Phenylalanine in Aqueous Solutions

Calorimetry is used to determine the heats of interaction between D,L-alanil–D,L-phenylalanine and solutions of nitric acid and potassium hydroxide at 298.15 K and ionic strengths of 0.5, 0.75, and 1.0 in solutions with KNO 3 . Standard thermodynamic characteristics (Δ r H °, Δ r G °, Δ r S °) are calculated for acid–base interaction in aqueous solutions of D,L-alanil–D,L-phenylalanine. The effect the concentration of background electrolyte has on the heats of dissociation of D,L-alanil–D,L-phenylalanine is considered. A comparative analysis is performed of the standard thermodynamic characteristics of the stepwise dissociation of L-phenylalanine and D,L-alanil–D,L-phenylalanine in light of modern ideas about the structure and physicochemical properties of these compounds and solutions of them.