Protonation Constants of Glycylisoleucine at Different Ionic Strengths and Various Ionic Media

The protonation of different species of glycylisoleucine were studied in the pH range of 1.5 - 10 at25 °C using potentiometric technique. Investigations were performed in sodium perchlorate andtetraethylammonium iodide as background electrolytes at I (0.1, 0.2, 0.3, 0.4, 0.5, and 0.6) moldm-3. The parameters based on the protonation constants were calculated, and their dependenceson ionic strength are described by a Debye-Huckel type equation. The dependence on ionicstrength of the protonation constants was also analyzed by the specific ion interaction theory (SIT)model. The constants at infinite dilution, obtained using this model, are logK°1 = 2.72 and logK°2= 8.24. The specific interaction coefficients are also reported.