Effect of pH on the reactivity of dipeptides and α-amino acids in the N-acylation

The reaction kinetics of Gly, L-α-Ala, Gly-Gly, L-α-Ala-L-α-Ala and β-Ala-β-Ala with picryl benzoate in water (40 wt %)-2-propanol was investigated. At pH = 4–8 the rate constants of N-acylation of the anionic form of dipeptides are less than those of the corresponding amino acid anions, in agreement with their basicity, whereas the relative effective rate constants of reactions depend on pH: in acidic, neutral and slightly alkaline media the kef values are higher for the dipeptides, and in a strongly alkaline medium, for the amino acids. These differences are due to the changes in the concentrations of reactive forms of amino acids and dipeptides in the system at varying the medium pH.