Thermodynamics of the second proton dissociation processes of nine α-amino-acids and the third ionization processes of glutamic acid, aspartic acid and tyrosine

The thermodynamics of the second proton dissociation processes for nine α-amino-acids were evaluated using electrochemical and calorimetric data. A calorimetric acid strength scale in water is presented. The acidity order is explained as a function of the solvation of the zwitterions and anions. The differences between the thermodynamics of the first and second ionization processes of the compounds result from the fact that the two processes involve different solvation processes. The anions of the compounds containing a hydroxyl group are less solvated than the anions of the α-amino-acids having a hydrophobic group.