Hydration of protonated aromatic amino acids: phenylalanine, tryptophan, and tyrosine

The hydration of the protonated aromatic amino acids phenylalanine, tryptophan, and tyrosine are analyzed by using a mass spectrometer equipped with a drift cell to examine the sequential addition of individual water molecules. The studies have shown that both the ammonium and carboxyl groups have offered good water binding sites for the first water molecule, whereas subsequent water molecules are bound less strongly.