In basic solution (above pH 9.7), the predominant species
is negatively charged and migrates toward the anode:
R— C— C— 0~
(pi) of an amino acid is the pH
at which the molecule has an average net charge of
zero and therefore does not migrate in an electric field.
The pi is calculated by averaging the pK' values for the
two functional groups that react as the zwitterion becomes
alternately a monovalent cation or a monovalent anion.
amino acids, e.g., glycine and alanine, exist as zwitterions.
F IG U R E
Titration profile of histidine.