Electrolyte and Acid-Base Properties

Amino acids are ampholytes, i.e., they contain both acidic and basic groups. Free amino acids can never occur as neutral nonionic molecules  

Instead, they exist as neutral zwitterions that contain both positively and negatively charged groups  

Zwitterions are electrically neutral and so do not migrate in an electric field. In acidic solution (below pH 2.0), the predominant species of an amino acid is positively charged and migrates toward the cathode  

The isoelectric point (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. 

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