AAT Bioquest

Are amino acids zwitterionic?

Posted November 8, 2022


Yes, amino acids are zwitterionic. 

The term zwitterionic refers to the property of carrying both a positive and a negative charge. Amino acids have a positively charged amino group (NH3+) and a negatively charged carboxylic group (COO-). This allows them to act as both an acid and a base at different pH values. When an amino acid is put in an acidic solution, the carboxylic group captures a positively charged hydrogen ion (H+) and the amino acid acquires a positive charge. When the same amino acid is put in an alkaline solution, it loses an H+ ion, acquiring a negative charge. In both instances, the amino acid acts to maintain the pH of the system. Amino acids are the most well-known zwitterions. 

Additional resources

Weak Acid pH Calculator

Dye to Peptide Conjugation

EDANS acid [5-((2-Aminoethyl)amino)naphthalene-1-sulfonic acid]

Zwitterionic versus canonical amino acids over the various defects in zeolites: A two-layer ONIOM calculation