What is a zwitterion?

A zwitterion is a specific type of ion that possesses both positive and negative electrical charges. Zwitterions are mostly electrically neutral. This is because the two functional groups cancel out each other’s charges, resulting in a zero charge. Amino acids are the most well-known example of zwitterions. Besides amino acids, any compound that contains both base and acid centers is able to acquire a zwitterion form. 

Every zwitterion has an isoelectric point, which is indicated as pI. This is the point at which a zwitterion has a neutral charge. When placed in a sufficiently alkaline solution, the neutrally-charged zwitterion will acquire a negative charge and become an anion. When placed in a sufficiently acidic solution, the zwitterion will acquire a positive charge and become a cation. 

One of the more common applications of zwitterions is in SDS PAGE, a form of electrophoresis that is used to separate protein molecules by molecular mass.