English

Etymology

Noun

1. A molecule, such as an amino acid, that carries both a positive and a negative charge.

Synonyms

• inner salt

A zwitterion (first part pronounced "tsvitter", from German "Zwitter" — "hybrid," "hermaphrodite") is a chemical compound that is electrically neutral but carries formal positive and negative charges on different atoms. Zwitterions are polar and usually have a high solubility in water and a poor solubility in most organic solvents.

Ampholytes are molecules that contain both acidic and basic groups (and are therefore amphoteric) and will exist mostly as zwitterions in a certain range of pH. The pH at which the average charge is zero is known as the molecule's isoelectric point.

Applications

Ampholytes are used to establish a stable pH gradient for use in isoelectric focusing.

Typical examples of zwitterions are:

• Most amino acids at physiological pH are for the most part zwitterionic.
• Used as buffering agents in Good's buffers:
  • The amino-sulfonic acid based MES, MOPS, HEPES, PIPES or CAPS
  • The amino-carboxylic acid (amino acid) based glycine, its derivatives bicine and tricine, and alanine
• Used as detergents:
  • CHAPSO
• Natural products like the alkaloids psilocybin and lysergic acid.
• Betaines

Less common examples of zwitterions are:

• Quinonoid zwitterions.
• Drugs such as Fexofenadine (Allegra) and Cephaloridine.
• decaphenylferrocene [(η5-C5Ph5)2Fe] has been shown to have a zwitterionic linkage isomer [(η5-C5Ph5)Fe+(η6-C6H5C5Ph4−)].

References