Zwitterion
From Wikipedia, the free encyclopedia
An amino acid, in its (1) nominal (unionized) and (2) usual, zwitterionic forms.
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.[1] 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.
[edit] 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:
- 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−)].

