Zwitterion
A zwitterion is a molecule that has at least two functional groups: one having a positive charge and the other having a negative charge, with an overall charge of zero. The name comes from the German word zwitter which means hybrid. So, the zwitterion is a hybrid of a positive (cation) and negative (anion) charge. Therefore, zwitterion can also be referred to as half-cation or half-anion.
Zwitterions can form from other molecules called ampholytes, or amphoteric compounds and can act as both an acid and a base.
Amino acids are the most common example of zwitterions. They have an amino group (NH3+) which is positive and a carboxyl group (COO-) which is negative. The R group represents the side chain of different amino acids.
Alanine, Tetracycline, bicine, solid sulfamic acid, phosphatidylcholine, and anthranilic acid are some other examples of zwitterions.
Structure of Zwitterions
Taking an example of Amino acids which act as the building blocks of proteins. Its structure contains an alkaline amino group (-NH2) an acidic carboxyl group (-COOH) and a side chain known as R-group all attached to a single carbon atom.
When an amino acid becomes a zwitterion, the amino group has a positive charge, and the carboxyl group has a negative charge which nullifying the net charge. Hence, amino acids is a zwitterion that is electrically neutral and has both acidic and basic group within its molecule.
Properties of Zwitterions
The important properties of Zwitterions are given below-
☛ Zwitterions have an isoelectric point that helps to calculate their pH value.
☛ Zwitterions consist of both positive and negative charges held together by covalent bonds.
☛ Zwitterions are highly soluble in water and interaction with water molecules is done by hydrogen bonding.
☛ Zwitterions generally have a greater melting point, however, it varies depending on their chemical structure.
☛ Quaternary ammonium cations are also present in Zwitterions.
