zwitterionic

Zwitterionic describes molecules that contain both positive and negative charges at different sites while overall remaining electrically neutral. Zwitterions arise when a molecule contains an acidic group and a basic group that transfer a proton internally, forming an internal salt between the cationic and anionic centers.

In biology, amino acids at physiological pH are typically zwitterions. For example, glycine in water exists as NH3+–CH2–COO−, with no net charge but with separated positive and negative charges. This internal charge separation influences solubility, conformation, and reactivity, and underpins the behavior of amino acids and peptides in aqueous solutions.

Polyzwitterions, or zwitterionic polymers, carry both positive and negative groups along their chains. These materials tend to be highly hydrated and often resist non-specific protein adsorption, giving them distinctive antifouling properties. They are explored for coatings, hydrogels, drug delivery systems, and separation technologies because their charge distribution and water affinity can be tuned by composition.

The properties of zwitterions are sensitive to pH and solvent conditions. The balance between the internal charge separation and the surrounding environment affects solubility, dielectric behavior, and interactions with ions and biomolecules. Zwitterionic motifs thus provide a versatile platform across chemistry, biology, and materials science.

See also: zwitterion, amino acid, polyzwitterion.