What does zwitterion mean?
A zwitterion is an electrically neutral chemical species containing both positive and negative formal charges. Its charges balance, so it has no net charge overall, but the separation of those charges can strongly affect how it behaves and interacts with other molecules. The term is especially common in discussions of amino acids, peptides, and proteins, whose acidic and basic groups may acquire positive and negative charges while the complete molecule remains neutral. For example, an amino acid can exist as a zwitterion after accepting or losing a proton at different pH levels. Unlike a cation or anion, a zwitterion is not described simply as positively or negatively charged; its defining feature is the coexistence of both kinds of charge within one neutral entity. The word is more precise than “neutral molecule,” which can also refer to molecules whose charges are not formally separated. The related adjective zwitterionic is widely used in chemical and biological literature.
nounAn electrically neutral chemical species that carries both positive and negative formal charges, with its total positive and negative charges balancing.
- An electrically neutral molecule or molecular species bearing both positive and negative formal charges.
"An amino acid can exist as a zwitterion when its amino group is positively charged and its carboxyl group is negatively charged."
"The peptide shifted between zwitterionic and charged forms as the pH of the solution changed."
"Each zwitterion contains positively and negatively charged regions within the same molecular structure."
The regular plural of zwitterion; each zwitterion is a separate electrically neutral chemical species.
"The researchers compared the behavior of the two zwitterions under different pH conditions."
A zwitterion has two opposing electric personalities—and no net charge to show for it.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of zwitterion
The word was formed in nineteenth-century German scientific usage from Zwitter, meaning “hermaphrodite” or “hybrid,” and Ion, meaning a charged particle. It was adopted into English for use in chemistry and biology by the late nineteenth century. Its original sense referred to a form containing both male and female reproductive elements, while the chemical meaning developed from the idea of a molecule bearing both kinds of electrical charge.
Related word forms
How zwitterion is actually used
This is specialized terminology used chiefly in chemistry and biochemistry. The adjective form zwitterionic is more common in many technical descriptions.
Easily confused with zwitterion
An ion generally has a net electric charge, whereas a zwitterion is electrically neutral overall while containing separated positive and negative charges.