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A zwitterion (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. Many molecules that contain both acidic and basic groups (and are therefore amphoteric) will exist as zwitterions at a certain pH. This pH is known as the molecule's isoelectric point. Such molecules make good buffer solutions — they resist change to the pH of a solution by selective ionisation. In the presence of acids, they will accept the hydrogen ions, removing them from the solution. In the presence of bases, they will donate hydrogen ions to the solution, again balancing the pH. Typical examples of zwitterions are: Less common examples of zwitterions are:
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