Isoelectricity

Isoelectricity refers to the property of a molecule or substance to exhibit no net electrical charge. This state is particularly relevant for amphoteric molecules, which contain both acidic and basic functional groups. In aqueous solutions, these molecules can exist in various ionic forms depending on the pH of the surrounding environment.

The isoelectric point (pI) is the specific pH at which the number of positive charges on a molecule exactly equals the number of negative charges. At this pH, the molecule carries no net charge and therefore exhibits minimum solubility in water. This phenomenon is crucial in various fields, including biochemistry and analytical chemistry. For instance, in protein purification, understanding the isoelectric point of a protein allows for separation techniques like isoelectric focusing.

When the pH of a solution is below the isoelectric point, the molecule will be protonated, carrying a net positive charge. Conversely, when the pH is above the isoelectric point, the molecule will be deprotonated, carrying a net negative charge. The isoelectric point is an intrinsic property of a molecule and can be determined experimentally or calculated based on the pKa values of its ionizable groups. Isoelectricity is a fundamental concept for understanding the behavior of charged molecules in solution and their interactions with electric fields and other charged species.