The isoelectric point ( pI , or sometimes abbreviated as IEP) is the pH at which a particular molecule or surface carries no net electrical charge .
The Isoelectric Point Plugin calculates the gross charge distribution of a molecule as a function of pH. The result appears in a separate window, containing the molecule with the pI and (if enabled) the pH:charge plot. Hovering the mouse over the points of the curve, the pH:charge value pairs appear.
Fig. 1 Isoelectric Point Plugin result window
The Isoelectric Point Options window offers the following options to set:
Decimal places: the number of decimal places used to display the results
Show charge distribution: enabling this option shows the calculated pH:charge plot on the result chart
pH step size: the step size for the prediction and display plot
Fig. 2 Isoelectric Point Options window