Page tree

This manual gives you a walk-through on how to use the Isoelectric Point Plugin:



The isoelectric point (pI, or sometimes abbreviated to 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