At what range of pH is Val a zwitterion in its free amino ac

At what range of pH is Val a zwitterion in its free amino acid form? (b) At what pH will free Val have a net negative charge? (c) At what pH is Val non-ionized?

Solution

(a). The pKa of alpha carboxy group of valine is, 2.32 and the pKa of alpha amino group of valine is 9.62. So, in between the pH range of 2.32 to 9.62, valine exists in zwitter ionic form.

(b). At the pH above the isoelectric point, the carboxyl group of amino acid loses the hydrogen and becomes negatively charged. So, at a pH above 9.62, valine becomes negatively charged.

(c). At the pH below the isoelectric point, the amine group of amino acid gains the hydrogen and becomes positively charged. So, at pH below 2.32, valine becomes positively charged.