Atkins & de Paula:
Physical Chemistry for the Life Sciences
The fractional composition of the protonated and deprotonated forms of Lysine and Histidine in aqueous solution as a function of pH is given by
Note that conjugate pairs are present at equal concentrations when the pH is equal to the pKa of the acid member of the pair.
To graph the fractional composition enter the pKa's for Lysine or Histidine (see table) and hit Plot.
| pKa1 | pKa2 | pKa3 | |
|---|---|---|---|
| Lysine | 2.18 | 8.95 | 10.53 |
| Histidine | 1.77 | 6.10 | 9.18 |
The Clear button will remove all plots. To see the parameters
for each form hit the Legend on/off button. The Redraw button
will refresh the graph. This is useful when the function domain (i.e., pH ) has
been changed. To pick off a value on the graph, move your cursor
to the desired location then click and hold... the (pH, f(pH)) pair will appear.