Arginine Guanidinium Group pKa
Arginine is a basic amino acid characterized by its side chain, which contains a guanidinium group. This group is strongly basic due to resonance stabilization of its conjugate acid.
The pKa value quantifies the acidity of a group. For the guanidinium group of Arginine, the relevant pKa value is approximately 12.5.
This high pKa means that the guanidinium group is fully protonated (positively charged) under typical physiological conditions (pH around 7.4).
Key pKa values for Arginine:
- Alpha-carboxyl group: ~2.2
- Alpha-amino group: ~9.0
- Guanidinium group: ~12.5
Therefore, the pKa value of the guanidinium group of Arginine is 12.5.
Important Questions from Chemical Biology {p}K_a Henderson Hasselbalch
- The equilibrium dissociation constant of acetic acid is $1.74 \times 10^{-5}$ $M$. The $pK_a$ of acetic acid (rounded off to one decimal place) is ________.
- The ionic product of water at $40$ °C is $2.92 \times 10^{-14}$ $M^2$. The pH of water at $40$ °C is ________ (rounded off to 2 decimal places).
- In a lactic acid solution at pH $4.8$, the concentrations of lactic acid and lactate are $0.01$ M and $0.087$ M, respectively. The calculated pKa of lactic acid is ________ (Round off to one decimal place)
An aqueous solution of aspirin (HA) is prepared at pH 7.4. The ratio of concentration of $A^-$ and HA at equilibrium is ________ (round off to the nearest integer).
Given: $K_a$ of aspirin is $3.98 \times 10^{-4}$
- If 50 mL of 0.02 M HCl is added to 950 mL of $H_2O$, then the pH of the final solution will be _________
