Calculating pKa from the Titration Curve

When analysing these compounds’ behaviour during a titration, the pKa values are essential. Ionisation reactions can occur between the basic and acidic functional groups found in amino acids. The individual amino acid and the ionizable group (such as carboxyl or amino groups) involved determine the pKa values, which indicate the pH at which these groups are half-ionized.

1. Ionization of Functional Groups: It exists mostly in its protonated form (COOH) at pH values lower than the carboxyl group’s pKa. Deprotonation of the carboxyl group starts when the pH rises. It exists mostly in its deprotonated form at pH values higher than the amino group’s (NH₂) pKa. Amino groups begin to protonate when pH falls.
2. Zwitterion Formation: Zwitterion formation occurs at pH values around the isoelectric point (pI), which is the point at which an amino acid’s total charge is zero. The carboxyl group is deprotonated and the amino group is protonated in this condition.

Henderson-Hasselbalch equation

The pH of a solution containing a weak acid and its conjugate base, or a weak base and its conjugate acid, may be determined using the Henderson-Hasselbalch equation.

The Henderson-Hasselbalch equation for a weak acid (HA) and its conjugate base (A⁻) is:

pH=pKa+log ⁡([A−]/[HA])

And for a weak base (B) and its conjugate acid (BH⁺):

pH=pKa+log⁡ ([BH⁺]/[B])

where:

• pH: The negative logarithm of the concentration of hydrogen ions in the solution.
• pKa: The weak acid’s acidity is measured by the negative logarithm of the acid dissociation constant.
• [A⁻] and [HA]: For the weak acid equation, the conjugate base and weak acid concentrations are denoted by [A⁻] and [HA], respectively.
• [BH⁺] and [B]: For the weak base equation, the conjugate acid and weak base concentrations are denoted by [BH⁺] and [B], respectively.

The Titration Curve of Amino Acid shows how the pH changes and how the amino acid looks after adding different pH values as a strong base (OH equivalents). Amino acids have different pKa values for each of their many ionizable groups, which include the amino and carboxyl groups. Titration curves offer valuable information about the pH range in which amino acids are most stable as well as their ability to function as a buffer.

In this article, we will learn about the definition of titration, its characteristics, the titration curve, how to calculate pKa from the titration curve, how the factors influenced titration curves, experimental technique and methodology, and the significance of the titration curve of amino acids.