Amino acids react with alkalis by losing a hydrogen ion from their positively charged amino group (-NH3+).
Understanding the Reaction
When an alkali, which contains hydroxide ions (OH-), is added to an amino acid solution, it causes a chemical reaction. The primary effect of this reaction is to alter the charge of the amino acid molecule.
The Role of Hydroxide Ions
Hydroxide ions, from the alkali, are basic and react with acidic protons. In an amino acid, the -NH3+ group is a source of a hydrogen ion (proton). The reaction involves the following process:
- Initial State: The amino acid exists with a positively charged amino group (-NH3+).
- Reaction with Alkali: When hydroxide ions (OH-) from the alkali are introduced, they accept a proton (H+) from the -NH3+ group.
- Resulting Change: This proton removal converts the positively charged -NH3+ group into a neutral -NH2 group. Consequently, the overall charge of the amino acid molecule becomes more negative. As noted in the reference, the amino acid now exists as a negative ion.
Here’s a simplified representation:
-NH3+ + OH- --> -NH2 + H2OEvidence of the Reaction
The negative charge of the amino acid after reacting with an alkali can be verified through electrophoresis. This is a technique where molecules are separated based on their electrical charge.
Practical Implications
The reaction of amino acids with alkalis has practical applications in the study and manipulation of proteins:
- Separation and Purification: Understanding the change in charge allows scientists to separate and purify specific amino acids and proteins using techniques like ion-exchange chromatography.
- Protein Structure Studies: By controlling the pH and thereby the charge state of amino acids, scientists can gain insights into protein structure and function.
Summary
| Feature | Description |
|---|---|
| Reactant | Alkali (contains hydroxide ions, OH-) |
| Amino Acid Group | -NH3+ (positively charged amino group) |
| Reaction | Removal of a proton (H+) from the -NH3+ group by OH- |
| Product | Neutral -NH2 group, increased negative charge of the amino acid, and water (H2O) |
| Evidence | Confirmed through electrophoresis, demonstrating the resulting negative charge of the amino acid. |
In essence, adding alkali to an amino acid causes it to lose a proton (H+) from its amino group, making the molecule more negatively charged.
