A reagent suitable for the determination of N-terminal residue of a peptide is

Options

A. p-toluene sulphonyl chloride
B. 2,4-dinitrophenyl hydrazine
C. carboxypeptidase
D. 2,4-dinitrofluorobenzene

Explanation

To determine the N-terminal residue of a peptide, we can use the following step-by-step solution:

### Step 1: Identify the Reagent
The reagent suitable for the determination of the N-terminal residue of a peptide is **2,4-dinitrofluorobenzene**. This reagent is also known as **Sanger's reagent**.

### Step 2: Mechanism of Action
When Sanger's reagent reacts with the N-terminal amino group of the peptide, it forms a stable derivative. The reaction involves the nucleophilic attack of the amino group on the electrophilic carbon of the dinitrofluorobenzene, leading to the formation of a yellow-colored compound.

### Step 3: Resulting Compound
The resulting compound from this reaction is a dinitrophenyl derivative of the amino acid at the N-terminal position. This compound can be identified due to its distinct yellow color, which allows for easy detection and analysis.

### Step 4: Comparison with Other Reagents
While Sanger's reagent is specific for the N-terminal residue, other reagents like carboxypeptidases cleave from the C-terminal end of peptides. Additionally, reagents like 2,4-dinitrophenyl hydrazine are used for detecting carbonyl compounds, and para-toluene sulfonyl chloride is used to convert weak leaving groups into stronger ones.

### Conclusion
In summary, the reagent suitable for determining the N-terminal residue of a peptide is **2,4-dinitrofluorobenzene (Sanger's reagent)**, which forms a yellow-colored derivative upon reaction with the N-terminal amino group.

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