Xanthoproteic Test Practical Experiment

Summary

The video explains the xanthoproteic test, a biochemical method used to detect aromatic amino acids like tyrosine, tryptophan, and phenylalanine in proteins. The test involves treating samples with concentrated nitric acid, which turns yellow upon reaction with aromatic groups. Adding a basic solution like sodium hydroxide or ammonia deepens the color to orange. Proteins like egg albumin and casein show positive reactions due to their aromatic amino acid content. Phenylalanine reacts weakly and only after extended heating. The video demonstrates the test procedure and highlights its results with various samples.

Takeaways

• 🧪 Xanthoprotic test is a qualitative biochemical test used to detect and differentiate aromatic amino acids such as phenylalanine, tyrosine, and tryptophan.
• 💛 The test is named after 'xanthoproteic acid,' a yellow substance formed when aromatic amino acids react with concentrated nitric acid.
• 🔬 Aromatic amino acids are nitrated by heating with concentrated nitric acid, producing yellow-colored nitro derivatives.
• ⚗️ The yellow xanthoproteic acid turns deep orange when a basic or alkaline solution like ammonia or sodium hydroxide is added.
• 🧫 The xanthoprotic test is used to detect proteins containing aromatic amino acid units.
• 🧪 Phenylalanine gives a weak positive reaction only after extended heating due to the stability of its phenyl group.
• 🔍 The experiment uses tyrosine, tryptophan, phenylalanine, glutamine (a non-aromatic amino acid), egg albumin, casein, and distilled water as samples.
• ⚗️ After heating with nitric acid, the aromatic amino acids and proteins (like egg albumin and casein) turn yellow, indicating a positive reaction.
• 🌡️ After adding alkali, the yellow color turns orange or brownish, confirming the presence of aromatic amino acids.
• 🧪 Non-aromatic amino acids and the control sample do not show any significant color changes, indicating a negative reaction.

Q & A

What is the purpose of the xanthoproteic test?

The xanthoproteic test is a qualitative biochemical test used to detect and differentiate aromatic amino acids, such as phenylalanine, tyrosine, and tryptophan, from non-aromatic amino acids. It also helps identify the presence of proteins containing these aromatic amino acid units.

Why is the test named 'xanthoproteic'?

The test is called 'xanthoproteic' because it leads to the formation of a yellow substance known as xanthoproteic acid, which results from the reaction of aromatic amino acids or proteins with concentrated nitric acid.

What principle does the xanthoproteic test rely on?

The xanthoproteic test is based on the principle that aromatic groups in amino acids or proteins are nitrated by heating with concentrated nitric acid, producing yellow nitro derivatives known as xanthoproteic acid.

What happens when an alkaline solution is added after nitration in the xanthoproteic test?

When an alkali, such as sodium hydroxide or ammonium hydroxide, is added, the xanthoproteic acid turns orange due to the formation of a salt of the nitrated compound.

Why does phenylalanine give a weak reaction in the xanthoproteic test?

Phenylalanine gives a weak positive reaction because the phenyl group is stable and doesn’t react easily with nitric acid under normal conditions. A faint yellow color may appear after extended heating.

What changes can be observed after adding concentrated nitric acid to aromatic amino acids?

After adding concentrated nitric acid and heating, the test tubes containing aromatic amino acids like tyrosine, tryptophan, and proteins with aromatic units such as egg albumin and casein will turn yellow.

What color change occurs after adding an alkaline solution in the xanthoproteic test?

After adding an alkaline solution, the yellow color from the nitrated aromatic amino acids turns orange or brownish, indicating a positive xanthoproteic reaction.

How can the presence of aromatic amino acids in proteins be confirmed using the xanthoproteic test?

Proteins such as egg albumin and casein, which contain aromatic amino acids, show a positive xanthoproteic reaction by turning yellow or orange after nitration and the addition of alkali, confirming the presence of aromatic amino acids.

Why is there no color change in the control tube with distilled water?

The control tube with distilled water does not contain any aromatic amino acids or proteins, so no color change occurs, indicating a negative xanthoproteic reaction.

What are the main reagents used in the xanthoproteic test?

The main reagents used in the xanthoproteic test are concentrated nitric acid, which nitrates the aromatic amino acids, and sodium hydroxide or ammonium hydroxide, which induces the color change by forming a salt of the nitro compound.