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.

Outlines

00:00

🧪 Overview of the Xanthoproteic Test

The Xanthoproteic test is a qualitative biochemical test used to detect and differentiate aromatic amino acids containing phenolic or indolic groups, such as phenylalanine, tyrosine, and tryptophan, from non-aromatic amino acids. It is also used to identify proteins with these aromatic amino acid units. The test produces a yellow substance, xanthoprotic acid, which turns deep orange upon adding an alkaline solution. Aromatic amino acids undergo nitration when treated with concentrated nitric acid, yielding nitro derivatives called xanthoprotic acid. Phenylalanine gives a weak reaction due to the stability of its phenyl group, reacting only after extended heating. The video demonstrates both positive and negative reactions using samples of aromatic amino acids, non-aromatic amino acids, and proteins.

05:01

🔬 Xanthoproteic Test Procedure

This section describes the procedure for conducting the Xanthoproteic test. Seven labeled test tubes are filled with different samples, including aromatic amino acids (tyrosine, tryptophan, phenylalanine), non-aromatic amino acids (glutamine), proteins (egg albumin, casein), and distilled water (control). One ml of concentrated nitric acid is added to each tube, and the mixture is heated in a boiling water bath. Aromatic amino acids and proteins containing aromatic units turn yellow, indicating a positive result. Upon cooling and adding sodium hydroxide or ammonium hydroxide, the yellow color deepens to orange or brownish in the positive samples. Egg albumin and casein show this reaction, indicating the presence of aromatic amino acids in their structure.

🧬 Negative Reactions and Phenylalanine's Unique Behavior

This part highlights the lack of significant color changes in the control and non-aromatic amino acid samples, which confirms a negative Xanthoproteic reaction. Phenylalanine, despite being aromatic, shows a delayed and weak reaction due to its stable phenyl group. The yellowish color in phenylalanine's test tube only appears after prolonged heating and an increased concentration of nitric acid. This delayed positive result emphasizes the unique reactivity of phenylalanine compared to other aromatic amino acids. The experiment effectively demonstrates both the positive reaction of aromatic amino acids and the slower, weaker response of phenylalanine.

🎥 Conclusion and Additional Resources

The video concludes by summarizing the Xanthoproteic test's role in identifying aromatic amino acids and proteins with these amino acid units. The unique behavior of phenylalanine is revisited, and viewers are encouraged to explore more biochemical tests by clicking on end screen links or checking the video description for additional resources. This wrap-up encourages further learning on related biochemical topics.

Keywords

💡Xanthoprotic test

The xanthoprotic test is a qualitative biochemical test used to detect aromatic amino acids with phenolic or indolic groups, such as tyrosine, tryptophan, and phenylalanine. It helps differentiate these from non-aromatic amino acids and identifies proteins that contain aromatic amino acids. In the video, this test is used to observe color changes, which indicate the presence of these aromatic amino acids.

💡Aromatic amino acids

Aromatic amino acids are amino acids that contain an aromatic ring in their structure, such as phenylalanine, tyrosine, and tryptophan. These amino acids play a central role in the xanthoprotic test, as they react with nitric acid to form yellow compounds. The video demonstrates how these amino acids can be identified through this specific test.

💡Nitric acid

Nitric acid is a strong acid used in the xanthoprotic test to react with aromatic amino acids, causing nitration. This chemical reaction results in the formation of a yellow compound called xanthoprotic acid. In the video, nitric acid is added to test tubes containing different samples to observe color changes, which help detect the presence of aromatic amino acids.

💡Xanthoprotic acid

Xanthoprotic acid is a yellow substance formed when aromatic amino acids or proteins react with concentrated nitric acid. This acid undergoes further color change to orange or brown when an alkaline solution is added. The video illustrates how xanthoprotic acid formation confirms the presence of aromatic amino acids in the samples.

💡Alkaline solution

Alkaline solutions like sodium hydroxide or ammonium hydroxide are used in the xanthoprotic test to change the color of xanthoprotic acid from yellow to deep orange or brown. This step is crucial for confirming a positive result in the test, as seen in the video, where these solutions are added to detect aromatic amino acids and proteins.

💡Phenylalanine

Phenylalanine is an aromatic amino acid that shows a weak reaction in the xanthoprotic test. This amino acid is less reactive compared to other aromatic amino acids like tyrosine and tryptophan.

Highlights

Xanthoprotic test is used to detect and differentiate aromatic amino acids containing phenolic or indolic groups such as phenylalanine, tyrosine, and tryptophan.

The test detects proteins with aromatic amino acids in their structure.

The yellow substance formed during the test is called xanthoprotic acid.

Xanthoprotic acid is a non-crystallizable yellow substance derived from proteins and aromatic amino acids upon treatment with concentrated nitric acid.

The yellow nitrated product turns deep orange when a basic solution like ammonia or hydroxide is added.

The test is based on the principle that aromatic groups in amino acids or proteins are nitrated by heating with concentrated nitric acid to form yellow nitro derivatives.

Phenylalanine gives a weak positive reaction due to the stability of its phenyl group, reacting only after extended heating.

The test can differentiate between aromatic amino acids and non-aromatic amino acids based on color changes.

Positive reactions show a color change from yellow to orange, particularly with tyrosine, tryptophan, and proteins like egg albumin and casein.

Casein and egg albumin proteins show a faint yellow color, indicating the presence of aromatic amino acids.

Non-aromatic amino acids do not show significant color changes, indicating a negative xanthoprotic reaction.

Phenylalanine may show a faint yellow color after extended exposure to concentrated nitric acid and alkali.

The experiment demonstrates delayed but positive reactions in phenylalanine due to the stability of its phenyl group.

The experiment helps distinguish between aromatic and non-aromatic amino acids through visible color changes.

The yellow to orange color change in casein and egg albumin shows that these proteins contain aromatic amino acids.

Transcripts

xanthoprotic test is a qualitative

biochemical test to detect and

differentiate aromatic amino acids

containing phenolic or indolic groups

such as phenylalanine tyrosine and

tryptophan from other non-aromatic amino

acids

it is also used to detect the presence

of proteins containing such aromatic

amino acid units in their structure

the test is named xanthoprotege due to

the formation of a yellow substance

called xanthoprotic acid

during the test

xanthoprotic acid is a

non-crystallizable yellow substance

derived from proteins and aromatic amino

acids upon the treatment with

concentrated nitric acid this yellow

nitrated product then turns deep orange

with the addition of a basic or alkaline

solution such as ammonia or a hydroxide

the xanthoprotea test is a based on the

principle that aromatic groups in the

amino acids or proteins are nitrated by

heating with concentrated nitric acid to

yield yellow colored nitro derivatives

called xanthoprotic acid

upon the addition of an alkali however

the xanthoproteate acid turns orange due

to the formation of a salt of this nitro

compound

the aromatic amino acid phenylalanine

gives a weak positive reaction only

after an extended period of heating

because the phenyl group in

phenylalanine is quite stable and

doesn't react with nitric acid under

normal conditions

in this video we'll demonstrate positive

and negative xanthoprotein tests using

samples of aromatic amino acid

non-aromatic amino acid and a protein

with aromatic amino acid units to

perform this test we'll need the

following

test samples consisting of one percent

solutions each of tyrosine tryptophan

phenylalanine glutamine or any other

non-aromatic amino acid

egg albumin

casein or any other protein containing

aromatic amino acids and distilled water

is controlled sample

concentrated nitric acid 40 sodium

hydroxide or ammonium hydroxide solution

seven clean dry identical test tubes

nine graduated droppers or pipettes of

one or two ml capacities test tube stand

test tube holder

to begin the test take the seven

appropriately labeled test tubes in the

test tube stand using seven different

droppers or pipettes add one ml each of

the five test samples including the

distilled water the tube containing the

distilled water will serve as the

negative control for this experiment

now using a separate dropper or pipette

add one ml each of concentrated nitric

acid to all the seven tubes mix the

tubes well by gently swirling them

the tube containing the protein solution

such as egg albumin might develop a

white or cloudy precipitate due to the

denaturation of the protein by the acid

place the tubes in boiling water bath

for about 30 seconds to a minute observe

the change in color if any in the seven

tubes you'll notice that the tube

containing the aromatic amino acids

tyrosine tryptophan and the tube

containing the egg albumin and casein

immediately turns yellow after the

addition of the nitric acid and heating

in the water bath

remove the tubes and cool them under

running tap water or by immersing them

in ice cold water

now add 1 or 2 ml each of 40 sodium

hydroxide or ammonium hydroxide solution

to the tubes mix well and observe for

color change if any in the tubes

again the tubes containing the tyrosine

tryptophan

the egg albumin and casein will turn

yellow

to orange or brownish in color the tube

containing the casein solution also

shows a very faint yellowish color this

implies that egg albumin as well as

casein are two such proteins that

contain some amount of aromatic amino

acids in their structure

both colors are considered positive

xanthoprotic reaction

the rest of the tubes including the

control tube do not show any significant

color changes throughout the test

whether yellow or orange this is a

negative xanthoprotique reaction in the

case of the test tube containing

phenylalanine if the concentration of

the sample is increased and kept in the

water bath and allowed to react with the

nitric acid for a prolonged period of

time it might show a faint yellowish

color on addition of the alkali solution

this experiment using different test

samples clearly demonstrates the

positive

reaction shown by aromatic amino acids

and proteins containing aromatic amino

acid units it also demonstrates the

delayed but positive reaction shown by

phenylalanine which has a very stable

phenyl group as previously explained at

the start of this video

this is all about the xanthoprotein test

for aromatic amino acids make sure to

watch my other biochemical test videos

as well by clicking on the end screen

card shown on the screen right now or

the various links given in the

description below thanks for watching