Answer to Question #30331 in Inorganic Chemistry for Jen

Question #30331
What can use the Biruet , ninydrin and xanthoproteic test ?HELLPP? Which test choice above (can be 1,2 or all 3) yields a positive result for: 1)cysteine 2)cysteine-asparagine 3)cysteine-asparagine-asaparagine-cyst… 4)PHENYLALANINE (sorry caps) 5)phenylalanine-cysteine-asparagine
Expert's answer
Biuret test:It is an universal test for proteins..all proteins answer this test. Here there is a formation of colored coordination complex between the unshared electron pairs of peptide nitrogen ,cupric ions and the oxygen of water. The procedure involves 3 ml of protein + 3 drops pf 5% copper sulphate solution + 3 or 4 drops pf 1% copper sulphate solution you get a purple or pink colour as a positive test. This test is positive when there are 2 or more peptide linkages. Histidine is the only amino acid which answers this test.

Ninihydrin test:

When amino acids are heated with ninihydrin they are quantitatively deaminated and a bluish purple color appears due to formation of ruhemann's purple. Procedure involves addition of 1ml of protein solution with 2 drops of ninihydrin reagent and boil a bluish purple color is obtained proline and hydroxy proline give a yellow color.

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