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The peptides and amino acids experiment relied on TLC and other qualitative tests. Why were IR...

The peptides and amino acids experiment relied on TLC and other qualitative tests. Why were IR or NMR spectroscopy not an option for analysis?..

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Expert Solution

Explanation:

Amino acids are the basic structural form of all proteins. Amino acids are linked by peptide bond (-CONH-) to form the proteins. Amino acids have an amino group at one end and a carboxylic acid group at another end. There are 20 naturally occurring amino acids of which some are essential and non-essential.

Qualitative tests below detect helps in easy identification of amino acids and peptides. Some examples are ninhydrin test identifies whether a compound is peptide or amino acid based on the presence of ammonia or amine group. Millon's test is used for identification of phenolic amino acid tyrosine. Similarly, Isatin test identifies imino group of amino acids such as proline and hydroxyproline.

The color tests are qualitative tests that can easily identify compounds within a short span or time. Since all amino acids do not have the same reactive group the color tests are easier as specific tests produce positive results for specific compounds. The yield of colors varies in intensity and type of color according to the nature of groups present in the particular amino acids.

Thin layer chromatography (TLC) separation and identification of compounds based on the solubility in water or organic solvents and also size of compounds and detects qualitatively as well as quantitatively. It is simple and rapid test and can separate 15–20 amino acids at the same time within 3–4 hr.

Infrared spectroscopy and nuclear magnetic resonance (NMR) spectroscopy identifies amino acids, peptides and their derivatives. The advantage is it detects amino acids in the intact protein with minimal sample but the sample must be pure for detection. Chemical methods used in these methods may undergo partial hydrolysis or partial decomposition of some amino acids to identify structures. Both are time consuming process that the preprocessing of protein or peptide sample is essential.


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