The extent of branching (number of 1 6 glycosidic bonds) in amylopectin can be d

Question

The extent of branching (number of 16 glycosidic bonds) in amylopectin can be determined by

extensive methylation followed by identification of the hydrolysis products of the methylated

polysaccharide, as follows: A sample of amylopectin is exhaustively treated with a methylating agent

(methyl iodide) that replaces all the hydrogens of the sugar hydroxyls with methyl groups, converting –

OH to –OCH3, an ether functional group. All the glycosidic bonds in the methylated sample are then

hydrolyzed in aqueous acid, and the various methylated derivatives are quantitated.

What derivatives you would expect of the monosaccharides that were

A. from the non-reducing termini of the amylopectin molecules?

B. from the reducing termini of the amylopectin molecules?

Explanation / Answer

A).With the non reducing terminii of amylopectin molecules, there will be no free ends to form bond with methyl groups. So, it does give any derivatives with ethyl groups. B).But the reducing ends have anomeric carbon (C1) that is not involved in a glycosidic bond which will take the methyl group. These are responsible for the derivatives. They give -OCH3 derivatives. when glycosidic bonds were hydrolyzed in acqueous solution, then free ends are available.

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