Oligosaccharide specific rotation

The determination of sugars by polarimetry is carried out preferably with analytically pure derivatives in higher concentration. Mono-, di-, and smaller oligosaccharides are optically active as a result of the presence of their chiral centers and rotate the plane of the polarized light. The highly specific rotation of disaccharides is dependent not only on the wavelength of the light and temperature, but also to a small extent on the concentration as shown by two common examples of simple disaccharides such as maltose and sucrose. 

Fig. 26.—Specific optical rotations of linear and cyclic oligosaccharides, plotted against the reciprocal of the number of n-glucose units per molecule. Circles, linear compounds squares, Schardinger dextrins. Series for which Freudenberg s rule holds should fall on a straight line which extrapolates at infinite molecular size (1/n = 0) to the specific rotation of the high molecular-weight parent polysaccharide, in this case, starch.

Specific rotation constants, designated as [a] for sodium D-line light at 20-25°C, are listed in Table 4.8 for some important mono- and oligosaccharides. The specific rotation constant [a] at a selected wavelength and temperature is calculated from the angle of rotation, a, by the equation ... 

Table 4.8. Specific rotation of various mono- and oligosaccharides...

Linear chain polymers exist as a polysaccharide protein in the organism. Specific rotation [a]D = -15° (in concentrated hydrochloric acid). White powder. When completely hydrolyzed in acid, it obtains a D-glucosamine acetic acid. When in alkali, decomposes to chitosan and acetic acid. Disassociates by enzyme chitinase of snails and worms or lysozyme and creates an N-acetyl-D-glucosamine or its oligosaccharides. 

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