Introductory to Surcose

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Sucrose is a disaccharide formed from D-glucose and D-fructose.

The glycosidic linkage is between C1 of glucose and the C2 of fructose.

1H NMR of Sucrose:

Mass Spectrum of Sucrose:

13C NMR spectra of sucrose:

3. Why is it difficult to isolate sugars?

For simple sugars, they are small molecules and they behave similar properties that make them hard to separate. Besides, sugars are most electrically neutral. The separation of electrically neutral sugars is a relatively difficult and costly task, compared with such charged molecules as metallic ions.

Here is an example for isolating sucrose from Euphorbia lathyris L. (EL).

4. What is the best way to detect sugars?

To overcome the high detection limit of carbohydrates, most of the methods described in the literatures rely on some sort of derivatization technique since the introduction of a chromophoric moiety can substantially improve the sensitivity, and a suitable tagging of reducing saccharides usually results in enhanced resolution and less matrix disturbances. Chromatography is the method most used for commercial sugar separations. Such separations are batch processes and normally imply expensive installations, low productivity and low yields of the desired product. Gas chromatographic analysis of mono and disaccharides requires conversion of sugars into their volatile derivatives. Conversion of sugars into alditol acetates and trimethylsilyl (TMS) ethers have been the most widely used methods for GC analysis of sugars. "Alditol acetate" method involves reduction of sugars with sodium borohydride following conversion of polyols to polyacetate esters. TMS ethers of sugars can be prepared from a number of commercially available silylation reagents.

Both derivatization methods have disadvantages. Preparation of TMS ethers may result in as many as four derivatives for each sugar that is caused by anomer formation and ring isomerisation. On the other side, glucose, for instance, can...
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