Glucose is a sugar that appears in different forms. Dextroglucose, or d-glucose, which appears in fruits and animal tissues represents one form while levoglucose, or l-glucose, is another. While these compounds contain the same number and type of atoms, the arrangement of those atoms makes for differences between the two forms of glucose.
Enantiomers refer to a pair of compounds or molecules that are mirror images of each other. Their molecular structure is identical; it is just reversed. D-glucose and l-glucose represent two such structures. Take a sheet of paper with the molecular structure of d-glucose written on it. Hold it up to a mirror. The reverse image in the mirror will be the structure of l-glucose. All sugars with d and l designations will be mirror images of each other.
Four carbon atoms comprise the central part of both d-glucose and l-glucose molecules. At the top of each carbon chain is a carbon atom with an oxygen and hydrogen atom attached. The bottom contains the sixth carbon atom as part of CH2OH attachment. All of these structures are identical for both forms of glucose. The mirror image, or reversal, comes from the atoms attached to the sides of the four carbon atoms. D-glucose has three OH attachments and one H on its right side while l-glucose has one H on the left side and three HO on its left. In the final analysis, the chemical structure of C6H12O6 is the same for both.
D or L
The designation d for dextro or l for levo depends upon the location of the OH on the last of the four carbon atoms. When the OH is on the right side, it is a dextro sugar like d-glucose. Place the OH on the left side and you have a levo sugar as in l-glucose.
L-glucose has been shown to be effective as a colon cleanser for patients preparing to have a colonoscopy. A trial using l-glucose was reported in the July 2003 issue of "Gastrointestinal Endoscopy" which found that 80 percent of the patients received excellent or good results. L-glucose was palatable and no adverse effects or abnormalities were reported.
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