Products
Pure monosaccharides are available in specialty stores, such as pharmacies and drugstores. The best-known monosaccharides include glucose (grape sugar), fructose (fruit sugar) and galactose (mucilage sugar).
Structure and properties
Monosaccharides are the simplest carbohydrates (“sugars”), consisting of carbon (C), hydrogen (H), and oxygen (O) atoms. The organic compounds have the general formula Cn(H2O)n. There are exceptions, for example, deoxyribose. Derivatives such as the amino sugars may contain other chemical elements such as nitrogen (N). Depending on the number of carbon atoms, a distinction is made between trioses (3), tetroses (4), pentoses (5), hexoses (6), heptoses (7) and so on. The most important ones belong to the pentoses and hexoses. Depending on whether they are aldehydes or ketones, they are called aldoses or ketoses. Monosaccharides can be open or in the form of rings. Monosaccharides, with the exception of dihydroxyacetone, contain chiral carbon atoms. For example, glucose has four centers of chirality and 16 isomers exist. They can be easily distinguished using the Fischer projection. The designation D- (Dextro, right) and L- (Levo, left) refers to the configuration of the chiral C atom farthest from the carbonyl group (C=O). Thus, glucose, mannose and galactose are all isomers of each other. Condensation produces disaccharides (e.g., sucrose, lactose), trisaccharides (e.g., raffinose), oligosaccharides, and polysaccharides such as starch, xylan, and celluloses from the monosaccharides. Monosaccharides are usually highly soluble in water due to the hydroxyl groups and are usually present as crystalline powders.
Representative
Trioses:
- Glyceraldehyde
- (dihydroxyacetone)
Tetrosis:
- Erythrosis
- Erythrulosis
- Threose
Pentoses:
- Arabinose
- Deoxyribose
- Lyxose
- Ribose
- Ribulose
- Xylose (wood sugar)
- Xylulose
Hexoses:
- Fructose (fruit sugar)
- Fucose
- Galactose (mucilage sugar)
- Glucose (dextrose)
- Mannose
Examples: Aldose
The following figure shows examples of aldoses:
Effects
Some monosaccharides have a sweet taste. Many can be metabolized by the body and serve as energy sources. As carbohydrates, monosaccharides are among the most important biomolecules, and they are essential for life on Earth, for example, for obtaining and storing energy (e.g., glycogen, starch), for building living organisms (e.g., celluloses), for building nucleic acids, and for metabolism.
Areas of application
- As sweeteners and flavor correctors.
- As pharmaceutical excipients.
- As rapid energy suppliers, for the treatment of hypoglycemia (glucose).
- Prevention and treatment of cystitis (D-mannose).
- As food additives, in food products.
