Disaccharide

A disaccharide or biose^[1] is the carbohydrate formed when two monosaccharides undergo a condensation reaction which involves the elimination of a small molecule, such as water, from the functional groups only. Like monosaccharides, disaccharides also dissolve in water, taste sweet and are called sugars.^[2]

'Disaccharide' is one of the four chemical groupings of carbohydrates (monosaccharide, disaccharide, oligosaccharide, and polysaccharide).

Classification

There are two different types of disaccharides: reducing disaccharides, in which one monosaccharide, the reducing sugar, still has a free hemiacetal unit; and non-reducing disaccharides, in which the components bond through an acetal linkage between their anomeric centers and neither monosaccharide has a free hemiacetal unit. Cellobiose and maltose are examples of reducing disaccharides. Sucrose and trehalose are examples of non-reducing disaccharides. ^[3] ^[4]

Formation

Disaccharides are formed when two monosaccharides are joined together and a molecule of water is removed. For example; milk sugar (lactose) is made from glucose and galactose whereas the sugar from sugar cane and sugar beets (sucrose) is made from glucose and fructose.^{[citation needed]}

The two monosaccharides are bonded via a dehydration reaction (also called a condensation reaction or dehydration synthesis) that leads to the loss of a molecule of water and formation of a glycosidic bond.^{[citation needed]}

Properties

The glycosidic bond can be formed between any hydroxyl group on the component monosaccharide. So, even if both component sugars are the same (e.g., glucose), different bond combinations (regiochemistry) and stereochemistry (alpha- or beta-) result in disaccharides that are diastereoisomers with different chemical and physical properties.

Depending on the monosaccharide constituents, disaccharides are sometimes crystalline, sometimes water-soluble, and sometimes sweet-tasting and sticky-feeling.

Common disaccharides

Disaccharide	Unit 1	Unit 2	Bond
Sucrose (table sugar, cane sugar, beet sugar, or saccharose)	glucose	fructose	αあるふぁ(1→2)βべーた
Lactulose	galactose	fructose	βべーた(1→4)
Lactose (milk sugar)	galactose	glucose	βべーた(1→4)
Maltose	glucose	glucose	αあるふぁ(1→4)
Trehalose	glucose	glucose	αあるふぁ(1→1)αあるふぁ
Cellobiose	glucose	glucose	βべーた(1→4)

Maltose and cellobiose are hydrolysis products of the polysaccharides, starch and cellulose, respectively.

Less common disaccharides include^[5]:

Disaccharide	Units	Bond
Kojibiose	two glucose monomers	αあるふぁ(1→2) ^[6]
Nigerose	two glucose monomers	αあるふぁ(1→3)
Isomaltose	two glucose monomers	αあるふぁ(1→6)
βべーた,βべーた-Trehalose	two glucose monomers	βべーた(1→1)βべーた
αあるふぁ,βべーた-Trehalose	two glucose monomers	αあるふぁ(1→1)βべーた^[7]
Sophorose	two glucose monomers	βべーた(1→2)
Laminaribiose	two glucose monomers	βべーた(1→3)
Gentiobiose	two glucose monomers	βべーた(1→6)
Turanose	a glucose monomer and a fructose monomer	αあるふぁ(1→3)
Maltulose	a glucose monomer and a fructose monomer	αあるふぁ(1→4)
Palatinose	a glucose monomer and a fructose monomer	αあるふぁ(1→6)
Gentiobiulose	a glucose monomer and a fructose monomer	βべーた(1→6)
Mannobiose	two mannose monomers	either αあるふぁ(1→2), αあるふぁ(1→3), αあるふぁ(1→4), or αあるふぁ(1→6)
Melibiose	a galactose monomer and a glucose monomer	αあるふぁ(1→6)
Melibiulose	a galactose monomer and a fructose monomer	αあるふぁ(1→6)
Rutinose	a rhamnose monomer and a glucose monomer	αあるふぁ(1→6)
Rutinulose	a rhamnose monomer and a fructose monomer	βべーた(1→6)
Xylobiose	two xylopyranose monomers	βべーた(1→4)

References

^ Biose on www.merriam-webster.com
^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "disaccharides". doi:10.1351/goldbook.D01776
^ "Nomenclature of Carbohydrates (Recommendations 1996)2-Carb-36 Disaccharides". {{cite web}}: Missing or empty |url= (help); Text "url: http://www.chem.qmul.ac.uk/iupac/2carb/36.html" ignored (help)
^ "Disaccharides and Oligiosaccharides". Retrieved 2008-01-29.
^ F.W.Parrish (July 1968). "Crypticity of Myrothecium verrucaria Spores to Maltose and Induction of Transport by Maltulose, a Common Maltose Contaminant" (PDF). J. Bacteriol. 96 (1). American Society for Microbiology: 227–233. PMC 252277. PMID 5690932. Retrieved 2008-11-21. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
^ Matsuda, K.; Abe, Y; Fujioka, K (1957). "Kojibiose (2-O-alpha-D-Glucopyranosyl-D-Glucose): Isolation and Structure: Chemical Synthesis". Nature. 180 (4593): 985. doi:10.1038/180985a0. PMID 13483573. {{cite journal}}: Unknown parameter |month= ignored (help)
^ T. Taga (1997). "αあるふぁ,βべーた-Trehalose Monohydrate". Acta Cryst. C53: 234–236. doi:10.1107/S0108270196012693. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)

External links

Disaccharides at the U.S. National Library of Medicine Medical Subject Headings (MeSH)

[1] Biose on www.merriam-webster.com

[2] IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "disaccharides". doi:10.1351/goldbook.D01776

[3] "Nomenclature of Carbohydrates (Recommendations 1996)2-Carb-36 Disaccharides". {{cite web}}: Missing or empty |url= (help); Text "url: http://www.chem.qmul.ac.uk/iupac/2carb/36.html" ignored (help)

[4] "Disaccharides and Oligiosaccharides". Retrieved 2008-01-29.

[5] F.W.Parrish (July 1968). "Crypticity of Myrothecium verrucaria Spores to Maltose and Induction of Transport by Maltulose, a Common Maltose Contaminant" (PDF). J. Bacteriol. 96 (1). American Society for Microbiology: 227–233. PMC 252277. PMID 5690932. Retrieved 2008-11-21. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)

[6] Matsuda, K.; Abe, Y; Fujioka, K (1957). "Kojibiose (2-O-alpha-D-Glucopyranosyl-D-Glucose): Isolation and Structure: Chemical Synthesis". Nature. 180 (4593): 985. doi:10.1038/180985a0. PMID 13483573. {{cite journal}}: Unknown parameter |month= ignored (help)

[7] T. Taga (1997). "αあるふぁ,βべーた-Trehalose Monohydrate". Acta Cryst. C53: 234–236. doi:10.1107/S0108270196012693. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)

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