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 form an aqueous solution when dissolved in water. One of the more known examples is sucrose, the other lactose.^[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(1→2)β
Lactulose	galactose	fructose	β(1→4)
Lactose (milk sugar)	galactose	glucose	β(1→4)
Maltose	glucose	glucose	α(1→4)
Trehalose	glucose	glucose	α(1→1)α
Cellobiose	glucose	glucose	β(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(1→2) [6]
Nigerose	two glucose monomers	α(1→3)
Isomaltose	two glucose monomers	α(1→6)
β,β-Trehalose	two glucose monomers	β(1→1)β
α,β-Trehalose	two glucose monomers	α(1→1)β[7]
Sophorose	two glucose monomers	β(1→2)
Laminaribiose	two glucose monomers	β(1→3)
Gentiobiose	two glucose monomers	β(1→6)
Turanose	a glucose monomer and a fructose monomer	α(1→3)
Maltulose	a glucose monomer and a fructose monomer	α(1→4)
Palatinose	a glucose monomer and a fructose monomer	α(1→6)
Gentiobiulose	a glucose monomer and a fructose monomer	β(1→6)
Mannobiose[disambiguation needed ]	two mannose monomers	either α(1→2), α(1→3), α(1→4), or α(1→6)
Melibiose	a galactose monomer and a glucose monomer	α(1→6)
Melibiulose	a galactose monomer and a fructose monomer	α(1→6)
Rutinose	a rhamnose monomer and a glucose monomer	α(1→6)
Rutinulose	a rhamnose monomer and a fructose monomer	β(1→6)
Xylobiose	two xylopyranose monomers	β(1→4)

See also

• Monosaccharide
• Trisaccharide
• Oligosaccharide
• Polysaccharides

References

1. ^ Biose on www.merriam-webster.com
2. ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version:  (2006–) "disaccharides".
3. ^ "Nomenclature of Carbohydrates (Recommendations 1996)2-Carb-36 Disaccharides.". http://www.chem.qmul.ac.uk/iupac/2carb/36.html. 
4. ^ "Disaccharides and Oligiosaccharides". http://faculty.virginia.edu/mcgarveylab/Carbsyn/Carblist/html/disacch.html. Retrieved 2008-01-29. 
5. ^ F.W.Parrish; W.B.Hahn,G.R.Mandels (July 1968). "Crypticity of Myrothecium verrucaria Spores to Maltose and Induction of Transport by Maltulose, a Common Maltose Contaminant". J. Bacteriol. (American Society for Microbiology) 96 (1): 227–233. PMC 252277. PMID 5690932. http://jb.asm.org/cgi/reprint/96/1/227.pdf. Retrieved 2008-11-21. 
6. ^ Matsuda, K.; Abe, Y; Fujioka, K (November 1957). "Kojibiose (2-O-alpha-D-Glucopyranosyl-D-Glucose): Isolation and Structure: Chemical Synthesis". Nature 180 (4593): 985–6. doi:10.1038/180985a0. PMID 13483573. 
7. ^ T. Taga; Y. Miwa, Z. Min (1997). "α,β-Trehalose Monohydrate". Acta Cryst. C53 (2): 234–236. doi:10.1107/S0108270196012693. http://scripts.iucr.org/cgi-bin/paper?S0108270196012693. 

External links

• MeSH Disaccharides