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Maltose

α-Maltose
β-Maltose
Names
IUPAC name (3R,4R,5S,6R)-6-(hydroxymethyl)-5-{[(2R,3R,4S,5S,6R)-3,4,5-trihydroxy-6-(hydroxymethyl)oxan-2-yl]oxy}oxane-2,3,4-triol
Other names 4-O-α-D-Glucopyranosyl-D-glucose
Identifiers
CAS Number	69-79-4 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:17306 Y
ChEMBL	ChEMBL1234209 N
ChemSpider	388329 α-maltose Y 6019 β-maltose Y
ECHA InfoCard	100.000.651
EC Number	200-716-5
PubChem CID	6255
UNII	66Y63L379N Y
InChI InChI=1S/C12H22O11/c13-1-3-5(15)6(16)9(19)12(22-3)23-10-4(2-14)21-11(20)8(18)7(10)17/h3-20H,1-2H2/t3-,4-,5-,6+,7-,8-,9-,10-,11?,12-/m1/s1 Y Key: GUBGYTABKSRVRQ-PICCSMPSSA-N Y InChI=1S/C12H22O11/c13-1-3-5(15)6(16)9(19)12(22-3)23-10-4(2-14)21-11(20)8(18)7(10)17/h3-20H,1-2H2/t3-,4-,5-,6+,7-,8-,9-,10-,11?,12-/m1/s1 Key: GUBGYTABKSRVRQ-PICCSMPSSA-N
SMILES O([C@H]1[C@H](O)[C@@H](O)C(O)O[C@@H]1CO)[C@H]2O[C@@H]([C@@H](O)[C@H](O)[C@H]2O)CO
Properties[1]
Chemical formula	C12H22O11
Molar mass	342.30 g·mol−1
Appearance	White powder or crystals
Density	1.54 g/cm3
Melting point	160 to 165 °C (320 to 329 °F; 433 to 438 K) (anhydrous) 102–103 °C (monohydrate)
Solubility in water	1.080 g/mL (20 °C)
Chiral rotation ([α]D)	+140.7° (H2O, c = 10)
Hazards
Safety data sheet	External MSDS
Related compounds
Related	Sucrose Lactose Trehalose Cellobiose
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

Amylase reaction consisting of hydrolyzing amylose, producing maltose

Maltose (/ˈmɔːltoʊs/^[2] or /ˈmɔːltoʊz/^[3]), also known as maltobiose or malt sugar, is a disaccharide formed from two units of glucose joined with an α(1→4) bond. In the isomer isomaltose, the two glucose molecules are joined with an α(1→6) bond. Maltose is the two-unit member of the amylose homologous series, the key structural motif of starch. When beta-amylase breaks down starch, it removes two glucose units at a time, producing maltose. An example of this reaction is found in germinating seeds, which is why it was named after malt.^[4] Unlike sucrose, it is a reducing sugar.^[5]

History

Maltose was 'discovered' by Augustin-Pierre Dubrunfaut, although this discovery was not widely accepted until it was confirmed in 1872 by Irish chemist and brewer Cornelius O'Sullivan.^[5][6] Its name comes from malt, combined with the suffix '-ose' which is used in names of sugars.^[4]

Maltose making and use in China goes as far back as the Shang dynasty. In Japan, the use of maltose has been recorded since the period of Emperor Jimmu.

Structure and nomenclature

Maltose is a disaccharide: the carbohydrates are generally divided into monosaccharides, oligosaccharides, and polysaccharides depending on the number of sugar subunits. Maltose, with two sugar units, is an oligosaccharide, specifically a disaccharide, because it consists of two glucose molecules. Glucose is a hexose: a monosaccharide containing six carbon atoms. The two glucose units are in the pyranose form and are joined by an O-glycosidic bond, with the first carbon (C₁) of the first glucose linked to the fourth carbon (C₄) of the second glucose, indicated as (1→4). The link is characterized as α because the glycosidic bond to the anomeric carbon (C₁) is in the opposite plane from the CH
₂OH substituent in the same ring (C₆ of the first glucose). If the glycosidic bond to the anomeric carbon (C₁) were in the same plane as the CH
₂OH substituent, it would be classified as a β(1→4) bond, and the resulting molecule would be cellobiose. The anomeric carbon (C₁) of the second glucose molecule, which is not involved in a glycosidic bond, could be either an α- or β-anomer depending on the bond direction of the attached hydroxyl group relative to the CH
₂OH substituent of the same ring, resulting in either α-maltose or β-maltose.

An isomer of maltose is isomaltose. This is similar to maltose but instead of a bond in the α(1→4) position, it is in the α(1→6) position, the same bond that is found at the branch points of glycogen and amylopectin.

Properties

Like glucose, maltose is a reducing sugar, because the ring of one of the two glucose units can open to present a free aldehyde group; the other one cannot because of the nature of the glycosidic bond. Maltose can be broken down to glucose by the maltase enzyme, which catalyses the hydrolysis of the glycosidic bond.

Maltose in aqueous solution exhibits mutarotation, because the α and β isomers that are formed by the different conformations of the anomeric carbon have different specific rotations, and in aqueous solutions, these two forms are in equilibrium.

It has a sweet taste, but is only about 30-60% as sweet as sugar, depending on the concentration.^[7] A 10% solution of maltose is 35% as sweet as sucrose.^[8]

Sources and absorption

Maltose syrup

Maltose is a component of malt, a substance which is obtained in the process of allowing grain to soften in water and germinate. It is also present in highly variable quantities in partially hydrolysed starch products like maltodextrin, corn syrup and acid-thinned starch.^[9]

In humans, maltose is broken down by various maltase enzymes, providing two glucose molecules which can be further processed: either broken down to provide energy, or stored as glycogen. The lack of the sucrase-isomaltase enzyme in humans causes sucrose intolerance, but because there are four different maltase enzymes, complete maltose intolerance is extremely rare.^[10]

References

External links

• 
  Media related to Maltose at Wikimedia Commons


• 
  Maltose, Elmhurst College Virtual Chembook.