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In 1897, an unfermentable product obtained by treatment of fructose with bases, in particular lead(II) hydroxide, was given the name glutose, a portmanteau of glucose and fructose, and was claimed to be a 3-ketohexose. [12] [13] However, subsequent studies showed that the substance was a mixture of various other compounds. [13] [14]
A open-chain form of glucose makes up less than 0.02% of the glucose molecules in an aqueous solution at equilibrium. [57] The rest is one of two cyclic hemiacetal forms. In its open-chain form, the glucose molecule has an open (as opposed to cyclic) unbranched backbone of six carbon atoms, where C-1 is part of an aldehyde group H(C=O)−.
Figure 1: Relationship between the acyclic and the cyclic isomers of fructose d - and l-isomers of fructose (open-chain form) Fructose is a 6-carbon polyhydroxyketone. [16] Crystalline fructose adopts a cyclic six-membered structure, called β-d-fructopyranose, owing to the stability of its hemiketal and internal hydrogen-bonding.
For many monosaccharides (including glucose), the cyclic forms predominate, in the solid state and in solutions, and therefore the same name commonly is used for the open- and closed-chain isomers. Thus, for example, the term "glucose" may signify glucofuranose, glucopyranose, the open-chain form, or a mixture of the three.
For example, in living organisms, the open-chain isomer of glucose usually exists only transiently, in small amounts; D-glucose is the usual isomer; and L-glucose is rare. Straight-chain molecules are often not literally straight, in the sense that their bond angles are often not 180°, but the name reflects that they are schematically straight ...
The open-chain form has a carbonyl at the end of the chain. Four isomers are cyclic, two of them with a pyranose (six-membered) ring, two with a furanose (five-membered) ring. Galactofuranose occurs in bacteria, fungi and protozoa, [ 8 ] [ 9 ] and is recognized by a putative chordate immune lectin intelectin through its exocyclic 1,2-diol.
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Its monosaccharides: glucose and fructose; Their ring types: glucose is a pyranose and fructose is a furanose; How they are linked together: the oxygen on carbon number 1 (C1) of α-D-glucose is linked to the C2 of D-fructose. The -oside suffix indicates that the anomeric carbon of both monosaccharides participates in the glycosidic bond.