Mutarotation(redirected from birotation)
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a gradual change in the optical activity of freshly prepared solutions of monosaccharides and some other optically active compounds. Mutarotation is a result of the inter-conversion of tautomeric forms of monosaccharides, leading to the establishment of a dynamic equilibrium between the forms. Thus, upon completion of mutarotation a solution of glucose has a specific rotation [α ]p20 of +52.5° and consists of 37 percent α-glucose with [α]p20 of +112° and 63 percent β-glucose with [a]p20 of +18.7°.
The rate of mutarotation depends on the temperature and nature of the solvent; it increases in the presence of acids and bases and particularly in the presence of bifunctional acid-base catalysts such as 2-oxypyridine. In living organisms, the mutarotation of monosaccharides and disaccharides is catalyzed by the enzyme aldose 1-epimerase.