Principles of Biochemistry (2+1)

The optical rotation of a freshly prepared solution of glucose gradually decreases and finally becomes constant. This change in the rotation of sugar solutions upon standing is called “mutarotation”. It is a general property of reducing sugars.

When D-glucose is crystallized from water or dilute alcohol at room temperature, a form separates having an initial specific optical rotation of +112^o which changes to +52.5^o. If, it is crystallized from water at temperatures above 98^oC, a different form of glucose, having an initial specific rotation of +19^o which changes to +52.5^o, is obtained. The first of these isomers of glucose was called “α-D-glucose” and the second “β-D-glucose”. Glucose exists in different isomeric forms in solution which change into the same equilibrium mixture regardless of which form is dissolved.