Determination of the Optical Rotation of beta-Fructofuranose by Means of Kinetic Measurements.

Abstract

The furanose form of fructose which is found in sucrose has been investigated. By means of highly active [beta]-fructofuranosidase sucrose has been hydrolyzed to 99[degree]% in 3 minutes. The reaction has been followed by polarimetric measurements directly on the reacting solution. After complete hydrolysis of the sucrose the optical rotation still changes owing to the sum of the further transformations of a-glucopyranose and of [beta]-fructofuranose. From the sum of the 2 exponentials the one representing the transformation of [beta]-fructofuranose is evaluated by subtracting the one with the small rate constant due to the glucose. It is shown that the rate constant obtained in this way is identical with that obtained by dissolving crystalline fructopyranose in the same enzyme-buffer solution and measuring the change in optical rotation. The optical rotation of the [beta]-fructofuranose has been found by extrapolating the equation to the time when the concentration of [beta]-fructofuranose is identical with the initial sucrose concentration. The value of [[alpha]] 25544 is found to be 1. 7[degree]. The composition of the equilibrium mixture of furanose and pyranose at 25[degree]C based on the optical rotation of the pyranose and the furanose form and the optical rotation of the equilibrium mixture is 31. 56[degree]% furanose and 68. 44% pyranose.