Conformational behavior of a gel-forming (1→3)-β- D-glucan in alkaline solution

Abstract

Conformational behavior of a gel-forming (1→3)-β- D-glucan in sodium hydroxide solution was studied by optical rotatory dispersion, viscosity, and flow birefringence measurements, the alkali concentration being changed from 5m M up to 4.8 M. In the wavelength range studied (230–500nm), optical rotatory dispersion curves were anomalous, except the curve obtained with 4.8 M sodium hydroxide. At longer wavelengths and low alkali concentration, the sign of rotation angle was positive, and at shorter wavelengths, it decreased sharply resulting in a broad maximum near 265nm. The angle of rotation at a given wavelength fell sharply with alkali concentration in the range of 0.19–0.24 M. These changes were reversible when the sodium hydroxide concentration was varied. Intrinsic viscosity and flow birefringence also showed large changes corresponding to the rotation angle change. These observations suggest that, in solutions of low sodium hydroxide concentration, the (1→3)-β- D-glucan takes an ordered conformation, whereas it practically behaves as a random coil at high concentration, a conformational transition occurring in the region between 0.19 and 0.24 M. When sodium hydroxide was replaced with lithium hydroxide, a similar dependence of the optical rotation and the viscosity on the alkali concentration was observed.