Optical rotatory dispersion of amylose films

Abstract

There is a direct correlation between the structure of amylose in the solid state, as determined by X-ray diffraction, and the conformation of amylose in solution. The specific rotations of amylose films showing a methyl sulfoxide complex (V Me 2SO ), amorphous, or alkali-amylose structure are the same as those of amylose in corresponding solutions of methyl sulfoxide, 0.5 m potassium chloride, or 0.1–0.5 m potassium hydroxide. The rotation of amylose films that give a B-type of X-ray pattern is higher than that of either amylose V or amorphous films; this higher rotation is attributed to the presence of intermolecular hydrogen-bonds between adjacent amylose chains in the B structure. It is also shown that rotatory dispersion data, alone, cannot be used to establish the conformation of amylose in solution, since the parameter λ c in the Drude equation is insensitive to changes in structure; that is, amylose V Me 2SO , V, and water-soaked B films all have a λ c of 150 nm. Consideration of X-ray, optical rotation, and published viscosity data leads to the conclusion that there is a continuous transition from a stiff, tightly coiled helix in methyl sulfoxide to a flexible coil in neutral, aqueous solution.