Ultrasonic velocity and circular dichroism in aqueous gellan solutions

Abstract

Circular dichroism spectra and ultrasonic velocities of aqueous gellan solutions with and without added salts were measured at various temperatures. At higher temperatures the molecular ellipticity at 204 nm [ θ] 204 is almost independent of the temperature but decreases steeply at a given temperature ( T c) with further lowering temperature. With decreasing temperature, the difference in velocities between aqueous gellan solution and solvent ( ΔV) increases in the same manner as that of most aqueous systems, followed by a slight maximum or shoulder at T c, and then increases again. These abrupt changes in sound velocity and circular dichroism at T c may be caused by a thermally induced conformational change of gellan molecule in aqueous solutions. The decrease in the ultrasonic velocity was explained in terms of the dehydration of the water molecules. Effects of addition of some monovalent cations on the ultrasonic velocities were also studied.