Structure of molecular association of curdlan at dilute regime in alkaline aqueous systems

Abstract

Small-angle X-ray scattering (SAXS) and static light scattering (SLS) measurements were carried out to clarify the fine structure of a molecular association of curdlan at the dilute regime in various concentrations of NaOH aqueous solutions. The SAXS data shows that the molecular association at higher concentrations of NaOH seems to exist in a rod-like structure at 25°C and 60°C. The cross sectional radius of gyration, R gc, for the rod-like molecular association, which is determined from the cross sectional Guinier plot, was evaluated in higher concentrations of NaOH aqueous solutions. In contrast, the rod-like structure cannot be detected in lower concentrations of NaOH. The rod length of the rod-like molecular association can be calculated from the radius of gyration, and also evaluated from the dissymmetry method for shape-identified particles. These values, for higher concentrations of NaOH, calculated from both the above methods show a good coincidence, and the rod length is estimated as about 300 nm at 25°C and 60°C. The distance distribution function for curdlan in higher concentrations of NaOH aqueous solutions also showed a typical profile of the helical conformations at both the temperatures.