MOLECULAR-STRUCTURE AND PRECIPITATES OF A RODLIKE POLYSACCHARIDE IN AQUEOUS-SOLUTION BY SAXS EXPERIMENTS

Cinerean is a microbial beta-(1-3)(1-6)-D-glucan produced by the fungu s Botrytis cinerea. The native cinerean molecule is a wormlike chain w ith a large persistence length. Fragments are formed by sonication tha t are nearly rigid rods. The mass per unit length of these rods (M/L = 2400 +/- 300 Da nm(-1)) and their diameter (D = 1.7 +/- 0.2 nm) were determined by small-angle X-ray scattering (SAXS). From these results, a triple-helical conformation for the cinerean molecules can be concl uded, which accounts for the rigidity of the rods. Fragmented cinerean in aqueous solution shows a phase diagram explained qualitatively by Flory's theory for rigid rods. SAXS experiments in the miscibility gap reveal a diffraction peak at Q(M) = 0.37 Angstrom(-1) for H2O as solv ent. For close packing of the rods this Debye-Scherrer ring leads to a diameter of 1.9 nm, which is consistent with the value from experimen ts in the isotropic phase.