Molecular Structure and Precipitates of a Rodlike Polysaccharide in Aqueous Solution by SAXS Experiments

Cinerean is a microbial β-(1−3)(1−6)-d-glucan produced by the fungus Botrytis cinerea. The native cinerean molecule is a wormlike chain with a large persistence length. Fragments are formed by sonication that 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 concluded, 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 QM = 0.37 Å-1 for H2O as solvent. 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 experiments in the isotropic phase.