X-ray structure analysis of the sodium salt of beijeran

The three-dimensional structure of the sodium salt of beijeran has been determined by X-ray fiber diffraction analysis. The acidic polysaccharide forms an extended twofold helix. Two chains are nestled tightly in a monoclinic unit cell of dimensions a = 12.72, b = 11.41, c (fiber axis) = 24.62 Angstrom and gamma = 123.7degrees in an antiparallel fashion. In the crystalline lattice, helices are stacked tightly to form a thick sheet along the vertical plane passing through the short diagonal of the basal net. Adjacent sheets associate via a network of sodium ions and water molecules embedded between them. The morphology of sodium beijeran in the solid state is consistent with its observed theological properties. (C) 2002 Elsevier Science Ltd. All rights reserved.