title: Molecular and crystal structure of the regenerated form of (1----3)-alpha-D-mannan.
abstract: The crystal structure of the hydrated form of (1----3)-alpha-D-mannan, obtained by solid-state deacetylation of the partially O-acetylated mannan, was analyzed by combined X-ray diffraction and stereochemical-model refinement techniques. The structure crystallizes in a four-chain, monoclinic unit cell with parameters a = 11.33 A, b = 18.36 A, c (fiber repeat) = 8.25 A, and gamma = 101.75 degrees, and the most probable space group is P2(1). In the most probable structure the chain-backbone conformation is a two-fold helix, but with all four O-6 rotational positions nonequivalent. The chains pack with antiparallel polarity and are connected by pairs of intermolecular hydrogen bonds that form an infinite, zig-zag sheet. There are 16 water molecules in the unit cell, generally embedded between the sheets in crystallographic positions, providing additional hydrogen bonding and establishing a three-dimensional hydrogen-bond network in the crystal structure. The reliability of the structure analysis is indicated by the X-ray residual R" = 0.281, based on 98 hkl reflection intensities.
authors.affiliation: Chemistry Department, State University of New York, College of Environmental Science and Forestry, Syracuse 13210.
authors.forename: T
authors.initials: T
authors.lastname: Yui
authors.forename: K
authors.initials: K
authors.lastname: Ogawa
authors.forename: A
authors.initials: A
authors.lastname: Sarko
mesh_terms: D000107:Acetylation; D002236:Carbohydrate Conformation; D006860:Hydrogen Bonding; D008351:Mannans / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D014867:Water / Q000737:chemistry; D014961:X-Ray Diffraction
chemical_list: D008351:Mannans; D014867:Water; C076454:(1-3)-alpha-mannan