Polysaccharide structures from powder diffraction data: molecular models of arabinan

X-ray intensity data from a polycrystalline sample of debranched arabinan, [-> 5)-alpha-L-Ara(f)-(1 ->](n), have been obtained using a powder diffractometer in order to determine its three-dimensional structure. The observed peaks index on a monoclinic cell with a = 5.444(7), b = 6.395(10), c = 8.680(5) angstrom, and gamma = 99.6(3)degrees, V = 298 angstrom(3). One 2-fold helix along the c-axis can be accommodated in the unit cell. Molecular and packing models have been analyzed using the seven C-2'-endo/C-3'-endo allomorphs originally proposed by Radha and Chandrasekaran [Carbohydr. Res. 1997, 298, 105]. The generated powder pattern matches closely with the observed diffraction only for one C-2'-endo model. In this structure, the three main chain conformation angles are in the trans domains, there are no intra-chain hydrogen bonds, and the packing arrangement is stabilized by inter-chain O-3-(HO)-O-...-2 bonds. (c) 2005 Elsevier Ltd. All rights reserved.