THE TETRASACCHARIDE NYSTOSE TRIHYDRATE - CRYSTAL-STRUCTURE ANALYSIS AND HYDROGEN-BONDING

The crystal structure of nystose trihydrate, O-beta-D-fructofuranosyl- (2 --> 1)-O-beta-D-fructofuranosyl-(2 --> 1)-beta-D-fructofuranosyl al pha-D-glucopyranoside trihydrate, C24H42O21-3H2O, has been determined using CuKalpha X-ray data at 121 K. The space group is P2(1)2(1)2(1), with 4 molecules in a unit cell Of dimensions a = 10.155(1), b = 13.50 6(1), and c = 23.278(2) angstrom. The structure was refined to R = 0.0 52 and R(w) = 0.048 for 2734 observed structure amplitudes. The alpha- D-glucopyranose unit of the molecule has the normal C-4(1), chair conf ormation and the three fructofuranose units have twist conformations l ying between E3 and 4T5. One of the three water molecules is distribut ed over two sites: W-3 with occupancy 0.80 and W-3' with occupancy 0.2 0. All the hydrogen atoms were located on the difference synthesis wit h the exception of those attached to the low-occupancy water site. All hydroxyls, two of the three linkage oxygen atoms, and the water molec ules are involved in a complex three-dimensional network which can be decomposed into a series of infinite chains intersecting at the water molecules to form homo- and hetero-dromic cycles.