HYDROGEN-BONDING IN THE CRYSTAL-STRUCTURE OF THE TETRASACCHARIDE STACHYOSE HYDRATE - A 1-1-COMPLEX OF 2 CONFORMERS

The crystal structure of stachyose hydrate, O-alpha-D-galactopyranosyl-(1 --> 6)-O-alpha-D-galactopyranosyl-(1 --> 6)-alpha-D-glucopyranosyl beta-D-fructofuranoside tetrahydrate, has been refined using X-ray data at 199 K. The crystal structure is a 1:1 complex of conformers which differ in the fructofuranosyl and glucopyranosyl residues. Each conformer has an associated hydrogen-bond structure which includes different sites for the water molecules. When superimposed in the crystal, this gives rise to two sites of 0.5 occupancy for one carbon and one oxygen atom of the fructofuranose component, and for three oxygen atoms of the glucopyranose component. The corresponding three carbon atoms of the glucopyranose component have anomalous thermal motion parameters. The four water molecules are distributed over nine sites, six with occupancy 0.5, two with occupancy 0.4, and one with occupancy 0.2. Four of the water sites are associated with one conformer, and four with the other. The hydrogen bonding includes infinite chains which are linked to form irregular ribbons, extending in the direction of the a axis. All hydroxyl, ring, and linkage oxygen atoms are involved in the hydrogen bonding, which includes two-centered, three-centered, and four-centered hydrogen bonds.