title: The crystal structure of the alpha-cellobiose.2 NaI.2 H(2)O complex in the context of related structures and conformational analysis.
abstract: The crystal structure of beta-D-glucopyranosyl-(1-->4)-alpha-D-glucopyranose (alpha-cellobiose) in a complex with water and NaI was determined with Mo K(alpha) radiation at 150 K to R=0.027. The space group is P2(1) and unit cell dimensions are a=9.0188, b=12.2536, c=10.9016 A, beta=97.162 degrees. There are no direct hydrogen bonds among cellobiose molecules, and the usual intramolecular hydrogen bond between O-3 and O-5' is replaced by a bridge involving Na+, O-3, O-5', and O-6'. Both Na+ have sixfold coordination. One I(-) accepts six donor hydroxyl groups and three C-H***I(-) hydrogen bonds. The other accepts three hydroxyls, one Na+, and five C-H***I(-) hydrogen bonds. Linkage torsion angles phi(O-5) and psi(C-5) are -73.6 and -105.3 degrees, respectively (phi(H)=47.1 degrees and psi(H)=14.6 degrees ), probably induced by the Na+ bridge. This conformation is in a separate cluster in phi,psi space from most similar linkages. Both C-6-O-H and C-6'-O-H are gg, while the C-6'-O-H groups from molecules not in the cluster have gt conformations. Hybrid molecular mechanics/quantum mechanics calculations show <1.2 kcal/mol strain for any of the small-molecule structures. Extrapolation of the NaI cellobiose geometry to a cellulose molecule gives a left-handed helix with 2.9 residues per turn. The energy map and small-molecule crystal structures imply that cellulose helices having 2.5 and 3.0 residues per turn are left-handed.
authors: Department of Chemistry, University of New Orleans, LA 70148, USA.
authors: Zenaida
authors: Z
authors: Peralta-Inga
authors: Glenn P
authors: GP
authors: Johnson
authors: Michael K
authors: MK
authors: Dowd
authors: Jacob A
authors: JA
authors: Rendleman
authors: Edwin D
authors: ED
authors: Stevens
authors: Alfred D
authors: AD
authors: French
mesh_terms: D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D002475:Cellobiose / Q000737:chemistry* / Q000378:metabolism; D002482:Cellulose / Q000737:chemistry / Q000378:metabolism; D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D046911:Macromolecular Substances; D008958:Models, Molecular; D012974:Sodium Iodide / Q000737:chemistry* / Q000378:metabolism; D055672:Static Electricity
chemical_list: D046911:Macromolecular Substances; D002475:Cellobiose; D002482:Cellulose; D012974:Sodium Iodide