title: Molecular structure of 3-O-(3,6-anhydro-alpha-D-galactopyranosyl)-beta-D-galactopyranose (neocarrabiose) in the solid state and in solution: an investigation by X-ray crystallography, n.m.r. spectroscopy, and molecular mechanics calculations.
abstract: The crystal structure of neocarrabiose monohydrate, 3-O-(3,6-anhydro-alpha-D-galactopyranosyl)-beta-D-galactopyranose (C12H20O10.H2O) belongs to the monoclinic space group P2(1), and has a unit cell of dimensions a = 6.351(1), b = 7.675(2), c = 15.096(8) A, and beta = 91.11(1) degree. The reducing unit is in the 4C1 conformation, the non-reducing residue is 1C4, with the 3,6-anhydro bridge in an E conformation, and HO-6 is in a gauche-trans conformation. The orientation about the (1----3) linkage is defined by phi = 94.5 degrees and psi = 141.9 degrees. There is an intramolecular hydrogen bond (O-5'...O-2 = 2.777A). The conformation of the pyranose rings in solution, derived from 3JH.H values, were not significantly different from those in the crystal, but the 3,6-anhydro bridge assumed a half-chair conformation. All these features have been rationalised through molecular modelling and computation of potential energy surfaces.
authors.affiliation: Istituto di Strutturistica Chimica Girodano Giacomello, Roma, Italy.
authors.forename: D
authors.initials: D
authors.lastname: Lamba
authors.forename: A L
authors.initials: AL
authors.lastname: Segre
authors.forename: S
authors.initials: S
authors.lastname: Glover
authors.forename: W
authors.initials: W
authors.lastname: Mackie
authors.forename: B
authors.initials: B
authors.lastname: Sheldrick
authors.forename: S
authors.initials: S
authors.lastname: Pérez
mesh_terms: D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D002351:Carrageenan / Q000737:chemistry*; D003460:Crystallization; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D008958:Models, Molecular; D008969:Molecular Sequence Data; D012996:Solutions; D009626:Terminology as Topic; D014961:X-Ray Diffraction
chemical_list: D012996:Solutions; C068279:neocarrabiose; D002351:Carrageenan