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.
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.
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Istituto di Strutturistica Chimica Girodano Giacomello, Roma, Italy.
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Glover
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Mackie
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Sheldrick
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Pérez
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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
D012996:Solutions; C068279:neocarrabiose; D002351:Carrageenan