Two Polymorphs of Structures of ￥á,￥á-Trehalose Octaacetate Monohydrate

摘要

Structures of two polymorphs of メ,メ-trehalose octaacetate monohydrate, C28H38O19·H2O, have been studied by X-ray diffraction method. メ,メ -trehalose (メ-D-glucopyranosyl メ -D-glucopyranoside) is a nonreducing disaccharide. The polymorph グ belongs to the monoclinic P21, and has unit cell parameters of a=10.725(l), b=15.110(4), c=11.199(5) ∈, モ=108.16(2)∑ and Z=2. The polymorph ケ is orthorhombic P212121, with a=13.684(4), b=15.802(4), c=17.990(9) ∈ and Z=4. The final R and Rw values for monoclinic polymorph グ are 0.043 and 0.048 and for orthorhombic polymorph ケ are 0.116 and 0.118, respectively. Those R values of polymorph ケ are high because the large thermal motions of acetyl groups and the poor quality of the crystal. The molecular conformations in the two polymorphs are similar. Both D-glucopyranosyl rings have chair 4C1 conformations and atoms of glycosidic chain メ (1℃1) linkage are coplanar. The primary acetate groups of the pyranose residues assume both gauche-trans conformations. The molecules of two polymorphs have pseudo-C2 symmetry at glycosidic O(l) atom. The bond lengths and angles are normal compared with those in other acetylated sugar compounds. The molecules in the monoclinic crystal are held by the hydrogen bonds with the water molecules and by van der Waals forces.