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Dehydration of raffinose pentahydrate: structures of raffinose 5-, 4.433-, 4.289- and 4.127-hydrate at 93 K.

Abstract
Raffinose [or O-α-D-galactopyranosyl-(1→6)-α-D-glucopyranosyl-(1→2)-β-D-fructofuranoside] pentahydrate, C18H32O16·5H2O, (I), and three lower hydrates, namely the 4.433-, (II), 4.289-, (III), and 4.127-hydrated, (IV), forms, obtained in the course of the dehydration of (I), have been studied. The unit cells in the space group P2₁2₁2₁ are of similar dimensions for all the crystals. The conformation of the raffinose molecules remains almost the same across the four crystal structures. The raffinose molecules are linked into a three-dimensional hydrogen-bonded network involving all the -OH groups, the ring and glycosidic O atoms, and the water molecules. Six water sites were identified in the structures of (II), (III) and (IV), of which W1, W4 and W6 (W = water) are partially occupied with their populations coupled. W1, W4 and one of the -OH groups of the galactose ring form an infinite hydrogen-bonding chain around a 2₁ axis parallel to the a axis (denoted chain A), and W6 and the same -OH group form a similar chain (chain A') disordered with chain A. The occupancy ratio of chain A to chain A' for N-hydrates (N is a hydration number between 4 and 5) is (N - 4):(5 - N). The transformation of chain A to chain A' as part of the dehydration process has little effect on the rest of the structure. Thus, the dehydration proceeds without significant impact on the crystal structure.
AuthorsChotika Viriyarattanasak, Motoo Shiro, Shigeru Munekawa, Felix Franks, Satomi Ikeda, Kazuhito Kajiwara
JournalActa crystallographica. Section C, Structural chemistry (Acta Crystallogr C Struct Chem) Vol. 71 Issue Pt 11 Pg. 954-8 (Nov 2015) ISSN: 2053-2296 [Electronic] England
PMID26524166 (Publication Type: Journal Article)
Chemical References
  • Raffinose
Topics
  • Crystallography, X-Ray
  • Dehydration
  • Hydrogen Bonding
  • Models, Molecular
  • Molecular Structure
  • Raffinose (chemistry)

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