title: 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.
authors.affiliation: Pilot Plant Development and Training Institute, King Mongkut's University of Technology Thonburi (Bangkhuntien), 83 Moo 8 Thakham, Bangkhuntien, Bangkok 10150, Thailand.
authors.forename: Chotika
authors.initials: C
authors.lastname: Viriyarattanasak
authors.affiliation: Rigaku Corporation, 3-9-12, Matsubara-cho, Akisima-shi, Tokyo 196-8666, Japan.
authors.forename: Motoo
authors.initials: M
authors.lastname: Shiro
authors.affiliation: Rigaku Corporation, 3-9-12, Matsubara-cho, Akisima-shi, Tokyo 196-8666, Japan.
authors.forename: Shigeru
authors.initials: S
authors.lastname: Munekawa
authors.affiliation: BioUpdate Foundation, 25 The Fountains, 229 Ballards Lane, London N3 1NL, England.
authors.forename: Felix
authors.initials: F
authors.lastname: Franks
authors.affiliation: School of Bioscience and Biotechnology, Tokyo University of Technology, 1404-1, Katakura, Hachioji, Tokyo 192-0982, Japan.
authors.forename: Satomi
authors.initials: S
authors.lastname: Ikeda
authors.affiliation: School of Bioscience and Biotechnology, Tokyo University of Technology, 1404-1, Katakura, Hachioji, Tokyo 192-0982, Japan.
authors.forename: Kazuhito
authors.initials: K
authors.lastname: Kajiwara
mesh_terms: D018360:Crystallography, X-Ray; D003681:Dehydration; D006860:Hydrogen Bonding; D008958:Models, Molecular; D015394:Molecular Structure; D011887:Raffinose / Q000737:chemistry*
chemical_list: D011887:Raffinose
keywords: crystal structure; dehydration; hydrated raffinose; hydrogen-bonding network; trisaccharide