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

• Published in: Acta crystallographica. Section C, Crystal structure communications Crystal structure communications, 2015-11, Vol.71 (11), p.954-958
• Main Authors: Viriyarattanasak, Chotika, Shiro, Motoo, Munekawa, Shigeru, Franks, Felix, Ikeda, Satomi, Kajiwara, Kazuhito
• Format: Article
• Language: English
• Subjects: Chains; Crystal structure; Dehydration; Networks; Raffinose; Three dimensional; Transformations; Unit cell
• ISSN: 0108-2701; 2053-2296; 1600-5759; 2053-2296
• DOI: 10.1107/S2053229615017374

Raffinose [or O-[alpha]-D-galactopyranosyl-(1[arrow right]6)-[alpha]-D-glucopyranosyl-(1[arrow right]2)-[beta]-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.