Viriyarattanasak Chotika, Shiro Motoo, Munekawa Shigeru, Franks Felix, Ikeda Satomi, Kajiwara Kazuhito
Pilot Plant Development and Training Institute, King Mongkut's University of Technology Thonburi (Bangkhuntien), 83 Moo 8 Thakham, Bangkhuntien, Bangkok 10150, Thailand.
Rigaku Corporation, 3-9-12, Matsubara-cho, Akisima-shi, Tokyo 196-8666, Japan.
Acta Crystallogr C Struct Chem. 2015 Nov;71(Pt 11):954-8. doi: 10.1107/S2053229615017374. Epub 2015 Oct 13.
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.
棉子糖[即O-α-D-吡喃半乳糖基-(1→6)-α-D-吡喃葡萄糖基-(1→2)-β-D-呋喃果糖苷]五水合物，C₁₈H₃₂O₁₆·5H₂O，(I)，以及在(I)脱水过程中得到的三种较低水合物，即4.433水合物，(II)、4.289水合物，(III)和4.127水合物，(IV)，已被研究。空间群为P2₁2₁2₁的所有晶体的晶胞尺寸相似。在这四种晶体结构中，棉子糖分子的构象几乎保持不变。棉子糖分子通过涉及所有-OH基团、环和糖苷O原子以及水分子的三维氢键网络相连。在(II)、(III)和(IV)的结构中确定了六个水位置，其中W1、W4和W6（W = 水）部分占据，其占有率相互耦合。W1、W4和半乳糖环的一个-OH基团围绕平行于a轴的2₁轴形成一条无限的氢键链（表示为链A），W6和相同的-OH基团形成一条与链A无序的类似链（链A'）。N水合物（N是4到5之间的水合数）中链A与链A'的占有率比为(N - 4):(5 - N)。作为脱水过程一部分的链A到链A'的转变对结构的其余部分影响很小。因此，脱水过程对晶体结构没有显著影响。
