A VIBRATING FLEXIBLE CHAIN IN A MOLECULAR CAGE - CRYSTAL-STRUCTURE OF THE COMPLEX CYCLOMALTOHEPTAOSE (BETA-CYCLODEXTRIN)-1,4-BUTANEDIOL.6.25H2O

A single crystal X-ray diffraction study of the title complex carried out at room temperature revealed space group P2(1), a = 21.199(12), b = 9.973(3), c = 15.271(8) angstrom, beta = 110.87(3)-degrees, V = 3017(3) angstrom3, 4681 unique reflections with F(o) > 1-sigma(F(o)). The structure was refined to R = 0.069, resolution lambda/2sin-theta(max) = 0.89 angstrom. The crystal packing is of the cage type and is isomorphous to that of beta-cyclodextrin (beta-CD) dodecahydrate. One 1,4-butanediol and approximately 1.25 water molecules are enclosed in each beta-CD cavity. The hydroxyl groups of the 1,4-butanediol molecule are located at each end of the cavity and form hydrogen bonds with neighboring water and beta-CD molecules. The flexible (CH2)4 Moiety vibrates extensively in the central part of the cavity. Water molecules and hydroxyl groups are chelated between O-6 and O-5 of at least five glucose residues.