title: A highly hydrated α-cyclodextrin/1-undecanol inclusion complex: crystal structure and hydrogen-bond network from high-resolution neutron diffraction at 20 K.
abstract: The monoclinic C2 crystal structure of an α-cyclodextrin/1-undecanol host-guest inclusion complex was solved using single-crystal neutron diffraction. Large high-quality crystals were specially produced by optimizing temperature-controlled growth conditions. The hydrate crystallizes in a channel-type structure formed by head-to-head dimer units of α-cyclodextrin molecules stacked like coins in a roll. The alkyl chain of the guest lipid is entirely embedded inside the tubular cavity delimited by the α-cyclodextrin dimer and adopts an all-trans planar zigzag conformation, while the alcohol polar head group is outside close to the α-cyclodextrin primary hydroxyl groups. The cyclodextrin dimer forms columns, which adopt a quasi-square arrangement much less compact than the quasi-hexagonal close packing already observed in the less hydrated α-cyclodextrin channel-type structures usually found with similar linear guests. The lack of compactness of this crystal form is related to the high number of interstitial water molecules. The replacement of 1-undecanol by 1-decanol does not modify the overall crystal structure of the hydrate as shown by additional X-ray diffraction investigations comparing the two host-guest assemblies. This is the first study that analyses the entire hydrogen-bonding network involved in the formation of a cyclodextrin dimer surrounded by its shell of water molecules.
authors.affiliation: UMR CNRS 8612, LabEx LERMIT Universite Paris-Sud, 5 rue Jean-Baptiste Clément, F-92296 Chatenay-Malabry CEDEX, France.
authors.forename: Delphine
authors.initials: D
authors.lastname: Gallois-Montbrun
authors.forename: Geneviève
authors.initials: G
authors.lastname: Le Bas
authors.forename: Sax A
authors.initials: SA
authors.lastname: Mason
authors.forename: Thierry
authors.initials: T
authors.lastname: Prangé
authors.forename: Sylviane
authors.initials: S
authors.lastname: Lesieur
keywords: channel assembly; cyclodextrin dimer; host–guest inclusion compound; hydrogen bonding; monoalkyl lipid; single-crystal neutron diffraction