O-H···O Hydrogen Bonding in Crystal Structures of Cyclic and Linear Oligoamyloses: Cyclodextrins, Maltotriose, and Maltohexaose

Abstract

For the study of the hydrogen bonding, the cyclodextrins are unique in being molecules in the 1000- to 1300-Da range which provide excellent quality crystals for both X-ray and neutron diffraction experiments. Their hydrogen-bonding functionality is relatively simple in that they contain only hydroxyl groups and water molecules as donors and acceptors with the sugar ring and glycosidic linkage oxygen atoms as additional acceptors.1 As will be shown, the crystal structures of cyclodextrin hydrates provide remarkable examples of the importance of σ-bond cooperativity in determining the hydrogen-bond structures. There are relatively few three-center bonds except for those intramolecularly to the glycosidic oxygen atoms. In the hydrates of the β- and γ-cyclodextrins, water molecules and hydroxyl groups display positional and/or rotational disorder and provide examples of the flip-flop type hydrogen-bond disorder.