title: Crystal structure of hexakis(2,6-di-O-methyl)-alpha-cyclodextrin-acetonitrile dihydrate: a channel formed by methyl groups harbors a chain of five partially occupied water sites.
abstract: Hexakis(2,6-di-O-methyl)-alpha-cyclodextrin (DIMEA) crystallizes from 1:1 water-acetonitrile as DIMEA-acetonetril-dihydrate in the orthorhombic space group P2(1)2(1)2(1), unit cell dimensions a = 14.2775(5), b = 15.7312(5), c = 31.1494(11) A. Refinement of the structure against 5540 X-ray diffraction data converged at an R factor of 0.083. The macrocycle exhibits a 'round' conformation and is stabilized by intramolecular, interglucose O-3-H(n)...O-2(n + 1) and C-6-H(n)...O-5(n + 1) hydrogen bonds. Acetonitrile is included in the central cavity of DIMEA and held in position by C-5-H...N interactions. The two water molecules in the asymmetric units are distributed over six sites. One is fully occupied due to hydrogen bonding to O-3 groups of two symmetry-related DIMEA molecules, whereas the five remaining sites show occupancies between 0.15 and 0.25. These sites are in hydrogen bonding contact with O...O distances between 2.59 and 3.50 A and are located in infinite, hydrophobic channels parallel to the alpha-axis, which are coated with methyl groups of symmetry-related DIMEA.
authors.affiliation: Institut für Kristallographie, Freie Universität Berlin, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Aree
authors.forename: H
authors.initials: H
authors.lastname: Hoier
authors.forename: B
authors.initials: B
authors.lastname: Schulz
authors.forename: G
authors.initials: G
authors.lastname: Reck
authors.forename: W
authors.initials: W
authors.lastname: Saenger
mesh_terms: D002942:Circular Dichroism; D018360:Crystallography, X-Ray; D003505:Cyclodextrins / Q000737:chemistry*; D006860:Hydrogen Bonding; D008958:Models, Molecular; D014867:Water / Q000737:chemistry*; D047391:alpha-Cyclodextrins
chemical_list: D003505:Cyclodextrins; D047391:alpha-Cyclodextrins; C410157:hexakis(2,6-di-O-methyl)-alpha-cyclodextrin-acetonitrile dihydrate; D014867:Water; C032613:alpha-cyclodextrin