title: Pseudomerohedrally twinned monoclinic structure of unfolded 'free' nonactin: comparative analysis of its large conformational change upon encapsulation of alkali metal ions.
abstract: The title compound, C40H64O12, crystallizes in a pseudomerohedrally twinned primitive monoclinic cell with similar contributions of the two twin components. There are two symmetry-independent half-molecules of nonactin in the asymmetric unit. Each molecule has a pseudo-S4 symmetry and resides on a crystallographic twofold axis; the axes pass through the molecular center of mass and are perpendicular to the plane of the macrocycle. The literature description of the room-temperature structure of nonactin as an order-disorder structure in an orthorhombic unit cell is corrected. We report a low-temperature high-precision ordered structure of ;free' nonactin that allowed for the first time precise determination of its bond distances and angles. It possesses an unfolded and more planar geometry than its complexes with encapsulated Na+, K+, Cs+, Ca2+ or NH4+ cations that exhibit more isometric overall conformations.
authors.affiliation: Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, WI 53706, USA. iguzei@chem.wisc.edu
authors.forename: Ilia A
authors.initials: IA
authors.lastname: Guzei
authors.forename: Cheng
authors.initials: C
authors.lastname: Wang
authors.forename: Yulian
authors.initials: Y
authors.lastname: Zhan
authors.forename: Oleg V
authors.initials: OV
authors.lastname: Dolomanov
authors.forename: Yi-Qiang
authors.initials: YQ
authors.lastname: Cheng
mesh_terms: D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D018942:Macrolides / Q000737:chemistry; D008672:Metals, Alkali / Q000737:chemistry*; D008968:Molecular Conformation
chemical_list: D018942:Macrolides; D008672:Metals, Alkali; C050476:nonactin