Pseudomerohedrally twinned monoclinic structure of unfolded 'free' nonactin: comparative analysis of its large conformational change upon encapsulation of alkali metal ions

Acta Cryst. (2009). C65, o521-o524 (doi.org/10.1107/S0108270109033083)

The elusive structure of anhydrous 'free' nonactin has been unambiguously established and for the first time its precise bond distances and angles were determined. Nonactin crystallizes in a pseudomerohedrally twinned primitive monoclinic cell with two similarly sized twin components. 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. The geometries were analyzed with a new routine that computes the dimensions of the smallest parallelepiped superscribing a molecule.

I. A. Guzei, C. Wang, Y. Zhan, O. V. Dolomanov and Y.-Q. Cheng