Pseudomerohedrally twinned monoclinic structure of unfolded 'free' nonactin: comparative analysis of its large conformational change upon encapsulation of alkali metal ions
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
+, Ca
2+ or NH
4+ 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