Curvy Capsules

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Science  09 Sep 2011:
Vol. 333, Issue 6048, pp. 1361
DOI: 10.1126/science.333.6048.1361-b

Over the past several decades, chemists have taken advantage of the precise directionality of hydrogen bonding and metal-ligand coordination to assemble cages and capsules in solution from relatively simple building blocks. These assemblies can trap molecular guests inside and thereby facilitate separations, detection, and a range of chemical reactions exhibiting intriguing selectivity. However, in part to render the cavity geometries predictably equivalent throughout the ensemble, the structures have tended to be fairly high-symmetry affairs. Tiefenbacher et al. now demonstrate a more versatile set of building blocks that enable a sort of molecular shrink-wrapping of awkwardly shaped guests. The key is the introduction of loosely Y-shaped propanediurea blocks that can flexibly bridge two capping groups offset from one another's central axis (somewhat akin to the accordion-like connectors holding together tandem buses as they turn a corner). The authors explored guests ranging from C14 to C23 linear hydrocarbons and confirmed associated capsules in S and banana shapes using nuclear magnetic resonance spectroscopy.

Angew. Chem. Int. Ed. 50, 10.1002/anie.201102548 (2011).

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