A team from the University of Denver has investigated methods to overcome solvent competition to increase encapsulation of guests in the hexameric host pyrogallolarene. They found that both direct melting and melting in paraffin wax “solvent” were successful approaches, thus enabling stability and exchange studies of these assemblies by using NMR spectroscopy.

More than 25 guests were tested for binding in hexameric pyrogallolarene and often produced densely packed host-guest systems (see picture). The complex signals of the NMR spectra and the slow kinetics are a special feature of these pyrogallolarene capsules. These type of kinectially trapped guest complexes cannot be prepared in the presence of solvent.

Images: (c) Wiley-VCH

• Efficient Loading and Kinetic Trapping of Hexameric Pyrogallolarene Capsules in Solution
  M. Kvasnica, J. C. Chapin, B. W. Purse,
  Angew. Chem. Int. Ed. 2011.
  DOI: 10.1002/anie.201007800
• M. Kvasnica, J. C. Chapin, B. W. Purse,
  Angew. Chem. 2011.
  DOI: 10.1002/ange.201007800