Structural examination of supramolecular architectures by electrospray ionization mass spectrometry

Reversibly self-assembling host-guest complexes of the softball type are ch aracterized by electrospray ionization mass spectrometry. Quaternary ammoni um ions serve simultaneously as guests and ion labels. Isotope pattern anal ysis, inclusion of labeled guests, heterodimer experiments, size and shape dependence, and collision-induced fragmentation reveal that the capsular st ructure of these hydrogen-bonded complexes is retained in the gas phase wit h the guests inside their cavity. The results parallel findings from soluti on-phase NMR experiments and show that the guests are encapsulated inside t he cavity. These results also demonstrate the value of mass spectrometry fo r high-order structural examination of supramolecular architecture.