Christoph Schalley and his colleagues from Humboldt Universität zu Berlin use electrospray ionization Fourier-transform ion-cyclotron-resonance (ESI-FTICR) to provide new insights into metallo-supramolecular reaction mechanisms. ESI-FTICR mass spectroscopy (MS) can be used on isolated compounds to examine their intramolecular rearrangements in the gas phase.

Usually when trying to examine intramolecular rearrangements within assemblies the reactivity is always superimposed by the intermolecular exchange processes. Schalley explains 'no clear distinction can be made between them in solution. However, in the gas phase, no reactions can occur because isolated ions are investigated. Consequently, a mass spectrometer is the perfect tool to study such processes, in the absence of any subunit exchanges.' 

This is the first time that tandem MS (ESI-FTICR) has been applied to 3D assemblies. Schalley says 'our mechanistic study is the first one to show that a two-fold contraction from a larger metallo-supramolecular bowl to a smaller cage can occur.'

Many metallo-supramolecular assemblies, which have formed through self-assembly, have been reported in the literature but crucial MS studies are missing. Schalley explains that 'the examination of intrinsic properties of non-covalent complexes will have a significant impact on out fundamental understanding of the nature of non-covalent bonding.' 

It seems that there is huge potential for MS to be used by supramolecular chemists. 'MS adds a completely new view on the reactivity when compared to the results obtained from other methods' explains Schalley. This is certainly an exciting development, which should have a big impact on the future investigations of intramolecular reactivity in other supramolecular systems.

Emma Shiells