Sonic spray ionization mass spectrometry: a powerful tool used to characterize fragile metal-assembled cages

Sonic spray ionization mass spectrometry (SSI MS) is shown to be effective in characterizing metal-assembled cage structures that are not observed using conventional electrospray ionization mass spectrometry (ESI MS) techniques. A palladium-assembled resorcinarene-based cage containing nitrile ligands and a palladium(II) triazine cage were characterized and their +1 molecular ion peaks were observed using this method. An N,N-bis(pyridylmethyl)amine resorcinarene cavitand-metal ion complex was observed to yield peaks corresponding to open tetranuclear complexes and closed cage complexes depending on the metal ion. Molecular ion peaks for these complexes were not detected when ESI MS was used. The soft ionization inherent in SSI MS coupled with its relatively simple design provides a powerful tool to characterize such supramolecular assemblies, which are of current interest.