Characterization of Self-Assembled Supramolecular [Ga4L6] Host–Guest Complexes by Electrospray Ionization Mass Spectrometry

Self-assembled supramolecular host–guest complexes have been characterized by electrospray ionization mass spectrometry. The spectra obtained by use of a Q-TOF instrument equipped with a Z-spray ion source show primarily the 3- and 4- charge states of the assemblies. The assemblies have the general formula [guest ⊂ Ga4L6]11− where L represents the chelating bidentate catechol ligand 1,5-bis(2′,3′-dihydroxy-benzamido)naphthalene and guests are tetramethyl ammonium (Me4N+), tetraethyl ammonium (Et4N+), tetra-n-propyl ammonium (Pr4N+) and decamethylcobaltocenium (Cp*2Co+) cations. For the first time, the mass spectrum of the empty assembly [Ga4L6]12− is reported. This article also reports that provided the electrospray ion source is capable of preserving noncovalent interactions, it is possible to observe host–guest complexes containing both weak binding guests as well as sterically demanding guests in the mass spectra. The present data suggest that electrospray mass spectrometry is a powerful tool for characterization of supramolecular host–guest complexes.