ION-SPRAY TANDEM MASS-SPECTROMETRY OF SUPRAMOLECULAR COORDINATION-COMPLEXES

Double-helical [M2L2]n+, triple-helical [M2L3]n+, and toroidal [M3L3]n + (M = Cu, Co, Fe, Ni, La, Eu, Gd, Tb, or Lu) supramolecular complexes have been fully characterized by ion spray mass spectrometry (IS-MS). The IS-MS spectra from pure acetonitrile solutions reflect the nature of the cations present in solution with conservation of the charge st ate and allow an efficient qualitative speciation of the compounds. Th e mass spectrometry results can be correlated with other powerful tech niques (nuclear magnetic resonance and electronic spectroscopy) for th e characterization of supramolecular complexes in solution. Structural information is obtained by collision-induced dissociation, which stro ngly depends on the metal ions used in the supramolecular complexes an d on the various connectivities and topologies of the ligands. When th e ligand contains 3,5-dimethoxybenzyl groups bound to the benzimidazol e rings, the partial fragmentation of the complexes is associated with a decrease of the total charge of the complexes and the appearance of the characteristic fragment at m/z 151 that corresponds to the 3,5-di methoxybenzyl cation. A detailed analysis of the fragmentation pathway s of these supramolecular complexes suggests that the metal-nitrogen c oordination bonds are very strong in the gas phase.