Gradient tandem mass spectrometry interfaced with ion mobility separation for the characterization of supramolecular architectures

Traveling wave ion mobility mass spectrometry (TWIM MS) was combined with gradient tandem mass spectrometry (gMS(2)) to deconvolute and characterize superimposed ions with different charges and shapes formed by electrospray ionization (ESI) of self-assembled, hexameric metallomacrocycles composed of terpyridine-based ligands and Cd(II) ions. ESI conditions were optimized to obtain intact hexameric cation assemblies in a low charge state (2+), in order to minimize overlapping fragments of the same mass-to-charge ratio. With TWIM MS, intact hexameric ions could be separated from remaining fragments and aggregates. Collisional activation of these hexameric ions at varying collision energies (gMS(2)), followed by TWIM separation, was then performed to resolve macrocyclic from linear hexameric species. Because of the different stabilities of these architectures, gMS(2) changes their relative amounts, which can be monitored individually after subsequent ion mobility separation. On the basis of this unique strategy, hexameric cyclic and linear isomers have been successfully resolved and identified. Complementary structural information was gained by the gMS(2) fragmentation pattern of the metallosupramolecules, acquired by collisionally activated dissociation after TWIM dispersion. TWIM MS interfaced with gMS(2) should be particularly valuable for the characterization of a variety of supramolecular polymers, which often contain isomeric architectures that yield overlapping fragments and aggregates upon ESI MS analysis.