Adduct Ions as Diagnostic Probes of Metallosupramolecular Complexes Using Ion Mobility Mass Spectrometry

Following electrospray ionization, it is common for analytes to enter the gas phase accompanied by a charge-carrying ion, and in most cases, this addition is required to enable detection in the mass spectrometer. These small charge carriers may not be influential in solution but can markedly tune the analyte properties in the gas phase. Therefore, measuring their relative influence on the target molecule can assist our understanding of the structure and stability of the analyte. As the formed adducts are usually distinguishable by their mass, differences in the behavior of the analyte resulting from these added species (e.g., structure, stability, and conformational dynamics) can be easily extracted. Here, we use ion mobility mass spectrometry, supported by density functional theory, to investigate how charge carriers (H+, Na+, K+, and Cs+) as well as water influence the disassembly, stability, and conformational landscape of the homo-metallic ring [Cr8F8(O2CtBu)16] and the heterometallic rotaxanes [NH2RR '][Cr7MF8(O2CtBu)16], where M = MnII, FeII, CoII, NiII, CuII, ZnII, and CdII. The results yield new insights on their disassembly mechanisms and support previously reported trends in cavity size and transition metal properties, demonstrating the potential of adduct ion studies for characterizing metallosupramolecular complexes in general.

Automated summary

After the electrospray ionization, analytes usually enter the gas phase with a charge-carrying ion, which is necessary for detection in the mass spectrometer. These charge carriers may not have much effect in solution, but they can significantly alter the properties of the analytes in the gas phase. By measuring their influence on the target molecule, we can gain insights into the structure and stability of the analyte. In this study, ion mobility mass spectrometry and density functional theory are used to investigate the impact of charge carriers and water on the disassembly, stability, and conformation of various metal-containing compounds.