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

Abstract

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 homometallic ring [Cr 8 F 8 (O 2 C t Bu) 16 ] and the heterometallic rotaxanes [NH 2 RR′][Cr 7 MF 8 (O 2 C t Bu) 16 ], where

Emerging scientists in analytical sciences: Niklas Geue

“…During my PhD, I have successfully shown that it is possible to evaluate the stability of (metallo)supramolecular compounds using tandem MS, and I have used this methodology to systematically examine how the substitution of d‐metals, ligands, and charge carriers alter this property 2,3 . I was able to discriminate competing disassembly mechanisms, uncovering trends for closed versus open systems and small versus large polymetallic ions (Figure 2).…”

“… 2,4 These results provided new insight into the contested criteria a threaded supramolecular assembly must fulfill to be considered a rotaxane, which is when the thread in the centre of the ring cannot slip off (Figure 2). 2 I have also correlated computationally derived structures, using density functional theory (DFT), with experimental IM‐MS data to propose atomically resolved structures, 2 and demonstrated how different charge‐carrying ions can measure the cavity size of polymetallic complexes 3 …”

“…During my PhD, I have successfully shown that it is possible to evaluate the stability of (metallo)supramolecular compounds using tandem MS, and I have used this methodology to systematically examine how the substitution of d-metals, ligands, and charge carriers alter this property. 2,3 I was able to discriminate competing disassembly mechanisms, uncovering trends for closed versus open systems and small versus large polymetallic ions (Figure 2). 2,4 These results provided new insight into the contested criteria a threaded supramolecular assembly must fulfill to be considered a rotaxane, which is when the thread in the centre of the ring cannot slip off (Figure 2).…”

“…2 I have also correlated computationally derived structures, using density functional theory (DFT), with experimental IM-MS data to propose atomically resolved structures, 2 and demonstrated how different charge-carrying ions can measure the cavity size of polymetallic complexes. 3 I further developed a strategy to form polymetallic rings in the gas phase that are relevant for quantum applications and electronics but are so far impossible to synthesize in solution. The gas-phase synthesis was achieved via collision-induced dissociation of larger precursors.…”

Charge Inversion of Mono- and Dianions to Cations via Triply Charged Metal Complexes: Application to Lipid Mixtures

“…Electrospray ionization (ESI) is a popular ionization technique in mass spectrometry (MS) for biomolecules such as peptides, proteins, lipids, etc. − ESI can generate various ion types such as protonated or metal-adducted species in positive ion mode and deprotonated or anion-adducted species in negative ion mode. Furthermore, ESI has been shown to generate ion species with charges greater than one when multiple readily ionized sites are present. ,, The solution prior to being subjected to ESI can be manipulated to generate different ion types, such as altering the pH or adding various salts. − This may be desirable to simplify the mass spectra or change the ion type to facilitate structural characterization via tandem MS. − However, modifying the solution to manipulate the ion type can suppress ion formation, resulting in a more complicated mass spectrum, and/or result in the analyte no longer being in biologically relevant solvent conditions, as is the focus of “native” mass spectrometry . A straightforward alternative approach is to manipulate the ion-type post-ionization via gas-phase ion/ion reactions. − Gas-phase ion/ion reactions, when conducted within the context of a tandem MS experiment, allow for selective manipulation of ion type by isolating a chosen reagent ion and then allowing it to react exclusively with a selected analyte ion.…”