Understanding of protomers/deprotomers by combining mass spectrometry and computation

Solvent Composition Can Have a Measurable Influence on the Ion Mobility-Derived Collision Cross Section of Small Molecules

“…Second, there seems to be a bimodal distribution in RSDs represented in the data, which persists when the data set is separated by the organic component (Figure b). This observation could indicate the presence of protomers in our analyte set, where the protic nature of the organic solvents prevails to influence protonation at different sites . Lastly, when collecting cross sections in solvent environments where there are nearly equal parts water-to-organic (40–60%, Figure b), cross section measurements are highly reproducible, with methanol and isopropyl alcohol systems falling below 0.3%.…”

“…This observation could indicate the presence of protomers in our analyte set, where the protic nature of the organic solvents prevails to influence protonation at different sites. 20 Lastly, when collecting cross sections in solvent environments where there are nearly equal parts water-to-organic (40−60%, Figure 4b), cross section measurements are highly reproducible, with methanol and isopropyl alcohol systems falling below 0.3%. Interestingly, the bimodal distribution of reproducibilities prevails in methanol systems but also becomes more apparent in acetonitrile systems, which supports the idea that unresolved protomers are present in the surveyed analytes.…”

“…19 Another phenomenon that is influenced by both solvent effects and the ESI process is the existence of charge isomers, including protomers, where ions of the same molecule exhibit measurably different conformations in the ion mobility experiment due to the charge carrier localizing at different sites within the molecule. 20 There is now broad literature examining the correspondence of solution-phase and gas-phase molecular structures. The present study does not seek to contribute to the discourse of the biological importance of gas-phase measurements of structure.…”

“…Khristenko et al have observed an apparent memory effect of the electrospray process on the gas phase conformation of single-stranded DNA, attributed to ionic strength differences of the initial solution . Another phenomenon that is influenced by both solvent effects and the ESI process is the existence of charge isomers, including protomers, where ions of the same molecule exhibit measurably different conformations in the ion mobility experiment due to the charge carrier localizing at different sites within the molecule …”

Mechanism of formation and ion mobility separation of protomers and deprotomers of diaminobenzoic acids and aminophthalic acids

“…2,3 Of particular interest is the protonation/ deprotonation of compounds with more than one basic/acidic site leading to the formation of isomers that are protonated/ deprotonated at different sites, so-called prototropic isomers that are frequently referred to as protomers and deprotomers, respectively. 4 Studies of such systems can take advantage of a limited range of techniques including infrared multiphoton dissociation (IRMPD), 5,6 UV-vis photodissociation (PD) spectroscopy, 7,8 and ion mobility-mass spectrometry (IM-MS), 9 which are used in combination with computational methods [10][11][12] to assign the charge location and to perform gas phase analysis. Among these experimental techniques, IM-MS performed in hybrid instrumentation is particularly attractive as it allows both separation of isomeric ions and independent MS and MS/ MS studies to be performed.…”