Monitoring intramolecular proton transfer with ion mobility-mass spectrometry and in-source ion activation

Valadbeigi, Younes; Causon, Tim J.

doi:10.1039/d2cc05237g

Cited by 6 publications

(20 citation statements)

References 22 publications

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“…Hence, this carbon atom can be protonated via direct NH 3 → C proton transfer in the gas phase. 36 However, as the calculated DT CCS N2 for this C-protomer (125.6 Å 2 ) is very close to that of the O-protomer (125.2 Å 2 ), there is no possibility to separate and experimentally confirm these protomers with the native resolution of this drift cell. In the case of 2,4-DABA, two N-protomers are possible for protonation at amine- 2 and amine- 4 .…”

Section: Resultsmentioning

confidence: 85%

“…The C-protomer might also be produced via intramolecular NH 3 + -C proton transfer or by direct C-protonation in APCI by the reactant ion H 3 O + . 36,50 The m/z-selected IM spectra of both in-source fragments [M+H-CO 2 ] + and [M-HCO 2 ] + reveal a peak for protonation at C atoms of the rings (Fig. 1).…”

Section: Protomers Of Diaminobenzoic Acid Isomersmentioning

confidence: 99%

“…31 In addition to the frequently studied N-and O-protomers, the C-protomers of aromatic derivatives (e.g., aniline and polycyclic aromatic amines) can also be formed due to the electrondonating character of the amine group increasing the basicity of the carbon atom at the para position. [32][33][34][35][36] Charge delocalization in C-protomers decreases their polarity leading to smaller CCS values compared with the corresponding N-protomers. 37 Although the carbon atom of these aromatic rings displays a high basicity in the gas phase, they are weak bases in solution and are protonated in the gas phase via direct NH 3 + -C proton transfer.…”

Section: Introductionmentioning

confidence: 99%

“…Experimental and theoretical analysis of the protonation of these molecules showed that the NH 3 + -C proton transfer is controlled by the energy barrier of the proton transfer rather than the solvent composition. 36 While less extensively studied than protomer examples, deprotomers have also emerged as a topic of interest for experimental IM-MS studies for systems requiring negative mode ionisation. Carboxylate and phenolate deprotomers are the most well-known examples studied by IM-MS due to resonance and electron delocalization in the latter.…”

Section: Introductionmentioning

confidence: 99%

“…Experimental and theoretical analysis of the protonation of these molecules showed that the NH 3 + → C proton transfer is controlled by the energy barrier of the proton transfer rather than the solvent composition. 36…”

Section: Introductionmentioning

confidence: 99%

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

Valadbeigi

Causon

2023

Phys. Chem. Chem. Phys.

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Section: Resultsmentioning

confidence: 85%

Section: Protomers Of Diaminobenzoic Acid Isomersmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

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

Valadbeigi

Causon

2023

Phys. Chem. Chem. Phys.

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Charge site manipulation to enhance top‐down fragmentation efficiency

et al. 2023

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In recent years, top‐down mass spectrometry has become a widely used approach to study proteoforms; however, improving sequence coverage remains an important goal. Here, two different proteins, α‐synuclein and bovine carbonic anhydrase, were subjected to top‐down collision‐induced dissociation (CID) after electrospray ionisation. Two high‐boiling solvents, DMSO and propylene carbonate, were added to the protein solution in low concentration (2%) and the effects on the top‐down fragmentation patterns of the proteins were systematically investigated. Each sample was measured in triplicate, which revealed highly reproducible differences in the top‐down CID fragmentation patterns in the presence of a solution additive, even if the same precursor charge state was isolated in the quadrupole of the instrument. Further investigation supports the solution condition‐dependent selective formation of different protonation site isomers as the underlying cause of these differences. Higher sequence coverage was often observed in the presence of additives, and the benefits of this approach became even more evident when datasets from different solution conditions were combined, as increases up to 35% in cleavage coverage were obtained. Overall, this approach therefore represents a promising opportunity to increase top‐down fragmentation efficiency.

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Using dopants in the atmospheric pressure chemical ionization ion source to determine the site of protonation by ion mobility spectrometry

Valadbeigi,

Mirzahosseini,

Ilbeigi

et al. 2024

Rapid Comm Mass Spectrometry

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RationaleCompounds like caffeine metabolites with more than one proton acceptor site can produce a mixture of isomeric protonated ions (protomers) in electrospray ionization and atmospheric pressure chemical ionization (APCI) ion sources. Discrimination between the protomers is of interest as the charge location influences ion structure and chemical and physical properties.MethodsProtonation of caffeine in an APCI ion source was studied using ion mobility spectrometry. The hydronium ions, H3O+(H2O)n, are the main reactant ions in the APCI ion source. Different dopant gases including NO2, NH3, and CH3NH2 were used to produce new reactant ions NO+, NH4+, and CH3NH3+, respectively. Density functional theory was employed to explain the experimental results and calculate the energies of the ionization reactions.ResultsThe ion mobility spectrum of caffeine showed three peaks. In the presence of NO2 dopant and NO+ reactant ion, caffeine was ionized via charge transfer and formation of M+ ion. As NH3 and CH3NH2 are stronger bases than H2O, the reactant ions NH4+ and CH3NH3+ selectively protonated the more basic site of caffeine, that is, the imidazole nitrogen. Using these dopants, we could attribute the first ion mobility peak to M+ ion, the second peak to the protonation of caffeine at the carbonyl oxygen atom, and the third peak to the protonation of the imidazole nitrogen atom. The calculated collisional cross‐sections of M+ and the protomers of caffeine confirmed the peaks' assignment.ConclusionsThe criterion for the selection of an appropriate dopant is that its proton affinity (PA) should be between those of the proton acceptor sites of the molecule studied.

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Monitoring intramolecular proton transfer with ion mobility-mass spectrometry and in-source ion activation

Abstract: Here, we show how intramolecular proton transfer can be induced and monitored with the example of polycyclic aromatic amines using in-source ion-activation and ion mobility-mass spectrometry.

Cited by 6 publications

References 22 publications

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

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

Charge site manipulation to enhance top‐down fragmentation efficiency

Using dopants in the atmospheric pressure chemical ionization ion source to determine the site of protonation by ion mobility spectrometry

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