Hydration-induced protomer switching in p-aminobenzoic acid studied by cold double ion trap infrared spectroscopy

Abstract

Para-aminobenzoic acid (PABA) is a benchmark molecule to study solvent-induced proton site switching. Protonation of the carboxy and amino groups of PABA generates O- and N-protomers of PABAH+, respectively. Ion...

Observation of Slow Eigen-Zundel Interconversion in H+(H2O)6 Clusters upon Isomer-Selective Vibrational Excitation and Buffer Gas Cooling in a Cryogenic Ion Trap

“…Metastable isomers are often present when floppy molecules (e.g., peptides) − and clusters (e.g., microhydrated ions) − are cooled quickly, whether through supersonic expansion or by collisions with buffer gas in a cryogenic radiofrequency ion trap. In the latter case, this occurs when the ambient (300 K) ions undergo rapid isomer interconversion in the source region, and this dynamic ensemble is cooled by collisions with He buffer gas in the cryogenic trap.…”

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

“…21,22 While the formation of O-protomers in ESI with protic solvents (e.g., H 2 O and CH 3 OH) is attributed to a solvent-assisted intramolecular proton transfer from the NH 3 + group to the oxygen atom (Grotthuss mechanism), [23][24][25][26] there is no experimental evidence for the formation of these solvent bridges in the gas phase. 27,28 Other than the influence of solvent, the substitution pattern of the NH 2 and COOR groups on the ring (ortho, meta, and para) also influences the protonation of the oxygen atom of ABA derivatives. An IM-IR study showed that p-ABA forms both N-and O-protomers, while m-ABA and o-ABA exhibit only N-protonation.…”

“…, H 2 O and CH 3 OH) is attributed to a solvent-assisted intramolecular proton transfer from the NH 3 + group to the oxygen atom (Grotthuss mechanism), 23–26 there is no experimental evidence for the formation of these solvent bridges in the gas phase. 27,28…”

Ion Recognition beyond Size Matching: Cooperative Hydration Effect on the K+ Selectivity of Valinomycin over Na+ Revealed by Cryogenic Double Ion Trap Infrared Spectroscopy

“…In solution-phase experiments, the noncovalent interactions between a solute and a solvent are difficult to characterize due to the spectral interference from solvent molecules that do not participate in the solvation. Solvated clusters are regarded as a model for clarifying the nature of solvation. − One can interrogate the microsolvation effect using this double ion trap technique because the degree of solvation (i.e., number of solvent molecules) can be precisely selected by mass spectrometry. ,− In this study, the hydration effect on the conformation of Na + VM was examined by cryogenic double ion trap IR spectroscopy. We have found a significant hydration effect on the Na + VM conformations (not observed for K + VM), as a function of hydration number.…”