Investigation of the Temperature Dependence in Ion–Molecule Reactions with Proton Transfer Using Ion Mobility-Mass Spectrometry

Long-range proton transfer reactions are essential across various fields. The vehicle mechanism, a type of long-range proton transfer, involves a single molecule carrying a proton. A protonated p-aminobenzoic acid (PABA·H+) has either N-protonated or O-protonated isomers (protomers).We have previously demonstrated that intramolecular proton transfer via the vehicle mechanism leads to the formation of the O-protomer in gas-phase bimolecular reactions between the N-protomer of PABA·H+ and an NH3 molecule. Here, we combined cryogenic ion mobility-mass spectrometry (Cryo-IM-MS) with a temperature-variable ion trap to observe and identify reaction intermediates. Cryogenic conditions revealed the reaction intermediate which is confirmed by collision cross-section measurements. This study not only provides insights into the dynamics of proton transfer in non-solvent environments, but also aids in the design of new proton transfer catalysts by elucidating the mechanisms and efficiencies.