Hydration-induced protomer switching in p-aminobenzoic acid studied by cold double ion trap infrared spectroscopy
| العنوان: | Hydration-induced protomer switching in p-aminobenzoic acid studied by cold double ion trap infrared spectroscopy |
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| المؤلفون: | Kyota Akasaka, Keisuke Hirata, Fuad Haddad, Otto Dopfer, Shun-ichi Ishiuchi, Masaaki Fujii |
| المصدر: | Physical Chemistry Chemical Physics. 25:4481-4488 |
| بيانات النشر: | Royal Society of Chemistry (RSC), 2023. |
| سنة النشر: | 2023 |
| مصطلحات موضوعية: | para-aminobenzoic acid, spectrometry, PABAH+, gas-phase, synthesis, 500 Naturwissenschaften und Mathematik::540 Chemie::541 Physikalische Chemie, General Physics and Astronomy, Physical and Theoretical Chemistry |
| الوصف: | 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 mobility mass spectrometry (IMS) and infrared photodissociation (IRPD) studies have claimed that the O-protomer most stable in the gas phase is converted to the N-protomer most stable in solution upon hydration with six water molecules in the gas-phase cluster. However, the threshold size has remained ambiguous because the arrival time distributions in the IMS experiments exhibit multiple peaks. On the other hand, IRPD spectroscopy could not detect the N-protomer for smaller hydrated clusters because of broad background due to annealing required to reduce kinetic trapping. Herein, we report the threshold size for O → N protomer switching without ambiguity using IR spectroscopy in a double ion trap spectrometer from 1300 to 1800 cm−1. The pure O-protomer is prepared by electrospray, and size-specific hydrated clusters are formed in a reaction ion trap. The resulting clusters are transferred into a second cryogenic ion trap and the distribution of O- and N-protomers is determined by mid-IR spectroscopy without broadening. The threshold to promote O → N protomer switching is indeed five water molecules. It is smaller than the value reported previously, and as a result, its pentahydrated structure does not support the Grotthuss mechanism proposed previously. The extent of O → N proton transfer is evaluated by collision-assisted stripping IR spectroscopy, and the N-protomer population increases with the number of water molecules. This result is consistent with the dominant population of the N-protomer in aqueous solution. |
| تدمد: | 1463-9084 1463-9076 |
| URL الوصول: | https://explore.openaire.eu/search/publication?articleId=doi_dedup___::b188933ca5fc332a344fe75235aaa5eb https://doi.org/10.1039/d2cp04497h |
| حقوق: | OPEN |
| رقم الأكسشن: | edsair.doi.dedup.....b188933ca5fc332a344fe75235aaa5eb |
| قاعدة البيانات: | OpenAIRE |
| تدمد: | 14639084 14639076 |
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