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

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dc.contributor.authorAkasaka, Kyota
dc.contributor.authorHirata, Keisuke
dc.contributor.authorHaddad, Fuad
dc.contributor.authorDopfer, Otto
dc.contributor.authorIshiuchi, Shun-ichi
dc.contributor.authorFujii, Masaaki
dc.date.accessioned2023-02-20T12:59:37Z
dc.date.available2023-02-20T12:59:37Z
dc.date.issued2022-12-06
dc.description.abstractPara-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.en
dc.description.sponsorshipTU Berlin, Open-Access-Mittel – 2022
dc.identifier.eissn1463-9084
dc.identifier.issn1463-9076
dc.identifier.urihttps://depositonce.tu-berlin.de/handle/11303/18220
dc.identifier.urihttps://doi.org/10.14279/depositonce-17013
dc.language.isoen
dc.rights.urihttps://creativecommons.org/licenses/by/3.0/
dc.subject.ddc500 Naturwissenschaften und Mathematik::540 Chemie::541 Physikalische Chemie
dc.subject.othersynthesisen
dc.subject.otherpara-aminobenzoic aciden
dc.subject.otherPABAH+en
dc.subject.othergas-phaseen
dc.subject.otherspectrometryen
dc.titleHydration-induced protomer switching in p-aminobenzoic acid studied by cold double ion trap infrared spectroscopyen
dc.typeArticle
dc.type.versionpublishedVersion
dcterms.bibliographicCitation.doi10.1039/d2cp04497h
dcterms.bibliographicCitation.issue6
dcterms.bibliographicCitation.journaltitlePhysical Chemistry Chemical Physics
dcterms.bibliographicCitation.originalpublishernameRoyal Society of Chemistry (RSC)
dcterms.bibliographicCitation.originalpublisherplaceCambridge
dcterms.bibliographicCitation.pageend4488
dcterms.bibliographicCitation.pagestart4481
dcterms.bibliographicCitation.volume25
dcterms.rightsHolder.referenceCreative-Commons-Lizenz
tub.accessrights.dnbfree*
tub.affiliationFak. 2 Mathematik und Naturwissenschaften::Inst. Optik und Atomare Physik::FG Lasermolekülspektroskopie und Umweltphysik
tub.publisher.universityorinstitutionTechnische Universität Berlin

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