{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,10]],"date-time":"2026-09-10T13:24:32Z","timestamp":1789046672153,"version":"build-2803163510"},"reference-count":30,"publisher":"American Chemical Society (ACS)","issue":"36","license":[{"start":{"date-parts":[[2026,8,27]],"date-time":"2026-08-27T00:00:00Z","timestamp":1787788800000},"content-version":"stm-asf","delay-in-days":0,"URL":"https:\/\/doi.org\/10.15223\/policy-029"},{"start":{"date-parts":[[2026,8,27]],"date-time":"2026-08-27T00:00:00Z","timestamp":1787788800000},"content-version":"stm-asf","delay-in-days":0,"URL":"https:\/\/doi.org\/10.15223\/policy-037"},{"start":{"date-parts":[[2026,8,27]],"date-time":"2026-08-27T00:00:00Z","timestamp":1787788800000},"content-version":"stm-asf","delay-in-days":0,"URL":"https:\/\/doi.org\/10.15223\/policy-045"}],"funder":[{"DOI":"10.13039\/501100001691","name":"Japan Society for the Promotion of Science","doi-asserted-by":"publisher","award":["JP16H04098"],"award-info":[{"award-number":["JP16H04098"]}],"id":[{"id":"10.13039\/501100001691","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100001691","name":"Japan Society for the Promotion of Science","doi-asserted-by":"publisher","award":["JP20H00374"],"award-info":[{"award-number":["JP20H00374"]}],"id":[{"id":"10.13039\/501100001691","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100001691","name":"Japan Society for the Promotion of Science","doi-asserted-by":"publisher","award":["JP21H05429"],"award-info":[{"award-number":["JP21H05429"]}],"id":[{"id":"10.13039\/501100001691","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100001691","name":"Japan Society for the Promotion of Science","doi-asserted-by":"publisher","award":["JP25K08689"],"award-info":[{"award-number":["JP25K08689"]}],"id":[{"id":"10.13039\/501100001691","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"published-print":{"date-parts":[[2026,9,10]]},"abstract":"<jats:title>Abstract<\/jats:title>\n                  <jats:p>Biological and synthetic systems featuring coexisting amino and carboxy groups, such as amino acids and peptides, serve as vital models for understanding hydrogen-bonded proton transport networks. Unambiguously identifying protonation isomers (protomers) is crucial yet challenging, as their structures are heavily modulated by both intrinsic stabilities and extrinsic solvent environments. Here, we present a comprehensive investigation into the protonation sites and geometric structures of protonated 4-aminobenzoic acid (H+(4ABA)) and 4-aminocinnamic acid (H+(4ACA)) utilizing a synergistic combination of cryogenic ion mobility-mass spectrometry (Cryo-IM-MS), UV photodissociation (UVPD) and IR-UV double-resonance (IR-UV DR) spectroscopy, and quantum chemical calculations. Cryo-IM-MS demonstrates a pronounced solvent-dependent protomer distribution, where electrospray ionization from H2O\/CH3OH = 1:1 and CH3CN solution predominantly yields the O- and N-protomers, respectively. Isomer-selective IR-UV DR spectroscopy successfully pins down the precise spatial orientations of the functional groups. Crucially, H+(4ABA) and H+(4ACA) exhibit markedly distinct photofragmentation pathways driven by the unsaturated alkenyl link in H+(4ACA). While the H+(4ABA) O-protomer undergoes competitive decarboxylation (CO2 loss) and dehydration (H2O loss), the extended \u03c0-conjugation in H+(4ACA) introduces a substantial kinetic bottleneck that completely suppresses CO2 elimination. In the case of the H+(4ACA) N-protomer, the alkenyl group acts as an active, structurally preorganized hydrogen source, facilitating highly efficient H2O loss via a tightly constrained transition state. These results provide profound fundamental insights into how structural modifications and local environments dictate competitive deactivation pathways, offering broader implications for the design and understanding of functional charge-transport materials.<\/jats:p>","DOI":"10.1021\/acs.jpca.6c04038","type":"journal-article","created":{"date-parts":[[2026,9,1]],"date-time":"2026-09-01T15:22:36Z","timestamp":1788276156000},"page":"7141-7152","source":"Crossref","is-referenced-by-count":0,"title":["Elucidating Protomer\nStructures and Fragmentation\nDynamics of Protonated Aminobenzoic and Aminocinnamic Acids via Cryo-Ion\nMobility and Laser Spectroscopy"],"prefix":"10.1021","volume":"130","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-7959-5315","authenticated-orcid":true,"given":"Yoshiya","family":"Inokuchi","sequence":"first","affiliation":[{"name":"Hiroshima University , , , , , and","place":["Higashi-Hiroshima, Hiroshima, Japan, 739-8526"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Kengo","family":"Tsunoda","sequence":"additional","affiliation":[{"name":"Tohoku University , , Aramaki Aza-Aoba, Aoba-ku , ,","place":["Sendai, Japan, 980-8578"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Amiru","family":"Ohata","sequence":"additional","affiliation":[{"name":"Hiroshima University , , , , , and","place":["Higashi-Hiroshima, Hiroshima, Japan, 739-8526"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Motoki","family":"Kida","sequence":"additional","affiliation":[{"name":"Hiroshima University , , , , , and","place":["Higashi-Hiroshima, Hiroshima, Japan, 739-8526"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1575-7570","authenticated-orcid":true,"given":"Satoru","family":"Muramatsu","sequence":"additional","affiliation":[{"name":"Hiroshima University , , , , , and","place":["Higashi-Hiroshima, Hiroshima, Japan, 739-8526"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Keigo","family":"Hattori","sequence":"additional","affiliation":[{"name":"Tohoku University , , Aramaki Aza-Aoba, Aoba-ku , ,","place":["Sendai, Japan, 980-8578"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Daiki","family":"Fuse","sequence":"additional","affiliation":[{"name":"Tohoku University , , Aramaki Aza-Aoba, Aoba-ku , ,","place":["Sendai, Japan, 980-8578"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2397-6896","authenticated-orcid":true,"given":"Keijiro","family":"Ohshimo","sequence":"additional","affiliation":[{"name":"Tohoku University , , Aramaki Aza-Aoba, Aoba-ku , ,","place":["Sendai, Japan, 980-8578"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0822-6285","authenticated-orcid":true,"given":"Fuminori","family":"Misaizu","sequence":"additional","affiliation":[{"name":"Tohoku University , , Aramaki Aza-Aoba, Aoba-ku , ,","place":["Sendai, Japan, 980-8578"]}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"316","published-online":{"date-parts":[[2026,8,27]]},"reference":[{"key":"2026091008071023300_cit1","doi-asserted-by":"publisher","first-page":"1871","DOI":"10.2174\/0929867023368872","article-title":"Drug Evolution: p-Aminobenzoic\nAcid as a Building Block","volume":"9","author":"Kluczyk","year":"2002","journal-title":"Curr. Med. Chem."},{"key":"2026091008071023300_cit2","doi-asserted-by":"publisher","first-page":"88","DOI":"10.3390\/photochem2010008","article-title":"UV Photolysis Study\nof para-Aminobenzoic Acid Using Parahydrogen Matrix Isolated Spectroscopy","volume":"2","author":"McKinnon","year":"2022","journal-title":"Photochem"},{"key":"2026091008071023300_cit3","doi-asserted-by":"publisher","first-page":"8598","DOI":"10.1021\/jp994379r","article-title":"Thermodynamics\nof Macroscopic and Microscopic Proton Ionization from Protonated 4-Aminobenzoic\nAcid in Aqueous Solution from 298.15 to 393.15 K","volume":"104","author":"Zhang","year":"2000","journal-title":"J. Phys. Chem. B"},{"key":"2026091008071023300_cit4","doi-asserted-by":"publisher","first-page":"25474","DOI":"10.1039\/C6CP04941A","article-title":"The Impact\nof Environment and Resonance Effects on the Site of Protonation of\nAminobenzoic Acid Derivatives","volume":"18","author":"Seo","year":"2016","journal-title":"Phys. Chem. Chem.\nPhys."},{"key":"2026091008071023300_cit5","doi-asserted-by":"publisher","first-page":"1321","DOI":"10.1002\/anie.200805392","article-title":"Gas-Phase versus\nLiquid-Phase Structures by Electrospray\nIonization Mass Spectrometry","volume":"48","author":"Tian","year":"2009","journal-title":"Angew. Chem.,\nInt. Ed."},{"key":"2026091008071023300_cit6","doi-asserted-by":"publisher","first-page":"15805","DOI":"10.1021\/ja304929h","article-title":"Where\u2019s the\nCharge? Protonation Sites in Gaseous Ions Change with Hydration","volume":"134","author":"Chang","year":"2012","journal-title":"J. Am. Chem. Soc."},{"key":"2026091008071023300_cit7","doi-asserted-by":"publisher","first-page":"17434","DOI":"10.1039\/C7CP02817B","article-title":"Experiment and\nTheory Confirm that UV Laser Photodissociation\nSpectroscopy Can Distinguish Protomers Formed via Electrospray","volume":"19","author":"Matthews","year":"2017","journal-title":"Phys. Chem. Chem. Phys."},{"key":"2026091008071023300_cit8","doi-asserted-by":"publisher","first-page":"79","DOI":"10.1016\/j.jms.2016.10.020","article-title":"Amine vs. Carboxylic Acid Protonation\nin ortho-, meta-, and para-Aminobenzoic Acid: an IRMPD Spectroscopy\nStudy","volume":"332","author":"Cismesia","year":"2017","journal-title":"J. Mol. Spectrosc."},{"key":"2026091008071023300_cit9","doi-asserted-by":"publisher","first-page":"116427","DOI":"10.1016\/j.ijms.2020.116427","article-title":"Vibrational Spectroscopy\nof the Cryogenically\nCooled O- and N-Protomers of 4-Aminobenzoic Acid: Tag Effects, Isotopic\nLabels, and Identification of the E,Z Isomer of the O-Protomer","volume":"457","author":"Khuu","year":"2020","journal-title":"Int. J. Mass Spectrom."},{"key":"2026091008071023300_cit10","doi-asserted-by":"publisher","first-page":"1428","DOI":"10.1021\/jasms.3c00118","article-title":"Gas-Phase Internal\nProton-Transfer of Protonated para-Aminobenzoic Acid Catalyzed by\nOne Methanol Molecule","volume":"34","author":"Ucur","year":"2023","journal-title":"J. Am. Soc. Mass Spectrom."},{"key":"2026091008071023300_cit11","doi-asserted-by":"publisher","first-page":"2725","DOI":"10.1039\/D3SC05455A","article-title":"Transition\nfrom Vehicle to Grotthuss Proton Transfer in a Nanosized Flask: Cryogenic\nIon Spectroscopy of Protonated p-Aminobenzoic Acid Solvated with D2O","volume":"15","author":"Hirata","year":"2024","journal-title":"Chem. Sci."},{"key":"2026091008071023300_cit12","doi-asserted-by":"publisher","first-page":"1143","DOI":"10.1126\/science.ady1723","article-title":"Microcanonical Kinetics\nof Water-Mediated Proton Transfer in Microhydrated 4-Aminobenzoic\nAcid","volume":"389","author":"Rana","year":"2025","journal-title":"Science"},{"key":"2026091008071023300_cit13","doi-asserted-by":"publisher","first-page":"113532","DOI":"10.1016\/j.phytochem.2022.113532","article-title":"Application of Cinnamic Acid in the\nStructural Modification of Natural Products: A Review","volume":"206","author":"Deng","year":"2023","journal-title":"Phytochemistry"},{"key":"2026091008071023300_cit14","doi-asserted-by":"publisher","first-page":"8999","DOI":"10.1039\/c2cp24056d","article-title":"Nonradiative\nDecay Dynamics of Methyl-4-Hydroxycinnamate and Its Hydrated Complex\nRevealed by Picosecond Pump-Probe Spectroscopy","volume":"14","author":"Shimada","year":"2012","journal-title":"Phys. Chem. Chem. Phys."},{"key":"2026091008071023300_cit15","doi-asserted-by":"publisher","first-page":"244313","DOI":"10.1063\/1.4904268","article-title":"Experimental\nand Theoretical Study\non the Excited-State Dynamics of ortho-meta-and para-Methoxy Methylcinnamate","volume":"141","author":"Miyazaki","year":"2014","journal-title":"J. Chem. Phys."},{"key":"2026091008071023300_cit16","doi-asserted-by":"publisher","first-page":"4001","DOI":"10.1021\/acs.jpclett.6b01643","article-title":"Multistep Intersystem Crossing Pathways in Cinnamate-Based UV-B Sunscreens","volume":"7","author":"Yamazaki","year":"2016","journal-title":"J. Phys. Chem. Lett."},{"key":"2026091008071023300_cit17","doi-asserted-by":"publisher","first-page":"19755","DOI":"10.1039\/C9CP02914A","article-title":"The Direct Observation of the Doorway\n1n\u03c0* State of Methylcinnamate and Hydrogen-Bonding Effects on\nthe Photochemistry of Cinnamate-Based Sunscreens","volume":"21","author":"Kinoshita","year":"2019","journal-title":"Phys. Chem. Chem. Phys."},{"key":"2026091008071023300_cit18","doi-asserted-by":"publisher","first-page":"5580","DOI":"10.1021\/acs.jpca.0c03646","article-title":"Electronic States and\nNonradiative Decay of Cold Gas-Phase Cinnamic Acid Derivatives Studied\nby Laser Spectroscopy with a Laser-Ablation Technique","volume":"124","author":"Iida","year":"2020","journal-title":"J. Phys. Chem. A"},{"key":"2026091008071023300_cit19","doi-asserted-by":"publisher","first-page":"1272","DOI":"10.1021\/acs.jpca.9b11893","article-title":"Electronic State and\nPhotophysics of 2-Ethylhexyl-4-methoxycinnamate as UV-B Sunscreen\nunder Jet-Cooled Condition","volume":"124","author":"Muramatsu","year":"2020","journal-title":"J. Phys. Chem. A"},{"key":"2026091008071023300_cit20","doi-asserted-by":"publisher","first-page":"834","DOI":"10.1039\/D0CP04402D","article-title":"Substitution Effect\non the Nonradiative\nDecay and trans -&gt; cis Photoisomerization Route: a Guideline to\nDevelop\nEfficient Cinnamate-Based Sunscreens","volume":"23","author":"Kinoshita","year":"2021","journal-title":"Phys.\nChem. Chem. Phys."},{"key":"2026091008071023300_cit21","doi-asserted-by":"publisher","first-page":"11","DOI":"10.1140\/epjti\/s40485-023-00098-1","article-title":"Cryogenic\nIon Mobility-Mass Spectrometry for the Study of Conformations of Host-Guest\nComplexes","volume":"10","author":"Ohshimo","year":"2023","journal-title":"EPJ. Technol. Instrum."},{"key":"2026091008071023300_cit22","doi-asserted-by":"publisher","first-page":"8512","DOI":"10.1021\/acs.jpca.5b05328","article-title":"Ultraviolet Photodissociation\nSpectroscopy of the Cold K+\u2022Calix[4]arene Complex\nin the Gas Phase","volume":"119","author":"Inokuchi","year":"2015","journal-title":"J. Phys. Chem. A"},{"key":"2026091008071023300_cit23","doi-asserted-by":"publisher","first-page":"10410","DOI":"10.1021\/acs.jpca.1c09091","article-title":"Conformation of Benzo-12-Crown-4 Complexes with Ammonium\nIons Investigated by Cold Gas-Phase Spectroscopy","volume":"125","author":"Goda","year":"2021","journal-title":"J. Phys. Chem. A"},{"key":"2026091008071023300_cit24","doi-asserted-by":"publisher","DOI":"10.1002\/asia.202500750","article-title":"Photoallylation Mechanism\nof Dicyanobenzenes with Allyltrimethylsilane\nin Solution Investigated by Cold UV and IR Spectroscopy in the Gas\nPhase","volume":"20","author":"Goda","year":"2025","journal-title":"Chem\u2500Asian J."},{"key":"2026091008071023300_cit25","doi-asserted-by":"publisher","first-page":"164319","DOI":"10.1063\/1.2913157","article-title":"Ion Core Structure in (CS2)n+ and (CS2)n\u2013 (n = 3\u201310) Studied by Infrared Photodissociation\nSpectroscopy","volume":"128","author":"Kobayashi","year":"2008","journal-title":"J. Chem. Phys."},{"key":"2026091008071023300_cit26","unstructured":"Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Petersson, G. A.; Nakatsuji, H.; Li, X.; Caricato, M.; Marenich, A. V.; Bloino, J.; Janesko, B. G.; Gomperts, R.; Mennucci, B.; Hratchian, H. P.; Ortiz, J. V.; Izmaylov, A. F.; Sonnenberg, J. L.; Williams-Young, D.; Ding, F.; Lipparini, F.; Egidi, F.; Goings, J.; Peng, B.; Petrone, A.; Henderson, T.; Ranasinghe, D.; Zakrzewski, V. G.; Gao, J.; Rega, N.; Zheng, G.; Liang, W.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Throssell, K.; Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M. J.; Heyd, J. J.; Brothers, E. N.; Kudin, K. N.; Staroverov, V. N.; Keith, T. A.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A. P.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Millam, J. M.; Klene, M.; Adamo, C.; Cammi, R.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Farkas, O.; Foresman, J. B.; Fox, D. J.;  Gaussian 16 Rev. C.01: Wallingford, CT, 2016."},{"key":"2026091008071023300_cit27","doi-asserted-by":"publisher","first-page":"1540","DOI":"10.1007\/s13361-017-1661-8","article-title":"Benchmark\nComparison for a Multi-Processing Ion Mobility Calculator in the Free\nMolecular Regime","volume":"28","author":"Shrivastav","year":"2017","journal-title":"J. Am. Soc. Mass Spectrom."},{"key":"2026091008071023300_cit28","doi-asserted-by":"publisher","first-page":"8281","DOI":"10.1021\/acs.jpclett.3c01996","article-title":"Highly Efficient\nIntramolecular Proton\nTransfer in p-Aminobenzoic Acid by a Single Ammonia Molecule as a\nVehicle","volume":"14","author":"Ohshimo","year":"2023","journal-title":"J. Phys. Chem. Lett."},{"key":"2026091008071023300_cit29","doi-asserted-by":"publisher","first-page":"2081","DOI":"10.1021\/acs.jpcb.9b10576","article-title":"Tracking the Structural\nEvolution of 4-Aminobenzoic\nAcid in the Transition from Solution to the Gas Phase","volume":"124","author":"Hebert","year":"2020","journal-title":"J. Phys. Chem. B"},{"key":"2026091008071023300_cit30","doi-asserted-by":"publisher","first-page":"725","DOI":"10.1021\/jasms.0c00430","article-title":"Impact of Ambient Vapors Present in an Electrospray\nIonization Source on Gas-Phase Ion Structures","volume":"32","author":"Zheng","year":"2021","journal-title":"J. Am. Soc. Mass Spectrom."}],"container-title":["The Journal of Physical\nChemistry A"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/pubs.acs.org\/doi\/pdf\/10.1021\/acs.jpca.6c04038","content-type":"application\/pdf","content-version":"vor","intended-application":"unspecified"},{"URL":"https:\/\/pubs.acs.org\/jpcafh\/article-pdf\/130\/36\/7141\/67463308\/acs.jpca.6c04038.pdf","content-type":"application\/pdf","content-version":"vor","intended-application":"syndication"},{"URL":"https:\/\/pubs.acs.org\/jpcafh\/article-pdf\/130\/36\/7141\/67463308\/acs.jpca.6c04038.pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,9,10]],"date-time":"2026-09-10T12:19:48Z","timestamp":1789042788000},"score":1,"resource":{"primary":{"URL":"https:\/\/pubs.acs.org\/jpcafh\/article\/130\/36\/7141\/5334516\/Elucidating-Protomer-Structures-and-Fragmentation"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,8,27]]},"references-count":30,"journal-issue":{"issue":"36","published-online":{"date-parts":[[2026,8,27]]},"published-print":{"date-parts":[[2026,9,10]]}},"URL":"https:\/\/doi.org\/10.1021\/acs.jpca.6c04038","relation":{},"ISSN":["1089-5639","1520-5215"],"issn-type":[{"value":"1089-5639","type":"print"},{"value":"1520-5215","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,8,27]]}}}