{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,4]],"date-time":"2026-03-04T08:17:51Z","timestamp":1772612271373,"version":"3.50.1"},"reference-count":49,"publisher":"Wiley","issue":"5","license":[{"start":{"date-parts":[[2024,1,15]],"date-time":"2024-01-15T00:00:00Z","timestamp":1705276800000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/creativecommons.org\/licenses\/by-nc-nd\/4.0\/"}],"content-domain":{"domain":["analyticalsciencejournals.onlinelibrary.wiley.com"],"crossmark-restriction":true},"short-container-title":["Rapid Comm Mass Spectrometry"],"published-print":{"date-parts":[[2024,3,15]]},"abstract":"<jats:sec>\n                    <jats:title>Rationale<\/jats:title>\n                    <jats:p>\n                      There are a growing number of examples of protomers formed via electrospray ionization (ESI) that do not fragment under mobile proton conditions, giving rise to distinct tandem mass spectra. To model the\n                      <jats:italic>N<\/jats:italic>\n                      \u2010protomer of 4\u2010aminobenzoic acid, here we study the gas\u2010phase unimolecular and bimolecular chemistry of the 4\u2010(carboxyphenyl)trimethylammonium ion.\n                    <\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Methods<\/jats:title>\n                    <jats:p>\n                      4\u2010(Carboxyphenyl)trimethylammonium iodide was synthesized, purified via recrystallization and transferred to the gas phase via ESI. 4\u2010(Carboxyphenyl)trimethylammonium ion,\n                      <jats:bold>7<\/jats:bold>\n                      , was mass selected and subjected to collision\u2010induced dissociation and ion\u2013molecule reactions in a linear ion trap mass spectrometer.\n                    <\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Results<\/jats:title>\n                    <jats:p>\n                      The major fragmentation channel for the fixed\u2010charge cation\n                      <jats:bold>7<\/jats:bold>\n                      is methyl radical loss, whereas loss of trimethylamine and CO\n                      <jats:sub>2<\/jats:sub>\n                      represents minor pathways. The free carboxylic acid functional group of\n                      <jats:bold>7<\/jats:bold>\n                      is unreactive toward a number of neutral reagents (methanol, acetone, acetonitrile, and\n                      <jats:italic>N<\/jats:italic>\n                      ,\n                      <jats:italic>N\u2032<\/jats:italic>\n                      \u2010diisopropylcarbodiimide).\n                      <jats:bold>7<\/jats:bold>\n                      reacts very slowly with trimethylborate via addition\u2010elimination, consistent with density functional theory (DFT) calculations that show this reaction is slightly endothermic. The deuterated cation\n                      <jats:bold>7(D)<\/jats:bold>\n                      undergoes slow D\/H exchange with ethanol, and DFT calculations reveal that a flip\u2010flop mechanism operates.\n                    <\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Conclusions<\/jats:title>\n                    <jats:p>\n                      The free carboxylic group of\n                      <jats:bold>7<\/jats:bold>\n                      is not very reactive toward neutral reagents in the gas phase.\n                    <\/jats:p>\n                  <\/jats:sec>","DOI":"10.1002\/rcm.9681","type":"journal-article","created":{"date-parts":[[2024,1,15]],"date-time":"2024-01-15T06:24:17Z","timestamp":1705299857000},"update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":4,"title":["A fixed\u2010charge model of the\n                    <i>N<\/i>\n                    \u2010protomer of 4\u2010aminobenzoic acid to facilitate the study of the unimolecular and bimolecular chemistry of its \u201cneutral\u201d carboxylic acid group"],"prefix":"10.1002","volume":"38","author":[{"given":"Beiang","family":"Zhang","sequence":"first","affiliation":[{"name":"School of Chemistry and Bio21 Molecular Science and Biotechnology Institute University of Melbourne  Parkville Victoria Australia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Laura","family":"Burchill","sequence":"additional","affiliation":[{"name":"School of Chemistry and Bio21 Molecular Science and Biotechnology Institute University of Melbourne  Parkville Victoria Australia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Weam A. 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