The product of NH3 loss from gas phase protonated tyrosine

Griffin Loebsack; Neville J. A. Coughlan; Lara van Tetering; Yuting Li; Nour Mashmoushi; Yiming Xiao; Mircea Guna; Bradley B. Schneider; J. C. Yves Le Blanc; Jonathan Martens; W. Scott Hopkins

doi:10.1039/D5CP04446D

The product of NH₃ loss from gas phase protonated tyrosine

Griffin Loebsack,

†^abc Neville J. A. Coughlan,†^ab Lara van Tetering,

^de Yuting Li,^ab Nour Mashmoushi,^ab Yiming Xiao,^a Mircea Guna,^f Bradley B. Schneider,^f J. C. Yves Le Blanc,^f Jonathan Martens^de and W. Scott Hopkins*^abc

Author affiliations

* Corresponding authors

^a Department of Chemistry, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, Canada
E-mail: scott.hopkins@uwaterloo.ca

^b Waterloo Institute of Nanotechnology, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, Canada

^c WaterFEL Free Electron Laser Laboratory, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, Canada

^d HFML-FELIX, Toernooiveld 7, 6525 ED Nijmegen, the Netherlands

^e Institute for Molecules and Materials, Radboud University, Heyendaalseweg 135, 6525 AJ Nijmegen, the Netherlands

^f SCIEX, Four Valley Drive, Concord, Ontario, Canada

Abstract

The lowest energy unimolecular dissociation product channel of protonated tyrosine, [Tyr + H]⁺, is loss of NH₃. The structure of the [Tyr − NH₃ + H]⁺ ion is still debated; past calculations suggest that the global minimum benzyl cation form is only accessible via a relatively high barrier and that a lower energy pathway to formation of the higher-energy phenonium isomer is likely to occur via collision-induced dissociation (CID). To resolve this open question, [Tyr − NH₃ + H]⁺ was studied computationally and experimentally using ion mobility spectrometry, ultraviolet photodissociation (UVPD) spectroscopy, and infrared ion spectroscopy (IRIS). Traveling wave ion mobility spectrometry (TWIMS) yields a collision cross section of Ω_N₂ = 130.0 ± 1.4 Å², which compares favorably with computed values of Image ID:d5cp04446d-t1.gif and Image ID:d5cp04446d-t2.gif for the benzyl cation and phenonium products, respectively. Differential mobility spectrometry and mass spectrometry were used to mobility- and mass-select [Tyr + H]⁺ prior to producing [Tyr − NH₃ + H]⁺via CID and subsequently measuring its UVPD spectrum. Similarly, [Tyr − NH₃ + H]⁺ was produced via CID prior to measuring its IRIS spectrum. The UVPD and IRIS spectra indicate that the phenonium ion is the major product formed via CID.