Characterization of the Oxazolone and Macrocyclic Motifs in the bn (n = 2-5) Product Ions from Collision-Induced Dissociation of Protonated Oligoglycine Peptides with Isomer-Selective, Cryogenic Vibrational Spectroscopy

Ahmed Mohamed; Abhijit Rana; Evan Perez; Franziska Dahlmann; Allison Fry; Fabian S Menges; Michael van Stipdonk; Svenja Jäger; Mark A Boyer; Anne B McCoy; Mark A Johnson

doi:10.1021/jasms.3c00372

Characterization of the Oxazolone and Macrocyclic Motifs in the b_n (n = 2-5) Product Ions from Collision-Induced Dissociation of Protonated Oligoglycine Peptides with Isomer-Selective, Cryogenic Vibrational Spectroscopy

J Am Soc Mass Spectrom. 2024 Feb 7;35(2):326-332. doi: 10.1021/jasms.3c00372. Epub 2023 Dec 27.

Authors

Affiliations

¹ Sterling Chemistry Laboratory, Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States.
² The University of Utah, 315 S. 1400 E. Rm 2020, Henry Eyring Bldg, Salt Lake City, Utah 84112, United States.
³ Institut for Ion Physics and Applied Physics, University of Innsbruck, Technikerstraße 25, 6020 Innsbruck, Austria.
⁴ Center of Excellence in Mass Spectrometry, Center for Metal Ions in Biological and Chemical Systems, Department of Chemistry and Biochemistry, Duquesne University, 600 Forbes Avenue, Pittsburgh, Pennsylvania 15282, United States.
⁵ Chair of Physical Chemistry II, Ruhr-University Bochum, Universitätsstraße 150, 44801 Bochum, Germany.
⁶ Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States.
⁷ Department of Chemistry, University of Washington, Seattle, Washington 98195, United States.

PMID: 38150530
DOI: 10.1021/jasms.3c00372

Abstract

Collision-induced dissociation (CID) of small, protonated peptides leads to the formation of b-type fragment ions that can occur with several structural motifs driven by different covalent intramolecular bonding arrangements. Here, we characterize the so-called "oxazolone" and "macrocycle" b_n ion structures that occur upon CID of oligoglycine peptides (G_n) ions (n = 2-6). This is determined by acquiring the vibrational band patterns of the cryogenically cooled, D₂-tagged b_n ions obtained using isomer-selective, two-color IR-IR photobleaching and analyzing them with predicted (DFT) harmonic spectra for the candidate structures. Both oxazolone and macrocyclic isomers are formed by b₄, whereas only oxazolone species are created for b₂ and b₃ and the macrocycle is created for b₅. As such, n = 4 corresponds to the minimum size where both Oxa and MC forms are present.