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Foley CD, Lee C, Abou Taka A, Au K, Chollet E, Kubasik MA, McCaslin LM, Zwier TS. Site-Specific Photochemistry along a Protonated Peptide Scaffold. J Am Chem Soc 2024; 146:13282-13295. [PMID: 38687970 DOI: 10.1021/jacs.4c01576] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/02/2024]
Abstract
We present a detailed study of the time-dependent photophysics and photochemistry of a known conformation of the two protonated pentapeptides Leu-enkephalin (Tyrosine-Glycine-Glycine-Phenylalanine-Leucine, YGGFL) and its chromophore-swapped analogue FGGYL, carried out under cryo-cooled conditions in the gas phase. Using ultraviolet-infrared (UV-IR) double resonance, we record excited state IR spectra as a function of time delay between UV and IR pulses. We identify unique Tyr OH stretch transitions due to the S1 state and the vibrationally excited triplet state(s) formed by intersystem crossing, Tn(v). Photofragment mass spectra are recorded out of the S1 origin and following UV-IR double resonance. Several competing site-specific fragmentation pathways are discovered involving peptide backbone cleavage, Tyr side chain loss, and N-terminal NH3 loss mediated by electron transfer. In YGGFL, IR excitation in the S1 state promotes electron transfer (ET) from the aromatic ring to the N-terminal R-NH3+ group leading to loss of neutral NH3. This product channel is missing in FGGYL due to the larger distance for ET from Y(4) to NH3+. Selective loss of the Tyr side chain occurs out of an excited state process following UV excitation and is further enhanced by IR excitation in S1 and Tn(v) states of both YGGFL and FGGYL. Finally, IR excitation in the S1 or Tn(v) states fragments the peptide backbone exclusively at amide(4), producing the b4 cation. We postulate that this selective fragmentation results from intersystem crossing to produce vibrationally excited triplets with enough energy to launch the proton along a proton conduit present in the known starting structure.
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Affiliation(s)
- Casey D Foley
- Gas Phase Chemical Physics, Sandia National Laboratories, Livermore, California 94550, United States
| | - Chin Lee
- Gas Phase Chemical Physics, Sandia National Laboratories, Livermore, California 94550, United States
| | - Ali Abou Taka
- Gas Phase Chemical Physics, Sandia National Laboratories, Livermore, California 94550, United States
| | - Kendrew Au
- Gas Phase Chemical Physics, Sandia National Laboratories, Livermore, California 94550, United States
| | - Etienne Chollet
- Department of Chemistry and Biochemistry, Fairfield University, Fairfield, Connecticut 06824, United States
| | - Matthew A Kubasik
- Department of Chemistry and Biochemistry, Fairfield University, Fairfield, Connecticut 06824, United States
| | - Laura M McCaslin
- Gas Phase Chemical Physics, Sandia National Laboratories, Livermore, California 94550, United States
| | - Timothy S Zwier
- Gas Phase Chemical Physics, Sandia National Laboratories, Livermore, California 94550, United States
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Parker K, Bollis NE, Ryzhov V. Ion-molecule reactions of mass-selected ions. MASS SPECTROMETRY REVIEWS 2024; 43:47-89. [PMID: 36447431 DOI: 10.1002/mas.21819] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
Gas-phase reactions of mass-selected ions with neutrals covers a very broad area of fundamental and applied mass spectrometry (MS). Oftentimes, ion-molecule reactions (IMR) can serve as a viable alternative to collision-induced dissociation and other ion dissociation techniques when using tandem MS. This review focuses on the literature pertaining applications of IMR since 2013. During the past decade considerable efforts have been made in analytical applications of IMR, including advances in one of the major techniques for characterization of unsaturated fatty acids and lipids, ozone-induced dissociation, and the development of a new technique for sequencing of large ions, hydrogen atom attachment/abstraction dissociation. Many advances have also been made in identifying gas-phase chemistry specific to a functional group in organic and biological compounds, which are useful in structure elucidation of analytes and differentiation of isomers/isobars. With "soft" ionization techniques like electrospray ionization having become mainstream for quite some time now, the efforts in the area of metal ion catalysis have firmly moved into exploring chemistry of ligated metal complexes in their "natural" oxidation states allowing to model individual steps of mechanisms in homogeneous catalysis, especially in combination with high-level DFT calculations. Finally, IMR continue to contribute to the body of knowledge in the area of chemistry of interstellar processes.
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Affiliation(s)
- Kevin Parker
- Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, Illinois, USA
| | - Nicholas E Bollis
- Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, Illinois, USA
| | - Victor Ryzhov
- Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, Illinois, USA
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Wu HT, Riggs DL, Lyon YA, Julian RR. Statistical Framework for Identifying Differences in Similar Mass Spectra: Expanding Possibilities for Isomer Identification. Anal Chem 2023; 95:6996-7005. [PMID: 37128750 PMCID: PMC10157605 DOI: 10.1021/acs.analchem.3c00495] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2023] [Accepted: 04/04/2023] [Indexed: 05/03/2023]
Abstract
Isomeric molecules are important analytes in many biological and chemical arenas, yet their similarity poses challenges for many analytical methods, including mass spectrometry (MS). Tandem-MS provides significantly more information about isomers than intact mass analysis, but highly similar fragmentation patterns are common and include cases where no unique m/z peaks are generated between isomeric pairs. However, even in such situations, differences in peak intensity can exist and potentially contain additional information. Herein, we present a framework for comparing mass spectra that differ only in terms of peak intensity and include calculation of a statistical probability that the spectra derive from different analytes. This framework allows for confident identification of peptide isomers by collision-induced dissociation, higher-energy collisional dissociation, electron-transfer dissociation, and radical-directed dissociation. The method successfully identified many types of isomers including various d/l amino acid substitutions, Leu/Ile, and Asp/IsoAsp. The method can accommodate a wide range of changes in instrumental settings including source voltages, isolation widths, and resolution without influencing the analysis. It is shown that quantification of the composition of isomeric mixtures can be enabled with calibration curves, which were found to be highly linear and reproducible. The analysis can be implemented with data collected by either direct infusion or liquid-chromatography MS. Although this framework is presented in the context of isomer characterization, it should also prove useful in many other contexts where similar mass spectra are generated.
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Affiliation(s)
- Hoi-Ting Wu
- Department of Chemistry, University of California, Riverside, California 92521, United States
| | - Dylan L. Riggs
- Department of Chemistry, University of California, Riverside, California 92521, United States
| | - Yana A. Lyon
- Department of Chemistry, University of California, Riverside, California 92521, United States
| | - Ryan R. Julian
- Department of Chemistry, University of California, Riverside, California 92521, United States
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Lau JKC, Esuon F, Berden G, Oomens J, Hopkinson AC, Ryzhov V, Siu KWM. Generation, Characterization, and Dissociation of Radical Cations Derived from Prolyl-glycyl-glycine. J Phys Chem B 2021; 125:6121-6129. [PMID: 34097420 DOI: 10.1021/acs.jpcb.1c01732] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Radical cations of an aliphatic tripeptide prolyl-glycyl-glycine (PGG•+) and its sequence ions [a3 + H]•+ and [b2 - H]•+ have been generated by collision-induced dissociation of the [Cu(Phen)(PGG)]•2+ complex, where Phen = 1,10-phenanthroline. Infrared multiple photon dissociation spectroscopy, ion-molecule reaction experiments, and theoretical calculations have been used to investigate the structures of these ions. The unpaired electron in these three radical cations is located at different α-carbons. The PGG•+ radical cation has a captodative structure with the radical at the α-carbon of the proline residue and the proton on the oxygen of the first amide group. This structure is at the global minimum on the potential energy surface (PES). By contrast, the [a3 + H]•+ and [b2 - H]•+ ions are not the lowest-energy structures on their respective PESs, and their radicals are formally located at the C-terminal and second α-carbons, respectively. Density functional theory calculations on the structures of the ternary copper(II) complex ion suggest that the charge-solvated isomer of the metal complex is the precursor ion that dissociates to give the PGG•+ radical cation. The isomer of the complex in which PGG is bound as a zwitterion dissociates to give the [a3 + H]•+ and [b2 - H]•+ ions.
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Affiliation(s)
- Justin Kai-Chi Lau
- Department of Chemistry and Centre for Research in Mass Spectrometry, York University, 4700 Keele Street, Toronto, Ontario M3J 1P3, Canada.,Department of Chemistry and Biochemistry, University of Windsor, 401 Sunset Avenue, Windsor, Ontario N9B 3P4, Canada
| | - Francis Esuon
- Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, Illinois 60115, United States
| | - Giel Berden
- FELIX Laboratory, Institute for Molecules and Materials, Radboud University, Toernooiveld 7, Nijmegen 6525 ED, the Netherlands
| | - Jos Oomens
- FELIX Laboratory, Institute for Molecules and Materials, Radboud University, Toernooiveld 7, Nijmegen 6525 ED, the Netherlands
| | - Alan C Hopkinson
- Department of Chemistry and Centre for Research in Mass Spectrometry, York University, 4700 Keele Street, Toronto, Ontario M3J 1P3, Canada
| | - Victor Ryzhov
- Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, Illinois 60115, United States
| | - K W Michael Siu
- Department of Chemistry and Centre for Research in Mass Spectrometry, York University, 4700 Keele Street, Toronto, Ontario M3J 1P3, Canada.,Department of Chemistry and Biochemistry, University of Windsor, 401 Sunset Avenue, Windsor, Ontario N9B 3P4, Canada
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