1
|
Koopman J, Grimme S. Calculation of Mass Spectra with the QCxMS Method for Negatively and Multiply Charged Molecules. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2022; 33:2226-2242. [PMID: 36343304 DOI: 10.1021/jasms.2c00209] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
Analysis and validation of a mass spectrometry (MS) experiment are usually performed by comparison to reference spectra. However, if references are missing, measured spectra cannot be properly matched. To close this gap, the Quantum Chemical Mass Spectrometry (QCxMS) program has been developed. It enables fully automatic calculations of electron ionization (EI) and positive ion collision-induced dissociation (CID) mass spectra of singly charged molecular ions. In this work, the extension to negative and multiple ion charge for the CID run mode is presented. QCxMS is now capable of calculating structures carrying any charge, without the need for pretabulated fragmentation pathways or machine learning of database spectra. Mass spectra of four single negatively charged and two multiple positively charged organic ions with molecular sizes from 12 to 92 atoms were computed and compared to reference spectra. The underlying Born-Oppenheimer molecular dynamics (MD) calculations were conducted using the semiempirical quantum mechanical GFN2-xTB method, while for some small molecules, ab initio DFT-based MD simulations were performed. Detailed insights into the fragmentation pathways were gained, and the effects of the computed charge assignments on the resulting spectrum are discussed. Especially for the negative ion mode, the influence of the deprotonation site to create the anion was found to be substantial. Doubly charged fragments could successfully be calculated fully automatically for the first time, while higher charged structures introduced severe assignment problems. Overall, this extension of the QCxMS program further enhances its applicability and underlines its value as a sophisticated toolkit for CID-based tandem MS structure elucidation.
Collapse
Affiliation(s)
- Jeroen Koopman
- Mulliken Center for Theoretical Chemistry, Institute for Physical and Theoretical Chemistry, University of Bonn, Beringstr. 4, 53115Bonn, Germany
| | - Stefan Grimme
- Mulliken Center for Theoretical Chemistry, Institute for Physical and Theoretical Chemistry, University of Bonn, Beringstr. 4, 53115Bonn, Germany
| |
Collapse
|
2
|
Wang Y, Lau JKC, Lai CK, Hopkinson AC, Siu KWM. Doubly Charged Small Organic Fragments Derived from [Ce(tripeptide)(CH 3CN) m] 3+ Complexes: Observation of the Elusive [b n + H] 2+ Ions. J Phys Chem B 2019; 123:10192-10201. [PMID: 31693371 DOI: 10.1021/acs.jpcb.9b09090] [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
[a3 + H]2+ ions generated from Ln3+/tripeptide complexes, where Ln = La or Ce, have similar structures to the linear [an]+ ions but with protonation at both the terminal NH2 and N═CH2 groups. Ion stability is favored by having the basic secondary amine of the proline residue at the N-terminus and by an amino acid residue accommodating one of the protons on the side chain. Dissociation of [a3 + H]2+ ions derived from peptides containing only aliphatic residues is by cleavage of the second amide bond to give [b2]+ or [a2]+ ions along with internal [a1]+ ions. For [a3 + H]2+ ions containing a tryptophan residue in the central location, in addition to cleavage of the amide bond, losses of neutrals NH3, HN═CHR, (NH3 + CO), and HNCO were observed. Dissociations of some unsolvated Ln3+/tripeptide complexes gave [b3 + H]2+ ions in low abundance; formation of these [b3 + H]2+ ions was favored by the presence of a proline residue at the N-terminus and by either a histidine or tryptophan residue in the central position. Dissociation of these [b3 + H]2+ ions was by the loss of (H2O + CO) and not only CO, indicating that these ions did not have the same type of oxazolone structure as found for [bn]+ ions. Density functional theory calculations suggest that the observed [b3 + H]2+ ions of ProGlyGly were formed from [Ce(ProGlyGly)]3+ complexes in which the peptide was bound to the metal ion as an enolate. Dissociation of the slightly lower-energy complex, where the peptide is bound in the keto form, would produce an oxazolone but the high barrier required to create this isomer of the [b3 + H]2+ ion would be sufficient to result in further dissociation. Two isomers of the [b3 + H]2+ ion of ProHisGly have been created, one from the [Ce(ProHisGly)]3+ complex that characteristically dissociates by the combined loss of (H2O + CO) and the other by the loss of glycine from [ProHisGlyGly + 2H]2+. The [b3 + H]2+ ion derived from [ProHisGlyGly + 2H]2+ dissociated by the loss of only CO.
Collapse
Affiliation(s)
- Yating Wang
- Department of Chemistry and Centre for Research in Mass Spectrometry , York University , 4700 Keele Street , Toronto , ON M3J 1P3 , Canada
| | - Justin Kai-Chi Lau
- Department of Chemistry and Centre for Research in Mass Spectrometry , York University , 4700 Keele Street , Toronto , ON M3J 1P3 , Canada.,Department of Chemistry and Biochemistry , University of Windsor , 401 Sunset Avenue , Windsor , ON N9B 3P4 , Canada
| | - Cheuk-Kuen Lai
- Department of Chemistry and Centre for Research in Mass Spectrometry , York University , 4700 Keele Street , Toronto , ON M3J 1P3 , Canada
| | - Alan C Hopkinson
- Department of Chemistry and Centre for Research in Mass Spectrometry , York University , 4700 Keele Street , Toronto , ON M3J 1P3 , Canada
| | - K W Michael Siu
- Department of Chemistry and Centre for Research in Mass Spectrometry , York University , 4700 Keele Street , Toronto , ON M3J 1P3 , Canada.,Department of Chemistry and Biochemistry , University of Windsor , 401 Sunset Avenue , Windsor , ON N9B 3P4 , Canada
| |
Collapse
|
3
|
Vertesaljai P, Lebedyeva IO, Oliferenko AA, Qi X, Fu J, Ostrov DA, Asiri AM, Dennis Hall C, Katritzky A. Mimicking a proline tripeptide with pyrazolidines and a cyclopentane linker. Tetrahedron Lett 2015. [DOI: 10.1016/j.tetlet.2015.09.063] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
|
4
|
Verkerk UH, Zhao J, Saminathan IS, Lau JKC, Oomens J, Hopkinson AC, Siu KWM. Infrared multiple-photon dissociation spectroscopy of tripositive ions: lanthanum-tryptophan complexes. Inorg Chem 2012; 51:4707-10. [PMID: 22455512 DOI: 10.1021/ic2026973] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Collision-induced charge disproportionation limits the stability of triply charged metal ion complexes and has thus far prevented successful acquisition of their gas-phase IR spectra. This has curtailed our understanding of the structures of triply charged metal complexes in the gas phase and in biological environments. Herein we report the first gas-phase IR spectra of triply charged La(III) complexes with a derivative of tryptophan (N-acetyl tryptophan methyl ester), and an unusual dissociation product, a lanthanum amidate. These spectra are compared with those predicted using density functional theory. The best structures are those of the lowest energies that differ by details in the π-interaction between La(3+) and the indole rings. Other binding sites on the tryptophan derivative are the carbonyl oxygens. In the lanthanum amidate, La(3+) replaces an H(+) in the amide bond of the tryptophan derivative.
Collapse
Affiliation(s)
- Udo H Verkerk
- Department of Chemistry and Centre for Research in Mass Spectrometry, York University, 4700 Keele Street, Toronto, Ontario M3J 1P3, Canada
| | | | | | | | | | | | | |
Collapse
|
5
|
Saminathan IS, Zhao J, Siu KWM, Hopkinson AC. Doubly charged protonated a ions derived from small peptides. Phys Chem Chem Phys 2011; 13:18307-14. [PMID: 21773645 DOI: 10.1039/c1cp21522a] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Protonated a(2) and a(3) (therefore doubly charged) ions in which both charges lie on the peptide backbone are formed in collision-induced dissociations of [La(III)(peptide)(CH(3)CN)(m)](3+) complexes. Abundant (a(3)+H)(2+) ions are formed from triproline (PPP) and peptides with a proline residue at the N-terminus; these peptides are the most effective in producing ions of the type (a(2)+H)(2+) and (a(3)+H)(2+). A systematic study of the effect of the location of the proline residue and other residues of aliphatic amino acids on the generation of protonated a ions is reported. Density functional theory calculations at B3LYP/6-311++G(d,p) gave the proton affinity of the a(3) ion derived from PPP to be 167.6 kcal mol(-1), 2.6 kcal mol(-1) higher than that of water. The protonated a(2) ions of diglycine and diproline and a(3) ions of triglycine have lower proton affinities and are only observed in lower abundances, possibly due to proton transfer to water in ion-molecule reactions.
Collapse
Affiliation(s)
- Irine S Saminathan
- Department of Chemistry and Centre for Research in Mass Spectrometry, York University, 4700 Keele Street, Toronto, Canada M3J 1P3
| | | | | | | |
Collapse
|