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- Publisher Website: 10.1021/jp303562e
- Scopus: eid_2-s2.0-84873930474
- PMID: 22697598
- WOS: WOS:000315181700010
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Article: Mechanistic Examination of Cβ–Cγ Bond Cleavages of Tryptophan Residues During Dissociations of Molecular Peptide Radical Cations
Title | Mechanistic Examination of Cβ–Cγ Bond Cleavages of Tryptophan Residues During Dissociations of Molecular Peptide Radical Cations |
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Authors | |
Issue Date | 2013 |
Publisher | American Chemical Society. The Journal's web site is located at http://pubs.acs.org/jpca |
Citation | The Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment and General Theory, 2013, v. 117 n. 6, p. 1059-1068 How to Cite? |
Abstract | In this study, we used collision-induced dissociation (CID) to examine the gas-phase fragmentations of [G(n)W](*+) (n = 2-4) and [GXW](*+) (X = C, S, L, F, Y, Q) species. The C(beta)-C(gamma) bond cleavage of a C-terminal decarboxylated tryptophan residue ([M - CO(2)](*+)) can generate [M - CO(2) - 116](+), [M - CO(2) - 117](*+), and [1H-indole](*+) (m/z 117) species as possible product ions. Competition between the formation of [M - CO(2) - 116](+) and [1H-indole](*+) systems implies the existence of a proton-bound dimer formed between the indole ring and peptide backbone. Formation of such a proton-bound dimer is facile via a protonation of the tryptophan gamma-carbon atom as suggested by density functional theory (DFT) calculations. DFT calculations also suggested the initially formed ion 2, the decarboxylated species that is active against C(beta)-C(gamma) bond cleavage, can efficiently isomerize to form a more stable pi-radical isomer (ion 9) as supported by Rice-Ramsperger-Kassel-Marcus (RRKM) modeling. The C(beta)-C(gamma) bond cleavage of a tryptophan residue also can occur directly from peptide radical cations containing a basic residue. CID of [WG(n)R](*+) (n = 1-3) radical cations consistently resulted in predominant formation of [M - 116](+) product ions. It appears that the basic arginine residue tightly sequesters the proton and allows the charge-remote C(beta)-C(gamma) bond cleavage to prevail over the charge-directed one. DFT calculations predicted that the barrier for the former is 6.2 kcal mol(-1) lower than that of the latter. Furthermore, the pathway involving a salt-bridge intermediate also was accessible during such a bond cleavage event. |
Persistent Identifier | http://hdl.handle.net/10722/163808 |
ISSN | 2023 Impact Factor: 2.7 2023 SCImago Journal Rankings: 0.604 |
ISI Accession Number ID |
DC Field | Value | Language |
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dc.contributor.author | Song, T | en_US |
dc.contributor.author | Ma, CY | en_US |
dc.contributor.author | Chu, IK | en_US |
dc.contributor.author | Siu, CK | en_US |
dc.contributor.author | Laskin, J | - |
dc.date.accessioned | 2012-09-20T07:52:02Z | - |
dc.date.available | 2012-09-20T07:52:02Z | - |
dc.date.issued | 2013 | en_US |
dc.identifier.citation | The Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment and General Theory, 2013, v. 117 n. 6, p. 1059-1068 | en_US |
dc.identifier.issn | 1089-5639 | - |
dc.identifier.uri | http://hdl.handle.net/10722/163808 | - |
dc.description.abstract | In this study, we used collision-induced dissociation (CID) to examine the gas-phase fragmentations of [G(n)W](*+) (n = 2-4) and [GXW](*+) (X = C, S, L, F, Y, Q) species. The C(beta)-C(gamma) bond cleavage of a C-terminal decarboxylated tryptophan residue ([M - CO(2)](*+)) can generate [M - CO(2) - 116](+), [M - CO(2) - 117](*+), and [1H-indole](*+) (m/z 117) species as possible product ions. Competition between the formation of [M - CO(2) - 116](+) and [1H-indole](*+) systems implies the existence of a proton-bound dimer formed between the indole ring and peptide backbone. Formation of such a proton-bound dimer is facile via a protonation of the tryptophan gamma-carbon atom as suggested by density functional theory (DFT) calculations. DFT calculations also suggested the initially formed ion 2, the decarboxylated species that is active against C(beta)-C(gamma) bond cleavage, can efficiently isomerize to form a more stable pi-radical isomer (ion 9) as supported by Rice-Ramsperger-Kassel-Marcus (RRKM) modeling. The C(beta)-C(gamma) bond cleavage of a tryptophan residue also can occur directly from peptide radical cations containing a basic residue. CID of [WG(n)R](*+) (n = 1-3) radical cations consistently resulted in predominant formation of [M - 116](+) product ions. It appears that the basic arginine residue tightly sequesters the proton and allows the charge-remote C(beta)-C(gamma) bond cleavage to prevail over the charge-directed one. DFT calculations predicted that the barrier for the former is 6.2 kcal mol(-1) lower than that of the latter. Furthermore, the pathway involving a salt-bridge intermediate also was accessible during such a bond cleavage event. | - |
dc.language | eng | en_US |
dc.publisher | American Chemical Society. The Journal's web site is located at http://pubs.acs.org/jpca | - |
dc.relation.ispartof | The Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment and General Theory | en_US |
dc.subject.mesh | Cations - chemistry | - |
dc.subject.mesh | Peptides - chemistry | - |
dc.subject.mesh | Quantum Theory | - |
dc.subject.mesh | Thermodynamics | - |
dc.subject.mesh | Tryptophan - chemistry | - |
dc.title | Mechanistic Examination of Cβ–Cγ Bond Cleavages of Tryptophan Residues During Dissociations of Molecular Peptide Radical Cations | en_US |
dc.type | Article | en_US |
dc.identifier.email | Song, T: songtaoo@hku.hk | en_US |
dc.identifier.email | Ma, CY: macy@hkucc.hku.hk | en_US |
dc.identifier.email | Chu, IK: ivankchu@hku.hk | - |
dc.identifier.authority | Ma, CY=rp00759 | en_US |
dc.identifier.doi | 10.1021/jp303562e | - |
dc.identifier.pmid | 22697598 | - |
dc.identifier.scopus | eid_2-s2.0-84873930474 | - |
dc.identifier.hkuros | 208687 | en_US |
dc.identifier.hkuros | 234200 | - |
dc.identifier.volume | 117 | - |
dc.identifier.issue | 6 | - |
dc.identifier.spage | 1059 | - |
dc.identifier.epage | 1068 | - |
dc.identifier.isi | WOS:000315181700010 | - |
dc.publisher.place | United States | - |
dc.identifier.issnl | 1089-5639 | - |