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Article: Mechanistic Examination of Cβ–Cγ Bond Cleavages of Tryptophan Residues During Dissociations of Molecular Peptide Radical Cations

TitleMechanistic Examination of Cβ–Cγ Bond Cleavages of Tryptophan Residues During Dissociations of Molecular Peptide Radical Cations
Authors
Issue Date2013
PublisherAmerican 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?
AbstractIn 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 Identifierhttp://hdl.handle.net/10722/163808
ISSN
2015 Impact Factor: 2.883
2015 SCImago Journal Rankings: 1.231
ISI Accession Number ID

 

DC FieldValueLanguage
dc.contributor.authorSong, Ten_US
dc.contributor.authorMa, CYen_US
dc.contributor.authorChu, IKen_US
dc.contributor.authorSiu, CKen_US
dc.contributor.authorLaskin, J-
dc.date.accessioned2012-09-20T07:52:02Z-
dc.date.available2012-09-20T07:52:02Z-
dc.date.issued2013en_US
dc.identifier.citationThe Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment and General Theory, 2013, v. 117 n. 6, p. 1059-1068en_US
dc.identifier.issn1089-5639-
dc.identifier.urihttp://hdl.handle.net/10722/163808-
dc.description.abstractIn 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.languageengen_US
dc.publisherAmerican Chemical Society. The Journal's web site is located at http://pubs.acs.org/jpca-
dc.relation.ispartofThe Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment and General Theoryen_US
dc.subject.meshCations - chemistry-
dc.subject.meshPeptides - chemistry-
dc.subject.meshQuantum Theory-
dc.subject.meshThermodynamics-
dc.subject.meshTryptophan - chemistry-
dc.titleMechanistic Examination of Cβ–Cγ Bond Cleavages of Tryptophan Residues During Dissociations of Molecular Peptide Radical Cationsen_US
dc.typeArticleen_US
dc.identifier.emailSong, T: songtaoo@hku.hken_US
dc.identifier.emailMa, CY: macy@hkucc.hku.hken_US
dc.identifier.emailChu, IK: ivankchu@hku.hk-
dc.identifier.authorityMa, CY=rp00759en_US
dc.identifier.doi10.1021/jp303562e-
dc.identifier.pmid22697598-
dc.identifier.scopuseid_2-s2.0-84873930474-
dc.identifier.hkuros208687en_US
dc.identifier.hkuros234200-
dc.identifier.volume117-
dc.identifier.issue6-
dc.identifier.spage1059-
dc.identifier.epage1068-
dc.identifier.isiWOS:000315181700010-
dc.publisher.placeUnited States-

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