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Article: Intramolecular hydrogen atom migration along the backbone of cationic and neutral radical tripeptides and subsequent radical-induced dissociations

TitleIntramolecular hydrogen atom migration along the backbone of cationic and neutral radical tripeptides and subsequent radical-induced dissociations
Authors
Issue Date2012
PublisherRoyal Society of Chemistry. The Journal's web site is located at http://www.rsc.org/pccp
Citation
Physical Chemistry Chemical Physics, 2012, v. 14 n. 24, p. 8723-8731 How to Cite?
Abstract
Dissociation of peptide radical ions involves competition between charge-induced and radical-induced reactions that can be preceded by isomerization. The isomeric radical cations of the peptide methyl ester [GGR-OMe] + and [GGR-OMe] + provide very similar collision-induced dissociation (CID) spectra, suggesting that isomerization occurs prior to fragmentation. They undergo characteristic radical-induced bond cleavage of the peptide N-terminal amide bond resulting in the y 2 + ion, and of the arginine side-chain's C α-C β bond giving protonated allylguanidine {[CH 2CHCH 2NHC(NH 2) 2] +, m/z 100}. The absence of a y 2 + fragment ion in the CID of the radical cationic tripeptide [A CH3GR] + and of an m/z 100 ion in the spectrum of [GA CH3R] + (where A CH3 is an α-aminoisobutyric acid residue, which cannot form an α-carbon-centered radical through hydrogen atom transfer) establishes the importance of hydrogen atom migration along the peptide backbone prior to specific radical-induced fragmentations. Herein we use density functional theory (DFT) at the B3LYP/6-31++G(d,p) level to evaluate the barriers for interconversion between the α-carbon-centered radicals and for dissociation. The radical cations [GGR] + and [GGR] + have their radicals located on the α-carbon atoms of the peptide backbone and their charge densities largely sequestered on the guanidine groups of the side-chain of arginine residues. This is in contrast to the isomeric radical cations of [GGG] +, in which the charge resides necessarily on the peptide backbone. The lower charge densities on the backbones of [GGR] + and [GGR] + result in greater structural flexibility, decreasing the barrier for interconversion between these α-carbon-centered radicals to 36.2 kcal mol -1 (cf. 44.7 kcal mol -1 for [GGG] +). The total absence of charge, assessed by examining intramolecular hydrogen atom transfers among the three α-carbon centers of the isomeric neutral α-carbon-centered triglycine radicals [GGG-H], leads to an additional but slight reduction in enthalpy, to approximately 34 kcal mol -1. This journal is © the Owner Societies 2012.
Persistent Identifierhttp://hdl.handle.net/10722/168652
ISSN
2013 Impact Factor: 4.198
ISI Accession Number ID
References

 

DC FieldValueLanguage
dc.contributor.authorZhao, Jen_US
dc.contributor.authorSong, Ten_US
dc.contributor.authorXu, Men_US
dc.contributor.authorQuan, Qen_US
dc.contributor.authorSiu, KWMen_US
dc.contributor.authorHopkinson, ACen_US
dc.contributor.authorChu, IKen_US
dc.date.accessioned2012-10-08T03:24:00Z-
dc.date.available2012-10-08T03:24:00Z-
dc.date.issued2012en_US
dc.identifier.citationPhysical Chemistry Chemical Physics, 2012, v. 14 n. 24, p. 8723-8731en_US
dc.identifier.issn1463-9076en_US
dc.identifier.urihttp://hdl.handle.net/10722/168652-
dc.description.abstractDissociation of peptide radical ions involves competition between charge-induced and radical-induced reactions that can be preceded by isomerization. The isomeric radical cations of the peptide methyl ester [GGR-OMe] + and [GGR-OMe] + provide very similar collision-induced dissociation (CID) spectra, suggesting that isomerization occurs prior to fragmentation. They undergo characteristic radical-induced bond cleavage of the peptide N-terminal amide bond resulting in the y 2 + ion, and of the arginine side-chain's C α-C β bond giving protonated allylguanidine {[CH 2CHCH 2NHC(NH 2) 2] +, m/z 100}. The absence of a y 2 + fragment ion in the CID of the radical cationic tripeptide [A CH3GR] + and of an m/z 100 ion in the spectrum of [GA CH3R] + (where A CH3 is an α-aminoisobutyric acid residue, which cannot form an α-carbon-centered radical through hydrogen atom transfer) establishes the importance of hydrogen atom migration along the peptide backbone prior to specific radical-induced fragmentations. Herein we use density functional theory (DFT) at the B3LYP/6-31++G(d,p) level to evaluate the barriers for interconversion between the α-carbon-centered radicals and for dissociation. The radical cations [GGR] + and [GGR] + have their radicals located on the α-carbon atoms of the peptide backbone and their charge densities largely sequestered on the guanidine groups of the side-chain of arginine residues. This is in contrast to the isomeric radical cations of [GGG] +, in which the charge resides necessarily on the peptide backbone. The lower charge densities on the backbones of [GGR] + and [GGR] + result in greater structural flexibility, decreasing the barrier for interconversion between these α-carbon-centered radicals to 36.2 kcal mol -1 (cf. 44.7 kcal mol -1 for [GGG] +). The total absence of charge, assessed by examining intramolecular hydrogen atom transfers among the three α-carbon centers of the isomeric neutral α-carbon-centered triglycine radicals [GGG-H], leads to an additional but slight reduction in enthalpy, to approximately 34 kcal mol -1. This journal is © the Owner Societies 2012.en_US
dc.languageengen_US
dc.publisherRoyal Society of Chemistry. The Journal's web site is located at http://www.rsc.org/pccpen_US
dc.relation.ispartofPhysical Chemistry Chemical Physicsen_US
dc.titleIntramolecular hydrogen atom migration along the backbone of cationic and neutral radical tripeptides and subsequent radical-induced dissociationsen_US
dc.typeArticleen_US
dc.identifier.emailChu, IK:ivankchu@hku.hken_US
dc.identifier.authorityChu, IK=rp00683en_US
dc.description.naturelink_to_subscribed_fulltexten_US
dc.identifier.doi10.1039/c2cp40708fen_US
dc.identifier.pmid22614151-
dc.identifier.scopuseid_2-s2.0-84863619477en_US
dc.identifier.hkuros208685-
dc.relation.referenceshttp://www.scopus.com/mlt/select.url?eid=2-s2.0-84863619477&selection=ref&src=s&origin=recordpageen_US
dc.identifier.volume14en_US
dc.identifier.issue24en_US
dc.identifier.spage8723en_US
dc.identifier.epage8731en_US
dc.identifier.isiWOS:000304605600030-
dc.publisher.placeUnited Kingdomen_US
dc.identifier.scopusauthoridZhao, J=8611619900en_US
dc.identifier.scopusauthoridSong, T=36087959100en_US
dc.identifier.scopusauthoridXu, M=23475706200en_US
dc.identifier.scopusauthoridQuan, Q=37018675200en_US
dc.identifier.scopusauthoridSiu, KWM=8967015800en_US
dc.identifier.scopusauthoridHopkinson, AC=15067169300en_US
dc.identifier.scopusauthoridChu, IK=7103327484en_US

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