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Article: Intramolecular hydrogen atom migration along the backbone of cationic and neutral radical tripeptides and subsequent radical-induced dissociations
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TitleIntramolecular hydrogen atom migration along the backbone of cationic and neutral radical tripeptides and subsequent radical-induced dissociations
 
AuthorsZhao, J1
Song, T2
Xu, M2
Quan, Q2
Siu, KWM1
Hopkinson, AC1
Chu, IK2
 
Issue Date2012
 
PublisherRoyal Society of Chemistry. The Journal's web site is located at http://www.rsc.org/pccp
 
CitationPhysical Chemistry Chemical Physics, 2012, v. 14 n. 24, p. 8723-8731 [How to Cite?]
DOI: http://dx.doi.org/10.1039/c2cp40708f
 
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.
 
ISSN1463-9076
2013 Impact Factor: 4.198
 
DOIhttp://dx.doi.org/10.1039/c2cp40708f
 
ISI Accession Number IDWOS:000304605600030
 
ReferencesReferences in Scopus
 
DC FieldValue
dc.contributor.authorZhao, J
 
dc.contributor.authorSong, T
 
dc.contributor.authorXu, M
 
dc.contributor.authorQuan, Q
 
dc.contributor.authorSiu, KWM
 
dc.contributor.authorHopkinson, AC
 
dc.contributor.authorChu, IK
 
dc.date.accessioned2012-10-08T03:24:00Z
 
dc.date.available2012-10-08T03:24:00Z
 
dc.date.issued2012
 
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.
 
dc.description.naturelink_to_subscribed_fulltext
 
dc.identifier.citationPhysical Chemistry Chemical Physics, 2012, v. 14 n. 24, p. 8723-8731 [How to Cite?]
DOI: http://dx.doi.org/10.1039/c2cp40708f
 
dc.identifier.doihttp://dx.doi.org/10.1039/c2cp40708f
 
dc.identifier.epage8731
 
dc.identifier.hkuros208685
 
dc.identifier.isiWOS:000304605600030
 
dc.identifier.issn1463-9076
2013 Impact Factor: 4.198
 
dc.identifier.issue24
 
dc.identifier.pmid22614151
 
dc.identifier.scopuseid_2-s2.0-84863619477
 
dc.identifier.spage8723
 
dc.identifier.urihttp://hdl.handle.net/10722/168652
 
dc.identifier.volume14
 
dc.languageeng
 
dc.publisherRoyal Society of Chemistry. The Journal's web site is located at http://www.rsc.org/pccp
 
dc.publisher.placeUnited Kingdom
 
dc.relation.ispartofPhysical Chemistry Chemical Physics
 
dc.relation.referencesReferences in Scopus
 
dc.titleIntramolecular hydrogen atom migration along the backbone of cationic and neutral radical tripeptides and subsequent radical-induced dissociations
 
dc.typeArticle
 
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<contributor.author>Siu, KWM</contributor.author>
<contributor.author>Hopkinson, AC</contributor.author>
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<description.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&apos;s C &#945;-C &#946; 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 &#945;-aminoisobutyric acid residue, which cannot form an &#945;-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 &#945;-carbon-centered radicals and for dissociation. The radical cations [GGR] + and [GGR] + have their radicals located on the &#945;-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 &#945;-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 &#945;-carbon centers of the isomeric neutral &#945;-carbon-centered triglycine radicals [GGG-H], leads to an additional but slight reduction in enthalpy, to approximately 34 kcal mol -1. This journal is &#169; the Owner Societies 2012.</description.abstract>
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Author Affiliations
  1. York University
  2. The University of Hong Kong