Article: Intramolecular hydrogen atom migration along the backbone of cationic and neutral radical tripeptides and subsequent radical-induced dissociations
| Title | Intramolecular hydrogen atom migration along the backbone of cationic and neutral radical tripeptides and subsequent radical-induced dissociations |
|---|---|
| Authors | Zhao, J1 Song, T2 Xu, M2 Quan, Q2 Siu, KWM1 Hopkinson, AC1 Chu, IK2 |
| Issue Date | 2012 |
| Publisher | Royal 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?] DOI: http://dx.doi.org/10.1039/c2cp40708f |
| 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. |
| ISSN | 1463-9076 2011 Impact Factor: 3.573 2011 SCImago Journal Rankings: 0.304 |
| DOI | http://dx.doi.org/10.1039/c2cp40708f |
| References | References in Scopus |
| dc.contributor.author | Zhao, J |
|---|---|
| dc.contributor.author | Song, T |
| dc.contributor.author | Xu, M |
| dc.contributor.author | Quan, Q |
| dc.contributor.author | Siu, KWM |
| dc.contributor.author | Hopkinson, AC |
| dc.contributor.author | Chu, IK |
| dc.date.accessioned | 2012-10-08T03:24:00Z |
| dc.date.available | 2012-10-08T03:24:00Z |
| dc.date.issued | 2012 |
| dc.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'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.nature | Link_to_subscribed_fulltext |
| dc.identifier.citation | Physical Chemistry Chemical Physics, 2012, v. 14 n. 24, p. 8723-8731 [How to Cite?] DOI: http://dx.doi.org/10.1039/c2cp40708f |
| dc.identifier.doi | http://dx.doi.org/10.1039/c2cp40708f |
| dc.identifier.epage | 8731 |
| dc.identifier.issn | 1463-9076 2011 Impact Factor: 3.573 2011 SCImago Journal Rankings: 0.304 |
| dc.identifier.issue | 24 |
| dc.identifier.pmid | 22614151 |
| dc.identifier.scopus | eid_2-s2.0-84863619477 |
| dc.identifier.spage | 8723 |
| dc.identifier.uri | http://hdl.handle.net/10722/168652 |
| dc.identifier.volume | 14 |
| dc.language | eng |
| dc.publisher | Royal Society of Chemistry. The Journal's web site is located at http://www.rsc.org/pccp |
| dc.publisher.place | United Kingdom |
| dc.relation.ispartof | Physical Chemistry Chemical Physics |
| dc.relation.references | References in Scopus |
| dc.title | Intramolecular hydrogen atom migration along the backbone of cationic and neutral radical tripeptides and subsequent radical-induced dissociations |
| dc.type | Article |
Author Affiliations
- York Universite Canada
- The University of Hong Kong