title: Competitive Hydrogen Atom Migrations Accompanying Cascade Dissociations of Peptide Cation-Radicals of thez+•Type.
abstract: We report a combined experimental and computational study of energy-resolved collision-induced dissociation (ER-CID) and time-resolved infrared multiphoton dissociation (TR-IRMPD) ofz4ions prepared by electron transfer dissociation of peptide (Ala-Ala-Asn-Ala-Arg + 2H)2+ions. Thez4cation-radicals,•ANAR+, undergo competitive dissociations by backbone cleavage and loss of a CONH2radical from the Asn side chain. The backbone cleavage proceeds by radical-assisted dissociation of the Asn Cα-CO bond, forming anx2ion intermediate which rapidly dissociates by HNCO elimination to yield a stablez2fragment ion,•AR+. The ER-CID and TR-IRMPD data were consistent with the consecutive nature of the backbone dissociation but showed different branching ratios for the two major fragmentations. The ER-CID data showed branching ratios 0.6-1.0 for the side-chain and backbone cleavages whereas the TR-IRMPD data showed an earlier onset for the latter dissociation. Computational analysis of the potential energy surface with density functional theory and ab initio calculations was carried out to provide structures and energies for the reactant ions as well as several intermediates, products, and transition states. Dissociation pathways for cis and trans amide conformers were distinguished and their energies were evaluated. The threshold dissociation energies for the backbone and side-chain dissociations were similar in accordance with the experimental ER-CID branching ratio. The TR-IRMPD data were interpreted by different absorbances of intermediates produced by hydrogen atom migrations along the dissociation pathways.
authors.affiliation: Department of Chemistry, University of Wisconsin, Madison, WI, USA.
authors.forename: Aaron R
authors.initials: AR
authors.lastname: Ledvina
authors.affiliation: Department of Chemistry, University of Wisconsin, Madison, WI, USA ; Department of Biomolecular Chemistry, University of Wisconsin, Madison, WI, USA.
authors.forename: Joshua J
authors.initials: JJ
authors.lastname: Coon
authors.affiliation: Department of Chemistry, Bagley Hall, Box 351700, University of Washington, Seattle, WA 98195-1700, USA.
authors.forename: František
authors.initials: F
authors.lastname: Tureček
references.citation: Anal Chem. 2009 May 1;81(9):3208-15
references.pmid: 19364119
references.citation: Anal Chem. 2003 Mar 15;75(6):1267-74
references.pmid: 12659185
references.citation: Anal Chem. 2010 Dec 15;82(24):10068-74
references.pmid: 21062032
references.citation: Anal Chem. 2008 Feb 15;80(4):1111-7
references.pmid: 18198896
references.citation: J Am Soc Mass Spectrom. 2005 Sep;16(9):1523-35
references.pmid: 16023365
references.citation: Chem Rev. 2013 Aug 14;113(8):6691-733
references.pmid: 23651325
references.citation: J Proteome Res. 2007 Aug;6(8):3062-9
references.pmid: 17608403
references.citation: J Am Soc Mass Spectrom. 2010 Aug;21(8):1279-95
references.pmid: 20299240
references.citation: J Proteome Res. 2008 Jan;7(1):130-7
references.pmid: 17997514
references.citation: Mass Spectrom (Tokyo). 2013;2(Spec Iss):S0003
references.pmid: 24349922
references.citation: Eur J Mass Spectrom (Chichester). 2003;9(3):221-2
references.pmid: 12939500
references.citation: J Phys Chem A. 2013 Feb 14;117(6):1360-9
references.pmid: 23311990
references.citation: Proc Natl Acad Sci U S A. 2004 Jun 29;101(26):9528-33
references.pmid: 15210983
references.citation: J Am Chem Soc. 2003 Jul 23;125(29):8949-58
references.pmid: 12862492
references.citation: J Am Soc Mass Spectrom. 2010 Apr;21(4):646-56
references.pmid: 20171118
references.citation: Anal Chem. 2007 Jan 15;79(2):477-85
references.pmid: 17222010
references.citation: J Am Soc Mass Spectrom. 2002 Mar;13(3):241-9
references.pmid: 11908804
references.citation: J Am Chem Soc. 2008 Jan 9;130(1):351-8
references.pmid: 18078340
references.citation: J Am Soc Mass Spectrom. 2012 Aug;23(8):1336-50
references.pmid: 22669761
references.citation: Anal Chem. 2002 Jan 15;74(2):402-12
references.pmid: 11811415
references.citation: J Am Soc Mass Spectrom. 2006 Apr;17(4):576-585
references.pmid: 16503151
references.citation: J Am Soc Mass Spectrom. 2012 Aug;23(8):1351-63
references.pmid: 22669762