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J Am Soc Mass Spectrom. 2014 May;25(5):778-89. doi: 10.1007/s13361-014-0832-0. Epub 2014 Feb 19.

Collision-induced dissociation of diazirine-labeled peptide ions. Evidence for Brønsted-acid assisted elimination of nitrogen.

Author information

1
Department of Chemistry, University of Washington, Bagley Hall, Seattle, WA, 98195-1700, USA.

Abstract

Gas-phase dissociations were investigated for several peptide ions containing the Gly-Leu* N-terminal motif where Leu* was a modified norleucine residue containing the photolabile diazirine ring. Collisional activation of gas-phase peptide cations resulted in facile N₂ elimination that competed with backbone dissociations. A free lysine ammonium group can act as a Brønsted acid to facilitate N₂ elimination. This dissociation was accompanied by insertion of a lysine proton in the side chain of the photoleucine residue, as established by deuterium labeling and gas-phase sequencing of the products. Electron structure calculations were used to provide structures and energies of reactants, intermediates, and transition states for Gly-Leu*-Gly-Gly-Lys amide ions that were combined with RRKM calculations of unimolecular rate constants. The calculations indicated that Brønsted acid-catalyzed eliminations were kinetically preferred over direct loss of N₂ from the diazirine ring. Mechanisms are proposed to explain the proton-initiated reactions and discuss the reaction products. The non-catalyzed diazirine ring cleavage and N₂ loss is proposed as a thermometer dissociation for peptide ion dissociations.

PMID:
24549894
DOI:
10.1007/s13361-014-0832-0
[Indexed for MEDLINE]

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