title: On the mechanism of electron-capture-induced dissociation of peptide dications from 15n-labeling and crown-ether complexation.
abstract: 15N-labeling of di- and tripeptides reveals that electron capture to doubly protonated peptides results almost exclusively in ammonia loss from the N-terminal end, which clearly shows that a significant fraction of electron capture occurs at this end. In accordance with this finding, the competing channel of N-Calpha bond breakage leads to z+* ions and neutral c fragments after electron capture to small dications. In larger peptides that live long enough for internal proton exchanges to occur, c+ ions are also formed and in some cases in dominant yield. Attachment of one or two crown ethers to ammonium groups is likely to reduce the probability of proton transfer, which enhances the formation of z+* relative to c+. The total yield of z+* and c+ is, however, more or less unchanged, which indicates that proton transfer or hydrogen transfer from a NH3 group to the amide group is not required for the N-Calpha bond breakage.
authors.affiliation: Department of Physics and Astronomy, University of Aarhus, Ny Munkegade, DK-8000 Aarhus C, Denmark, School of Physics and Electronics, Henan University, Kaifeng, 475001, China.
authors.forename: Anne I S
authors.initials: AI
authors.lastname: Holm
authors.forename: Preben
authors.initials: P
authors.lastname: Hvelplund
authors.forename: Umesh
authors.initials: U
authors.lastname: Kadhane
authors.forename: Mikkel Koefoed
authors.initials: MK
authors.lastname: Larsen
authors.forename: Bo
authors.initials: B
authors.lastname: Liu
authors.forename: Steen Brøndsted
authors.initials: SB
authors.lastname: Nielsen
authors.forename: Subhasis
authors.initials: S
authors.lastname: Panja
authors.forename: Jan Mondrup
authors.initials: JM
authors.lastname: Pedersen
authors.forename: Troels
authors.initials: T
authors.lastname: Skrydstrup
authors.forename: Kristian
authors.initials: K
authors.lastname: Støchkel
authors.forename: Evan R
authors.initials: ER
authors.lastname: Williams
authors.forename: Esben S
authors.initials: ES
authors.lastname: Worm