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Issue 3, 2016
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R vs. S fluoroproline ring substitution: trans/cis effects on the formation of b2 ions in gas-phase peptide fragmentation

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Abstract

The b2 structures of model systems Xxx-Flp-Ala (Flp = 4R-fluoroproline) and Xxx-flp-Ala (flp = 4S-fluoroproline) (where Xxx is Val or Tyr) were studied by action IRMPD spectroscopy. Proline ring substitutions influence the trans/cis isomerization of the precursor ion, resulting in different b2 fragment ion structures by collision induced dissociation. Vibrational spectra of the b2 ions of Val-Flp and Val-flp exhibit highly intense bands at ~1970 cm−1, revealing that the dominant ion in each case is an oxazolone. The major difference between the spectra of b2 ions for R vs. S fluoroproline is a collection of peaks at 1690 and 1750 cm−1, characteristic of a diketopiperazine structure, which were only present in the 4S-fluoroproline (flp) cases. This suggests only one b2 ion structure (oxazolone) is being formed for Flp-containing peptides, whereas flp-containing peptides produce a mixture of a dominant oxazolone with a lower population of diketopiperazine. In solution, Flp is known to possess a higher trans percentage in the N-terminally adjacent peptide bond, with flp inducing a greater proportion of the cis conformation. The diketopiperazine formation observed here correlates directly with the Ktrans/cis trend previously shown in solution, highlighting that the trans/cis isomerization likelihood for proline residues modified in the 4th position is retained in the gas-phase.

Graphical abstract: R vs. S fluoroproline ring substitution: trans/cis effects on the formation of b2 ions in gas-phase peptide fragmentation

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Publication details

The article was received on 28 Aug 2015, accepted on 07 Dec 2015 and first published on 22 Dec 2015


Article type: Paper
DOI: 10.1039/C5CP05155J
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Phys. Chem. Chem. Phys., 2016,18, 2202-2209

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    R vs. S fluoroproline ring substitution: trans/cis effects on the formation of b2 ions in gas-phase peptide fragmentation

    M. C. Bernier, J. Chamot-Rooke and V. H. Wysocki, Phys. Chem. Chem. Phys., 2016, 18, 2202
    DOI: 10.1039/C5CP05155J

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