Formation of deprotonated 2-imidazoline-4(5)-one product ions in the collision-induced dissociation of some serine-containing dipeptides

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International Journal of Mass Spectrometry, ISSN: 1387-3806, Vol: 381, Issue: 1, Page: 25-32

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Swan, James S.; Findeis, Peter M.; Hilton, Sheena; Lebold, Kathryn M.; Temelso, Berhane; Shields, George C.
Elsevier BV
Physics and Astronomy; Chemistry; Deprotonated Dipeptide; Peptide Fragmentation; 2-Imidazoline-4(5)-One; Density Functional Theory; Diketopiperazine
article description
A deprotonated 2-imidazoline-4(5)-one product ion was observed as a major fragment in the collision-induced dissociation (CID) of several dipeptides containing serine at the C-terminal and an amino acid with an alkyl substituent at the N-terminal. This fragment becomes predominant at high collision energies. The same type of product ion was seen in the CID of cyclo(GlyGly). Labeling GlySer with O-18 suggests that the fragmentation may proceed through a symmetrical intermediate such as a deprotonated diketopiperazine. Density functional theory calculations of GlySer provided a possible mechanism for the fragmentation.