Publication: a2 Ion Derived from Triglycine: An N1-Protonated 4-Imidazolidinone

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Title	a2 Ion Derived from Triglycine: An N1-Protonated 4-Imidazolidinone
Authors/Editors*	Udo H. Verkerk, Chi-Kit Siu, Jeffrey D. Steill, Houssain El Aribi, Junfang Zhao, Christopher F. Rodriquez, Jos Oomens, Alan C. Hopkinson and K. W. Michael Siu
Where published*	The Journal of Physical Chemistry Letters
How published*	Journal
Year*	2010
Volume	1
Number	5
Pages	868-872
Publisher
Keywords
Link	http://pubs.acs.org/doi/abs/10.1021/jz900464a
Abstract	Fragmentation of protonated peptides in the gas phase constitutes the basis for gas-phase sequencing of peptides using tandem mass spectrometry. Several mechanistic studies have indicated possible loss of bn ion sequence information as a consequence of macrocycle formation from internal nucleophilic attacks. Here, we show by infrared multiple-photon dissociation spectroscopy and density functional theory that the prototypical a2 ion generated from protonated triglycine is predominantly a cyclic N1-protonated 4-imidazolidinone. Cyclization resulting from internal nucleophilic attacks therefore may be a more general phenomenon than anticipated.