Diagnostic NH and OH Vibrations for Oxazolone and Diketopiperazine Structures: b^sub 2^ from Protonated Triglycine

• Published in: Journal of the American Society for Mass Spectrometry 2011-07, Vol.22 (7), p.1197
• Main Authors: Wang, Da, Gulyuz, Kerim, Stedwell, Corey N, Polfer, Nick C
• Format: Article
• Language: English
• Subjects: Carbonyls; Diagnostic systems; Ions; Mass spectrometry; Peptides; Stretching
• ISSN: 1044-0305; 1879-1123
• DOI: 10.1007/s13361-011-0147-3

We present infrared multiple photon dissociation (IRMPD) spectra in the hydrogen stretching region of the simplest b fragment, b2 from protonated triglycine, contrasted to that of protonated cyclo(Gly-Gly). Both spectra confirm the presence of intense, diagnostic vibrations linked to the site of proton attachment. Protonated cyclo(Gly-Gly) serves as a reference spectrum for the diketopiperazine structure, showing a diagnostic O-H+ stretch of the protonated carbonyl group at 3585 cm–1. Conversely, b2 from protonated triglycine exhibits a strong band at 3345 cm–1, associated with the N-H stretching mode of the protonated oxazolone ring structure. Other weaker N-H stretches can also be discerned, such as the amino NH2 and amide NH bands. These results demonstrate the usefulness of the hydrogen stretching region, and hence benchtop optical parametric oscillator/amplifier (OPO/A) set-ups, in making structural assignments of product ions in collision-induced dissociation (CID) of peptides.