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. 2009 Dec 9;131(48):17528-9.
doi: 10.1021/ja9054542.

Evidence of diketopiperazine and oxazolone structures for HA b2+ ion

Brittany R Perkins  1 , Julia Chamot-Rooke, Sung Hwan Yoon, Ashley C Gucinski, Arpád Somogyi, Vicki H Wysocki
Affiliations

Evidence of diketopiperazine and oxazolone structures for HA b2+ ion

Brittany R Perkins et al. J Am Chem Soc. .

Abstract

Peptide fragmentation can lead to an oxazolone or diketopiperazine b(2)(+) ion structure. IRMPD spectroscopy combined with computational modeling and gas-phase H/D exchange was used to study the structure of the b(2)(+) ion from protonated HAAAA. The experimental spectrum of the b(2)(+) ion matches both the experimental spectrum for the protonated cyclic dipeptide HA (a commercial diketopiperazine) and the theoretical spectrum for a diketopiperazine protonated at the imidazole pi nitrogen. A characteristic band at 1875 cm(-1) and increased abundance of the peaks at 1619 and 1683 cm(-1) indicate a second population corresponding to an oxazolone species. H/D exchange also shows a mixture of two populations consistent with a mixture of b(2)(+) ion diketopiperazine and oxazolone structures.

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Figures

FIGURE 1
FIGURE 1
IRMPD spectra (fragmentation efficiency vs. wavenumber) of a) the b2+ ion produced by CID fragmentation of protonated HA4 and b) protonated cyclic HA dipeptide. Calculated spectra for selected c) diketopiperazine and d) oxazolone structures. Arrows indicate protonation site.
FIGURE 2
FIGURE 2
H/D exchange of a) protonated cHA and b) HA b2+ ion with increasing exchange time.
See this image and copyright information in PMC

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