title: Evidence of diketopiperazine and oxazolone structures for HA b2+ ion.
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.
authors.affiliation: Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona 85721, USA.
authors.forename: Brittany R
authors.initials: BR
authors.lastname: Perkins
authors.forename: Julia
authors.initials: J
authors.lastname: Chamot-Rooke
authors.forename: Sung Hwan
authors.initials: SH
authors.lastname: Yoon
authors.forename: Ashley C
authors.initials: AC
authors.lastname: Gucinski
authors.forename: Arpád
authors.initials: A
authors.lastname: Somogyi
authors.forename: Vicki H
authors.initials: VH
authors.lastname: Wysocki
mesh_terms: D041961:Deuterium Exchange Measurement; D054659:Diketopiperazines / Q000737:chemistry*; D004151:Dipeptides / Q000737:chemistry*; D008958:Models, Molecular; D010081:Oxazolone / Q000737:chemistry*; D010456:Peptides, Cyclic / Q000737:chemistry*; D017785:Photons; D011487:Protein Conformation; D013057:Spectrum Analysis
chemical_list: D054659:Diketopiperazines; D004151:Dipeptides; D010456:Peptides, Cyclic; D010081:Oxazolone