title: IRMPD spectroscopy shows that AGG forms an oxazolone b2+ ion.
abstract: Infrared multiple photon dissociation (IRMPD) spectroscopy combined with theoretical vibrational spectra provides a powerful tool for probing structure. This technique has been used to probe the structure of protonated cyclic AG and the b(2)(+) ion from AGG. The experimental spectrum for protonated cyclo AG compares very well with the theoretical spectra for a diketopiperazine. The spectrum corresponds best to a combination of two structures protonation at the alanine and glycine amide oxygens. The experimental spectrum for the b(2)(+) ion from protonated AGG matches best to the theoretical spectrum for an oxazolone structure protonated on the ring nitrogen. In particular, the carbonyl stretching band at 1970 cm(-1) is blue-shifted by approximately 200 cm(-1) compared to the experimental spectrum for protonated cAG, indicating that these two structures are distinct. This is the first time that an IRPD spectrum of a b(2)(+) ion has been obtained and, for this ion, the oxazolone structure proposed based on prior calculations and experiments is confirmed by the spectroscopic method.
authors.affiliation: Department of Chemistry, University of Arizona, Tucson, Arizona 85721, USA.
authors.forename: Sung Hwan
authors.initials: SH
authors.lastname: Yoon
authors.forename: Julia
authors.initials: J
authors.lastname: Chamot-Rooke
authors.forename: Brittany R
authors.initials: BR
authors.lastname: Perkins
authors.forename: Amy E
authors.initials: AE
authors.lastname: Hilderbrand
authors.forename: John C
authors.initials: JC
authors.lastname: Poutsma
authors.forename: Vicki H
authors.initials: VH
authors.lastname: Wysocki
mesh_terms: D005583:Fourier Analysis; D008958:Models, Molecular; D009842:Oligopeptides / Q000737:chemistry*; D010081:Oxazolone / Q000031:analogs & derivatives* / Q000737:chemistry; D017785:Photons; D010879:Piperazines / Q000737:chemistry; D011789:Quantum Theory; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods; D013055:Spectrophotometry, Infrared / Q000379:methods; D013816:Thermodynamics
chemical_list: D009842:Oligopeptides; D010879:Piperazines; C516501:alanyl-glycyl-glycine; D010081:Oxazolone