IRMPD spectroscopy shows that AGG forms an oxazolone b2+ ion.
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.
Yoon
Sung Hwan
SH
Department of Chemistry, University of Arizona, Tucson, Arizona 85721, USA.
Chamot-Rooke
Julia
J
Perkins
Brittany R
BR
Hilderbrand
Amy E
AE
Poutsma
John C
JC
Wysocki
Vicki H
VH
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
D009842:Oligopeptides; D010879:Piperazines; C516501:alanyl-glycyl-glycine; D010081:Oxazolone