title: Infrared Multiple-Photon Dissociation Action Spectroscopy of the b2+Ion from PPG: Evidence of Third Residue Affecting b2+Fragment Structure.
abstract: Infrared multiple-photon dissociation (IRMPD) action spectroscopy was performed on the b2+fragment ion from the protonated PPG tripeptide. Comparison of the experimental infrared spectrum with computed spectra for both oxazolone and diketopiperazine structures indicates that the majority of the fragment ion population has an oxazolone structure with the remainder having a diketopiperazine structure. This result is in contrast with a recent study of the IRMPD action spectrum of the PP b2+fragment ion from PPP, which was found to be nearly 100% diketopiperazine (Martens et al. Int. J. Mass Spectrom. 2015, 377, 179). The diketopiperazine b2+ion is thermodynamically more stable than the oxazolone but normally requires a trans/cis peptide bond isomerization in the dissociating peptide. Martens et al. showed through IRMPD action spectroscopy that the PPP precursor ion was in a conformation in which the first peptide bond is already in the cis conformation and thus it was energetically favorable to form the thermodynamically-favored diketopiperazine b2+ion. In the present case, solution-phase NMR spectroscopy and gas-phase IRMPD action spectroscopy show that the PPG precursor ion has its first amide bond in a trans configuration suggesting that the third residue is playing an important role in both the structure of the peptide and the associated ring-closure barriers for oxazolone and diketopiperazine formation. Graphical Abstract ᅟ.
authors.affiliation: Department of Chemistry, College of William and Mary, Williamsburg, VA, 23187, USA. jcpout@wm.edu.
authors.forename: John C
authors.identifier: 0000-0002-0085-4079
authors.initials: JC
authors.lastname: Poutsma
authors.affiliation: Radboud University, Institute for Molecules and Materials, FELIX Laboratory, Toernooiveld 7c, NL-6525ED, Nijmegen, The Netherlands.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Martens
authors.affiliation: Radboud University, Institute for Molecules and Materials, FELIX Laboratory, Toernooiveld 7c, NL-6525ED, Nijmegen, The Netherlands.|Van't Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 908, 1098XH, Amsterdam, The Netherlands.
authors.forename: Jos
authors.initials: J
authors.lastname: Oomens
authors.affiliation: Laboratoire de Chimie Physique, CNRS UMR 8000, Université Paris Sud, Université Paris Saclay, CNRS, Orsay, France.
authors.forename: Phillipe
authors.initials: P
authors.lastname: Maitre
authors.affiliation: Laboratoire de Chimie Physique, CNRS UMR 8000, Université Paris Sud, Université Paris Saclay, CNRS, Orsay, France.
authors.forename: Vincent
authors.initials: V
authors.lastname: Steinmetz
authors.affiliation: Department of Chemistry, Ohio State University, Columbus, OH, 43210, USA.
authors.forename: Matthew
authors.initials: M
authors.lastname: Bernier
authors.affiliation: Department of Chemistry, Ohio State University, Columbus, OH, 43210, USA.
authors.forename: Mengxuan
authors.initials: M
authors.lastname: Jia
authors.affiliation: Department of Chemistry, Ohio State University, Columbus, OH, 43210, USA. wysocki11@osu.edu.
authors.forename: Vicki
authors.initials: V
authors.lastname: Wysocki
keywords: IRMPD spectroscopy; Peptide fragments; b2 ions