Infrared Multiple-Photon Dissociation Action Spectroscopy of the b2 + Ion from PPG: Evidence of Third Residue Affecting b2 + Fragment Structure
- 205 Downloads
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.
KeywordsPeptide fragments IRMPD spectroscopy b2 ions
This work was supported by the National Science Foundation, JCP: (CHEM:1464763), the National Institutes of Health, JCP (1R15GM116180-01), and the Ohio State University Eminent Scholar Funds. The authors acknowledge the excellent assistance from the FELIX and CLIO operators and staff. J.M. and J.O. are financially supported in part by NWO Chemical Sciences under VICI project no. 724.011.002. The authors also thank the Ohio State NMR Facility for obtaining and analyzing the PPG NMR spectrum.
- 12.Bleiholder, C., Suhai, S., Harrison, A.G., Paizs, B.: Towards understanding the tandem mass spectra of protonated oligopeptides. 2: The proline effect in collision-induced dissociation of protonated Ala-Ala-Xxx-Pro-Ala Xxx = Ala, Ser, Leu, Val, Phe, and Trp). J. Am. Soc. Mass Spectrom. 22, 1032 (2011)CrossRefGoogle Scholar
- 20.Bleiholder, C., Suhai, S., Harrison, A.G., Paizs, B.: Towards understanding the tandem mass spectra of protonated oligopeptides. 2: The proline effect in collision-induced dissociation of protonated Ala-Ala-Xxx-Pro-Ala (Xxx = Ala, Ser, Leu, Val, Phe, and Trp). J. Am. Soc. Mass Spectrom. 21, 1032 (2011)CrossRefGoogle Scholar
- 28.Martens, J.K., Berden, G., Gebhardt, C.R., Oomens, J.: Infrared ion spectroscopy in a nodified quadrupole ion trap mass spectrometer at the FELIX free electron laser laboratory. Rev. Sci. Instrum. 87, doi: 10.1063/1.4964703 (2016)
- 29.Prazeres, R., Glotin, F., Insa, C., Jaroszynski, D.A., Ortega, J.M.: Two-color operation of a free-electron laser and applications in the mid-infrared. Eur. J. Mass Spectrom. 3, 87 (1998)Google Scholar
- 36.Curtin, D.Y.: Stereochemical control of organic reactions. Differences in behavior of diastereomers. 1. Ethane derivatives. The cis effect. Rec. Chem. Prog. 15, 111 (1954)Google Scholar