Conformation-Specific Spectroscopy of Peptide Fragment Ions in a Low-Temperature Ion Trap
Wassermann, Tobias ; Boyarkin, Oleg ; Paizs, Béla ; Rizzo, Thomas
In: Journal of The American Society for Mass Spectrometry, 2012, vol. 23, no. 6, p. 1029-1045
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- We have applied conformer-selective infrared-ultraviolet (IR-UV) double-resonance photofragment spectroscopy at low temperatures in an ion trap mass spectrometer for the spectroscopic characterization of peptide fragment ions. We investigate b- and a-type ions formed by collision-induced dissociation from protonated leucine-enkephalin. The vibrational analysis and assignment are supported by nitrogen-15 isotopic substitution of individual amino acid residues and assisted by density functional theory calculations. Under such conditions, b-type ions of different size are found to appear exclusively as linear oxazolone structures with protonation on the N-terminus, while a rearrangement reaction is confirmed for the a 4 ion in which the side chain of the C-terminal phenylalanine residue is transferred to the N-terminal side of the molecule. The vibrational spectra that we present here provide a particularly stringent test for theoretical approaches