title: Conformation-specific spectroscopy of peptide fragment ions in a low-temperature ion trap.
abstract: 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.
authors.affiliation: Laboratoire de Chimie Physique Moléculaire, École Polytechnique Fédérale de Lausanne, 1015, Lausanne, Switzerland.
authors.forename: Tobias N
authors.initials: TN
authors.lastname: Wassermann
authors.forename: Oleg V
authors.initials: OV
authors.lastname: Boyarkin
authors.forename: Béla
authors.initials: B
authors.lastname: Paizs
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Rizzo
mesh_terms: D003080:Cold Temperature; D004743:Enkephalin, Leucine / Q000737:chemistry; D007477:Ions / Q000737:chemistry; D007536:Isomerism; D008968:Molecular Conformation; D009587:Nitrogen Isotopes / Q000737:chemistry; D010455:Peptides / Q000737:chemistry*; D013057:Spectrum Analysis / Q000379:methods*; D053719:Tandem Mass Spectrometry / Q000379:methods
chemical_list: D007477:Ions; D009587:Nitrogen Isotopes; D010455:Peptides; D004743:Enkephalin, Leucine