VUV photofragmentation of protonated leucine-enkephalin peptide dimer below ionization energy
Résumé
The experimental investigation of 5-8 eV photons induced dissociation of the leucine-enkephalin (Leu-Enk) peptide dimer, performed by coupling a linear ion trap with a synchrotron beamline, in combination with the tandem mass spectrometry, has been reported. The present work extends the existing results on Leu-Enk VUV-induced dissociation to lower sub-ionization photon energy range. The measured tandem mass spectra show that even at the photon energies below the ionization threshold, VUV irradiation of the protonated Leu-Enk dimer precursor can lead to a rich fragmentation pattern, including peptide sequence ions and neutral losses. The photodissociation yields of selected ionic fragments reveal the absorption bands at about 6.7-7.1 eV (185-175 nm). The experimental results have been supported by theoretical description of the [2Leu-Enk + H](+) precursors, optimized at B3LYP/6-31+G(d,p) level of DFT.