VUV action spectroscopy of protonated leucine-enkephalin peptide in the 6-14 eV range

Abstract

We have studied the Vacuum Ultraviolet (VUV) photodissociation of gas-phase protonated leucine-enkephalin peptide ion in the 5.7 to 14 eV photon energy range by coupling a linear quadrupole ion trap with a synchrotron radiation source. We report VUV activation tandem mass spectra at 6.7, 8.4, and 12.8 eV photon energies and photodissociation yields for a number of selected fragments. The obtained results provide insight into both near VUV radiation damage and electronic properties of a model peptide. We could distinguish several absorption bands and assign them to particular electronic transitions, according to previous theoretical studies. The photodissociation yields appear to be very different for the various observed fragmentation channels, depending on both the types of fragments and their position along the peptide backbone. The present results are discussed in light of recent gas-phase spectroscopic data on peptides.

The influence of the methionine residue on the dissociation mechanisms of photoionized methionine-enkephalin probed by VUV action spectroscopy

“…2b. Overall, the high-mass region (above m/z 150) of the mass spectrum of LeuEnk is in good agreement with the spectrum measured at 6.7 eV by Ranković et al [17]. The most intense peak for both peptides is the a 4 fragment at m/z 397.…”

“…In the present article we report an experimental investigation of the protonated pentapeptides leucine-enkephalin (LeuEnk, Tyr-Gly-Gly-Phe-Leu) and its sulfur-containing pendant methionineenkephalin (MetEnk, Tyr-Gly-Gly-Phe-Met) by VUV action spectroscopy. LeuEnk, which has become a mass spectrometry standard [16], has been studied intensively by various activation methods, including VUV radiation [1,17,18], and we have recently reported an X-ray action spectroscopy study of protonated MetEnk at the sulfur L-edge [19]. Our experimental results demonstrate a characteristic influence of the methionine residue on the fragmentation pathways following photoexcitation and photoionization of MetEnk and also complement the existing results on LeuEnk.…”

“…1b) show two weak features A and B at ∼7 eV and ∼10 eV, respectively, an intense main feature C ranging from 14 to 21 eV and a broad, weak feature D in the photon energy range of 21-31 eV. Features A and B are also clearly visible in the ion yield spectra measured by Ranković et al [17].…”

“…8c) is almost entirely absent for both LeuEnk and MetEnk. In contrast, significant yields of b 4 have previously been reported upon VUV photon-induced dissociation of gasphase LeuEnk by Ranković et al [17] at photon energies as low as 5.7 eV. The production of b 4 is the dissociation channel of LeuEnk with the lowest activation energy [16,29,30] and can, consequently, be induced by very low collision energies.…”

“…The b 3 fragment of LeuEnk has a mass of 278 u as well. Previous studies [1,17] could not solve the ambiguity whether the peak at m/z 278 is due to the [LeuEnk+H] 2+• ion, the b 3 fragment or both species. However, the presence of the photoionized LeuEnk precursor ion is clearly confirmed by the isotopic peak detected at m/z 278.5.…”