Near-Edge X‑ray Absorption Mass Spectrometry of a Gas-Phase Peptide González-Magaña, O; Reitsma, G; Tiemens, M ...
The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory,
11/2012, Letnik:
116, Številka:
44
Journal Article
Recenzirano
We have studied the dissociation of the gas-phase protonated peptide leucine enkephalin YGGFL+H+ upon X-ray absorption in the region of the C K-edge. The yield of photodissociation products was ...recorded as a function of photon energy. The total photoabsorption yield is qualitatively similar to near-edge X-ray absorption fine structure (NEXAFS) spectra recorded from condensed phase peptides and proteins. Fragment specificity reveals distinct quantitative differences between spectra obtained for different masses. Fragmentation channels can be assigned to specific electronic transitions some of which are site specific. For instance, C 1s → π★ excitations in the leucine enkephalin aromatic side chains lead to relatively little fragmentation, whereas such excitations along the peptide backbone induce strong fragmentation.
We have investigated the response of superhydrogenated gas-phase coronene cations upon soft x-ray absorption. Carbon (1s)⟶π^{⋆} transitions were resonantly excited at hν=285 eV. The resulting core ...hole is then filled in an Auger decay process, with the excess energy being released in the form of an Auger electron. Predominantly highly excited dications are thus formed, which cool down by hydrogen emission. In superhydrogenated systems, the additional H atoms act as a buffer, quenching loss of native H atoms and molecular fragmentation. Dissociation and transition state energies for several H loss channels were computed by means of density functional theory. Using these energies as input into an Arrhenius-type cascade model, very good agreement with the experimental data is found. The results have important implications for the survival of polyaromatic hydrocarbons in the interstellar medium and reflect key aspects of graphene hydrogenation.
Until now, photodissociation studies on free complex protonated peptides were limited to the UV wavelength range accessible by intense lasers. We have studied photodissociation of gas-phase ...protonated leucine-enkephalin cations for vacuum ultraviolet (VUV) photons energies ranging from 8 to 40 eV. We report time-of-flight mass spectra of the photofragments and various photofragment-yields as a function of photon energy. For sub-ionization energies our results are in line with existing studies on UV photodissociation of leucine-enkephalin. For photon energies exceeding 10 eV we could identify a new dissociation scheme in which photoabsorption leads to a fast loss of the tyrosine side chain. This loss process leads to the formation of a residual peptide that is remarkably cold internally.
We have studied photoionization of protonated synthetic peptides YG(n)F (n = 0, 1, 3, 5, 10). Photon energies ranging from 8 to 30 eV were used. For YG(n)F peptides up to n = 5 small fragment ions ...related to the sidechains of the aromatic terminal amino acids Y and F dominate the fragmentation patterns. The associated yields scale with total photoabsorption cross section, demonstrating efficient hole migration towards the terminal amino acids upon photoionization of the peptide backbone. For n = 10 the side-chain loss channel is quenched and a series of large dications appear.
The photoionization of Cl+ leading to Cl2+ was measured in the photon energy range of 19.5–28.0eV. A spectrum with a photon energy resolution of 15meV normalized to absolute cross-section ...measurements is presented. The measurements were carried out by merging a Cl+ ion beam with a photon beam of highly monochromatic synchrotron radiation at the Advanced Light Source at Lawrence Berkeley National Laboratory. The measured photoionization of Cl+ consists of several autoionization resonances surperimposed on the direct photoionization signal. Most of the prominent resonances are assigned to members of Rydberg series originating from the singlet ground state and from metastable triplet levels within the ground-state configuration of Cl+. The direct ionization cross section is no larger than 12Mb.
•The single photoionization absolute cross section of Cl+ ion was measured.•Numerous resonances were identified as belonging to Rydberg series.•A large population of the metastable Cl+(1D2) was identified.•Identified resulting Cl2+ state terms correspond to 2D5/2 and 2D3/2.
Double electron capture by protons in collisions with H 2 Salazar-Zepeda, M.H.; Gleason, Cristian; González, Eduardo ...
Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms,
05/2010, Letnik:
268, Številka:
10
Journal Article
Recenzirano
Double electron capture of protons in collisions with molecular hydrogen in the energy range 1.5–10
keV was studied by measuring the resulting
H
-
velocity distributions. In this paper, a technique ...that provides experimental evidence about double capture mechanisms is proposed. In addition, cross-sections for this process were measured in the energy range of 1–5
keV.
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