Photodissociation pathways and lifetimes of protonated peptides and their dimers
- Department of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C (Denmark)
- Chemistry Department, Moscow State University, Moscow 119991 (Russian Federation) and Department of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C (Denmark)
- Universite de Lyon, F-69622, Lyon (France) and Universite Lyon 1, Villeurbanne, CNRS, UMR 5579, LASIM (France)
- Universite de Lyon, F-69622, Lyon (France) and Universite Lyon 1, Villeurbanne, CNRS, UMR 5180, Sciences Analytiques (France)
Photodissociation lifetimes and fragment channels of gas-phase, protonated YA{sub n} (n = 1,2) peptides and their dimers were measured with 266 nm photons. The protonated monomers were found to have a fast dissociation channel with an exponential lifetime of {approx}200 ns while the protonated dimers show an additional slow dissociation component with a lifetime of {approx}2 {mu}s. Laser power dependence measurements enabled us to ascribe the fast channel in the monomer and the slow channel in the dimer to a one-photon process, whereas the fast dimer channel is from a two-photon process. The slow (1 photon) dissociation channel in the dimer was found to result in cleavage of the H-bonds after energy transfer through these H-bonds. In general, the dissociation of these protonated peptides is non-prompt and the decay time was found to increase with the size of the peptides. Quantum RRKM calculations of the microcanonical rate constants also confirmed a statistical nature of the photodissociation processes in the dipeptide monomers and dimers. The classical RRKM expression gives a rate constant as an analytical function of the number of active vibrational modes in the system, estimated separately on the basis of the equipartition theorem. It demonstrates encouraging results in predicting fragmentation lifetimes of protonated peptides. Finally, we present the first experimental evidence for a photo-induced conversion of tyrosine-containing peptides into monocyclic aromatic hydrocarbon along with a formamide molecule both found in space.
- OSTI ID:
- 22047152
- Journal Information:
- Journal of Chemical Physics, Vol. 136, Issue 1; Other Information: (c) 2012 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-9606
- Country of Publication:
- United States
- Language:
- English
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