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Issue 17, 2017
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Photodissociation spectroscopy of protonated leucine enkephalin

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Abstract

Protonated leucine enkephalin (YGGFL) was studied by ultraviolet photodissociation (UVPD) from 225 to 300 nm utilizing an optical parametric oscillator tunable wavelength laser system (OPO). Fragments were identified by absolute mass measurement in a 9.4 T Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS). Bond cleavage was preferred in the vicinity of the two aromatic residues, resulting in high ion abundances for a4, a1, b3, y2 and y1 fragments. a, b and y ions dominated the mass spectrum, and full sequence coverage was achieved for those types. Photodissociation was most effective at the short wavelength end of the studied range, which is assigned to the onset of the La π–π* transition of the tyrosine chromophore, but worked well also at the Lb π–π* chromophore absorption maxima in the 35 000–39 000 cm−1 region. Several side-chain and internal fragments were observed. H atom loss is observed only above 41 000 cm−1, consistent with the requirement of a curve crossing to a repulsive 1πσ* state. It is suggested that the photochemically generated mobile H atom plays a role in further backbone cleavages, similar to the mechanism for electron capture dissociation. The b4 fragment is most intense at the Lb chromophore absorptions, undergoing additional fragmentation at higher photon energies. The high resolution of the FT-ICR MS revealed that out of all x and z-type fragments only x3 and x4 were formed, with low intensity. Other previously reported x- and z-fragments were re-assigned to internal fragments, based on exact mass measurement.

Graphical abstract: Photodissociation spectroscopy of protonated leucine enkephalin

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Publication details

The article was received on 09 Dec 2016, accepted on 15 Feb 2017 and first published on 15 Feb 2017


Article type: Paper
DOI: 10.1039/C6CP08436B
Citation: Phys. Chem. Chem. Phys., 2017,19, 10786-10795
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    Photodissociation spectroscopy of protonated leucine enkephalin

    A. Herburger, C. van der Linde and M. K. Beyer, Phys. Chem. Chem. Phys., 2017, 19, 10786
    DOI: 10.1039/C6CP08436B

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