Combining UV photodissociation action spectroscopy with electron transfer dissociation for structure analysis of gas-phase peptide cation-radicals

摘要

We report the first example of using ultraviolet (UV) photodissociation action spectroscopy for the investigation of gas-phase peptide cation-radicals produced by electron transfer dissociation. z-Type fragment ions (.)Gly-Gly-Lys(+), coordinated to 18-crown-6-ether (CE), are generated, selected by mass and photodissociated in the 200-400nm region. The UVPD action spectra indicate the presence of valence-bond isomers differing in the position of the C radical defect, (-Gly)-Gly-Lys(+)(CE), Gly-(-Gly)-Lys(+)(CE) and Gly-Gly-(-Lys(+))(CE). The isomers are readily distinguishable by UV absorption spectra obtained by time-dependent density functional theory (TD-DFT) calculations. In contrast, conformational isomers of these radical types are calculated to have similar UV spectra. UV photodissociation action spectroscopy represents a new tool for the investigation of transient intermediates of ion-electron reactions. Specifically, z-type cation radicals are shown to undergo spontaneous hydrogen atom migrations upon electron transfer dissociation. Copyright (c) 2015 John Wiley & Sons, Ltd.