Visible Multiphoton Dissociation of Chromophore-Tagged Peptides

Abstract

The visible photodissociation mechanisms of QSY7-tagged peptides of increasing size have been investigated by coupling a mass spectrometer and an optical parametric oscillator laser beam. The experiments herein consist of energy resolved collision- and laser-induced dissociation measurements on the chromophore-tagged peptides. The results show that fragmentation occurs by similar channels in both activation methods, but that the branching ratios are vastly different. Observation of a size-dependent minimum laser pulse energy required to induce fragmentation, and collisional cooling rates in time resolved experiments show that laser-induced dissociation occurs through the absorption of multiple photons by the chromophore and the subsequent heating through vibrational energy redistribution. The differences in branching ratio between collision- and laser-induced dissociation can then be understood by the highly anisotropic energy distribution following absorption of a photon. Graphical Abstractᅟ Electronic supplementary materialThe online version of this article (doi:10.1007/s13361-017-1733-9) contains supplementary material, which is available to authorized users.

Fragmentation patterns of chromophore‐tagged peptides in visible laser induced dissociation

“…All the different AAs are equally distributed and there is no specific AA which is always close or far away from the derivatized cysteine. The different fragmentation ratios observed for the different AAs indicate that IVR is not complete before fragmentation occurs …”

“…However, several peptide‐backbone fragment ions are also detected (Figure a). The observation of fragmentation channels associated with the peptide backbone shows that part of the energy must be redistributed across the entire system despite excitation initially localized at the chromophore, which points to IVR and a global heating of the whole system prior to fragmentation . The major obtained fragments are b‐ and y‐type ions, with some consecutive water losses.…”

“…The observation of fragmentation channels associated with the peptide backbone shows that part of the energy must be redistributed across the entire system despite excitation initially localized at the chromophore, which points to IVR and a global heating of the whole system prior to fragmentation. 39 The major obtained fragments are b-and y-type ions, with some consecutive water losses. They represent more than 90% of all the generated product ions indicating a predominant cleavage of the C-N amide bonds during the LID fragmentation.…”

“…The different fragmentation ratios observed for the different AAs indicate that IVR is not complete before fragmentation occurs. 39 The presence of proline and tryptophan favors the fragmentation of the peptide at these sites. However, the total number of fragment ions along the peptide backbone is important for the identification.…”

Tailored photocleavable peptides: fragmentation and neutralization pathways in high vacuum

“…It has been shown that photocleavage can be optimized using tailored tag molecules that respond to UV light 19 , 20 and visible light, 21 also for peptides with ionization energies exceeding the photon energies of table-top lasers. 22 The heterolytic removal of the leaving group (LG) from a singly charged photo-tagged peptide anion is a promising strategy for the controlled generation of neutral zwitterions in the gas phase 23 ( Scheme 1 ) and can be relevant for proteomics.…”