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Title:Conformational specific infrared and ultraviolet spectroscopy of cold YA(D-Pro)AA·H+ ions: a sterochemical "twist" on the proline effect
Author(s):Harrilal, Christopher P.
Contributor(s):Zwier, Timothy S.; McLuckey, Scott A.; Burke, Nicole L.; DeBlase, Andrew F.
Subject(s):Spectroscopy in Traps
Abstract:The “proline effect” is a well-known fragmentation phenomenon in mass spectrometry, in which y-fragments are produced preferentially over b-fragments during the collision induced dissociation of protonated L-proline containing peptide ions. This specific fragmentation channel is favored because of the high basicity of the secondary amine intermediate and the ring instability in alternative b$_{n}^{+}$ products [ASMS 2014, 25, 1705]. In contrast, peptides containing the D-Pro stereoisomer have been shown to largely favor the production of b$_{4}^{+}$ ions over y$_{3}^{+}$ ions. This strongly suggests that differences in the conformational preferences between the D-Pro and L-Pro diastereomers are likely to be responsible but structural evidence has been lacking to date. Using tandem mass spectrometry and IR-UV double resonant action spectroscopy we are able to compare the 3D structures of cold [YA(D-Pro)AA+H]$^{+}$ to [YA(L-Pro)AA+H]$^{+}$ ions. The UV action spectra reveals two major conformers in [YA(D-Pro)AA+H]$^{+}$ and one major conformer in [YA(L-Pro)AA+H]$^{+}$. Clear differences in the hydrogen bonding patterns are apparent between the two conformers observed in the D-Pro specie which are both distinct from the L-Pro diastereomer. Furthermore, conformer and diastereomer specific photofragmentation patterns are observed. It is also noted that a ten-fold photofragment enhancement unique to one of the D-Pro conformers is observed upon absorption of a resonant IR photon after UV excitation. Differences in the excited state photophysics between the two D-Pro conformers suggest that vibrational excitation of S$_{1}$ turns on coupling to the dissociative –Tyr channel in one conformer, while this coupling is already present in the vibronic ground state of the other. Calculated harmonic spectra (M052X/6-31+G$^{}$) of conformers obtained from Monte Carlo searches to the experimental spectra.
Issue Date:2016-06-21
Publisher:International Symposium on Molecular Spectroscopy
Genre:Conference Paper/Presentation
Rights Information:Copyright 2016 by the authors
Date Available in IDEALS:2017-01-26

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