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Title:Cold, Gas-phase Uv And Ir Spectroscopy Of Protonated Leucine Enkephalin And Its Analogues
Author(s):Zwier, Timothy S.
Contributor(s):McLuckey, Scott A; Dean, Jacob C.; Redwine, James; Burke, Nicole L
Subject(s):Mini-symposium: Beyond the Mass-to-Charge Ratio: Spectroscopic Probes of the Structures of Ions
Abstract:The conformational preferences of peptide backbones and the resulting hydrogen bonding patterns provide critical biochemical information regarding the structure-function relationship of peptides and proteins. The spectroscopic study of cryogenically-cooled peptide ions in a mass spectrometer probes these H-bonding arrangements and provides information regarding the influence of a charge site. Leucine enkephalin, a biologically active endogenous opiod peptide, has been extensively studied as a model peptide in mass spectrometry. This talk will present a study of the UV and IR spectroscopy of protonated leucine enkephalin [YGGFL+H]$^{+}$ and two of its analogues: the sodiated [YGGFL+Na]$^{+}$ and C-terminally methyl esterified [YGGFL-OMe+H]$^{+}$ forms. All experiments were performed in a recently completed multi-stage mass spectrometer outfitted with a cryocooled ion trap. Ions are generated via nano-electrospray ionization and the analyte of interest is isolated in a linear ion trap. The analyte ions are trapped in a 22-pole ion trap held at 5 K by a closed cycle helium cryostat and interrogated via UV and IR lasers. Photofragments are trapped and isolated in a second LIT and mass analyzed. Double-resonance UV and IR methods were used to assign the conformation of [YGGFL+H]$^{+}$, using the NH/OH stretch, Amide I, and Amide II regions of the infrared spectrum. The assigned structure contains a single backbone conformation at vibrational/rotational temperatures of ~10 K held together with multiple H-bonds that self-solvate the NH$_{3}$$^{+}$ site. A “proton wire” between the N and C termini reinforces the H-bonding activity of the COO-H group to the F-L peptide bond, whose cleavage results in formation of the b$_{4}$ ion, which is a prevalent, low-energy fragmentation pathway for [YGGFL+H]$^{+}$. The reinforced H-bonding network in conjunction with the mobile proton theory may help explain the prevalence of the b$_{4}$ pathway. In order to elucidate structural changes caused by modifying this H-bonding activity, structural analogues were investigated. Determining the [YGGFL+Na]$^{+}$ structure will lend insight as to the impact of the ammonium group and methyl esterification of the C-terminus eliminates the carboxy proton. The talk will also report on high resolution, cold UV spectra, non-conformation specific IR gain spectra and conformation specific IR dip spectra for the analogues.
Issue Date:2014-06-17
Publisher:International Symposium on Molecular Spectroscopy
Citation Info:Zwier, T.S.; McLuckey, S.A.; Dean, J.C.; Redwine, J.; Burke, N.L. COLD, GAS-PHASE UV AND IR SPECTROSCOPY OF PROTONATED LEUCINE ENKEPHALIN AND ITS ANALOGUES. Proceedings of the International Symposium on Molecular Spectroscopy, Urbana, IL, June 16-21, 2014. DOI: 10.15278/isms.2014.TG11
Rights Information:Copyright 2014 by the authors. Licensed under a Creative Commons Attribution 4.0 International License.
Date Available in IDEALS:2014-09-17

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