TY - JOUR
T1 - 2,4-Dihydroxy and O2 Protonated Tautomers of dThd and Thd Coexist in the Gas Phase
T2 - Methylation Alters Protonation Preferences versus dUrd and Urd
AU - Wu, R. R.
AU - Yang, Bo
AU - Frieler, C. E.
AU - Berden, G.
AU - Oomens, J.
AU - Rodgers, M. T.
N1 - Publisher Copyright:
© 2015 American Society for Mass Spectrometry.
PY - 2016/3/1
Y1 - 2016/3/1
N2 - The gas-phase structures of protonated thymidine, [dThd + H]+, and its modified form, protonated 5-methyluridine, [Thd + H]+, are examined by infrared multiple photon dissociation (IRMPD) action spectroscopy combined with electronic structure calculations. IRMPD action spectra are measured over the ranges extending from ~600 to 1900 cm-1 and ~2800 to 3800 cm-1 using the FELIX free electron laser and an optical parametric oscillator/amplifier (OPO/OPA) laser system, respectively. Comparisons between the B3LYP/6-311+G(d,p) linear IR spectra calculated for the stable low-energy conformers and the measured IRMPD spectra are used to determine the most favorable tautomeric conformations of [dThd + H]+ and [Thd + H]+ and to identify those populated in the experiments. Both B3LYP and MP2 levels of theory predict a minor 2,4-dihydroxy tautomer as the ground-state conformer of [dThd + H]+ and [Thd + H]+ indicating that the 2'-hydroxyl substituent of Thd does not exert a significant impact on the structural features. [dThd + H]+ and [Thd + H]+ share parallel IRMPD spectral profiles and yields in both the FELIX and OPO regions. Comparisons between the measured IRMPD and calculated IR spectra suggest that minor 2,4-dihydroxy tautomers and O2 protonated conformers of [dThd + H]+ and [Thd + H]+ are populated in the experiments. Comparison of this work to our previous IRMPD spectroscopy study of protonated 2'-deoxyuridine and uridine suggests that the 5-methyl substituent alters the preferences of O2 versus O4 protonation.
AB - The gas-phase structures of protonated thymidine, [dThd + H]+, and its modified form, protonated 5-methyluridine, [Thd + H]+, are examined by infrared multiple photon dissociation (IRMPD) action spectroscopy combined with electronic structure calculations. IRMPD action spectra are measured over the ranges extending from ~600 to 1900 cm-1 and ~2800 to 3800 cm-1 using the FELIX free electron laser and an optical parametric oscillator/amplifier (OPO/OPA) laser system, respectively. Comparisons between the B3LYP/6-311+G(d,p) linear IR spectra calculated for the stable low-energy conformers and the measured IRMPD spectra are used to determine the most favorable tautomeric conformations of [dThd + H]+ and [Thd + H]+ and to identify those populated in the experiments. Both B3LYP and MP2 levels of theory predict a minor 2,4-dihydroxy tautomer as the ground-state conformer of [dThd + H]+ and [Thd + H]+ indicating that the 2'-hydroxyl substituent of Thd does not exert a significant impact on the structural features. [dThd + H]+ and [Thd + H]+ share parallel IRMPD spectral profiles and yields in both the FELIX and OPO regions. Comparisons between the measured IRMPD and calculated IR spectra suggest that minor 2,4-dihydroxy tautomers and O2 protonated conformers of [dThd + H]+ and [Thd + H]+ are populated in the experiments. Comparison of this work to our previous IRMPD spectroscopy study of protonated 2'-deoxyuridine and uridine suggests that the 5-methyl substituent alters the preferences of O2 versus O4 protonation.
KW - 5-Methyluridine
KW - Electronic structure theory
KW - IRMPD action spectroscopy
KW - Protonation
KW - Thymidine
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U2 - 10.1007/s13361-015-1303-y
DO - 10.1007/s13361-015-1303-y
M3 - Article
C2 - 26676730
AN - SCOPUS:84958183449
SN - 1044-0305
VL - 27
SP - 410
EP - 421
JO - Journal of the American Society for Mass Spectrometry
JF - Journal of the American Society for Mass Spectrometry
IS - 3
ER -