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Infrared Spectra of Protonated Uracil, Thymine and Cytosine
Author(s) -
Salpin JeanYves,
Guillaumont Sébastien,
Tortajada Jeanine,
MacAleese Luke,
Lemaire Joël,
Maitre Philippe
Publication year - 2007
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.200700284
Subject(s) - infrared multiphoton dissociation , tautomer , thymine , chemistry , quadrupole ion trap , nucleobase , protonation , infrared spectroscopy , ion , infrared , spectroscopy , photochemistry , cytosine , dissociation (chemistry) , ion trap , analytical chemistry (journal) , stereochemistry , physics , dna , biochemistry , organic chemistry , chromatography , quantum mechanics , optics
The gas‐phase structures of protonated uracil, thymine, and cytosine are probed by using mid‐infrared multiple‐photon dissociation (IRMPD) spectroscopy performed at the Free Electron Laser facility of the Centre Laser Infrarouge d′Orsay (CLIO), France. Experimental infrared (IR) spectra are recorded for ions that were generated by electrospray ionization, isolated, and then irradiated in a quadrupole ion trap; the results are compared to the calculated infrared absorption spectra of the different low‐lying isomers (computed at the B3LYP/6‐31++G(d,p) level). For each protonated base, the global energy minimum corresponds to an enolic tautomer, whose infrared absorption spectrum matched very well with the experimental IRMPD spectrum, with the exception of a very weak IRMPD signal observed at about 1800 cm −1 in the case of the three protonated bases. This signal is likely to be the signature of the second‐energy‐lying oxo tautomer. We thus conclude that within our experimental conditions, two tautomeric ions are formed which coexist in the quadrupole ion trap.