title: Infrared spectra of protonated uracil, thymine and cytosine.
abstract: 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.
authors.affiliation: Laboratoire d'Analyse et de Modélisation pour la Biologie et l'Environnement (LAMBE), Université d'Evry Val d'Esonne-CNRS, Bâtiment Maupertuis, Boulevard François Mitterrand, 91025 Evry, France. jean-yves.salpin@univ-evry.fr
authors.forename: Jean-Yves
authors.initials: JY
authors.lastname: Salpin
authors.forename: Sébastien
authors.initials: S
authors.lastname: Guillaumont
authors.forename: Jeanine
authors.initials: J
authors.lastname: Tortajada
authors.forename: Luke
authors.initials: L
authors.lastname: MacAleese
authors.forename: Joël
authors.initials: J
authors.lastname: Lemaire
authors.forename: Philippe
authors.initials: P
authors.lastname: Maitre
mesh_terms: D003596:Cytosine / Q000737:chemistry*; D008958:Models, Molecular; D011522:Protons; D013055:Spectrophotometry, Infrared / Q000379:methods*; D013941:Thymine / Q000737:chemistry*; D014498:Uracil / Q000737:chemistry*
chemical_list: D011522:Protons; D014498:Uracil; D003596:Cytosine; D013941:Thymine