title: Diverse mixtures of 2,4-dihydroxy tautomers and O4 protonated conformers of uridine and 2'-deoxyuridine coexist in the gas phase.
abstract: The gas-phase conformations of protonated uridine, [Urd+H](+), and its modified form, protonated 2'-deoxyuridine, [dUrd+H](+), generated by electrospray ionization are investigated using infrared multiple photon dissociation (IRMPD) action spectroscopy techniques. IRMPD action spectra of [Urd+H](+) and [dUrd+H](+) are measured over the IR fingerprint and hydrogen-stretching regions. [Urd+H](+) and [dUrd+H](+) exhibit very similar IRMPD spectral profiles. However, the IRMPD yields of [Urd+H](+) exceed those of [dUrd+H](+) in both the IR fingerprint and hydrogen-stretching regions. The measured spectra are compared to the linear IR spectra predicted for the stable low-energy structures of these species computed at the B3LYP/6-311+G(d,p) level of theory to determine the tautomeric conformations populated by electrospray ionization. Both B3LYP and MP2 methods find O4 and O2 protonated canonical as well as 2,4-dihydroxy tautomers among the stable low-energy structures of [Urd+H](+) and [dUrd+H](+). Comparison between the measured IRMPD and calculated linear IR spectra suggests that these species exist in their ring-closed forms and that both 2,4-dihydroxy tautomers as well as O4 protonated canonical conformers coexist in the population generated by electrospray ionization for both [Urd+H](+) and [dUrd+H](+). The 2'-deoxy modification of [dUrd+H](+) reduces the variety of 2,4-dihydroxy tautomers populated in the experiments vs. those of [Urd+H](+).
authors.affiliation: Department of Chemistry, Wayne State University, Detroit, Michigan 48202, USA. mrodgers@chem.wayne.edu.
authors.forename: R R
authors.initials: RR
authors.lastname: Wu
authors.forename: Bo
authors.initials: B
authors.lastname: Yang
authors.forename: C E
authors.initials: CE
authors.lastname: Frieler
authors.forename: G
authors.initials: G
authors.lastname: Berden
authors.forename: J
authors.initials: J
authors.lastname: Oomens
authors.forename: M T
authors.initials: MT
authors.lastname: Rodgers
mesh_terms: D003857:Deoxyuridine / Q000737:chemistry*; D005740:Gases / Q000737:chemistry; D007536:Isomerism; D008958:Models, Molecular; D008968:Molecular Conformation; D011522:Protons; D013055:Spectrophotometry, Infrared; D014529:Uridine / Q000737:chemistry*
chemical_list: D005740:Gases; D011522:Protons; D003857:Deoxyuridine; D014529:Uridine