Photoelectron spectroscopy and density functional theory studies on the uridine homodimer radical anions

Abstract

We report the photoelectron spectrum (PES) of the homogeneous dimer anion radical of uridine, (rU)(2)(●-). It features a broad band consisting of an onset of ∼1.2 eV and a maximum at the electron binding energy (EBE) ranging from 2.0 to 2.5 eV. Calculations performed at the B3LYP∕6-31++G∗∗ level of theory suggest that the PES is dominated by dimeric radical anions in which one uridine nucleoside, hosting the excess charge on the base moiety, forms hydrogen bonds via its O8 atom with hydroxyl of the other neutral nucleoside's ribose. The calculated adiabatic electron affinities (AEAGs) and vertical detachment energies (VDEs) of the most stable homodimers show an excellent agreement with the experimental values. The anionic complexes consisting of two intermolecular uracil-uracil hydrogen bonds appeared to be substantially less stable than the uracil-ribose dimers. Despite the fact that uracil-uracil anionic homodimers are additionally stabilized by barrier-free electron-induced proton transfer, their relative thermodynamic stabilities and the calculated VDEs suggest that they do not contribute to the experimental PES spectrum of (rU)(2)(●-).

Photoelectron spectroscopic and density functional theoretical studies of the 2′-deoxycytidine homodimer radical anion

“…The finding that the strongest stabilization of the anionic nucleoside dimer structures arises from the O3 -H • • • N3 sugar • • • base interaction agrees with our previous studies on the uridine and thymidine homodimer anions. 46,47 Basically, two types of H-bonds that keep together the monomers in the studied dimers are discussed in the current paper as well as in Refs. 46 and 47.…”