Web Release Date: May 11,
Excess Electron Attachment Induces Barrier-Free Proton Transfer in Anionic Complexes of Thymine and Uracil with Formic Acid
czyk,
bkowska,
and
Chemical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352,
Department of Chemistry, University of Gdask, Sobieskiego 18, 80-952 Gdask, Poland, and
Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218
Received: December 18, 2003
Abstract:
The anionic complexes of formic acid with uracil and thymine reveal broad features in photoelectron spectroscopy (PES) experiments with maxima at 1.7 and 1.1 eV, respectively. The results of quantum chemical calculations suggest that electron vertical detachment energies (VDE) of 1.6-1.9 eV correspond to anionic structures in which a proton has been transferred from the carboxylic group of the formic acid to the O8 atom of uracil or thymine. Smaller values of VDE (0.8 to 1.3 eV) correspond to chemically untransformed complexes, in which anionic uracil or thymine interacts through two hydrogen bonds with the carboxylic group of the intact formic acid. The recorded spectra and the results of quantum chemical calculations suggest that both nucleic acid bases undergo barrier-free proton transfer in anionic complexes with formic acid. The difference in experimental spectra of UF- and TF- provides an indication that the methyl group of thymine could make a difference in the intermolecular proton transfer.
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