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Internet Electronic Journal of Molecular Design - IEJMD, ISSN 1538-6414, CODEN IEJMAT
| ABSTRACT - Internet Electron. J. Mol. Des. July 2004, Volume 3, Number 7, 368-378 |
Fluorine-Substituted Phenols as Probes to Study Intermolecular Proton Transfer
Induced by Excess Electron Attachment to Uracil-Phenol Complexes
Maciej Haranczyk and Maciej Gutowski
Internet Electron. J. Mol. Des. 2004, 3, 368-378
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Abstract:
The experiments suggest that low-energy electrons, possibly
localized on nucleic acid bases, induce DNA damage. The results
of our recent studies strongly suggest that the excess electron
attachment to the complex of a nucleic acid base with an amino
acid can induce a barrier-free proton transfer (BFPT) from the
amino acid to the O8 of uracil. The driving force for the proton
transfer is to stabilize the excess electron localized on a π*
orbital. Our further studies also demonstrated that BFPT occurs
in anionic complexes of uracil with alanine, formic acid, as well
as H2Se and H2S. We briefly determined factors
governing the occurrence of proton transfer in complexes between anionic
nucleic acid bases (NABs) and proton donors. We found that the
occurrence of BFPT in the uracil complexes is an outcome of the
interplay between the deprotonation energy of a proton donor
and the protonation energy of the anion of uracil. The density
functional theory (DFT) was applied as our research method. The
B3LYP and MPW1K exchange-correlation functionals with 6-31++G**
(5d) basis set were used. The substitution of five
hydrogen atoms with fluorine atoms in phenol molecule
decreases the energy of deprotonation from 15.3 eV to 14.4 eV.
There are 5 groups of F-substituted phenol isomers and 19
structures in total. These 19 molecules provide fine grid on the
scale of deprotonation energy and can be used as a probe to study
the BFPT phenomenon. In the case of uracil-2,3,4,5,6-pentafluorophenol
and uracil-2,4,6-trifluorophenol complexes,
the excess electron attachment can induce BFPT from the
hydroxyl group to the O8 atom of U, with the products being a
hydrogenated uracil and a deprotonated fluorophenol. No BFPT
is predicted for the anions of other uracil-phenol complexes. The
estimated critical value of deprotonation energy of a
F-substituted phenol for which BFPT takes place is 14.86-15.38
eV. Further studies can be preformed to obtain a higher accuracy
of this estimation.
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