Recent experimental and theoretical studies have demonstrated
that low-energy electron (LEE) attachment to DNA fragments
may induce strand breaks in DNA.[1C5] Reliable electron
affinities (EAs) for DNA fragments are thus of great importance
in understanding such biologically relevant processes. Studies
of electron attachment to nucleosides and nucleotides have
been performed to elucidate the mechanisms of the charge-induced
strand breaks in DNA.[6C12] These investigations reveal
that the formation of a nucleobase-centered radical anion is
the key stepfor either CO s bond breaking or N1glycosidic
bond rupture in DNA subjected to low-energy electrons.[6C12]
These findings raise new questions as to the influences of solvent
and deprotonation on the EAs of nucleotides. Solvent effects
on the electron-capture process are typically modeled
with gas-phase structures.[6, 7] It must be noted that the phosphate
group in nucleotides is mostly deprotonated under
physiological conditions. Furthermore, radical dianions of nucleotides
have been found to be unstable in the gas phase.[6]
DFT studies of such metastable dianions in the gas phase lack
theoretical rigor.[13] Therefore, the influence on the EAs of nucleotides,
due to the deprotonation of the phosphate group in
aqueous solution, needs to be examined carefully.
Here, we report an investigation of electron attachment to
nucleotides in aqueous solution in an effort to shed light on
the problems discussed above. The 2-deoxythymidine-5-
monophosphates in its neutral and deprotonated forms (denoted
as 5-dTMPH and 5-dTMP) have been selected as
models. For a better description of the influence of the 3-5-
phosphodiester linkage in DNA, the OPO3H moiety was terminated
with a CH3 group(see Scheme 1). This model provides
information, which is directly relevant to the important building
blocks of DNA.