Excess Electron Transfer in DNA
J. Phys. Chem. B, Vol. 107, No. 46, 2003 12841
in-Aid for Scientific Research from Ministry of Education,
Science, Sport and Culture of Japan.
Supporting Information Available: Synthesis of naphthal-
imide and iodouridine modified ODN (PDF). This material is
References and Notes
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I
Figure 3. Plots of the protection of the reaction of U by NI vs n
during the γ-radiolysis of aqueous solutions of NI-IU-ODNn and
IU-UNI-ODNn.
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influence across only three or four base pairs, suggesting the
low mobility of excess electron in DNA. Our results further
confirmed the results driven from Sevilla et al.12-16 and early
γ-radiolysis experiments using bromouracil as an electron
acceptor20,21 in which low mobility of electrons in DNA has
been demonstrated.
The measured short migration distances of the attached
electron might be explained in part by fast irreversible trapping
of electrons, due to irreversible protonation of T•- or C•-, in
contrast to the long lifetime of G•+ or deprotonated G• in DNA,
which plays an important role in long-range hole transfer in
DNA.5 Although the reaction of T•- and C•- has been well
studied at low temperature,32-34 there are few reports on the
kinetics of the reaction of T•- and C•- in DNA at room
temperature.35 Thus, the lifetime of T•- or C•- in DNA at
physiological temperature should be addressed in the future
study.
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Conclusions
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In the present study, the distance dependence of excess
electron transfer in DNA following one electron reduction of
DNA was investigated in detail using both pulse radiolysis
(transient absorption measurements) and γ-radiolysis (product
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(31) Since higher concentration of phosphate buffer (50 mM) was
employed for the experiments in Figure 2B, higher reactivities were observed
in Figure 2B compared to those in Figure 2A.
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I
analysis) of NI- and U-modified ODNs. Formation of NI•-
-
according to the decay of eaq was observed during the pulse
radiolysis of NI-modified ODN, while no secondary formation
build-up in the transient absorption of NI•- was observed after
the consumption of eaq-. It may be possible to assume that the
electron-transfer reactions occur faster than that observed during
the pulse radiolysis experiments but are not detected due to the
-
time taken for the bimolecular reaction of eaq with DNA.
However, the yield of NI•- was only 25% of the electron reacted
with NI-ODN, which corresponds to the electron attached at
three base pairs. Thus, electron transfer was observed over no
more than three base pairs. Similar results were also obtained
from the γ-radiolysis experiments where NI exerts its effect as
an electron acceptor for only three or four base pairs. The results
clearly demonstrated the low mobility of the excess electron in
DNA which is in strong contrast to the occurrence of the long-
range hole transfer in DNA.
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M. D. J. Phys. Chem. B 1997, 101, 1460-1467.
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Acknowledgment. We thank the members of the Radiation
Laboratory of SANKEN, Osaka University for running the linear
accelerator. This work has been partly supported by a Grant-