1
−
10.0 kcal mol− , respectively, which is comparable with the
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energies obtained from the fluorimetric titration Table S2 (ESI†).
It was also noteworthy that [Ru(bpy) (dppzi)] possessed a
2
+
2
much more favorable binding interaction (lower binding free
energy) with the hybrid-type G-quadruplex than the antiparallel
basket G-quadruplex. Such reliable end-stacking of compounds
onto the G-quartet are in agreement with previously reported
aromatic quadruplex ligands. Thus, the molecular modeling
studies explained why the photoluminescence of [Ru-
bpy) (dppzi)] can be tuned by the successive introduction of
2
Fe(CN)6] ions and G-quadruplex DNA and confirmed the
excellent complementarity in the binding modes.
In summary, cycling of the G-quadruplex DNA “light switch”
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(
[
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−
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2+
off and on has been accomplished for [Ru(bpy) (dppzi)]
2
4
−
through the successive introduction of [Fe(CN)6] ions and G-
quadruplex DNA, respectively. To the best of our knowledge,
this work presents the first example of a reversible G-quadruplex
DNA light switch. Furthermore, the mechanism of cycling of the
G-quadruplex DNA “light switch” in this work is different from
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9
,10
the mechanism reported in other “light switches”.
The switch
4−
can be cycled through the competition of [Fe(CN)6] ions and
G-quadruplex DNA. The discovery of the binding features of
2
+
[
Ru(bpy) (dppzi)]
with G-quadruplex DNA may show
2
promise for probing G-quadruplex DNA and provide a more
comprehensive understanding of the molecular recognition of
G-quadruplex DNA.
92, 370.
1
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Acknowledgements
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This work was supported by the National Natural Science Foun-
dation of China (20901060, 31170776, 20871094, 81171646)
and the Fundamental Research Funds for the Central
Universities.
1
5 (a) X. Li, Y. H. Peng, J. S. Ren and X. G. Qu, Proc. Natl. Acad.
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