ChemComm
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Notes and references
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Fig. 4 Photoexcited 1-aminoanthracene (AA*) conjugates are capable of injecting
electrons to pyrimidines (Py) but not purines (Pu).
1
3
(a) B. Giese and A. Biland, Chem. Commun., 2002, 667–672; (b) Top. Curr
Chem., ed. G. B. Schuster, Springer, New York, 2004, vol. 236 & 237;
by comparing AA-containing DNA1b and DNA3b with DNA2b and
DNA4b, respectively. The sensitivity of excess electron migration
through A/T base pairs vs. G/C base pairs is even more pro-
nounced for the selective AA donor as evident from a comparison
between DNA2b and DNA4b (Fig. 3). When all parameters are
optimized – donor placement, transport sequence and redox
potential of the excited-state donor – the efficiency of CT increases
by more than 8-fold as represented by DNA1a and DNA4b (Fig. 3).
Alternative explanations for this enhanced efficiency of excess
electron transport were also considered, but none were consistent
with the data or literature precedent. The integrated absorptivities
above 335 nm for both donors were nearly identical (ESI†) and
could not account for differences in electron injection into DNA.
Conformational differences between AA and DN linked to DNA
are also expected to be negligible. Their conjugation to the abasic
parent duplexes increased the thermal stability almost equiva-
lently with an average of +5 1C for DN and +6 1C for AA (ESI†).
(
c) Charge Transfer in DNA: From Mechanism to Application, ed. H.-A.
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(a) S. M. M. Conron, A. K. Thazhathveetil, M. R. Wasielewski, A. L. Burin
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1 C. Wagner and H.-A. Wagenknecht, Chem.–Eur. J., 2005, 11, 1871–1876.
0
Typically, aromatic compounds conjugated to the 5 -terminus
1
1
stack on top of the helix rather than unwind and intercalate into
6,21
the duplex.
The similarity in stabilization detected for terminal 12 (a) P. Kaden, E. Mayer-Enthart, A. Trifonov, T. Fiebig and H.-A.
Wagenknecht, Angew. Chem., Int. Ed., 2005, 44, 1636–1639;
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22
Br
site. Finally, reduction of dU through interduplex transfer of
an electron would not have exhibited the sensitivity to the internal
nucleobase sequence as evident with DNA1–DNA4. Moreover, our
original studies with a related DN conjugate were insensitive to
1
4265–14272; (e) T. Ito, T. Uchida, K. Tanabe, H. Yamada and
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6 (a) H. Sugiyama, Y. Tsutsumi and I. Saito, J. Am. Chem. Soc., 1990,
1
10
conditions that suppress intermolecular processes.
Limiting the available paths for electron migration and
suppressing back electron transfer from the initial charge-
separated states measurably promote excess electron transport
in duplex DNA. These parameters represent only two of the
many that affect transport, but their influence is significant
1
1
1
008, 112, 2144–2149.
1
12, 6720–6721; (b) G. P. Cook and M. M. Greenberg, J. Am. Chem.
enough to support a large increase in its efficiency from the
Soc., 1996, 118, 10025–10030.
Br
aromatic donor to the dU electron trap. Combined with the 17 (a) T. Lindahl, S. Ljungquist, W. Siegert, B. Nyberg and B. Sperens,
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known preference of excess electron transport for A/T vs. G/C
5
,11,18
base pairing,
the efficiency of CT can be controlled by
1
1
2
2
judicious choice of donor potential and DNA sequence. Such
considerations should be incorporated into future systems that
rely on excess electron transport through DNA to convey a
signal, trigger an actuator or initiate other related applications
of nanosystems based on DNA.
Authors would like to thank Dr Neil P. Campbell, Timothy J.
Simons and Angel Li for initial studies and useful discussions.
Financial support from NSF (CHE-0517498) and the Howard
Hughes Medical Institute Undergraduate Science Education
Program are also gratefully acknowledged.
1
1, 1768–1773.
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This journal is c The Royal Society of Chemistry 2013
Chem. Commun., 2013, 49, 7073--7075 7075