C. Hou et al. / Tetrahedron Letters 52 (2011) 2692–2696
2695
LFS-1, LFS-2 showed fluorescence quenching upon addition to
Pb2+ but without emission of the pyrene excimer, indicating dis-
tinct mechanisms underlying fluorescence quenching and the for-
mation of the pyrene dimer necessary for excimer formation. These
measurements emphasize a requirement for sufficient flexibility in
the probe scaffold in the rational design of fluorescent sensors
requiring pyrene–pyrene interactions.
Free LFS-1
1.0
0.8
0.6
0.4
0.2
0.0
LFS-1 + Pb2+
Acknowledgments
This research is supported by Mini-Grant, Undergraduate Re-
search Fellows Program, and University Research and Creative
Activity in the University of Nebraska at Kearney. Authors would
also like to acknowledge Sara Basiaga in University of Nebraska
at Lincoln for her assistance in collecting fluorescence spectra.
400
450
500
550
Wavelength (nm)
Supplementary data
Figure 4. Excimer formation upon chelation of Pb2+ by LFS-1 in blood plasma.
Fluoresence emission spectra of LFS-1 (1.0 M) in human blood plasma following
l
Supplementary data associated with this article can be found, in
a 10-fold dilution to reduce scattering prior to (black line) and following (red line)
addition of 1.0
Figure 2.
l
M Pb2+. Sample conditions are as described in the legend to
Reference and notes
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Pb2+
Hg2+
400
450
500
550
Wavelength (nm)
Figure 5. Selective fluorescence quenching of LFS-2 upon metal binding with no
excimer formation. Fluorescence emission spectra of LFS-2 (1.0 lM) upon addition
of K+, Na+, Ag+, Ba2+, Ca2+, Cd2+, Co2+, Cu2+, Fe2+, Hg2+, Mg2+, and Pb2+ (100 equiv) in
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expected to result in a direct quenching of the pyrene monomer
and an inability to form the pyrene dimer upon metal binding
due to insufficient scaffold flexibility.17 Fluorescence titration
experiments using different metal ions were performed under
the same condition used for LFS-1. Fluorescence quenching was
observed without excimer emission upon addition of following
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metal ions: K+, Na+, Ag+, Ba2+, Ca2+, Cd2+, Co2+, Cu2+, Fe2+, Hg2+
,
9. (a) Koskela, S. J. M.; Fyles, T. M.; James, T. D. Chem. Commun. 2005, 945–947; (b)
Jung, H. S.; Park, M.; Han, D. Y.; Kim, E.; Lee, C.; Ham, S.; Kim, J. S. Org. Lett. 2009,
11, 3378–3381; (c) Zeng, L.; Wang, P.; Zhang, H.; Zhuang, X.; Dai, Q.; Liu, W.
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10. A mixture of 1-pyrenebutyric acid (0.504 g, 1.7 mmol) and thionyl chloride
(3 mL, 41.0 mmol) in 20 mL dichloromethane was refluxed for 3 h under argon
atmosphere. The reaction mixture was distilled to remove excess thionyl
chloride and dichlormethane to afford the compound 2 as a white solid, which
was used for the next reaction without further purification. To a solution of
Mg2+, and Pb2+. While ion binding, particularly apparent in the
presence of Hg2+, significantly reduced the fluorescence emission
spectra of LFS-2––in no case is there emission of the pyrene exci-
mer (Fig. 5). This result is consistent with our observations using
LFS-1, indicating that geometrical considerations associated with
the linker between receptor moiety and fluorophore are essential
factors that contribute to the sensor design, which requires the for-
mation of the pyrene excimer upon Pb2+ binding.
unpurified
2 in 20 mL of dichloromethane was added 1,2-ethanedithiol
(0.072 mL, 0.8 mmol) and the solution was refluxed for 1 h under argon
protection. After the reaction mixture was cooled down to room temperature,
dichloromethane was removed by rotary evaporation to give the crude product
that was purified by column chromatography (silica, 220–400 mesh, hexane/
EtOAc = 2:1 v/v). The product is isolated as a pale powder LFS-1 (0.48 g, 88%).
1H NMR (300 MHz, DMSO) d: 1.21 (m, 4H), 2.03 (m, 4H), 2.39 (m, 4H), 3.45(m,
4H), 7.92–9, 124.6, 124.7, 125.2, 125.5, 126.7, 127.1, 127.7, 127,9, 128.0, 128.7,
In summary, we report a new pyrene-based sensor that func-
tions as a fluorescent probe for Pb2+ sensing with high selectivity.
LFS-1 coordinates Pb2+ with 1:1 complex stoichiometries. LFS-1
displayed significant pyrene excimer emission as well as the
quenching of monomer in the presence of Pb2+. In contrast to