Cu2+-selective ratiometric and "off-on" sensor based on the rhodamine derivative bearing pyrene group

Article abstract of DOI:10.1021/ol901804n

A new rhodamine-based derivative bearing a pyrene group (PRC) was synthesized as a ratiometric and "off-on" chemosensor for Cu ²⁺. PRC displayed a selective and chelation enhanced ratiometric fluorescence change and colorlmetric change with Cu<

Full text of DOI:10.1021/ol901804n

ORGANIC
LETTERS
Cu2+-Selective Ratiometric and “Off-On”
Sensor Based on the Rhodamine
Derivative Bearing Pyrene Group
2009
Vol. 11, No. 19
4442-4445
Ying Zhou,† Fang Wang,† Youngmee Kim,† Sung-Jin Kim,† and Juyoung Yoon*,†,‡
Department of Chemistry and DiVision of Nano Science and Department of Bioinspired
Science, Ewha Womans UniVersity, Seoul 120-750, Korea
jyoon@ewha.ac.kr
Received August 5, 2009
ABSTRACT
A new rhodamine-based derivative bearing a pyrene group (PRC) was synthesized as a ratiometric and “off-on” chemosensor for Cu2+. PRC
displayed a selective and chelation enhanced ratiometric fluorescence change and colorimetric change with Cu2+ among the metal ions
examined.
Various transition-metal ions are crucial for the life of
organisms.1 Among these is the copper ion, which plays a
critical role as a catalytic cofactor for a variety of metal-
loenzymes, including superoxide dismutase, cytochrome c
oxidase, and tyrosinase. However, under overloading condi-
tions, copper exhibits toxicity in that it causes neurodegen-
erative diseases (e.g., Alzheimer’s and Wilson’s diseases)
probably by its involvement in the production of reactive
oxygen species.2 Consequently, organisms tightly regulate
internal concentrations of copper. Owing to the Janus-faced
properties of copper in organisms, numerous efforts have
been undertaken to develop efficient and selective methods
to assess copper ions in cells and organisms. In addition,
(3) (a) Kramer, R. Angew. Chem., Int. Ed. 1998, 37, 772. (b) Kaur, S.;
Kumar, S. Tetrahedron Lett. 2004, 45, 5081. (c) Cebrian, E.; Agell, G.;
Marti, R.; Uriz, M. J. EnViron. Pollut. 2006, 141, 452.
(4) (a) de Silva, A. P.; Gunaratne, H. Q. N.; Gunnlaugsson, T. A.;
Huxley, T. M.; McCoy, C. P.; Rademacher, J. T.; Rice, T. E. Chem. ReV.
1997, 97, 1515. (b) Callan, J F.; de Silva, A. P.; Magri, D. C. Tetrahedron
2005, 61, 8551. (c) Kim, J. S.; Quang, D. T. Chem. ReV. 2007, 107, 3780.
(d) Zheng, Y.; Orbulescu, J.; Ji, X.; Andreopoulos, F. M.; Pham, S. M.;
Leblanc, R. M. J. Am. Chem. Soc. 2003, 125, 2680. (e) Liu, B.; Tian, H.
Chem. Commun. 2005, 3156. (f) Qi, X.; Jun, E. J.; Xu, L.; Kim, S.-J.; Hong,
J. S. J.; Yoon, Y. J.; Yoon, J. J. Org. Chem. 2006, 71, 2881. (g) Kim,
S. H.; Kim, J. S.; Park, S. M.; Chang, S.-K. Org. Lett. 2006, 8, 371. (h)
Jung, H. S.; Kwon, P. S.; Lee, J. W.; Kim, J. I.; Hong, C. S.; Kim, J. W.;
Yan, S.; Lee, J. Y.; Lee, J. H.; Joo, T.; Kim, J. S. J. Am. Chem. Soc. 2009,
131, 2008. (i) Huang, X.; Guo, Z.; Zhu, W.; Xie, Y.; Tian, H. Chem.
Commun. 2008, 5143.
† Department of Chemistry and Division of Nano Science.
‡ Department of Bioinspired Science.
(1) Lippard, S. J.; Berg, J. M. Principles of Bioinorganic Chemistry;
University Science Books: Mill Valley, CA, 1994.
(2) (a) Muthaup, G.; Schlicksupp, A.; Hess, L.; Beher, D.; Ruppert, T.;
Masters, C. L.; Beyreuther, K. Science 1996, 271, 1406. (b) Løvstad, R. A.
BioMetals 2004, 17, 111.
10.1021/ol901804n CCC: $40.75
Published on Web 08/31/2009
 2009 American Chemical Society

copper is a significant metal pollutant due to its widespread
use. The toxicity of copper ions for humans is rather low
compared to other heavy metals, but certain microorganisms
are affected by even submicromolar concentrations of Cu2+.3
Even though fluorescent probes for copper ion have been
extensively explored owing to biological significance of this
metal ion,4 there are still only a few examples of “off-on”
type sensors available in aqueous systems.5 Furthermore,
only a few ratiometric fluorescent probes for Cu2+ have been
found in the literature due the fluorescence quenching nature
of paramagnetic Cu2+,6 and most of them were working only
in pure organic solvents. Ratiometric fluorescent measure-
ments observe changes in the ratio of the intensities of the
emission at two wavelengths. Thus, ratiometric fluorescent
sensors have an important feature that they can be used to
evaluate the analyte concentration and provide built-in
correction for environmental effects.
Scheme 1
.
Synthesis of Chemosensors PRC and P4
On the other hand, rhodamine derivatives are nonfluores-
cent and colorless, whereas ring-opening of the corresponding
spirolactam gives rise to strong fluorescence emission and a
pink color. Recently, a spirolactam (nonfluorescent) to ring-
opened amide (fluorescent) process was utilized for the
detection of metal ions.5a,b,d,e,7
We introduced rhodamine fluorophore onto the pyrene
moiety, which was utilized as a selective fluorescent and
colorimetric sensor for Cu2+ in aqueous solution. Among
the various metal ions, the chemosensor PRC displayed
highly selective ratiometric changes upon the addition of
Cu2+. As expected, the pyrene moiety served successfully
as a source of these ratiometric changes. As far as we are
aware, PRC is the first ratiometric sensor based on rhodamine
derivative. For comparison, pyrene-based compound P4 was
synthesized to test the fluorescence change with Cu2+.
As shown in Scheme 1, P3 was first synthesized by
modifying the reported procedure8 with an improved yield
of 45%. P3 was then reacted with rhodamine-based deriva-
tive R15a,9 to give PRC in 46% yield. The detailed
1
experimental procedures and H and 13C NMR spectra are
explained in the Supporting Information. Sensor PRC and
P4 were further confirmed by X-ray analysis (Figure 1).
(5) (a) Dujols, V.; Ford, F.; Czarnik, A. W. J. Am. Chem. Soc. 1997,
119, 7386. (b) Liu, J.; Lu, Y. J. Am. Chem. Soc. 2007, 129, 9838. (c) Xiang,
Y.; Tong, A.; Jin, P.; Ju, Y. Org. Lett. 2006, 8, 2863. (d) Swamy, K. W. K.;
Ko, S.-K.; Kwon, S.; Lee, H.; Mao, C.; Kim, J.-M.; Lee, K.-H.; Kim, J.;
Shin, I.; Yoon, J. Chem. Commun. 2008, 5915. (e) Chen, X.; Jou, M.; Lee,
H.; Kou, S.; Lim, J.; Nam, S.-W.; Park, S.; Kim, K.-M.; Yoon, J. Sensors
and Actuators B 2009, 137, 597. (f) Wen, Z. C.; Yang, R.; He, H.; Jiang,
Y. B. Chem. Commun. 2006, 106. (g) Wu, Q.; Anslyn, E. V. J. Am. Chem.
Soc. 2004, 126, 14682.
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127, 1612. (b) Kim, H. J.; Park, S. Y.; Yoon, S.; Kim, J. S. Tetrahedron
2008, 64, 1294. (c) Kim, H. J.; Hong, J.; Hong, A.; Ham, S.; Lee, J. H.;
Kim, J. S. Org. Lett. 2008, 10, 1963. (d) Lin, W.; Yuan, L.; Tan, W.; Feng,
J.; Long, L. Chem.sEur. J. 2009, 15, 1030. (e) Shao, N.; Jin, J.; Wang,
H.; Zhang, Y.; Yang, R.; Chan, W. Anal. Chem. 2008, 80, 3466. (f) Xiang,
Y.; Tong, A. Luminescence 2008, 23, 28. (g) Mart´ınez, R.; Espinosa, A.;
Ta´rraga, A.; Molina, P. Tetrahedron 2008, 64, 2184. (h) Xu, Z.; Xiao, Y.;
Qian, X.; Cui, J.; Cui, D. Org. Lett. 2005, 7, 889. (i) Yang, H.; Liu, Z.;
Zhou, Z.; Shi, E.; Li, F. Tetrahedron Lett. 2006, 47, 2911.
Figure 1. X-ray crystal structures of PRC (a) and P4 (b). Blue: N
atom. Red: O atom.
Single crystals of PRC and P4 were grown in dichlo-
romethane, and unique spirolactam structures were observed.
The nitrate salts of Cu2+, Hg2+, Zn2+, Mg2+, Pb2+, Ca2+,
Cd2+, Ag+, and Fe3+ ions were used to evaluate the metal
ion binding property and selectivity of compound PRC (20
µM) in CH3CN-HEPES buffer (0.02 M, pH 7.4) (4:6, v/v).
Among these metal ions (10 equiv), PRC showed a selective
fluorescence enhancement only with Cu2+ among the various
(7) (a) Kim, H.; Lee, M.; Kim, H.; Kim, J.; Yoon, J. Chem. Soc. ReV.
2008, 37, 1465. references therein. (b) Chen, X.; Nam, S.-W.; Jou, M.;
Kim, Y.; Kim, S.-J.; Park, S.; Yoon, J. Org. Lett. 2008, 10, 5253. (c) Jana,
A.; Kim, J. S.; Jung, H. S.; Bharadwaj, P. K. Chem. Commun. 2009, 4417.
(d) Zhang, X.; Xiao, Y.; Qian, X. Angew. Chem., Int. Ed. 2008, 47, 8025.
(e) Huang, J.; Xu, Y.; Qian, X. J. Org. Chem. 2009, 74, 2167
(8) Demerseman, P.; Einhorn, J.; Gourvest, J. F.; Royer, R. J. Heterocycl.
Chem. 1985, 22, 39
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.
.
Chem.sEur. J. 2008, 14, 4719
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Org. Lett., Vol. 11, No. 19, 2009
4443

metal ions examined in aqueous solution, indicating that PRC
displayed a high Cu2+ selectivity (Figure 2). The fluorescence
As shown in Figure 4, upon addition of up to 7 equiv of
Cu2+ to the solution of PRC, the absorbance at 424 nm
Figure 2. Fluorescent spectra of PRC (20 µM) in CH3CN-HEPES
buffer (0.02 M, pH ) 7.4) (4:6, v/v) with 200 µM of Cu2+, Hg2+
,
Zn2+, Pb2+, Fe3+, Mg2+, Cd2+, Ca2+, and Ag+. Excitation wave-
length was 520 nm.
Figure 4. Absorbance spectra of PRC (20 µM) in CH3CN-HEPES
buffer (0.02 M, pH ) 7.4) (4:6, v/v) in the presence of different
amounts of Cu2+. Inset: the ratio of absorbance at 557 nm and
absorbance at 424 nm (black line) and the ratio of absorbance at
356 nm and absorbance at 424 nm (red line) as a function of Cu2+
concentration.
spectra were obtained by excitation of the rhodamine
fluorophore at 520 nm.
From the fluorescence titration experiments (Figure 3),
clear ratiometric and “off-on” fluorescence changes of PRC
decreased sharply, while the ones at 356 and 557 nm
increased significantly, which induced a color change from
primrose yellow to pink. Three isosbestic points at 377, 491,
and 584 nm were observed. A linear dependence of the ratio
of absorbance at 557 nm and absorbance at 424 nm (black
line) and the ratio of absorbance at 356 nm and absorbance
at 424 nm (red line) as a function of Cu2+ concentration were
observed.
All of the above absorption spectra responses were
reversible, which was confirmed by the reversible titration
using EDTA/Cu2+ (Figure S10, Supporting Information)
These results suggested that the spirolactam ring-opening
induced by the complexation of Cu2+ meant PRC could serve
as a ratiometric “nake-eye” chemosensor, which is selective
for Cu2+ in neutral buffered media.
The nonlinear fitting of the titration curve and the data of
Job’s plots from absorption spectra (Figures S8 and S9,
Supporting Information) assumed a 1:1 stoichiometry for the
PRC-Cu2+ complex with an association constant of 2.5 ×
104 M-1.
For comparison, compound P4 was synthesized to check
the fluorescence properties of pyrene moiety. In the UV-vis
absorption spectra of P4, the increasing bands at 375 and
480 nm were found with the addition of Cu2+ (Figure 5).
The fluorescence titration of P4 with Cu2+ showed fluores-
cence quenching effects of the peak at 550 nm. This result
indicates that the decreasing portion at 550 nm in the spectra
of PRC could be caused by the quenching effects of the
pyrene group in the presence of Cu2+.
Figure 3. Fluorescent emission spectra of PRC (20 µM) in the
presence of different concentrations of Cu2+ in CH3CN-HEPES
buffer (0.02 M, pH ) 7.4) (4:6, v/v). Excitation wavelength was
520 nm.
to Cu2+ were observed. When Cu2+ was added to the
solution, a significant decrease of the fluorescence intensity
of 424 nm and a new fluorescence emission band centered
at 575 nm, which was attributed to the Cu2+ induced ring-
opening of the spirolactam moiety, were observed with a
clear isoemission point at 558 nm (Figure 3).
We examined whether fluorescence energy transfer (FRET)
occurrs in our system by exciting the pyrene moiety at 360
nm. For rhodamine derivative, FRET can be observed only
when the spirolactam ring was opened upon binding with
analytes. In our case, an efficient FRET was not observed
since the fluorescence of pyrene was quenched upon addition
of Cu2+.
The proposed mechanism for these fluorescent changes
was explained in Figure 6. Upon addition of Cu2+ to a
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Org. Lett., Vol. 11, No. 19, 2009

Figure 5. Absorbance spectra of P4 (20 µM) in CH3CN-HEPES
buffer (0.02 M, pH ) 7.4) (4:6, v/v) in the presence of different
amounts of Cu2+. Inset: the fluorescent changes of P4 as a function
of Cu2+ concentration. Excitation wavelength was 450 nm.
Figure 6.
Proposed binding mechanism for PRC with Cu2+ and a
photo of PRC (20 µM) as a selective naked-eye chemosensor for
Cu2+ in CH3CN-HEPES buffer (0.02 M, pH ) 7.4) (4:6, v/v).
Bottom: 20 µM PRC, from second one added with 200 µM of
Ca2+, Cu2+, Hg2+, Zn2+, Fe3+, Ag+, Pb2+ (from left to right).
primrose yellow solution of compound PRC, a red color and
the fluorescence characteristics of rhodamine B appeared.
The large fluorescence enhancement as well as the colori-
metric change can be attributed to the spirolactam ring-
opening, which was induced by the complexation of Cu2+.
As shown in Figure 6, oxygen on the pyrene, oxygen on the
carbonyl group, as well as nitrogen on the hydrazone moiety
can cooperatively participate in the binding with Cu2+. It is
believed that this process is reversible, which has been proved
by the test using EDTA/Cu2+ (Figure S10, Supporting
Information).
amide (fluorescent) process was utilized. Furthermore, pyrene
moiety served successfully as a source of ratiometric changes
of PRC with Cu2+.
Acknowledgment. This research was supported by Na-
tionalResearchFoundationofKorea(NRF)(NRL:20090083065,
SRC: 20090063001) and WCU program (R32-2008-000-
10180-0). W. F. thanks to the BK21 fellowship.
In conclusion, a new rhodamine-pyrene derivative has
been synthesized as a ratiometric and “off-on” sensor for
the detection of copper ion in aqueous solution. PRC
displayed a highly selective and ratiometric fluorescence
change and a colorimetric change upon the addition of Cu2+,
in which the spirolactam (nonfluorescent) to ring opened
Supporting Information Available: Experimental pro-
cedures and characterization data of compounds. This
material is available free of charge via the Internet at
http://pubs.acs.org.
OL901804N
Org. Lett., Vol. 11, No. 19, 2009
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