Sulfonyl rhodamine hydrazide: A sensitive and selective chromogenic and fluorescent chemodosimeter for copper ion in aqueous media

Article abstract of DOI:10.1016/j.dyepig.2010.07.004

A novel, sulfonyl rhodamine hydrazide chemodosimeter displayed highly selective and sensitive recognition of Cu²⁺ in aqueous media, via colour change from colorless to pink. The colour change that occurred as a result of complexation with Cu²⁺ can be attributed to spirolactam ring-opening and hydrolysis of the hydrazide unit to afford C.I. Acid Red 52 (Rhodamine B) in the presence of Cu²⁺. An analytical method was developed and successfully used for the determination of the copper content in a sample.

Full text of DOI:10.1016/j.dyepig.2010.07.004

Dyes and Pigments 88 (2011) 257e261
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Sulfonyl rhodamine hydrazide: A sensitive and selective chromogenic
and fluorescent chemodosimeter for copper ion in aqueous media
,
a
a
a
b,
Zhi-Qiang Hu a , Xiao-Ming Wang , Yong-Cheng Feng , Lei Ding , Hai-Yan Lu
*
*
a College of Chemistry and Molecular Engineering, Qingdao University of Science and Technology, Qingdao 266042, China
b College of Chemistry and Chemical Engineering, Graduate University of Chinese Academy of Sciences, Beijing 100049, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A
novel, sulfonyl rhodamine hydrazide chemodosimeter displayed highly selective and sensitive
recognition of Cu2þ in aqueous media, via colour change from colorless to pink. The colour change that
occurred as a result of complexation with Cu2þ can be attributed to spirolactam ring-opening and
hydrolysis of the hydrazide unit to afford C.I. Acid Red 52 (Rhodamine B) in the presence of Cu2þ. An
analytical method was developed and successfully used for the determination of the copper content in
a sample.
Received 29 May 2010
Received in revised form
8 July 2010
Accepted 9 July 2010
Available online 21 July 2010
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Fluorescent chemodosimeter
Copper ion
Sulfonyl
Rhodamine hydrazide
Aqueous media
Hydrolysis
1. Introduction
background signal. In addition, some “turn-on” fluorescent probes
can only be applied in non-aqueous solvents which limit their
In recent years, the design and development of fluorescent probes
for the detection of transition-metal ions have received considerable
attention because fluorescent chemosensors have several advantages
over other methods such as high sensitivity, selectivity, and real-time
monitoring [1e3]. Considering the important roles of Cu2þ in bio-
logical and environment systems, a considerable effort has been put
forth in the past few years to develop fluorescent probes for the
detection of Cu2þ [4,5]. Whereas, most of the early reported fluo-
rescent probes usually employ a fluorescence quenching mechanism
upon binding with Cu2þ ion owing to the paramagnetic nature of
Cu2þ [6,7]. However such a false positive signal may be induced by
contaminants that are difficult to distinguish from the authentic
analyte. These problems can be alleviated by a fluorescence
enhancement mechanism that, instead, produces significant
increases in fluorescence responses upon analyte recognition [8e19].
Recently, some examples of the fluorescent probes that display
fluorescence enhancements by the addition of Cu2þ have been
reported [20e34]. However, the fluorescence enhancement signal in
most cases is still too weak, and it often suffers from a high
application in biological systems. Thus it is of significant importance
to develop “turn-on” fluorescent probes that would allow accurate,
sensitive, rapid recognition of Cu2þ in aqueous media.
C.I. Acid Red 52 enjoys extensive use as fluorescence label due to
its excellent photophysical properties such as long absorption and
emission wavelength, large absorption coefficient and high fluo-
rescence quantum yield [35]. Rhodamine derivatives are nonfluo-
rescent and colorless, but ring-opening of the corresponding
spirolactam via coordination with metal ions or irreversible
chemical reactions gives rise to a strong fluorescence emission and
a pink color. Based on this mechanism, some rhodamine-based
spirolactam derivatives have been designed as probes for the
recognition of different metal ions [36].
The chemodosimeter system has attracted
a tremendous
amount of attention due to its ability to selectively perform
a chemical reaction with a specific metal ion, which allows for
selective and sensitive sensing [37]. Herein we describe our results
concerning
a chemodosimeter based on sulfonyl rhodamine
hydrazide (SRH). The preliminary reaction relies upon a Cu2þ
-
promoted hydrolysis reaction of SRH into C.I. Acid Red 52 in
aqueous media [38], and SRH exhibited a pronounced chromogenic
and fluorescent signaling behavior toward Cu2þ over other
common interfering metal ions.
* Corresponding authors. Tel./fax: þ86 532 84023405.
E-mail address: huzhiqiang@qust.edu.cn (Z.-Q. Hu).
0143-7208/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2010.07.004

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Z.-Q. Hu et al. / Dyes and Pigments 88 (2011) 257e261
0.7
NEt2
NEt2
O
O
Et2N
Et2N
0.6
0.5
0.4
0.3
0.2
0.1
0.0
0.6
0.5
0.4
0.3
0.2
0.1
0.0
POCl3
383K, 4h
COCl
2+
O
O
Cu
0.0
0.5
1.0
2+
1.5
-5
2.0
[Cu ](*10 M)
NEt2
O
Et2N
p-toluene sulfohydrazide
ClCH2CH2Cl, Et3N
NNHS
O
O
CH3
O
SRH
500
550
600
Scheme 1. Synthesis of compound SRH.
Wavelength(nm)
Fig. 2. Change in absorption spectra of SRH (10
by 10 mM HEPES in the presence of different amount Cu2þ. [Cu2þ]: 0, 2.5, 5, 7.5, 10,
12.5, 15, 17.5, 20
M. Insert: absorbance at 557 nm as a function of Cu2þ concentration.
mM) in 50% (v/v) H2O/CH3CN buffered
2. Experimental
2.1. Apparatus and reagents
m
A Hitachi F-2500 spectrofluorimeter was used for fluorescence
measurements. The absorption spectra were recorded with a Tech-
comp UV-8500 spectrophotometer (Shanghai, China). NMR spectra
were measured on a Bruker DMX-500 spectrometer at 500 MHz in
CD3COCD3. Elemental analyses were carried out with a Flash EA 1112
instrument. Electrospray ionization (ESI) mass spectra were
measured with an LC-MS 2010A (Shimadzu) instrument. A Delta 320
pH-meter [Mettler-Toledo Instruments (Shanghai) Co., China] was
used for pH measurements. All other chemicals used in experiments
were ofanalytical grade. The solutions of metalions were all prepared
from their perchlorate salts. All solvents used in spectroscopic tests
were of a spectrostropic grade. Distilled-deionized water was used
throughout the experiment.
was stirred at room temperature for 12 h under N2 and was then
concentrated by evaporation. Water was added to the residue, and
the aqueous phase extracted with ClCH2CH2Cl (3 ꢀ 30 mL). The
organic layer was washed with water, dried over Na2SO4, and
concentrated by evaporation. The crude product was purified by
silica gel column chromatography with EtOAc/Cyclohexane (1/3,
v/v), affording SRH as a white solid 0.36 g, yield 60%. m.p.:
244e246 ꢁC. 1H NMR (CD3COCD3, 500 MHz, TMS):
d
¼ 1.18
(t, J ¼ 7 Hz,12H); 2.38 (s, 3H); 3.41 (q, J ¼ 7 Hz, 8H); 6.19 (s, 2H); 6.35
(m, 2H); 6.42 (s, 2H); 6.99 (d, J ¼ 7.5 Hz, 1H); 7.13 (d, J ¼ 8 Hz, 2H);
7.28 (d, J ¼ 8.5 Hz, 2H); 7.53 (t, J ¼ 7.5 Hz,1H); 7.58 (t, J ¼ 7.5 Hz,1H);
7.82 (d, J ¼ 7 Hz, 1H); 8.48 (s, 1H). 13C NMR (CD3COCD3, 250 MHz,
TMS):
d 166.5, 153.4, 142.3, 138.4, 133.4, 128.7, 128.3, 126.8, 124.3,
122.6, 107.6, 105.1, 97.4, 43.9, 20.7, 12.0. ESI-MS 611.4 [M þ H]þ;
Anal. Cacld for C35H38N4O4S: C, 68.83; H, 6.27; N, 9.17; Found: C,
68.67; H, 5.98; N, 9.32.
2.2. Synthetic procedure
A solution of C.I. Acid Red 52 (0.88 g, 2 mmol) in POCl3 (15 mL)
was heated under reflux for 4 h. The reaction mixture was then
cooled and evaporated under vacuo to give the acid chloride which
was dissolved in ClCH2CH2Cl (20 mL) together with p-toluene sul-
fohydrazide (0.37 g, 2 mmol) and triethylamine (2 mL). The mixture
2.3. General procedure for Cu2þ detection
A 1.0 ꢀ 10ꢂ3 M stock solution of compound SRH was prepared in
CH3CN. To 10 mL glass tubes containing 5 mL CH3CN and different
2+
0.5
0.4
0.3
0.2
0.1
0.0
Cu
2+
Free, Zn , Na
+
2+
2+
+
Ca , Mg , K
2+
2+
2+
Ba , Co , Ni
2+
2+
2+
Cd , Hg , Pb
3+
+
Ce , Ag
500
550
600
Wavelength (nm)
Fig. 3. Fluorescence intensity of SRH (1
10 mM HEPES upon the addition of 14 equiv. metal ions (Mnþ denotes Naþ, Kþ, Mg2þ
Ca2þ, Zn2þand Ba2þ).
ex ¼ 530 nm.
mM) in 50% (v/v) H2O/CH3CN buffered by
Fig. 1. Absorption spectra of SRH (10
mM) upon addition of respective metal ions (as
,
perchlorate salt, 6 equiv.) in 50% (v/v) H2O/CH3CN buffered by 10 mM HEPES.
l

Z.-Q. Hu et al. / Dyes and Pigments 88 (2011) 257e261
259
Fig. 4. Change in color of SRH (1
m
M) in 50% (v/v) H2O/CH3CN buffered by 10 mM HEPES with different metal ions (14
m
M). From left to right: Cu2þ, Mg2þ, Ce3þ, Cd2þ, Naþ, Zn2þ, Kþ
,
Pb2þ, Hg2þ, Agþ, Co2þ, Ni2þ, Ba2þ and Ca2þ
.
amounts of metal ions, appropriate volumes of this solution of SRH
was added directly with a micropipette. The solutions were diluted
with water to 10 mL, and then the absorption and fluorescence
spectra were recorded immediately.
3.3. Fluorescence spectral responses of SRH
Fig. 3 shows the fluorescence spectra (
l
ex ¼ 530 nm) of SRH
(1
mM) measured in 50% (v/v) H2O/CH3CN buffered by 10 mM
HEPES at pH 7.1 with the addition of respective metal cations
(14 equiv.). SRH showed only a very weak fluorescence in the
absence of metal ions. The addition of Cu2þ resulted in a remark-
ably enhanced fluorescence intensity (about 1000-fold). Also,
change of the color from colorless to red could be visually observed
3. Results and discussion
3.1. Synthesis and structural characterization of SRH
after addition of Cu2þ in 1
m
M concentration of SRH (Fig. 4.), indi-
cating that SRH can serve as a visual probe for Cu2þ. Under the same
condition, additions of other metal ions including Mg2þ, Ce3þ, Cd2þ
As shown in Scheme 1, SRH was synthesized from rhodamine B
by a two-step reaction, and its structure was confirmed by 1H NMR,
13C NMR, MS and EA (Supporting Information, Fig. S1-2).
,
Naþ, Zn2þ, Kþ, Hg2þ, Agþ, Co2þ, Ni2þ, Pb2þ, Ba2þ and Ca2þ induced
no obvious fluorescence enhancements and color changes. These
observations indicated that SRH could selectively recognize Cu2þ in
50% (v/v) H2O/CH3CN. To further investigate the interaction of Cu2þ
and SRH, a fluorescence titration experiment was carried out. As
shown in Fig. 5, a linear increase of fluorescence intensity could be
observed with increasing Cu2þ concentration over the range of
3.2. Uvevis spectral responses of SRH
A solution of SRH in 50% (v/v) H2O/CH3CN buffered by 10 mM
HEPES (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid) at pH
7.1 is colorless. As shown in Fig. 1, the absorption spectra of SRH
exhibited only a very weak band over 500 nm region. The addition
of Cu2þ into this solution immediately resulted in a significant
enhancement of absorbance (about 600 fold) in the visible range of
500e600 nm and a new peak at 557 nm was observed. With
increasing Cu2þ ion concentration, a shoulder peak could be
observed (Fig. 2.). The absorbance of SRH at 557 nm was propor-
1e14 mM. Binding analysis using the method of continuous varia-
tions (Job’s plot) established a 1:1 stoichiometry for the SRHeCu2þ
complex (Supporting Information, Fig. S3).
To explore the practical applicability of this new chemo-
dosimeter system, the detection limit toward Cu2þ was evaluated.
From the fluorescence titration profile as shown in Fig. 6, a detec-
tion limit for Cu2þ was obtained as 10 nM based on the signal-to-
noise ratio of three, which is sufficiently low for the detection of
Cu2þ ions present in many chemical and biological systems.
The influence of solution pH toward the fluorescence of probe
SRH itself is shown in Fig. 7. No obvious characteristic color and
fluorescence of rhodamine could be observed when the pH ranged
between 6.0 and 9.0, suggesting that SRH was insensitive to pH in
tional to Cu2þ concentration over a range of 0e20
mM. The color of
the solution changed from colorless to pink-red upon titration with
Cu2þ ions. Under identical condition, SRH exhibited no response to
the addition of Mg2þ, Ce3þ, Cd2þ, Naþ, Zn2þ, Kþ, Pb2þ, Hg2þ, Agþ,
Co2þ, Ni2þ, Ba2þ and Ca2þ
.
4500
4000
4000
3000
2000
1000
0
Cu2+
3.0
2.5
2.0
1.5
1.0
3500
3000
2500
2000
1500
1000
500
0
2
4
6
8
10 12 14
0
540
560
580
600
620
640
660
0
1
2
3
4
5
6
Wavelength(nm)
[Cu2+] (*10-8M)
Fig. 5. Fluorescence (
l
ex ¼ 530 nm) titration spectra of SRH (1
m
M) with Cu2þ
(1e14
m
M) in 50% (v/v) H2O/CH3CN buffered by 10 mM HEPES. Insert: The plot of
Fig. 6. An assay for Cu2þ, 10e50 nm. SRH (0.1
mM) in 50% (v/v) H2O/CH3CN buffered by
fluorescence intensity change of SRH (1
m
M) against varied concentration of Cu2þ
.
10 mM HEPES;
l
ex ¼ 530 nm.

260
Z.-Q. Hu et al. / Dyes and Pigments 88 (2011) 257e261
700
600
500
400
300
200
100
0
4
5
6
7
8
9
10
11
12
pH
Fig. 7. Variation of fluorescence intensity (
l
ex ¼ 530 nm) of SRH (1
mM) in 50% (v/v) H2O/CH3CN as a function of pH.
this range. The influence of solution pH on the fluorescence
enhancement of SRH upon addition of Cu2þ is shown in Fig. 8.
A best response toward Cu2þ ion could be achieved within the pH
range of about 7e8. This result indicates that SRH can be used as
a good fluorescent probe for Cu2þ determination in nearly neutral
conditions typical of many biological system.
611.4, 633.3 and 673.3, which are corresponding to [SRH þ H]þ,
[SRH þ Na]þ and [SRH þ CueH]þ, respectively. The peak at m/z
673.3 also demonstrated the presence of 2(SRHeCu2þ complex).
The reaction product of SRH and Cu2þ was separated, which was
proved to be rhodamine B by TLC (Thin layer Chromatography) and
1H NMR experiments. Moreover, the addition of Cu2þ into RSH
solution in CH3CN resulted in no obvious fluorescence and color
changes, which imply the essential role of water in the detection
process. Based on the above findings, we proposed that the reaction
in this system may proceed according to the route depicted in
Scheme 2, which is similar to that proposed by Czarnik [38].
3.4. The proposed reaction mechanism
In order to explore the reaction mechanism of SRH and Cu2þ, the
reaction products of SRH and Cu2þ were investigated by ESI mass
spectral analyses (Supporting Information, Fig. S4). The main ion
peak was detected at m/z 443.3, which was characterized to be
rhodamine B, indicating the generation of rhodamine B as a final
product. In addition, three minor ion peaks were detected at m/z
3.5. The possible interference by other metal ions
Interference by other metal ions was further assessed through
competitive experiments. The fluorescence changes of SRH were
measured by the treatment of 5 equiv. Cu2þ ions in the presence of
50 equiv. other interfering metal ions including Mg2þ, Ce3þ, Cd2þ
,
Naþ, Zn2þ, Kþ, Hg2þ, Agþ, Co2þ, Ni2þ, Pb2þ, Ba2þ and Ca2þ. As shown
in Fig. 9, the tested background metal ions showed almost no
interference with the detection of Cu2þ ion.
3.6. Preliminary analytical application
In order to examine the potential applicability of the rhoda-
mine-B based chemodosimeter SRH, it was preliminarily applied in
the determination of Cu2þ in two waste water samples from our
laboratory. The probe was treated with the water samples with or
Fig. 8. Variation of fluorescence intensity(
l
ex ¼ 530 nm) of SRH (1
mM) in 50% (v/v)
H2O/CH3CN in the presence of 14
m
M Cu2þ as a function of pH.
NEt2
Et2N
O
NEt2
O
O
Et2N
Cu2+
O
O
N
N
Cu
S
CH3
NNHS
O
O
CH3
O
2(SRH-Cu2+
[M]+
)
H2O
SRH
m/z 673.3
m/z 611.4 [M + H]+
NEt2
O
Et2N
O-
Rhodamine B
m/z 443.3 [M + H]+
O
Fig. 9. Fluorescence intensity of SRH (1
prescence of 50 M background ions.
mM) upon the addition of 5 m
M Cu2þ in the
Scheme 2. The proposed reaction mechanism of SRH with Cu2þ
.
m

Z.-Q. Hu et al. / Dyes and Pigments 88 (2011) 257e261
261
Table 1
[11] Zheng Y, Cao X, Orbulescu J, Konka V, Andreopoulos FM, Pham SM, et al.
Peptidyl fluorescent chemosensors for the detection of divalent copper. Anal
Chem 2003;75:1706e12.
Results of determination Cu2þ in waste water samples.
Sample
Proposed method
The known concentration (mM)
[12] Roy BC, Chandra B, Hromas D, Mallik S. Synthesis of new, pyrene-containing,
metal-chelating lipids and sensing of cupric ions. Org Lett 2003;5:11e4.
[13] Mokhir A, Kiel A, Herten DP, Kraemer R. Fluorescent sensor for Cu2þ with
a tunable emission wavelength. Inorg Chem 2005;44:5661e6.
[14] Comba P, Krämer R, Mokhir A, Naing K, Schatz E. Synthesis of new phenan-
throline-based heteroditopic ligands e highly efficient and selective fluores-
cence sensors for copper(II) ions. Eur J Inorg Chem; 2006:4442e8.
[15] Choi JK, Kim SH, Yoon J, Lee KH, Bartsch RA, Kim JS. A PCT-Based, pyrene-
armed calix[4]crown fluoroionophore. J Org Chem 2006;71:8011e5.
[16] Park SM, Kim MH, Choe JI, No KT, Chang SK. Cyclams bearing diametrically
disubstituted pyrenes as Cu2þ- and Hg2þ-selective fluoroionophores. J Org
Chem 2007;72:3550e3.
wast water1
wast water2
0.132 ꢃ 0.035
0.908 ꢃ 0.045
0.100 ꢃ 0.004
1.000 ꢃ 0.025
Mean of three replicates.
without addition of Cu2þ ions. As shown in Table 1, SRH was able to
measure the concentrations of spiked Cu2þ with good recovery,
revealed that RSH could potentially be used for detecting Cu2þ in
real samples.
[17] Wen YQ, Yue F, Zhong YR, Ye BH. A copper(II) ion-selective on-off-type flu-
oroionophore based on zinc porphyrin-dipyridylamino. Inorg Chem 2007;
46:7749e55.
4. Conclusion
[18] Xie J, Ménand M, Maisonneuve S, Métivier R. Synthesis of bispyrenyl sugar-
aza-crown ethers as new fluorescent molecular sensors for Cu(II). J Org Chem
2007;72:5980e5.
[19] Jung HS, Kwon PS, Lee JW, Kim J, Hong CS, Kim JW, et al. Coumarin-derived
Cu2þ-selective fluorescence sensor: synthesis, mechanisms, and applications
in living cells. J Am Chem Soc 2009;131:2008e12.
[20] Royzen M, Dai Z, Canary JW. Ratiometric displacement approach to Cu(II)
sensing by fluorescence. J Am Chem Soc 2005;127:1612e3.
[21] Pujol AM, Gateau C, Lebrun C, Delangle P. A cysteine-based tripodal chelator with
a high affinity and selectivity for copper(I). J Am Chem Soc 2009;131:6928e9.
[22] Xu Z, Qian X, Cui J. colorimetric and ratiometric fluorescent chemosensor with
A simple and new rhodamine-B based chemodosimeter SRH for
Cu2þ has been developed. Results revealed that compound SRH
could be used as an efficient Cu2þ-selective “turn-on” fluorescent
and chromogenic probe with an excellent selectivity and sensitivity
in aqueous media. The detection limit for Cu2þ was determined as
10 nM and the studied background metal ions showed either no or
negligible interference toward the detection of Cu2þ. We believe
that the current developed chemodosimeter SRH should be highly
attractive for many practical applications in chemical and biological
systems.
a
large red-shift in emission: Cu(II)-only sensing by deprotonation of
secondary amines as receptor conjugated to naphthalimide fluorophore. Org
Lett 2005;7:3029e32.
[23] Qi X, Jun EJ, Kim SJ, Hong JSJ, Yoon YJ, Yoon J. New BODIPY derivatives as offꢂon
fluorescent chemosensor and fluorescent chemodosimeter for Cu2þ: cooper-
ative selectivity enhancement toward Cu2þ. J Org Chem 2006;71:2881e4.
[24] Martinez R, Zapata F, Caballero A, Espinosa A, Tárraga A, Molina P.
2-Aza-1,3-butadiene derivatives featuring an anthracene or pyrene unit:
highly selective colorimetric and fluorescent signaling of Cu2þ cation. Org Lett
2006;8:3235e8.
[25] Xiang Y, Tong AJ, Jin PJ, Ju Y. New fluorescent rhodamine hydrazone chemo-
sensor for Cu(II) with high selectivity and sensitivity. Org Lett 2006;8:2863e6.
[26] Wen ZC, Yang R, He H, Jiang YB. A highly selective charge transfer fluo-
roionophore for Cu2þ. Chem Commun; 2006:106e8.
Acknowledgments
The authors are grateful for the financial support from the
National Natural Science Foundation of China No. 20602022 and
Natural Science Foundation of Shandong province No. Y2007B39.
Appendix. Supplementary data
[27] Zhang X, Shiraishi Y, Hiral T. Cu(II)-selective green fluorescence of a rhoda-
mineꢂdiacetic acid conjugate. Org Lett 2007;9:5039e42.
Supplementary data associated with this article can be found in
the online version, at doi:10.1016/j.dyepig.2010.07.004.
[28] Mei L, Xiang Y, Li N, Tong AJ. A new fluorescent probe of rhodamine B
derivative for the detection of copper ion. Talanta 2007;72:1717e22.
[29] Lee MH, Kim HJ, Yoon S, Park N, Kim JS. Metal ion induced FRET offꢂon in
tren/dansyl-appended rhodamine. Org Lett 2008;10:213e6.
References
[30] Li GK, Xu ZX, Chen CF, Huang ZT. A highly efficient and selective “turn-on”
fluorescent sensor for Cu2þ ion based on calyx arene bearing four iminoqui-
noline subunits on the upper rim. Chem Commun; 2008:1774e6.
[31] Zhao M, Yang XF, He S, Wang L. A rhodamine-based chromogenic and fluo-
rescent chemosensor for copper ion in aqueous media. Sens Actuators B
2009;135:625e31.
[32] Chen X, Jou MJ, Lee H, Kou S, Lim J, Nam SW, et al. New fluorescent and
colorimetric chemosensors bearing rhodamine and binaphthyl groups for the
detection of Cu2þ. Sens Actuators B 2009;137:597e602.
[1] De Silva AP, Gunaratne HQN, Gunnlaugsson T, Huxley AJM, McCoy CP,
Rademacher JT, et al. Signaling recognition events with fluorescent sensors
and switches. Chem Rev 1997;97:1515e6.
[2] Valeur B, Leray I. Design principles of fluorescent molecular sensors for cation
recognition. Coord Chem Rev 2000;205:3e40.
[3] Basabe-Desmonts L, Reinhoubt DN, Crego-Calama M. Design of fluorescent
materials for chemical sensing. Chem Soc Rev 2007;36:993e1017.
[4] Krämer R. Fluorescent chemosensors for Cu2þ ions: Fast, selective, and highly
sensitive. Angew Chem Int Ed 1998;37:772e3.
[5] Gaggelli E, Kozlowski H, Valensin D, Valensin G. Copper homeostasis and
neurodegenerative disorders. Chem Rev 2006;106:1995e2004.
[6] Varnes AW, Dodson RB, Wehry EL. Interactions of transition-metal ions with
photoexcited states of flavines. Fluorescence quenching studies. J Am Chem
Soc 1972;94:946e50.
[33] Swamy KMK, Ko S, Kwon K, Lee HN, Mao C, Kim J, et al. Boronic acid-linked
fluorescent and colorimetric probes for copper ions. Chem Commun;
2008:5915e7.
[34] Zhou Y, Wang F, Kim Y, Kim S, Yoon J. Cu2þ-selective ratiometric and “off-on”
sensor based on the rhodamine derivative bearing pyrene group. Org Lett
2009;11:4442e5.
[35] Lakowicz JR. Principles of fluorescence spectroscopy. 3rd ed. NewYork:
Sprink; 2006. p. 67e114.
[7] Kemlo JA, Shepherd TM. Quenching of excited singlet states by metal ions.
Chem Phys Lett 1977;47:158e62.
[36] Kim HN, Lee MH, Kim HJ, Kim JS, Yoon J. A new trend in rhodamine-based
chemosensors: application of spirolactam ring-opening to sensing ions. Chem
Soc Rev 2008;37:1465e72.
[8] Torrado A, Walkup GK, Imperiali B. Exploiting polypeptide motifs for the
design of selective Cu(II) ion chemosensors. J Am Chem Soc 1998;120:609e10.
[9] Zheng Y, Gattás-Asfura KM, Konka V, Leblanc RM. A dansylated peptide for the
selective detection of copper ions. Chem Commun; 2002:2350e1.
[10] Li Y, Yang CM. A rationally designed novel receptor for probing cooperative
interaction between metal ions and bivalent tryptophan side chain in solu-
tion. Chem Commun; 2003:2884e5.
[37] Choi MG, Kim YH, Namgoog JE, Chang S. Hg2þ-selective chromogenic and
fluorogenic chemodosimeter based on thiocoumarins. Chem Commun;
2009:3560e2.
[38] Dujols V, Ford F, Cranik AW. A long-wavelength fluorescent chemodosimeter
selective Cu(II) ion in water. J Am Chem Soc 1997;119:7386e7.