Cell compatible fluorescent chemosensor for Hg2+ with high sensitivity and selectivity based on the Rhodamine fluorophore

Article abstract of DOI:10.1002/ejic.201000512

An easily prepared "turn-on"-type fluorescent chemosensor for mercury based on Rhodamine-B, which exhibits high sensitivity and selectivity over other metal ions in aqueous systems, was obtained. The distinctive wavelengths in the UV/ Vis absorption range can sense Hg²⁺, Cu ²⁺, and Fe³⁺ separately. Furthermore, this "turn-on"-type fluorescent sensor, upon the addition of Hg ²⁺ over other competitive species, was successfully applied to bioimaging in yeast and HeLa cells. The potential of these types of chemosensors for use in environmental and biological systems is great.

Full text of DOI:10.1002/ejic.201000512

FULL PAPER
DOI: 10.1002/ejic.201000512
Cell Compatible Fluorescent Chemosensor for Hg2+ with High Sensitivity and
Selectivity Based on the Rhodamine Fluorophore
Li Jiang,[a] Ling Wang,[b] Bo Zhang,[a] Gui Yin,*[a] and Rui-Yong Wang*[b]
Keywords: Rhodamine-B / Fluorescence / Mercury / Bioimaging / Sensors
An easily prepared “turn-on”-type fluorescent chemosensor
for mercury based on Rhodamine-B, which exhibits high sen-
sitivity and selectivity over other metal ions in aqueous sys-
tems, was obtained. The distinctive wavelengths in the UV/
rately. Furthermore, this “turn-on”-type fluorescent sensor,
upon the addition of Hg2+ over other competitive species,
was successfully applied to bioimaging in yeast and HeLa
cells. The potential of these types of chemosensors for use in
Vis absorption range can sense Hg2+, Cu2+, and Fe3+ sepa- environmental and biological systems is great.
efficient, long absorption and emission wavelengths,[8] and
the well-known ring-opening mechanism from spirolactam
Introduction
As a toxic and hazardous metal, which distributes widely
in air, water, and soil,[1] the mercury ion causes serious
environmental and health problems because bacteria in the
natural environment can convert inorganic mercury into
neurotoxic methylmercury, which bioaccumulates through
the food chain.[2] Furthermore, because of its high activity
of producing toxic effects by binding strongly to sulfhydryl
and to a lesser degree to hydroxy, carboxyl, and phosphoryl
groups,[3] mercury can also easily accumulate in bodies of
animals and cause numerous diseases such as pneumonitis,
dermatitis, gastric disorders, anemia, and especially, neuro-
logical diseases.[4] Therefore, there is an urgent need for ef-
fective, rapid, and facile mercury ion detection, and so far
much excellent work has been reported.[5] However, in order
to make further progress, chemosensors with a less toxic
action should have practical application in biological sys-
tems. Recently, several chemosensors have been successfully
applied in living cells and tissues.[6]
Our strategy here is to utilize common molecules as a
platform and to facilitate the reaction to obtain high sensi-
tive, selective, and low toxic fluorescent probes, which could
be applied in biological systems successfully. Herein, we
synthesize compound c, (Scheme 1) in which Rhodamine
B is connected to 2-hydroxy-1-naphthaldehyde through a
hydrazine bridge; c is obtained through a one-step Schiff
base reaction.[7] As a result of the excellent photophysical
properties, such as high fluorescence, large absorption co-
derivatives (fluorescence “off”) to its corresponding open-
ring amide (fluorescence “on”),[9] a “turn-on”-type fluores-
cent and colorimetric probe (c) for Hg2+ with cell perme-
ability and biocompatibility was obtained. Compound c
does not only distinguish Hg2+, Cu2+, and Fe3+ by different
UV/Vis absorption wavelengths, but also exhibits excellent
selective and sensitive (2 ppb) fluorescent enhancement to-
ward Hg2+. Further, compared to most sulphur-bearing
Hg2+ sensors,[5a,5c,5n,6a–6c] our compound may avoid the
negative influence of sulfide toward natural systems.
Results and Discussion
In compound c, Rhodamine B acts as an electron ac-
ceptor, while β-naphthol acts as an electron donor through
the hydrazine bridge (see Scheme 1). However, because of
the existence of the spirolactam moiety, which inhibits in-
ternal charge transfer (ICT) between the xanthene moi-
ety[10]and the lone pair of electrons on the nitrogen of
–C=N– [resulting in a photoinduced electron transfer
(PET)],[11] the compounds exhibit no absorption in the vis-
ible region.
The miscellaneous ions Hg2+, Fe3+, Zn2+, Cu2+, Pb2+
,
Mn2+, Co2+, Na+, Li+, K+, Ca2+, Ag+, Mg2+, Cd2+, and
Ni2+ were used to evaluate the metal-ion bonding property
and selectivity of this compound in methanol (Figure 1).
Among these ions, only Hg2+ induces both a fluorescence
enhancement and a red color change (Figure 2), while Cu2+
and Fe3+ exhibit a color change only.
[a] School of Chemistry and Chemical Engineering, Nanjing
University,
Figure 1 shows the absorption of c in the presence of
miscellaneous ions in methanol solution. The addition of
Hg2+, Cu2+, Fe3+ obviously causes the appearance of new
bands at 562, 551, and 555.5 nm, respectively. The absorp-
tion shift among the three ions is about 5 nm, which can be
detected easily.
Nanjing 210093, China
Fax: +86-025-83314502
E-mail: yingui@nju.edu.cn
[b] School of Life Science, Nanjing University,
Nanjing 210093, China
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201000512.
View this journal online at
wileyonlinelibrary.com
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Fluorescent Chemosensor for Hg2+ with High Sensitivity and Selectivity
Scheme 1. Synthesis of c and reference compounds.
However, only Hg2+, in spite of the color change caused
by Cu2+ and Fe3+, can trigger the fluorescence response of
c (Figure 2) at 575 nm, while the other ions lead to much
smaller or no fluorescence changes. The enhancement fac-
tor in the fluorescence of c is more than 300-fold upon the
binding of Hg2+. Figure 3 illustrates that the response of the
fluorescence intensity of c toward Hg2+ is not influenced
significantly by the addition of alkaline-earth metals and
first-row transition metals. Both the UV/Vis and fluores-
cence results indicate that c shows great selectivity and sen-
sitivity toward Hg2+ over other cations.
Figure 1. Absorption spectra of c (10 µ) upon addition of the mis-
cellaneous ions (10 equiv.) in methanol solution at 25 °C.
Figure 3. The fluorescence intensity change profiles of c in the pres-
ence of 1 equiv. Hg2+ and 2 equiv. of the interfering ions (Cu2+
,
Zn2+, Co2+, Ni2+, Ca2+, Na+, Cd2+, Li+, Mg2+, Pb2+, Fe3+, Ag+,
Mn2+, K+, respectively).
Figure 4 shows the detailed absorption spectra of c in the
presence of different concentrations of Hg2+ in methanol
solution. The addition of increasing amounts of Hg2+ obvi-
ously causes the disappearance of the initial band at 371 nm
attributed to the β-naphthol moiety and the appearance of
a new band at 562 nm assigned to the ICT effect. The four
well-defined isosbestic points at 313, 334, 380 and 460 nm
Figure 2. Fluorescence spectra of c (10 µ) in methanol with Hg2+
,
Fe3+, Zn2+, Cu2+, Pb2+, Mn2+, Co2+, Na+, Li+, K+, Ca2+, Ag+,
Mg2+, Cd2+, Ni2+ (excitation at 535 nm) (excitation and emission
slit 5 nm).
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L. Jiang, L. Wang, B. Zhang, G. Yin, R.-Y. Wang
FULL PAPER
indicate the presence of a unique complex in equilibrium this stoichiometry between c and Hg2+ is supported by the
with the free ligand. Furthermore, a turning point at a 1:1 data obtained from the Job’s plots of the absorption spectra
ratio of Hg2+/ c can be observed in the plot of absorbance (Figure S2).
against the ratio of Hg2+ to c.
To get an insight into the binding mode between c and
1
Hg2+, H NMR and 13C NMR spectra of complex c–Hg2+
and c in CDCl3 were measured, as shown in Figure 6. The
active protons are assigned as displayed in Figure 6a, where
the downfield hydroxy hydrogen atom belongs to the
naphthol moiety and the upfield hydrogen atom belongs to
the xanthenyl moiety. All the peaks for the active protons
broadened after the addition of Hg2+, which indicates that
proton exchange increases, and both the peak shifted up-
field because of the electron-deshielding effect of Hg2+ on
them. Moreover, when 1 equiv. Hg2+ was added, the peaks
for the two protons disappeared, which implicates the carb-
onyl and hydroxy group of c in the bonding with Hg2+
.
Figure 4. UV/Vis spectral changes of c upon the addition of in-
creasing amounts of Hg2+ in methanol solution at 25 °C, [c] =
10 µ. The inset shows the plot of the absorbance at 562 nm in the
presence of different concentrations of Hg2+
.
From the absorption titrations, the association constant
of c with Hg2+ was found to be 3.9ϫ10–5 (R = 0.9966) by
using nonlinear least-square analysis shown in Figure S1.
The fluorescence titration of mercury was conducted
with 10 µ c in methanol. Upon the addition of increasing
concentrations of Hg2+, a new emission band at 575 nm
appears with increasing intensity. The detection limit is as
low as 2 ppb (Figure 5).
Figure 6. (a) Partial 1H NMR (300 MHz) spectra of c, c +
0.5 equiv. Hg2+, and c + 1 equiv. Hg2+. (b) Partial 13C MNR
(75 MHz) spectra of c and c + 1 equiv. Hg2+
.
Figure 5. Fluorescence titration of c in the presence of 0–0.1 µ
This fact is confirmed by 13C NMR spectroscopy. The
carbonyl carbon atom peak in the 13C NMR spectra shifted
Hg2+, [c] = 1 µ. The inset shows the detection limit of c to Hg2+
.
In the ESI-MS spectrum of c in the presence of Hg2+ from 164.2 to 197.8 ppm when 1 equiv. Hg2+ was added
(Figure S11), a peak at m/z = 843.17 (calculated value (Figure 6b). Moreover, the peak for the spiro carbon atom
843.28), which is assigned to [c + Hg2+ + CH3OH–H+]+, is in c at δ = 66.1 ppm disappears and shifts to 143.3 ppm,
clearly observed upon addition of Hg2+. This provides solid which presents the formation of an open-ring form com-
evidence for the formation of a 1:1 complex. Furthermore, plex.
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Fluorescent Chemosensor for Hg2+ with High Sensitivity and Selectivity
Scheme 2. Proposed mechanism for the fluorescent changes of c upon the addition of Hg2+
.
Accordingly, a reasonable explanation to these results indicate that c can permeate the cell membrane and com-
that can be proposed is that Hg2+ induces the formation of bine with Hg2+ specifically, which would serve to indicate
an open spiro ring and is coordinated to a carbonyl oxygen the presence of the free Hg2+ ion.
atom, a naphthol oxygen atom, and an imino nitrogen
atom, so that the xanthenyl moiety is restored in a manner
similar to that in Rhodamine B and that the ICT effect is
restored to show pink fluorescence (Scheme 2).
For practical applications, we needed to explore the in-
fluence of mercapto biomolecules in living cells, such as cys-
teine, which might interact with Hg2+. As shown in Fig-
ure S3, the addition of 10 equiv. cysteine hardly brings
about a change in fluorescence relative to that of the c–
Hg2+ system. We then applied c to confocal fluorescence
imaging of Hg2+ in yeast and HeLa cells (Figures 7 and 8,
respectively). After staining the yeast cells with 40 µ c for
1 h, they display weak intracellular fluorescence (Fig-
ure 7b), and the intensity increases enormously after the
further addition of 40 µ Hg2+ solution (Figure 7d). When
c was added to the HeLa cells, they scarcely display any
fluorescence (Figure 8b). After the addition of Hg2+ ions,
the fluorescence intensity increases dramatically to show a
clear red intracellular fluorescence (Figure 8d). The results
Figure 8. Confocal fluorescence and brightfield images of HeLa
cells: (a) and (c) Brightfield image of cells. (b) Cells incubated with
a 10 µ solution of c for 10 min at room temperature. (d) Cells
treated with a 10 µ solution of c for 10 min and then incubated
with 10 µ Hg2+ for 10 min at room temperature. (λex = 546 nm,
λem = 560–600 nm, 300ϫ).
The bioimaging tests on the yeast and HeLa cells con-
firm that c provides a fluorescence enhancement with excel-
lent cell-permeability and biocompatibility for tracing the
Hg2+ ion in cells, specifically and rapidly. As a result, c
could be considered as an effective Hg2+-specific fluores-
cence sensor for the detection of the Hg2+ uptake in organ-
isms.
Conclusions
We have designed and synthesized a new colorimetric flu-
orescent chemosensor c based on rhodamine B for the mer-
Figure 7. Confocal fluorescence and brightfield images of yeast
cells: (a) and (c) Brightfield image of cells. (b) Cells incubated with
a 40 µ solution of c for 1 h at room temperature. (d) Cells treated
with a 40 µ solution of c for 1 h and then incubated with 40 µ
Hg2+ for 30 min at room temperature. (λex = 546 nm, λem = 560–
600 nm, 1200ϫ).
cury ion. It exhibits extremely high sensitivity (as low as
2 ppb) and selectivity to Hg2+ over other cations, especially
Cu2+ and Fe3+ and leads to a great fluorescence enhance-
ment Further characterization confirms a 1:1 complex,
which restores the ICT effect to show fluorescence. The ex-
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L. Jiang, L. Wang, B. Zhang, G. Yin, R.-Y. Wang
FULL PAPER
119.4, 109.1, 108.3, 105.1, 97.1, 77.5, 77.1, 76.6, 66.2, 44.3,
cellent biological value of c is demonstrated by the fluores-
cence imaging in living yeast and HeLa cells.
12.6 ppm. IR (KBr): νmax= 3056, 2975, 1720, 1616, 1518, 1311,
˜
1125, 822, 787, 750 cm–1. ESI-MS (negative ion mode): = m/z =
609.42 [M – H]–.
Cell Imaging
Experimental Section
Yeast Cell Imaging: Saccharomyces Cerevisiae was cultured in the
YPD liquid medium (peptone 20 g, yeast extract 10 g, dextrose
20 g, distilled water 1000 mL) for 12 h at 30 °C. For cell staining,
the cells were incubated with a 40 µ solution of c in Tris-HCl
(0.01 , pH 7.2) for 1 h at 30 °C. The sensor solution was then
removed, and the cells were washed twice with PBS (0.01 , pH
7.4) to remove extracellular c. The cells were subsequently divided
into two groups. The first is a control group without the addition
of Hg2+ solution; the other was treated with a 40 µ solution of
Hg2+ for 30 min at 30 °C. The cells were dropped on glass slides
and excited at 546 nm by using a He–Ne laser. The emission was
monitored from 560 to 600 nm.
General: Methanol was of HPLC grade and obtained from Merck.
All other reagents were of analytical grade unless noted. 1H and
13C NMR spectra were measured on
a Bruker Ultrashield
300 MHz NMR spectrometer. UV/Vis and fluorescence spectra
were recorded on a Varian Cary 50 Probe UV/Vis spectrophotome-
ter. Mass spectroscopy was recorded with a Thermo LCQ Fleet
MS spectrometer. Yeast (Saccharomyces Cerevisiae) and HeLa cell
lines were provided by the School of Life Science, Nanjing Univer-
sity. The biological imaging tests were carried out with an Olympus
FV-1000 laser scanning confocal fluorescence microscope.
Compound a: β-Naphthol (50 g) and ethanol (175 mL) was added
into a three-neck flask and stirred vigorously. A solution of NaOH
(100 g) and water (200 mL) was then added quickly. Chloroform
(146 mL) was added drop by drop when the mixture was heated to
80 °C. Stirring was maintained for 1 h after the addition of chloro-
form was complete, and sodium 1-formlnaphthalen-2-olate then
precipitated. Ethanol and chloroform were removed under reduced
pressure. Hydrochloric acid was then added to the residual solu-
tions until the pH of the solution was 4–6. The solution was ex-
tracted by chloroform and dried by sodium sulfate. After removal
of chloroform, the resulting solid was distilled under reduced pres-
sure. Yield: 17.5 g (30%), white needlelike solid a (2-hydroxy-1-
naphthaldehyde). 1H NMR (300 MHz, CDCl3, 25 °C): δ = 7.18 (d,
3JH,H = 6.00 Hz, 1 H, naphthalene), 7.43–7.47 (m, 1 H, naphth-
alene), 7.59–7.65 (m, 1 H, naphthalene), 7.79–7.82 (m, 1 H, naphth-
HeLa Cell Imaging: HeLa cells were grown in Dulbecco’s modified
Eagle’s medium (DMEM) supplemented with bovine serum (10%),
penicillin (100 U/mL) and streptomycin (100 µg/mL) at 37 °C and
5% CO2. Before staining, the cells were washed twice with fresh
DMEM, and subsequently exposed to a 10 µ solution of c
(900 µL DMEM added with 100 µL of a 100 µ solution of c in
DMSO) for 10 min at room temperature. After washing twice with
fresh DMEM, the cells were immersed for 10 min into a 10 µ
solution of Hg2+ (900 µL DMEM added with 100 µL of a 100 µ
solution of HgCl2 in H2O), DMEM was then removed, and the
cells were washed twice with fresh DMEM and imaged. Excitation
was at 546 nm, and emission was monitored from 560 to 600 nm.
Supporting Information (see footnote on the first page of this arti-
cle): Fluorescence and absorbance spectra, NMR spectroscopic
data and ESI-MS data are presented.
3
3
alene), 8.03 (d, JH,H = 9.00 Hz, 1 H, naphthalene), 8.33 (d, JH,H
= 8.70 Hz, 1 H, naphthalene), 10.81 (s, 1 H, CHO), 13.16 (s, 1 H,
OH) ppm. IR (KBr): νmax= 3480, 1701, 1630, 1315, 1161, 745 cm–1.
˜
Compound b: To rhodamine B (4.98 g, 10.4 mmol) in methanol
solution (8 mL) in a 50-mL round-bottomed flask was added hy-
drazine hydrate (3 mL). The solution was then heated at reflux and
stirred for 3 h. After cooling to room temperature, a red solid pre-
cipitated and was washed by cool methanol until the filtrate turned
colorless. Yield: 73%, red powder b (2-amino-3Ј,6Ј-bis(diethyl-
amino)spiro[isoindoline-1,9Ј-xanthen]-3-one), kept without light.
1H NMR (300 MHz, CDCl3, 25 °C): δ = 7.95 (m, 1 H, benzene),
7.47 (t, 3JH,H = 3.9 Hz, 2 H, benzene), 7.10–7.13 (m, 1 H, benzene),
6.43–6.49 (m, 4 H, benzene), 6.31 (dd, 3JH,H = 2.4, 3JH,H = 9.0 Hz,
Acknowledgments
This work was supported at Nanjing University by the Science
Foundation of Jiangsu Province (BK2006717) and the National
Natural Science Foundation of China (40930742).
[1] a) J. M. Benoit, W. F. Fitzgerald, A. W. Damman, Environ. Res.
1998, 78, 118–133; b) A. Renzoni, F. Zino, E. Franchi, Environ.
Res. 1998, 77, 68–72.
[2] a) D. W. Boening, Chemosphere 2000, 40, 1335–1351; b) H. H.
Harris, I. J. Pickering, G. N. George, Science 2003, 301, 1203.
[3] P. B. Tchounwou, W. K. Ayensu, N. Ninashvili, D. Sutton, En-
viron. Toxicol. 2003, 18, 149–175.
[4] a) T. Takeuchi, N. Morikawa, H. Matsumoto, Y. Shiraishi,
Acta Neuropathol. 1962, 2, 40–57; b) W. Y. Boadi, J. Urbach,
J. M. Brandes, S. Yannai, Environ. Res. 1992, 57, 96–106; c) M.
Harada, Crit. Rev. Toxicol. 1995, 25, 1–24; d) A. C. Bittner Jr.,
D. Echeverria, J. S. Woods, H. V. Aposhian, C. Naleway, M. D.
Martin, R. K. Mahurin, N. J. Heyer, M. Cianciola, Neurotox-
icol. Teratol. 1998, 20, 429–439.
[5] a) S. Yoon, A. E. Albers, A. P. Wong, C. J. Chang, J. Am.
Chem. Soc. 2005, 127, 16030–16031; b) A. Caballero, R. Martı-
Јnez, V. Lloveras, I. Ratera, J. V.-Gancedo, K. Wurst, A.
Tárraga, P. Molina, J. Veciana, J. Am. Chem. Soc. 2005, 127,
15666–15667; c) Y. G. Zhao, Z. H. Lin, C. He, H. M. Wu, C. Y.
Duan, Inorg. Chem. 2006, 45, 10013–10015; d) J. B. Wang,
X. H. Qian, Chem. Commun. 2006, 109–111; e) H. Zheng, Z.-
H. Qian, L. Xu, F.-F. Yuan, L.-D. Lan, J.-G. Xu, Org. Lett.
2006, 8, 859–861; f) E. M. Nolan, S. J. Lippard, J. Am. Chem.
Soc. 2007, 129, 5910–5918; g) D. Wu, W. Huang, C. Duan, Z.
3
2 H, benzene), 3.36 (q, JH,H = 6.9 Hz, 8 H, methylene), 1.18 (t,
3JH,H = 6.9 Hz, 12 H, methyl) ppm.
Compound c: To compound b (0.7 g, 1.5 mmol) in methanol solu-
tion (16 mL) in a 50-mL round-bottomed flask was added a
(1 equiv.). The solution was then heated at reflux for 2.5 h. After
cooling to room temperature, a straw-yellow solid precipitated. The
solid was washed by cool methanol until the filtrate turned color-
less and was dried in vacuo. Yield: 0.75 g (80%), straw-yellow pow-
der c. 1H NMR (300 MHz, CDCl3, 25 °C): δ = 12.25 (s, 1 H, C-
OH), 9.87 (s, 1 H, benzylidenimin), 8.04–8.05 (m, 1 H, naphtha-
3
3
lene), 7.84 (d, JH,H = 7.5 Hz, 1 H, naphthalene), 7.68 (d, JH,H
=
5.1 Hz, 2 H, naphthalene), 7.56 (s, 2 H, naphthalene), 7.46 (s, 1 H,
3
3
benzene), 7.21 (d, JH,H = 3.9 Hz,1 H, benzene), 7.10 (t, JH,H
=
=
3
4.2 Hz, 1 H, benzene), 6.54 (s, 4 H, benzene), 6.28 (d, JH,H
7.2 Hz, 3 H, benzene), 3.32 (q, 3JH,H = 6 Hz, 8 H, methylene), 1.13
(t, 3JH,H = 6.9 Hz, 12 H, methyl) ppm. 13C NMR (75 MHz, CDCl3,
25 °C): δ = 164.2, 158.8, 153.5, 151.2, 149.2, 148.0, 133.5, 132.5,
129.8, 128.7, 128.6, 128.3, 128.0, 127.2, 124.1, 123.3, 123.2, 120.4,
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Fluorescent Chemosensor for Hg2+ with High Sensitivity and Selectivity
Lin, Q. Meng, Inorg. Chem. 2007, 46, 1538–1540; h) M. H. Lee,
J.-S. Wu, J. W. Lee, J. H. Jung, J. S. Kim, Org. Lett. 2007, 9,
2501–2504; i) J. H. Soh, K. M. K. Swamy, S. K. Kim, S. Kim,
S.-H. Lee, J. Yoon, Tetrahedron Lett. 2007, 48, 5966–5969; j) Y.
Yan, Y. Hu, G. Zhao, X. Kou, Dyes Pigm. 2008, 79, 210–215;
k) R. Shunmugam, G. J. Gabriel, C. E. Smith, K. A. Aamer,
G. N. Tew, Chem. Eur. J. 2008, 14, 3904–3907; l) M. Tian, H.
Ihmels, Chem. Commun. 2009, 3175–3177; m) V. Bhalla, R.
Tejpal, M. Kumar, R. K. Puri, R. K. Mahajan, Tetrahedron
Lett. 2009, 50, 2649–2652; n) C. Song, X. Zhang, C. Jia, P.
Zhou, X. Quan, C. Duan, Talanta 2010, 81, 643–649; o) H.
Liu, P. Yu, D. Du, C. He, B. Qiu, X. Chen, G. Chen, Talanta
2010, 81, 433–437.
Li, Y. Li, Y.-Q. Dang, L.-J. Ma, Y. Q. Wu, G. F. Hou, L. X.
Wu, Chem. Commun. 2009, 4453–4455; h) Y.-K. Yang, S.-K.
Ko, I. Shin, J. Tae, Org. Biomol. Chem. 2009, 7, 4590–4593; i)
W. Shi, S. Sun, X. Li, H. Ma, Inorg. Chem. 2010, 49, 1206–
1210; j) E. M. Nolan, S. J. Lippard, Chem. Rev. 2008, 108,
3443–3480.
[7] M. Adamczyk, J. Grote, Synth. Commun. 2001, 31, 2681–2690.
[8] J. R. Lakowicz in Principles of Fluorescence Spectroscopy Ple-
num, New York, 1983, vol. 1, pp. 14–18.
[9] a) V. Dujols, F. Ford, A. W. Czarnik, J. Am. Chem. Soc. 1997,
119, 7386–7387; b) J. Y. Kwon, Y. J. Jang, Y. J. Lee, K. M. Kim,
M. S. Seo, W. Nam, J. Yoon, J. Am. Chem. Soc. 2005, 127,
10107–10111; c) Y. Xiang, A. Tong, Org. Lett. 2006, 8, 1549–
1552; d) S.-K. Ko, Y.-K. Yang, J. Tae, I. Shin, J. Am. Chem.
Soc. 2006, 128, 14150–14155; e) J. S. Wu, I.-C. Hwang, K. S.
Kim, J. S. Kim, Org. Lett. 2007, 9, 907–910.
[10] T. Ueno, Y. Urano, K. Setsukinai, H. Takakusa, H. Kojima,
K. Kikuchi, K. Ohkubo, S. Fukuzumi, T. Nagano, J. Am.
Chem. Soc. 2004, 126, 14079–14085.
[11] R. Ahuja, N. K. Singhal, B. Ramanujam, M. Ravikumar, C. P.
Rao, J. Org. Chem. 2007, 72, 3430–3442.
[6] a) S. Yoon, E. W. Miller, Q. He, P. H. Do, C. J. Chang, Angew.
Chem. Int. Ed. 2007, 46, 6658–6661; b) X. L. Zhang, Y. Xiao,
X. Qian, Angew. Chem. Int. Ed. 2008, 47, 8025–8029; c) B.
Tang, L. J. Cui, K. H. Xu, L. L. Tong, G. W. Yang, L. G. An,
ChemBioChem 2008, 9, 1159–1164; d) W. Huang, P. Zhou, W.
Yan, C. He, L. Xiong, F. Li, C. Duan, J. Environ. Monit. 2009,
11, 330–335; e) H. Lu, L. Xiong, H. Liu, M. Yu, Z. Shen, F.
Li, X. You, Org. Biomol. Chem. 2009, 7, 2554–2558; f) M. Su-
resh, S. Mishra, S. K. Mishra, E. Suresh, A. K. Mandal, A.
Shrivastav, A. Das, Org. Lett. 2009, 11, 2740–2743; g) H.-W.
Received: May 10, 2010
Published Online: August 4, 2010
Eur. J. Inorg. Chem. 2010, 4438–4443
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
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