A new fluorescent probe for Zn2+ with red emission and its application in bioimaging

Article abstract of DOI:10.1039/c4dt00167b

A new fluorescent probe, (E)-3-(3-(4-([2,2′:6′,2′′- terpyridin]-4′-yl)phenyl)acryloyl)-7-(diethylamino)-2H-chromen-2-one (ZC-F4), composed of coumarin as the fluorophore and terpyridine as the receptor was designed and synthesized. This probe showed good

Full text of DOI:10.1039/c4dt00167b

Dalton
Transactions
View Article Online
View Journal | View Issue
PAPER
A new fluorescent probe for Zn2+ with red
emission and its application in bioimaging†
Cite this: Dalton Trans., 2014, 43,
8048
Yiqun Tan, Min Liu, Junkuo Gao, Jiancan Yu, Yuanjing Cui, Yu Yang* and
Guodong Qian*
A
new fluorescent probe, (E)-3-(3-(4-([2,2’:6’,2’’-terpyridin]-4’-yl)phenyl)acryloyl)-7-(diethylamino)-
2H-chromen-2-one (ZC-F4), composed of coumarin as the fluorophore and terpyridine as the receptor
was designed and synthesized. This probe showed good selectivity and sensitivity towards Zn2+ even
at the ppb level with significant variation of emission wavelength (more than 100 nm shifts) after combi-
nation with Zn2+. One can observe that the emission colour changed from green to red. A Job’s plot test
suggested a 1 : 1 stoichiometry between ZC-F4 and Zn2+, and the theoretical calculation based on density
functional theory has been carried out to gain an insight into the sensing mechanism. Furthermore,
imaging of Zn2+ in cells was also performed to test its feasibility in biology. This fluorescence probe
should be a promising candidate for applications in cell-imaging, environment protection, water
treatment and safety inspection.
Received 16th January 2014,
Accepted 10th March 2014
DOI: 10.1039/c4dt00167b
www.rsc.org/dalton
group.28,29 Ng et al. designed two fluorescence sensors for
differential detection of Zn2+ and Cd2+ based on BODIPY
Introduction
As the second most abundant transition metal ion in the which can respond towards Zn2+ and Cd2+ respectively.30 Lin
human body, zinc plays an important role in gene transcrip- et al. developed a single probe that displayed a distinct
tion, regulation of metalloenzymes, neural signal transmission response to Zn2+ and Cd2+ depending on different anions.31
and apoptosis.1–5 Its deficiency causes acrodermatitis entero- Nevertheless, there have not been any reports about the appli-
pathica,6 while excess zinc may also cause serious neurological cation of these probes in cell-imaging.
disorders such as Alzheimer’s and Parkinson’s diseases.7–9 It
The development of a novel fluorescence probe for metal
is found that the imbalance in zinc may cause several health ions with a high sensitivity and selectivity has long concerned
problems including superficial skin diseases, prostate cancer, our group.32–35 We have developed a new fluorescence probe
diabetes, and brain diseases.10–12 Thus, extensive research ZC-F1 based on the intra-molecular transfer (ICT) effect for
effort has been devoted to the quantitative measurement of recognizing Zn2+ from Cd2+ with the detection limit at the ppb
trace Zn2+ in vivo.13–15 Because of the lack of spectroscopic level.32 But it cannot be used in bio-imaging for the following
signature of Zn2+, a fluorescence probe has become one of the reasons: (a) the poor solubility of ZC-F1 in aqueous solution
best options for detecting and tracking Zn2+ in cell-imaging restricts its application in vivo. (b) The quantum yield of fluoro-
and neurobiological experiments.16
phores bearing the ICT effect usually reduces too much for
In recent years, a number of fluorescent probes for detect- practical application after the electron withdrawing group
ing Zn2+ have been developed and most of them exhibit good combines with metal ions, especially in solvents with high
performance in cellular use.17–27 However, many fluorescence polarity, for the decrease of the energy gap between the
sensors still have problems of selectivity, especially inter- ground state and the excited state.36–39 (c) ZC-F1 emits green
ference from Cd2+ which possesses very similar chemical fluorescence after combining with Zn2+ with the emission
properties to Zn2+ because of their location in the same group. located around 500 nm, while a longer wavelength is needed
Recently, Jiang et al. have reported an inspired distinguishing for bio-imaging. To overcome these obstacles, a new fluore-
method for Zn2+ and Cd2+ by introducing the carbonyl scence probe highly sensitive and selective towards Zn2+ with
better solubility and higher quantum yield is required.
Herein, we report a new fluorescence probe, (E)-3-(3-
State Key Laboratory of Silicon Materials, Cyrus Tang Center for Sensor Materials
(4-([2,2′:6′,2″-terpyridin]-4′-yl)phenyl)acryloyl)-7-(diethylamino)-
and Applications, Department of Materials Science & Engineering, Zhejiang
2H-chromen-2-one (ZC-F4). This probe contains 7-diethylamino-
University, Hangzhou, China. E-mail: gdqian@zju.edu.cn, yuyang@zju.edu.cn
coumarin, which is known to be a water soluble fluoro-
†Electronic supplementary information (ESI) available: Supplementary spectra
data. See DOI: 10.1039/c4dt00167b
phore, and terpyridine as the receptor for Zn2+.40 To alleviate
8048 | Dalton Trans., 2014, 43, 8048–8053
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
the fluorescence decrease induced by metal ion binding, the was refluxed for 12 h, and then cooled down to room tempera-
carbonyl group is introduced as the electron withdrawing ture. The precipitate was filtered and washed with methanol
group, which conjugates with both coumarin and terpyridine. and water to obtain a white powder (1.05 g, 40%). 1H NMR
Then, Zn2+ will influence the electronegativity of terpyridine (500 MHz, CDCl3): δ = 2.34 (s, 3H, CH3), 7.44 (s, 2H, ArH), 7.67
instead of carbonyl directly. Thus, the influence of metal ions (d, 2H, J = 2 Hz, ArH), 7.85 (d, 2H, J = 8 Hz, ArH), 7.97 (s, 2H,
on the energy gap will be reduced largely and a fluorescence ArH), 8.74 (d, 2H, J = 7 Hz, ArH), 8.78 (t, 4H, J = 12 Hz, ArH).
enhancement in aqueous solution can be expected, making it Anal. calcd for C22H17N3: C, 81.71; N, 12.99; H, 5.30. Found: C,
possible to detect and track Zn2+ in cell-imaging and cancer- 81.59; N, 13.10; H, 5.31.
biological experiments.
4-([2,2′:6′,2″-Terpyridin]-4′-yl)benzaldehyde (3). 1 (1.0 g,
3.1 mmol) was added into the solution of CCl4 (20 mL) and
stirred for 15 min under an atmosphere of Ar2. Then, benzoyl
peroxide (0.049 g, 0.2 mmol) and N-bromosuccinamide
(1.23 g, 6.2 mmol) were added into the solution followed by
reflux for 24 h. The solution was cooled to room temperature
and evaporated. The resulting yellow solid was then added into
the solution of CaCO3 (1.0 g, 10 mmol), 1,4-dioxane (40 mL)
and water (10 mL) and refluxed for another 24 h. The mixture
was then cooled to room temperature, evaporated and puri-
fied by chromatography, using EtOAC and petroleum (1 : 2) as
eluents, affording a pale solid 3 (0.50 g, 48%). 1H NMR
(500 MHz, CDCl3): δ = 7.35 (m, 2H, J = 5 Hz, ArH), 7.87 (m, 2H,
ArH), 8.01 (m, 4H, J = 8 Hz, ArH), 8.66 (d, 2H, J = 8 Hz, ArH),
8.72 (t, 4H, ArH), 10.8 (s, 1H, CHO). Anal. calcd for C22H15N3O:
C, 78.32; N, 12.46; H, 4.48. Found: C, 78.39; N, 12.50; H, 4.41.
(E)-3-(3-(4-([2,2′:6′,2″-Terpyridin]-4′-yl)phenyl)acryloyl)-7-
(diethylamino)-2H-chromen-2-one (ZC-F4). 1 (1.55 g, 6 mmol)
and 3 (1.34 g, 4 mmol) were resolved in CHCl3 (20 mL) fol-
lowed by the addition of piperidine (0.1 mL) and acetate acid
(0.2 mL) and refluxed for 24 h. After cooling to room tempera-
ture, the resulting mixture was then extracted three times. The
organic phase was combined, and dried with MgSO4. The
solvent was removed under reduced pressure and the remain-
ing black powder was purified by chromatography using
CH2Cl2 and EtOAC (20 : 1) to yield an orange solid ZC-F4
Experimental section
Reagents and apparatus
Solvents and reagents were obtained from commercial sources
and used as received without further purification.
1H NMR spectra were recorded in CDCl3 or DMSO-D6
on a 500 MHz Bruker Avance DMX500 spectrometer with
tetramethysilane (TMS) as an internal standard. Elemental
analysis was performed using a Thermo Finnigan Flash
EA1112 microelemental analyzer. Differential scanning calori-
metry (DSC) was performed on a Netzsch Instruments 200 F3
at a heating rate of 10 K min−1 under a nitrogen atmosphere.
Inductively coupled plasma spectroscopy (ICP) was performed
on a Thermo XSENIES ICP-MS. Fluorescence emission spectra
and excitation spectra were obtained on a Hitachi F4600 fluore-
scence spectrophotometer. UV-vis absorption spectra were
obtained using a Perkin-Elmer Lambda spectrophotometer. All
the theoretical calculations were performed based on density
functional theory (DFT) at the B3LYP/6-31G(d) level.41,42 The
solvent effect on molecular geometries was included by means
of the polarizable continuum model (PCM).43,44 Based on the
optimized geometry, all the molecular orbitals were calculated
at the same level. All the calculations were performed in
Gaussian09 software.45 Fluorescence quantum yield was
measured with the integrating sphere on an Edinburgh Instru-
ment F900. Fluorescence images were obtained on confocal
laser scanning microscopes (CLSM, fluoview FV1000, Olympus).
1
(1.41 g, 61%). H NMR (500 MHz, CDCl3): δ = 1.25 (t, 6H, J =
5 Hz, CH2CH3), 3.47 (m, 4H, J = 7.5 Hz, CH2CH3), 6.50 (s, 1H,
ArH), 6.63 (d, 1H, J = 9 Hz, ArH), 7.36 (m, 2H, ArH), 7.43 (d,
1H, J = 9 Hz, ArH), 7.82 (d, 2H, J = 8 Hz, CHvCH), 7.88 (m,
3H, ArH), 7.94 (d, 2H, J = 8 Hz, ArH), 8.23 (d, 1H, J = 16 Hz,
ArH), 8.57 (s, 1H, ArH), 8.67 (d, 2H, J = 8 Hz, ArH), 8.74
Synthesis
3-Acetyl-7-(diethylamino)-2H-chromen-2-one (1). Ethyl-aceto- (m, 4H, ArH). Anal. calcd for C37H30N4O3: C, 76.80; N, 9.68;
acetate (1.95 g, 15 mmol) and 4-diethylamino-salicylaldehyde H, 5.23. Found: C, 76.69; N, 9.80; H, 5.31.
(1.93 g, 10 mmol) were added into the solution of EtOH
Zn(ZC-F4)(NO3)2(H2O)2 (ZC-F4–Zn). ZC-F4 (0.058 g, 0.1 mmol)
(20 mL), followed by the addition of piperidine (0.2 mL). The was resolved in CHCl3 (3 mL) followed by the addition of
resulting mixture was refluxed for 6 h and then cooled to room Zn(NO3)2 (0.057 g, 0.3 mmol) in 5 mL methanol. Upon mixing,
temperature. The yellow crystal was filtered and recrystalliza- a deep red suspension formed immediately. The resulting
tion was performed in EtOH to get a pure product (1.55 g, mixture was stirred for another 15 min to ensure reaction
60%). 1H NMR (500 MHz, CDCl3): δ = 1.24 (t, 6H, J = 7 Hz, completion. The red solid was obtained by filtration and
CH2CH3), 2.68 (s, 3H, COCH3), 3.45 (m, 4H, J = 7 Hz, CH2CH3), then washed with ethanol (5 mL × 3). 1H NMR (500 MHz,
6.47 (d, 1H, J = 2.5 Hz, ArH), 6.62 (d, 1H, J = 9 Hz, ArH), 7.39 (d, DMSO-D6): δ = 1.17 (t, 6H, J = 7 Hz, CH2CH3), 3.53 (m, 4H,
1H, J = 4 Hz, ArH), 8.44 (s, 1H, ArH). Anal. calcd for C15H17NO3: CH2CH3), 6.64 (s, 1H, ArH), 6.85 (d, 1H, J = 8.5 Hz, ArH), 7.52
C, 69.48; N, 5.40; H, 6.61. Found: C, 69.83; N, 5.44; H, 6.64.
(t, 1H, J = 6 Hz, ArH), 7.74 (d, 1H, J = 9 Hz, ArH), 7.85 (m, 1H,
4′-(p-Methylphenyl)-2,2′:6′,2″-terpyridine (2). To a solution ArH), 7.99 (m, 2H, ArH), 8.04 (d, 1H, J = 8 Hz, ArH), 8.12 (d,
of 4-methylbenzaldehyde (0.65 g, 5.4 mmol) and 2-acetylpyri- 2H, J = 8 Hz, CHvCH), 8.31 (t, 2H, J = 7.5 Hz, ArH), 8.54 (d,
dine (1.3 g, 10.8 mmol) in methanol (120 mL) was added 2H, J = 8 Hz, ArH), 8.67 (s, 1H, ArH), 8.91 (d, 1H, J = 4 Hz), 9.10
NaOH (0.22 g, 5.4 mmol) and NH4OH (30 mL). The mixture (d, 1H, J = 8 Hz, ArH), 9.18 (d, 2H, J = 8.5 Hz, ArH), 9.46 (s, 1H,
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 8048–8053 | 8049

View Article Online
Paper
Dalton Transactions
ArH). Anal. calcd for C37H34N6O11Zn: C, 55.27; N, 10.45;
H, 4.26. Found: C, 55.00; N, 10.37; H, 4.04.
To certify the ratio between ZC-F4 and Zn2+ in ZC-F4–Zn, an
ICP experiment was conducted by resolving 5 mg complex into
20 mL aqueous solution (DMSO–H2O = 1 : 99) followed by the
addition of 100 μL hydrochloric acid. The concentration of
Zn2+ found in the solution is 20.5 mg L−1, which agrees with
that calculated (20.3 mg L−1).
Cell culture
HeLa human cervical carcinoma cells were cultured in
Dulbecco’s Modified Eagle’s Medium (DMEM, Neuronbc)
supplemented with 10% fetal bovine serum (FBS, Sijiqing),
penicillin (100 units ml−1, Boster), and streptomycin (100 μg mL−1
,
Boster). Two days before imaging, the cells were plated on
glass-bottom dishes. For labeling, the growth medium was
removed and replaced with DMEM without FBS. The cells were Scheme 1 Synthesis of ZC-F4.
treated and incubated with 10 μL of 1 mM ZC-F4 in DMSO
stock solution (10 μM ZC-F4) at 37 °C under 5% CO2 for
15 min, and were provided with 5 μL of fresh medium that
contained either 1 mM or 0 mM ZnCl2. Then, the cells were
incubated for another 15 min under the conditions mentioned
above. Prior to imaging, cells were rinsed three times with
phosphate buffered saline (PBS).
Results and discussion
Design and synthesis of ZC-F4
In the newly designed fluorescence probe ZC-F4, 7-diethylami-
nocoumarin is selected as the fluorophore to improve its solu-
bility in water, and 2,2′,6′,2′′-terpyridine is selected as the
receptor for Zn2+ owing to its good performance in previous
work. In addition, the amino group possesses a strong elec-
tron-donating ability, which may strengthen the ICT effect,
and large Stokes’ shifts, leading to red emission.46–49 However,
unlike ZC-F1, the fluorophore and the receptor are not conju-
gated directly, but linked via the carbonyl group. So ICT is
established between the carbonyl group and the diethylamino
part,50–52 while terpyridine impacts on the carbonyl group with
its weak electron-withdrawing ability. As a result, the zinc ions
will indirectly influence the electronegativity of the electron
acceptor after combining with terpyridine, which suggests a
weak influence on the ICT energy level. Thus, an improved
fluorescence emission of ZC-F4 in aqueous solution can be
expected.
As shown in Scheme 1, the compound ZC-F4 can be syn-
Fig. 1 (a) Fluorescence emission spectra of ZC-F4 (100 nM) excited at
468 nm upon titration of Zn2+ at the concentration of 0, 10, 20, 30, 40,
50, 60, 70, 80, 90, 100, 110, 120, 130 nM. Insets: luminescent photos of
ZC-F4 before and after the addition of Zn2+ under the excitation of a
315 nm UV lamp. (b) Fluorescence intensities observed at 500 nm and
609 nm as a function of the [Zn2+].
thesized in several steps from commercially available chemi-
cals in high yield. Details of the synthesis are described in the
Experimental section.
Optical response of probe ZC-F4
To test its feasibility for Zn2+ detection, the fluorescence
spectra and the response of ZC-F4 after titrating with Zn2+ peaks located at 500 nm could be observed when excited at
were first studied in aqueous solution (water–DMSO = 99 : 1). 468 nm. This emission band gradually disappeared with the
As shown in Fig. 1(a), a broadband emission spectrum with titration of Zn2+ and a new emission band located at 609 nm
8050 | Dalton Trans., 2014, 43, 8048–8053
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
Fig. 2 Fluorescence intensities of ZC-F4 (100 nM in water–DMSO =
99 : 1) towards Zn2+ and various interferences (40 equiv. for K+, Ca2+
,
Na+ and Al3+ and 20 equiv. for others) at 609 nm upon excitation
at 468 nm.
Fig. 3 Fluorescence intensities of ZC-F4 (black) and ZC-F4–Zn (red,
[ZC-F4] = 100 nM, [Zn2+] = 100 nM) at 609 nm under various pH con-
ditions in aqueous solution (water–DMSO = 99 : 1). λex = 468 nm.
owing to the combination of ZC-F4 and Zn2+ can be observed.
A significant enhancement of fluorescence intensity can be
observed even when [Zn2+] is as low as 10 nM, which equals
0.65 ppb, indicating that ZC-F4 is highly sensitive for Zn2+
even at the ppb level. It is worth noting that the fluorescence
intensities of ZC-F4 at both 500 nm and 609 nm have a well
fitted relationship with the concentration of Zn2+ (Fig. 1(b)),
suggesting its usage for quantitative detection of Zn2+. The
absorption response of ZC-F4 towards Zn2+ shows that the
absorption maximum shifts from 450 nm to 468 nm with an
isosbestic point located at 456 nm, indicating the formation of
the complex of ZC-F4 with Zn2+ (Fig. S1†). Job’s plot analysis
suggests a 1 : 1 stoichiometry (Fig. S2†).
increased dramatically with the pH increase from 4.5 to 6
which can be ascribed to the competition between the proton
and zinc ions. Meanwhile, stable fluorescence response
towards Zn2+ can be observed in the pH range 6–9, indicating
that the probe is suitable for applying in biology. The fluo-
rescence of ZC-F4–Zn was quenched under alkaline conditions
with pH > 9, which can be well explained by the formation of
Zn(OH)− or Zn(OH)2, thus reducing the concentration of Zn2+.
Theoretical calculations
To get insight into the probing mechanism, computations on
the probe before and after combination with Zn2+ were per-
formed based on density functional theory (DFT).
As shown in Fig. 4, electrons are mainly localized on the
coumarin part in the ground state and transfer to the carbonyl
group and the atoms around when excited, indicating a mod-
erate ICT effect in the molecule. It is worth noting that the two
end-capped pyridine rings are not coplanar to the other part of
the molecule, while they did not take part in electron
rearrangement, suggesting its weak influence on the charge
To verify the application of ZC-F4 in a complicated environ-
ment, metal ions with biological and environmental interests
such as Ni2+, Cd2+, Cr3+, Fe3+, Na+, Ca2+, Pb2+, Al3+, Co2+, Cu2+,
Mg2+, K+, Hg2+ and Ag+ have been introduced as interferences
to investigate their impact on the selectivity of ZC-F4 towards
Zn2+. As we can see in Fig. 2, main group metal ions and some
transition metal ions, including K+, Ca2+, Na+, Mg2+, Al3+, Co2+,
Cr3+, Ni2+ and Pb2+, have almost no influence on the fluo-
rescence response of ZC-F4 before and after the addition of
Zn2+, while Cu2+ and Fe3+ exert a slight quenching effect result-
ing from their strong absorption of light. However, compared
with the strong fluorescence enhancement caused by Zn2+,
their disturbances are quite minor. Although fluorescence vari-
ation could be observed when Cd2+ was added into ZC-F1 in
our previous work, ZC-F4 shows no fluorescence response
towards Cd2+ except a minor quenching effect. This might be
due to the weaker Lewis acidity of Cd2+ compared with Zn2+,
while different molecular structures between ZC-F1 and
ZC-F4 may also help to recognize Zn2+ from Cd2+. In addition,
Hg lies in the same group as Zn and Cd, but Hg2+ and its
common disruptor Ag+ exhibit no disturbance.
pH effect
To verify its potential usage in biology, the pH effect on the
fluorescence response of the probe is investigated by plotting
the fluorescence intensity of ZC-F4 with Zn2+ vs. pH values.
Fig. 4 HOMO–LUMO energy levels and the interfacial plots of
the molecular orbitals for ZC-F4 and its complex form with Zn2+
As shown in Fig. 3, the emission intensities of the probe (ZC-F4–Zn).
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 8048–8053 | 8051

View Article Online
Paper
Dalton Transactions
transfer effect. However, when Zn2+ coordinated with the
probe, the electrons are still located on the coumarin part in
Conclusion
the ground state, but are rearranged to the part from carbonyl In summary, a new fluorescence probe (ZC-F4) towards Zn2+
to the terpyridine group when excited, showing that terpyri- was designed and synthesized and its response was studied.
dine also participates in the ICT effect. This electron rearrange- This probe could recognize Zn2+ with signals in two channels.
ment was enhanced owing to the strong electronegativity of Meanwhile, ZC-F4 was highly sensitive to Zn2+ at the ppb level
terpyridine after combining with Zn2+, resulting in a large with little disturbances from other competing metal ions, con-
Stokes’ shift and red emission. Meanwhile, the pyridine rings firming its good selectivity. Furthermore, the cell imaging
have the same orientation within the conjugated plane, which experiments showed that ZC-F4 was cell permeable, suitable
may also enhance the ICT effect and fluorescence quantum for applying in biology, and it can be supplied as a useful
yield by improving the conjugation. Thus, the enhancement of probe for studying the distribution and physiological activity
fluorescence and Stokes’ shift can be seen.
of Zn2+ in live cells.
Cell imaging
Since the probe has exhibited excellent sensing properties for
Zn2+ in vitro, assessing whether ZC-F4 can detect Zn2+ in live
cells is possible by labelling HeLa cells with the probe. As con-
trols, the cells were incubated with 10 μM ZC-F4 for 30 min in
DMEM medium at 37 °C, which showed strong intracellular
fluorescence in the window of 480–550 nm, while no fluo-
rescence was displayed in the detection range of 570–700 nm.
Then, these cells were incubated with DMEM containing ZnCl2
(5 μM) for another 15 min at 37 °C. After incubation, these
cells were washed with PBS three times and a dramatically
enhanced fluorescence emission in the range of 570–700 nm
could be observed (excitation at 468 nm) (Fig. 5). The results
of the bright-field measurements (Fig. 5a and d) suggested
that the cells were viable throughout the imaging experiments
upon treatment with ZC-F4 and Zn2+, respectively. As depicted,
these dramatic changes suggested that ZC-F4 was membrane
permeable and could respond to the presence of Zn2+ in
live cells. ZC-F4 can be supplied as a useful probe for study-
ing the distribution and physiological activity of Zn2+ in live
cells.
Acknowledgements
The authors gratefully acknowledge the financial support for
this work from the National Natural Science Foundation of
China (no. 51010002, 51272231, 51229201 and 51372221), the
Natural Science Foundation of Zhejiang Province (no.
LY12E02004).
Notes and references
1 J. M. Berg and Y. Shi, Science, 1996, 271, 1081–1085.
2 C. J. Frederickson and A. I. Bush, BioMetals, 2001, 14,
353–366.
3 B. L. Vallee and K. H. Falchuk, Phys. Rev., 1993, 73, 79–118.
4 A. Voegelin, S. Pfister, A. C. Scheinost, M. A. Marcus and
R. Kretzschmar, Environ. Sci. Technol., 2005, 39, 6616–6623.
5 X. Xie and T. G. Smart, Nature, 1991, 349, 521–524.
6 S. Kury, B. Dreno, S. Bezieau, S. Giraudet, M. Kharfi,
R. Kamoun and J.-P. Moisan, Nat. Genet., 2002, 31, 239–
240.
7 A. I. Bush, W. H. Pettingell, M. D. Paradis and R. E. Tanzi,
J. Biol. Chem., 1994, 269, 12152–12158.
8 M. P. Cuajungco and G. J. Lees, Neurobiol. Dis., 1997, 4,
137–169.
9 J.-Y. Koh, S. W. Suh, B. J. Gwag, Y. Y. He, C. Y. Hsu and
D. W. Choi, Science, 1996, 272, 1013–1016.
10 E. Kimura, S. Aoki, E. Kikuta and T. Koike, Proc. Natl. Acad.
Sci. U. S. A., 2003, 100, 3731–3736.
11 A. Truong-Tran, J. Carter, R. Ruffin and P. Zalewski, Bio-
Metals, 2001, 14, 315–330.
12 P. D. Zalewski, I. J. Forbes, R. F. Seamark, R. Borlinghaus,
W. H. Betts, S. F. Lincoln and A. D. Ward, Chem. Biol.,
1994, 1, 153–161.
13 A. N. Anthemidis and C.-P. P. Karapatouchas, Microchim.
Acta, 2008, 160, 455–460.
14 A. C. Davis, C. P. Calloway Jr. and B. T. Jones, Talanta,
2007, 71, 1144–1149.
15 G. Kaya and M. Yaman, Talanta, 2008, 75, 1127–1133.
16 Z. Xu, J. Yoon and D. R. Spring, Chem. Soc. Rev., 2010, 39,
1996–2006.
Fig. 5 Images of HeLa cells incubated with ZC-F4 (10 μM) and ZnCl2 at
the concentration of 0 μM (a–c) and 5 μM (d–f) for 30 min. Panels (a)
and (d) show differential interference contrast (DIC) images, while
panels (b), (c), (e) and (f) show the corresponding confocal fluorescence
images collected at 450–530 nm (b and e) and 550–650 nm (c and f).
The wavelength for excitation is 405 nm. The scale bar is 50 μm.
8052 | Dalton Trans., 2014, 43, 8048–8053
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
17 N. Y. Baek, C. H. Heo, C. S. Lim, G. Masanta, B. R. Cho and 40 Z. Jiang, H. Lv, J. Zhu and B. Zhao, Synth. Met., 2012, 162,
H. M. Kim, Chem. Commun., 2012, 48, 4546–4548. 2112–2116.
18 X. Chen, J. Shi, Y. Li, F. Wang, X. Wu, Q. Guo and L. Liu, 41 A. D. Becke, J. Chem. Phys., 1993, 98, 5648.
Org. Lett., 2009, 11, 4426–4429. 42 W. J. Hehre, J. Chem. Phys., 1972, 56, 2257.
19 T. Cheng, T. Wang, W. Zhu, X. Chen, Y. Yang, Y. Xu and 43 M. Cossi, N. Rega, G. Scalmani and V. Barone, J. Comput.
X. Qian, Org. Lett., 2011, 13, 3656–3659. Chem., 2003, 24, 669–681.
20 H. M. Kim and B. R. Cho, Acc. Chem. Res., 2009, 42, 863– 44 J. Tomasi, B. Mennucci and R. Cammi, Chem. Rev., 2005,
872. 105, 2999–3094.
21 G. Masanta, C. S. Lim, H. J. Kim, J. H. Han, H. M. Kim and 45 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
B. R. Cho, J. Am. Chem. Soc., 2011, 133, 5698–5700.
22 X. Meng, S. Wang, Y. Li, M. Zhu and Q. Guo, Chem.
Commun., 2012, 48, 4196–4198.
23 K. Sreenath, J. R. Allen, M. W. Davidson and L. Zhu, Chem.
Commun., 2011, 47, 11730–11732.
24 H. Tian, B. Li, J. Zhu, H. Wang, Y. Li, J. Xu, J. Wang,
W. Wang, Z. Sun, W. Liu, X. Huang, X. Yan, Q. Wang,
X. Yao and Y. Tang, Dalton Trans., 2012, 41, 2060–2065.
25 Y. Pourghaz, P. Dongare, D. W. Thompson and Y. Zhao,
Chem. Commun., 2011, 47, 11014–11016.
26 Z. Xu, K.-H. Baek, H. N. Kim, J. Cui, X. Qian, D. R. Spring,
I. Shin and J. Yoon, J. Am. Chem. Soc., 2009, 132, 601–610.
27 S. Yin, J. Zhang, H. Feng, Z. Zhao, L. Xu, H. Qiu and
B. Tang, Dyes Pigm., 2012, 95, 174–179.
M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone,
B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato,
X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng,
J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda,
J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao,
H. Nakai, T. Vreven, J. A. Montgomery Jr., J. E. Peralta,
F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers,
K. N. Kudin, V. N. Staroverov, R. Kobayashi, J. Normand,
K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar,
J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene,
J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo,
R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin,
R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin,
K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador,
J. J. Dannenberg, S. Dapprich, A. D. Daniels, Ö. Farkas,
J. B. Foresman, J. V. Ortiz, J. Cioslowski and D. J. Fox,
R. A. Gaussian 09, Gaussian, Inc., Wallingford CT, 2009.
28 L. Xue, C. Liu and H. Jiang, Org. Lett., 2009, 11, 1655–1658.
29 L. Xue, Q. Liu and H. Jiang, Org. Lett., 2009, 11, 3454–3457.
30 H. He and D. K. Ng, Chem. –Asian J., 2013, 8, 1441–1446.
31 J. Wang, W. Lin and W. Li, Chem. –Eur. J., 2012, 18, 13629– 46 J. Delcamp, Y. Shi, J. Yum, T. Sajoto, E. Dell’orto, S. Barlow,
13632.
M. Nazeeruddin, S. Marder and M. Gratzel, Chem. –Eur. J.,
2013, 19, 1819–1827.
47 N. Karton-Lifshin, L. Albertazzi, M. Bendikov, P. S. Baran
and D. Shabat, J. Am. Chem. Soc., 2012, 134, 20412–20420.
48 Y.-Y. Wu, Y. Chen, G.-Z. Gou, W.-H. Mu, X.-J. Lv, M.-L. Du
and W.-F. Fu, Org. Lett., 2012, 14, 5226–5229.
49 Y. Tan, Q. Zhang, J. Yu, X. Zhao, Y. Tian, Y. Cui, X. Hao,
Y. Yang and G. Qian, Dyes Pigm., 2013, 97, 58–64.
50 H. M. Kim, M. S. Seo, M. J. An, J. H. Hong, Y. S. Tian,
J. H. Choi, O. Kwon, K. J. Lee and B. R. Cho, Angew. Chem.,
Int. Ed., 2008, 47, 5167–5170.
32 Y. Tan, J. Gao, J. Yu, Z. Wang, Y. Cui, Y. Yang and G. Qian,
Dalton Trans., 2013, 42, 11465–11470.
33 Y. Tan, J. Yu, J. Gao, Y. Cui, Z. Wang, Y. Yang and G. Qian,
RSC Adv., 2013, 3, 4872–4875.
34 Y. Tan, J. Yu, J. Gao, Y. Cui, Y. Yang and G. Qian, Dyes
Pigm., 2013, 99, 966–971.
35 Y. Tan, J. Yu, Y. Cui, Y. Yang, Z. Wang, X. Hao and G. Qian,
Analyst, 2011, 136, 5283–5286.
36 A. Marini, A. Muñoz-Losa, A. Biancardi and B. Mennucci,
J. Phys. Chem. B, 2010, 114, 17128–17135.
37 R. S. Mulliken, J. Phys. Chem., 1952, 56, 801–822.
38 R. S. Mulliken, J. Am. Chem. Soc., 1952, 74, 811–824.
51 D. M. Nguyen, A. Frazer, L. Rodriguez and K. D. Belfield,
Chem. Mater., 2010, 22, 3472–3481.
39 J. Wu, W. Liu, J. Ge, H. Zhang and P. Wang, Chem. Soc. 52 B. Zhu, C. Gao, Y. Zhao, C. Liu, Y. Li, Q. Wei, Z. Ma, B. Du
Rev., 2011, 40, 3483–3495.
and X. Zhang, Chem. Commun., 2011, 47, 8656–8658.
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 8048–8053 | 8053