A highly selective PET-based chemosensor for instant detecting of Zn 2+

Article abstract of DOI:10.1039/c4ra04130e

A simple Zn²⁺-selective chemosensor system based on acylhydrazone was designed and synthesized, which could detect Zn²⁺ ions in aqueous solution with high selectivity and sensitivity over a wide pH range by the mechanism of photo-ind

Full text of DOI:10.1039/c4ra04130e

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A highly selective PET-based chemosensor for
instant detecting of Zn2+†
Cite this: RSC Adv., 2014, 4, 35797
*
Jie Guan, Peng Zhang, Tai-bao Wei, Qi Lin, Hong Yao and You-ming Zhang
A simple Zn2+-selective chemosensor system based on acylhydrazone was designed and synthesized,
which could detect Zn2+ ions in aqueous solution with high selectivity and sensitivity over a wide pH
range by the mechanism of photo-induced electron transfer (PET). The obvious color changes and
pronounced OFF-ON-type fluorescent signaling behavior can be seen by the naked eye. The detection
limit of L2 for Zn2+ ion was as low as 0.13 mM. In addition, L2–Zn2+ complex can be used as an ON-OFF
chemosensor candidate for Cu2+, as the Zn2+-induced emission can be quenched upon addition of
Cu2+. Moreover, test strips for Zn2+ based on L2 were also fabricated, which could be used as a
convenient and efficient test kit for instantly detecting Zn2+ in aqueous solution.
Received 5th May 2014
Accepted 25th July 2014
DOI: 10.1039/c4ra04130e
www.rsc.org/advances
intermolecular proton transfer (ESIPT).11 Of all possible detec-
tion mechanisms, photoinduced electron transfer (PET)
Introduction
appears to be the most elegant, sensitive, and effective way to
report the presence of metal ions. A PET uorescent probe
usually consists of two structural units: the receptor unit and
the uorophore unit, the receptor unit is used for specically
recognizing the target ion, which usually contains N, O and S
atoms as chelator for ions, and the uorophore unit is used for
translating the host-guest recognition into uorescence signal,
which oen contain pyrene, cyanine, naphthalimide, uores-
cein, rhodamine, coumarin, quinolone and BODIPY groups to
provide a wide emission.12 Scheme 1 shows the mechanism of
PET progress, in the unbound dark state of these systems, the
receptor unit efficiently quenches the excited state of the uo-
rophore unit. This is normally achieved through electron
transfer processes that take place between the lone pair elec-
trons of the recognition groups and the relevant orbitals of the
uorophore that are involved in the optical absorption and
emission processes. The same lone pair electrons also bind the
One of the most active elds of supermolecular chemistry is the
design and synthesis of chemosensors with high selectivity and
sensitivity for heavy or transition metal ions.1 The zinc ion
(Zn2+), as the second most abundant transition metal essential
for human health, has drawn considerable interest due to its
broad biological functions, including modulation of catalytic
activity of hundreds of specic enzymes, regulation of gene
transcription, and involvement in brain pathology.2 Abnormal
concentrations of Zn2+ are known to be closely related to several
diseases, including chronic diarrhea, growth failure, immune
deciency, and Alzheimer's disease.3 In addition, with the
development of modern industry, the environmental pollution
caused by transition metals like Zn2+ has become more serious
and poses a threat to human health and the environment.4
Therefore, the accurate measurement of Zn2+ concentrations in
either the clinical setting or for environmental monitoring is of
great importance.
Fluorescence emission spectrometry has emerged as one of
the most popular methods for specic measurements because
of its high sensitivity, simplicity, and real time monitoring
without complicated pretreatment.5 To date, a variety of uo-
rescent chemosensors for Zn2+ have been reported pertaining to
the signaling mechanisms of photoinduced electron transfer
(PET),6 metal-ligand charge transfer (MLCT),7 intramolecular
charge transfer (ICT),8 excimer/exciplex formation,9 uores-
cence resonance energy transfer (FRET),10 and excited-state
Key Laboratory of Eco-Environment-Related Polymer Materials, Ministry of Education
of China, Key Laboratory of Polymer Materials of Gansu Province, College of Chemistry
and Chemical Engineering, Northwest Normal University, Lanzhou, Gansu 730070, PR
China. E-mail: zhangnwnu@126.com; Fax: +86-931-797-3120; Tel: +86-931-797-3120
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c4ra04130e
Scheme 1 Mechanism and a generalized energy diagram of PET-
based sensing.
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metal ions and protons to the recognition group. Therefore,
upon binding, the lone pair of the recognition group becomes
engaged in the newly formed bond and can no longer serve as
an efficient quencher for the uorophore.13
Our research group has a longstanding interest in molecular
recognition.14 Herein, we report a acylhydrazone-based Zn2+
chemosensor (compound L2) as a new advance in Zn2+ recog-
nition, which was synthesized by the reaction route as show in
Scheme 2. Our design is based on the well-known uorescent
mechanism of photoinduced electron transfer for Zn2+ recog-
nition: First, we chose the acylhydrazone group as the receptor
for coordinating with Zn2+ (based on the strong coordination
ability of N atoms toward the Zn2+ ion).15 On the other hand, the
naphthalofuran group as the signaling moiety is attached to the
recognition moiety with a PET progress from N atom (nonu-
orescent). The addition of Zn2+ could inhibit the PET progress,
which may lead to a “turn on” uorescent response. We are very
gratifying to see that the results go as we expect, sensor L2 could
allow selectively recognition of Zn2+ in aqueous solution. The
detection limit for Zn2+ ion was as low as 0.13 mM. In addition,
L2–Zn2+ displays an “OFF-ON-OFF” type signaling behavior for
Cu2+, because Cu2+ can displace Zn2+ to form a L2–Cu2+
complex.16 In this regard, the complex L2–Zn2+ can be consid-
Fig. 1 UV-vis spectra change of L2 (20 mM) upon addition of 20 equiv.
of Zn2+ in DMSO–H2O (8 : 2, v/v, containing 0.01 M HEPES, pH ¼ 7.24).
Inset: color changes of L2 after addition of Zn2+
.
ered as a good ON-OFF chemosensor candidate for Cu2+
.
Results and discussion
The synthesis of chemosensor L2 is outlined in Scheme 2. It was
characterized by 1H NMR, 13C NMR, IR and ESI-MS (Fig. S5, S9
and S10†).
A solution of probe L2 (20 mM) exhibits an absorption
maximum at 390 nm at room temperature in an aqueous
solution (0.01 M HEPES buffer, pH 7.24, 80% DMSO). However,
an obviously red shi take place (from 390 nm to 423 nm) upon
treatment with 20 equivalents of Zn(ClO4)2 (Fig. 1). And the
color of L2 changes from avescent to deep yellow aer addition
of Zn2+.
In order to investigate the binding properties of the receptor
L2 towards Zn2+ ion, the UV-vis titration of L2 (20 mM) with Zn2+
ion in the solution of DMSO–H2O (0.01 M HEPES buffer, pH ¼
7.24, 80% DMSO) was carried out. The absorption spectral
variation of L2 upon the gradual addition of Zn2+ ion is shown
in Fig. 2. Upon the gradual addition of Zn2+ ion (0–2.8 equiv.),
the absorption band centered at 423 nm gradually increase at
the expense of the absorbance at 390 nm. Two isosbestic points
at 339, 408 nm can be observed. Besides, while the amount of
Fig. 2 UV-vis spectra of L2 (20 mM) in DMSO–H2O (8 : 2, v/v, con-
taining 0.01 M HEPES, pH ¼ 7.24) upon adding of an increasing
concentration of Zn2+ from 0 to 2.4 equiv. Inset: the plot of Zn2+
concentration versus absorbance at 423 nm.
Zn2+ ion is beyond 1.0 equiv., the absorbance at 423 nm tends to
saturation, which reveals the possible formation of a 1 : 1
complex between L2 and Zn2+ (Fig. S1†). The result obtained
from a Job's plot by UV-vis spectra supports the formation of a
1 : 1 L2–Zn2+ complex (Fig. S2†). The plot of Zn2+ concentration
versus absorbance at 423 nm analysis of these changes gave a
binding constant of 4.69 ꢀ 106 (R2: 0.994). Nice ttings sup-
ported the 1 : 1 binding stoichiometry, see Fig. 1 inset.17
The uorescence spectral properties of receptor L2 with Zn2+
are also examined, compound L2 alone displays a very weak
uorescence emission band at 508 nm when it was excited at
423 nm. The board weak emission is likely due to the extended
p-electronic structure, but the lone pair electrons present on the
nitrogen atom of acylhydrazone unit result in the photo-
induced electron transfer (PET) that quenches the uores-
cence. When 20 equivalents of Zn2+ was added to the solution of
L2 (0.01 M HEPES buffer, pH 7.24, 80% DMSO), it led to a
prominent uorescence enhancement, (Fig.S3†) Other cations,
such as Hg2+, Fe3+, Ag+, Ca2+, Cu2+, Co2+, Ni2+, Cd2+, Pb2+, Cr3+,
and Mg2+, are completely nonresponsive (Fig. 3). The selectivity
of Zn2+ over other ions, especially Cd2+, is important because
Scheme 2 Synthetic procedures of sensor L2.
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The uorescence titration of receptor L2 toward Zn2+ ion was
also carried out. As shown in Fig. 4, free receptor L2 shows a
board weak emission band situated between 450 nm and 625
nm. The uorescent intensity remarkably increased as the Zn2+
concentration increasing from 0 to 4.0 equivalents. It can be
also saw clearly form Fig. S4†, while the amount of Zn2+ ion is
beyond 1.0 equivalents, the emission at 508 nm tends to satu-
ration, which reveals the possible formation of a 1 : 1 between
L2 and Zn2+. Besides, as shown in Fig. 4 inset, there is a good
linear (R2 ¼ 0.991) relationship between the uorescence
intensity at 508 nm and the concentration of Zn2+, which makes
a stoichiometric assay of Zn2+ ion possible. On the basis of the
1 : 1 stoichiometry and uorescence titration data, the binding
constant of L2 for Zn2+ was calculated to be 7.72 ꢀ 106 Mꢁ1. In
the meantime, the detection limit of the uorescence spectra
changes calculated on the basis of 3SB/S was 0.13 mM for Zn2+
ion in aqueous solution.17
In order to quantify the complexation ratio between L2 and
Zn2+ ion, besides the UV-vis titration and uorescence titration
experiments, the uorescence Job's plot measurement (Fig. 5)
was conducted by varying the concentration of both the receptor
and the Zn2+ ion with a total concentration of 40 mM. The
maximum point appears at the mole fraction of 0.5 which
indicates L2 and Zn2+ form a 1 : 1 complex. It was further
conrmed by the appearance of a peak at m/z 503.9 assignable
to [L2 + Zn2+ + 2H2O + H]+ (m/z calcd ¼ 503.4) in the ESI-MS
spectrum (Fig. S6†).
Fig. 3 Fluorescence spectra response of L2 (20 mM) upon addition of
different ions (20 equiv.) in DMSO–H2O (8 : 2, v/v, containing 0.01 M
HEPES, pH ¼ 7.24), (lex ¼ 423 nm). Inset: photograph of L2 (20 mM)
upon adding 20 equiv. of ions, which was taken under a UV-lamp (365
nm).
many reported Zn2+ sensors suffer from deleterious interference
of other ions. These results suggested that sensor L2 displays a
Zn2+-selective “OFF-ON” uorescent signaling behavior. The
reaction process completed as soon as the addition of Zn2+
,
implying that sensor L2 could be used for real-time detection of
Zn2+. The reason of the obvious uorescence enhancement at
508 nm lies in the following two aspects: Firstly, it operates via
PET, a process that oen induces chelation enhanced uores-
cence (CHEF). When Zn2+ ion coordinates with the nitrogen
atoms of the acylhydrazone moiety, the lone pair electrons on
the nitrogen atom no longer serve the PET process, which leads
to an enhancement of the emission (Scheme 1). Secondly, the
coordination of Zn2+ and L2 can enhance the planarity and
rigidity, which can also reduce the nonradiative decay of the
excited state and lead to the pronounced uorescence
enhancement.
The recognition mechanism of the sensor L2 with Zn2+ was
investigated by FT-IR spectra (Fig. S8†). In the IR spectra of L2,
the stretching vibration absorption peaks of O–H, N–H, C]O,
and C]N appeared at 3419 cmꢁ1, 3218 cmꢁ1, 1640 cmꢁ1, and
1601 cmꢁ1, respectively. However, when coordinated with Zn2+,
the absorption of O–H and N–H shied upeld, while the
stretching vibration absorption peaks of C]O and C]N shied
downeld to 1617 cmꢁ1 and 1567 cmꢁ1, which indicated that L2
coordinated with N, O atoms.
1
The proposed mechanism was also conrmed by H NMR
1
measurements. H NMR titration displayed the chemical shi
changes of L2 upon the addition of Zn2+, as shown in Fig. 6,
sensor L2 showed two single peaks at 12.23 and 11.25 ppm in
Fig. 4 Fluorescence titration spectra of L2 (20 mM) in DMSO–H2O
(8 : 2, v/v, containing 0.01 M HEPES, pH ¼ 7.24) upon adding of an Fig. 5 The Job's plot examined between Zn2+ and L2, indicating the
increasing concentration of Zn2+ from 0 to 4.0 equiv. (lex ¼ 423 nm). 1 : 1 stoichiometry, which was carried out by fluorescence spectra, (lex
Inset: the plot of Zn2+ concentration versus fluorescence intensity.
¼ 423 nm).
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range we tested, compound L2 alone was not sensitive to pH.
However, the uorescence intensity of L2–Zn2+ displayed a
strong pH dependence, as illustrated by its uorescence inten-
sity at 508 nm. An intense and stable uorescence of L2–Zn2+ in
the pH range 6.0–12.0 warrants the binding of L2 with Zn2+
occurred effectively between pH from 6 to 12.
The competition experiments were also measured by addi-
tion of 20 equivalents of Zn2+ to the solution of L2 in the pres-
ence of 20 equivalents of other metal ions, such as, Fe3+, Hg2+,
Ag+, Ca2+, Cu2+, Co2+, Ni2+, Cd2+, Pb2+, Cr3+ and Mg2+. Results of
our studies revealed that all potentially competitive metal
cations (except Cu2+) exerted no or little inuence on the uo-
rescence detection of Zn2+ in aqueous buffer solutions, as show
in Fig. 8. The good news is that the addition of S2ꢁ can mask the
inuence of Cu2+ effectively (Fig. S9†). In order to understand
the strong quenching behavior of Cu2+, we have measured the
change in emission intensity of L2–Zn2+ with addition 20 equiv.
Fig. 6 Partial 1H NMR spectra of L2 (2 mM, DMSO-d6) and in the
presence of varying amounts of Zn2+
.
DMSO-d6, we conrmed that which correspond to the protons of Cu2+ ion. The emission intensity of L2–Zn2+ at 508 nm
of –NH– and –OH, respectively. During the titration, the quenched (Fig. 9) due to the paramagnetic properties of Cu2+
,
concentration of L2 was kept constant and a gradual increase indicating that Cu2+ can displace Zn2+ to form a L2–Cu2+
was brought in the concentration of Zn2+ to vary the mole ratio
from 0 to 1.2 equiv. With the addition of Zn2+, both the singlet
signals of –NH– and –OH protons were broadened, but no
obvious shi, this phenomenon indicated that L2 coordinated
with N, O atoms, while no chemical reaction occurred between
them. Based on these reasons, we proposed the following
signaling mechanism for detection Zn2+ (Scheme 3). L2 alone
showed no emission at 500 nm, when Zn2+ ion coordinates with
the nitrogen atoms of the acylhydrazone unit, the lone pair
electrons of nitrogen atom no longer serve the PET process, that
leads to an enhancement of the emission.
The effects of pH on the uorescence of the free compound
L2 and its complex L2–Zn2+ are shown in Fig. 7. Over the pH
Fig. 8 Fluorescence spectra response of L2 (20 mM) in the presence of
20 equiv. of various ions containing 20 equiv. of Zn2+ in DMSO–H2O
(8 : 2, v/v, containing 0.01 M HEPES, pH ¼ 7.24), (lex ¼ 423 nm).
Scheme 3 Proposed sensing mechanism.
Fig. 9 Fluorescence spectra of L2 (20 mM) in the presence of Zn2+ or
Zn2+ and Cu2+ in DMSO–H2O (8 : 2, v/v, containing 0.01 M HEPES, pH
Fig. 7 Effect of pH on the fluorescence spectra of L2 (20 mM) in ¼ 7.24), (lex ¼ 423 nm). Inset: Photograph of L2 (20 mM), L2+ Zn2+ (20
response to Zn2+ (20 equiv.) in DMSO–H2O (8 : 2, v/v, containing 0.01 equiv.) and L2–Zn2+ + Cu2+ (20 equiv.), which was taken under a UV-
M HEPES) solution.
lamp (365 nm).
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tetramethylsilane (TMS, d scale with solvent resonances as
internal standards) UV-vis spectra were recorded on a Shimadzu
UV-2550 spectrometer. Photoluminescence spectra were per-
formed on a Shimadzu RF-5301 uorescence spectrophotom-
eter. Melting points were measured on an X-4 digital melting-
point apparatus (uncorrected). Infrared spectra were per-
formed on a Digilab FTS-3000 FT-IR spectrophotometer.
All uorescence spectroscopy was carried out just aer the
addition of perchlorate metal salts in DMSO solution, while
keeping the ligand concentration constant (2.0 ꢀ 10ꢁ5 M). The
solution of metal ions were prepared from the perchlorate salts
of Fe3+, Hg2+, Ag+, Ca2+, Cu2+, Co2+, Ni2+, Cd2+, Pb2+, Zn2+, Cr3+
and Mg2+.
Fig. 10 Photographs of test strips (a: only L2; b: L2 + Zn2+; c: only L2;
d: L2 + Zn2+.), (c) and (d) was taken under a UV-lamp (365 nm).
complex. Which was conrmed by the appearance of a peak at
m/z 463.1 assignable to [L2 + Cu2+]+ (m/z calcd ¼ 463.5) in the
ESI-MS spectrum (Fig. S7†). In this regard, the complex L2–Zn2+
Preparation and characterization of L2
The synthesis of chemosensor L2 is outlined in Scheme 2: 2-
hydroxy-1-naphthaldehyde (0.86 g, 5 mmol) and K2CO3 (1.38 g,
10 mmol), ethyl chloroacetate (0.72 g, 6 mmol) and KI (0.09 g,
0.6 mmol) were dissolved in appropriate absolute DMF and
stirred half an hour at room temperature,ꢂrespectively. Blended
them together and stirred for 4 h at 90 C, then raised up to
120 ꢂC kept for 9 h, aer cooling to room temperature, the
solution was dispersed in 200 mL distilled water, and ltered to
obtain pale yellow powdery product 1. Aer further purication,
compound 1 (0.48 g, 2 mmol) was dissolved in 20 mL EtOH,
hydrazine monohydrate (0.40 g, 8 mmol) was added and stirred
under reux for 8 h, then dispersed in 100 mL distilled water,
and ltered to obtain yellow powdery product 2. Aer further
purication, compound 2 (0.45 g, 2 mmol), 4-(N,N-dieth-
ylamino) salicylaldehyde (0.42 g, 2.2 mmol) and a catalytic
amount of acetic acid (AcOH) were combined in absolute
ethanol (40 mL). The solution was stirred under reux for 6 h.
Aer cooling to room temperature, the yellow precipitate was
ltered, washed three times with hot absolute ethanol, then
recrystallized with EtOH–DMF to give a luminous yellow powder
can be considered as a good ON-OFF chemosensor candidate
for Cu2+
.
15
To investigate the practical application of chemosensor L2,
test strips were prepared by immersing lter papers into a
aqueous solution of L2 (0.001 M) and then drying in air. The test
strips containing L2 were utilized to sense Zn2+. As shown in
Fig. 10, when Zn2+ solution was added on the test kits, the
obvious color change can be observed and the uorescence turn
on response can be saw under UV irradiation (lex ¼ 365 nm).
Therefore, the test strips could conveniently detect Zn2+ in
solution.
Conclusions
In summary, a photo-induced electron transfer based chemo-
sensor (L2) for Zn2+ was designed and synthesized, which could
detect Zn2+ ions in aqueous solution with high selectivity and
sensitivity at a wide pH range (from 6.0 to 12.0). The colori-
metric and ratiometric uorescent response to Zn2+ was real-
ized through the coordination of sensor L2 with Zn2+, namely,
when Zn2+ was added to the solution of L2, it resulted in an
obvious color changes and pronounced OFF-ON-type uores-
cent signaling behavior. The detection limit of L2 for Zn2+ ion in
aqueous solution was as low as 0.13 mM. In addition, the
complex L2–Zn2+ can be used as an ON-OFF chemosensor
candidate for Cu2+, for the Zn2+-induced emission can be
quenched upon addition of Cu2+. Moreover, test strips based on
L2 were fabricated, which also exhibited a good selectivity to
Zn2+ as in solution. We believe the test strips could act as a
convenient and efficient Zn2+ test kit.
product L2 (0.68 g) in 85% yield (m.p. > 300 ꢂC), IR: (KBr, cmꢁ1
)
v: 3419 (OH), 3215 (NH), 3080 (HC]N), 3030 (HC]C), 1631
(C]O), 1600 (C]N), 1550 (C]C), 1535 (C]C), 1283 (Ar–O),
1
1238 (N–N), 1131(C–C). H NMR (DMSO-d6, 400 MHz): d 12.23
(1H, s, OH), 11.25 (1H, s, NH), 8.54 (1H, s, N]CH), 8.41–8.43
(1H, d, J ¼ 8, ArH), 8.37 (1H, s, ArH), 8.10–8.12 (H, d, J ¼ 8, ArH),
8.03–8.05 (1H, d, J ¼ 8, ArH), 7.87–7.89(1H, d, J ¼ 8, ArH), 7.70–
7.73(1H, t, J ¼ 12, ArH), 7.59–7.62(1H, t, J ¼ 12, ArH), 7.22–7.24
(1H, d, J ¼ 8, ArH), 6.28–6.30 (1H, d, J ¼ 8, ArH), 6.14 (1H, s,
ArH), 3.35–3.40 (4H, m, J ¼ 20, CH2), 1.10–1.13 (6H, t, J ¼ 12,
CH3); 13C NMR (DMSO-d6, 100 MHz): d 161.87, 158.95, 157.50,
155.68, 155.47, 152.64, 136.75, 135.25, 133.99, 133.52, 132.61,
132.45, 130.58, 128.84, 127.83, 117.63, 115.23, 114.43, 108.93,
102.65, 48.95, 17.68; Anal. calcd for C24H23N3O3: C 71.61, H
5.72, N 10.44; found C, 7162; H, 5.70; N, 10.47%. ESI-MS calcd
for C24H23N3O3, [M + H]+ ¼ 402.2, found [M + H]+ ¼ 402.2.
Experimental
Chemicals used for syntheses were commercially available.
Solvents for spectral titrations were redistilled DMSO and
deionized water.
All reagents and solvents were commercially available at
analytical grade and were used without further purication.1H
NMR and 13C NMR spectra were recorded on a Mercury-400BB
Acknowledgements
spectrometer at 400 MHz and 100 MHz, respectively. Chem- This work was supported by the National Natural Science
ical shis are reported in ppm downeld from Foundation of China (no. 21064006, 21262032 and 21161018),
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the Program for Changjiang Scholars and Innovative Research
Team in University of Ministry of Education of China (no.
IRT1177), the Natural Science Foundation of Gansu Province
(no. 1010RJZA018), the Youth Foundation of Gansu Province
(no. 2011GS04735) and NWNU-LKQN-11-32.
8 (a) D. Srikun, E. W. Miller, D. W. Domaille and C. J. Chang, J.
Am. Chem. Soc., 2008, 130, 4596; (b) D. W. Domaille, L. Zeng
and C. J. Chang, J. Am. Chem. Soc., 2010, 132, 1194.
9 H. S. Jung, M. Park, D. Y. Han, E. Kim, C. Lee, S. Ham and
J. S. Kim, Org. Lett., 2009, 11, 3378.
10 Y. Maa, H. Y. Chen, F. Wang, S. Kambama, Y. Wang, C. Mao
and X. Q. Chen, Dyes Pigm., 2014, 102, 301.
11 M. J. Kim, K. Kaur, N. Singh and D. O. Jang, Tetrahedron,
2012, 68, 27.
Notes and references
1 (a) K. Shen, X. Yang, Y. X. Cheng and C. J. Zhu, Tetrahedron,
2012, 68, 5719; (b) G. Z. Yuan, Y. P. Huo, X. L. Nie, X. M. Fang
and S. Z. Zhu, Tetrahedron, 2012, 68, 8018; (c)
S. H. Mashraqui, R. Betkar, S. Ghorpade, S. Tripathi and
S. Britto, Sens. Actuators, B, 2012, 174, 299.
2 (a) C. J. Frederickson, J. Y. Koh and A. I. Bush, Nat. Rev.
Neurosci., 2005, 6, 449; (b) G. Aragay, J. Pons and
A. Merkoci, Chem. Rev., 2011, 111, 3433; (c) D. T. Quang
and J. S. Kim, Chem. Rev., 2010, 110, 6280; (d)
K. Szacilowski, Chem. Rev., 2008, 108, 3481; (e)
L. C. Costello, C. C. Fenselau and R. B. Franklin, J. Inorg.
Biochem., 2011, 105, 589.
3 (a) W. Maret, BioMetals, 2011, 24, 411; (b) W. Maret and Y. Li,
Chem. Rev., 2009, 109, 4682; (c) A. M. Adamo and P. I. Oteiza,
BioFactors, 2010, 36, 117; (d) A. S. Prasad, J. Am. Coll. Nutr.,
2009, 28, 257; (e) B. K. Y. Bitanihirwe and
M. G. Cunningham, Synapse, 2009, 63, 1029.
12 (a) Y. L. Cai, X. M. Meng, S. X. Wang, M. Z. Zhu, Z. W. Pan
and Q. X. Guo, Tetrahedron Lett., 2013, 54, 1125; (b)
L. W. Zhang, D. Z. Duan, X. M. Cui, J. Y. Sun and
J. G. Fang, Tetrahedron, 2013, 69, 15; (c) K. Baek,
M. S. Eom, S. Kim and M. S. Han, Tetrahedron Lett., 2013,
54, 1654; (d) A. N. Kursunlu, E. Guler, H. I. Ucan and
R. W. Boyle, Dyes Pigm., 2012, 94, 496; (e) A. Misra,
M. Shahid and P. Srivastava, Sens. Actuators, B, 2012, 169,
327; (f) N. Li, W. X. Tang, Y. Xiang, A. J. Tong, P. Y. Jin and
Y. Ju, Luminescence, 2010, 25, 445; (g) S. Ast, P. J. Rutledge
and M. H. Todd, Eur. J. Inorg. Chem., 2012, 5611; (h)
S. A. Ingale and F. Seela, J. Org. Chem., 2012, 77, 9352; (i)
J. Li, C. F. Zhang, Z. Z. Ming, G. F. Hao, W. C. Yang and
G. F. Yang, Tetrahedron, 2013, 69, 4743.
13 A. R. Sarkar, D. E. Kang, H. M. Kim and B. R. Cho, Inorg.
Chem., 2014, 53, 1794.
4 (a) Z. Yang, C. Yan, Y. Chen, C. Zhu, C. Zhang, X. Dong,
W. Yang, Z. Guo, Y. Lu and W. He, Dalton Trans., 2011, 40,
2173; (b) J. Mertens, K. Broos, S. A. Wakelin,
G. A. Kowalchuk, D. Springael and E. Smolders, ISME J.,
2009, 3, 916; (c) B. J. Alloway, Environ. Geochem. Health,
2009, 31, 537; (d) A. Ajayaghosh, P. Carol and S. Sreejith, J.
Am. Chem. Soc., 2005, 127, 14962.
5 (a) I. Ravikumar and P. Ghosh, Inorg. Chem., 2011, 50, 4229;
(b) L. M. Hyman and K. J. Franz, Coord. Chem. Rev., 2012,
256, 2333; (c) R. N. Dsouza, U. Pischel and W. M. Nau,
Chem. Rev., 2011, 111, 7941.
14 (a) P. Zhang, B. B. Shi, X. M. You, Y. M. Zhang, Q. Lin, H. Yao
and T. B. Wei, Tetrahedron, 2014, 70, 1889; (b) P. Zhang,
B. B. Shi, Y. M. Zhang, Q. Lin, H. Yao, X. M. You and
T. B. Wei, Tetrahedron, 2013, 69, 10292; (c) B. B. Shi,
P. Zhang, T. B. Wei, H. Yao, Q. Lin, J. Liu and Y. M. Zhang,
Tetrahedron, 2013, 69, 7981; (d) B. B. Shi, P. Zhang,
T. B. Wei, H. Yao, Q. Lin and Y. M. Zhang, Chem.
Commun., 2013, 49, 7812; (e) Q. Lin, X. Liu, T. B. Wei and
Y. M. Zhang, Chem.–Asian J., 2013, 8, 3015.
15 T. B. Wei, P. Zhang, B. B. Shi, P. Chen, Q. Lin, J. Liu and
Y. M. Zhang, Dyes Pigm., 2013, 97, 297.
6 (a) S. K. Kim, S. H. Lee, J. Y. Lee, R. A. Bartsch and J. S. Kim, J.
Am. Chem. Soc., 2004, 126, 16499; (b) K. C. Chang, I. H. Su,
A. Senthilvelan and W. S. Chung, Org. Lett., 2007, 9, 3363;
(c) L. J. Zhang, H. L. Chen, L. F. Zhi, Z. L. Lu and
R. B. Wang, Inorg. Chem. Commun., 2012, 23, 67.
16 Y. Zhou, Z. X. Li, S. Q. Zang, Y. Y. Zhu, H. Y. Zhang,
H. W. Hou and T. C. W. Mak, Org. Lett., 2012, 14, 1214.
17 (a) H. A. Benesi and J. H. Hildebrand, J. Am. Chem. Soc., 1949,
71, 2703; (b) J. J. B. Nevado, J. A. M. Pulgarin and
M. A. G. Laguna, Talanta, 2001, 53, 951.
7 H. S. Jung, P. S. Kwon, J. W. Lee, J. I. Kim, C. S. Hong,
J. W. Kim, S. Yan, J. Y. Lee, J. H. Lee, T. Joo and J. S. Kim,
J. Am. Chem. Soc., 2009, 131, 2008.
35802 | RSC Adv., 2014, 4, 35797–35802
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