Catalyst + chemodosimeter → chemosensor: Incorporation of catalytic functionality in an indicator displacement assay to realize reversible chemosensing detection

Article abstract of DOI:10.1039/c9tc06308k

A new bimetallic complex, (CN)₃Fe^II(tppz)Cu^IICl (tppz = 2,3,5,6-tetra(2′-pyridyl)pyrazine) including an Fe(ii)-diimine indicator and a dual functional Cu(ii) receptor/catalyst, was synthesized to demonstrate the concept of indicator/catalyst displacement assay for the simultaneous detection and detoxification of cyanide. The catalytic degradation property in the assay was necessary for making the detecting system reversible, which the traditional indicator displacement assays could never achieve. After the realization of this new property, silica-gel-based solid-supporting complex 1 was fabricated for application in a device, which was demonstrated for its use in the naked-eye detection and degradation of cyanide in tap, river, and underground water samples in a repeatable and real-time manner, even in the presence of interfering anions (CH₃COO^-, N₃^-, HCO₃^-, Cl^-, NO₃^-, HPO₄^2-, SO₄^2-, SCN^-, and OCN^-). Within 300 min, cyanide was quantitatively oxidized into the less toxic cyanate by 1 in the presence of H₂O₂. The detection limit of 1 for cyanide was found to be 1.16 × 10^-4 M (3.02 mg L^-1).

Full text of DOI:10.1039/c9tc06308k

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Nosang V. Myung, Yong-Ho Choa et al.
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DOI: 10.1039/C9TC06308K
ARTICLE
Catalyst + Chemodosimeter → Chemosensor: Incorporation of a
catalytic functionality in an indicator displacement assay to
realize reversible chemosensing detection
Received 00th January 20xx,
Accepted 00th January 20xx
Chang Shen, Qian Tang, Cheng-Bin Gong,* and Cheuk-Fai Chow*
DOI: 10.1039/x0xx00000x
A new bimetallic complex, (CN)3FeII(tppz)CuIICl (tppz = 2,3,5,6-tetra(2'-pyridyl)pyrazine) including a Fe(II)-diimine indicator
and a dual functional Cu(II) receptor/catalyst, was synthesized to demonstrate the concept of indicator/catalyst
displacement assay for the simultaneous detection and detoxification of cyanide. The catalytic degradation property in the
assay was necessary for making the detecting system reversible, which the traditional indicator displacement assays could
never achieve. After the realization of this new property, the silica-gel-based solid-supporting complex 1 was fabricated for
application in a device, which was demonstrated for its use in the naked-eye detection and degradation of cyanide in tap,
river, and underground water samples in a repeatable and real-time manner, even in the presence of interfering anions
-
-
(CH3COO-, N3-, HCO3 , Cl-, NO3 , HPO42-, SO42-, SCN-, and OCN-). Within 300 min, cyanide was quantitatively oxidized into the
less toxic cyanate by 1 in the presence of H2O2. The detection limit of 1 for cyanide was found to be 1.16 × 10-4 M (3.02
mg/L).
this study, a bimetallic donor-acceptor ensemble (BmDAE)5 has
been synthesized as the first displacement-based device for
reversible monitoring of pollutants by destroying the
Introduction
Reversible detection of analytes allows real-time medical,
industrial, and environmental applications.1 Reversibility is an
important characteristic of supramolecular chemistry, involving
association, dissociation, and exchange of molecules.2 Recent
research attention has been focused on the development of
displacement assays as one of the emerging tools for in-situ
monitoring of xenobiotics3a, in-vivo determination of bio-analytes3b-
d, drug and prodrug discovery3e-f, and latent catalysis3g because of
its simple design, good analyte selectivity, and/or high detection
sensitivity. The working principle of indicator displacement assays
(IDAs) involves (i) initial binding of an indicator to a receptor,
forming an “indicator-receptor ensemble”; (ii) introduction of a
competitive analyte into the system, causing the dissociation of the
ensemble, followed by release of the indicator and hence, triggering
an action such as a colorimetric and/or fluorometric signal; and (iii)
a new formation of “receptor-analyte ensemble”. In principle,
molecular device based on the displacement assay is a one-off
mechanism because the thermodynamically more stable “receptor-
analyte ensemble” formed does not allow the system to revert to
its original form, i.e., the less stable “indicator-receptor ensemble”.4
These irreversible and non-repeatable properties of the
displacement assay always limit its application.
pollutants. To this end, the BmDAE includes a metallic
indicator with a metallic receptor. Most importantly, the
receptor is also formulated as a catalyst for degrading the
analyte to be tested. In the presence of a toxic analyte, the
indicator displacement design allows the BmDAE to dissociate
into its signal indicator via the formation of the “receptor-
analyte ensemble”. Therefore, the analyte is quantitatively
monitored. Furthermore, since the receptor also acts as a
catalyst, the pollutant can be catalytically degraded into
harmless components simultaneously. Due to the degradation
of the pollutants, the “receptor-analyte ensemble” is
destroyed, reforming the “indicator-receptor ensemble” and
thus, providing the reversibility. Instead of using indicator
displacement assay for irreversible and cumulative detection,
use of this new indicator/catalyst displacement assay could
open a new direction for real-time analyte detection.
Herein we report a new BmDAE, complex 1 (CN)3FeII(tppz)CuIICl
(tppz = 2,3,5,6-tetra(2'-pyridyl)pyrazine), and its silica-gel-based
solid-supporting material for monitoring and detoxifying cyanide in
real water samples (tap, river, and underground water). Through
the indicator/catalyst displacement assay (ICDA), the advantages of
the system will be reported in terms of “SSDRRA”, i.e., selectivity,
sensitivity, detoxification, reversibility, repeatability, and
applicability. Cyanide is chosen as the analyte because of its high
toxicity, broad industrial applications, and because it has reportedly
caused widespread concern.6 Furthermore, such chemosensing and
chemodosimetric systems for cyanide detection can be used in rare
molecular devices to synergically detect and remediate the
pollutant in a one-step process.6a,6c,7
To realize the reversible functionality in the displacement
assay, incorporation of a catalytic unit is a possible solution. In
Department of Science and Environmental Studies, Centre for Education in
Environmental Sustainability, The Education University of Hong Kong, 10 Lo Ping
Road, Tai Po Hong Kong SAR, China and College of Chemistry and Chemical
Engineering, Southwest University, Chong Qing, China
†Experimental Procedures and UV-vis spectroscopic titrations can be found in the
Electronic supplementary information (ESI): [details of any supplementary
information available should be included here]. See DOI: 10.1039/x0xx00000x
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catalytic activity. The spectroscopic changes of the
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supernatant solution at 532 nm and theDrOeIm: 10o.v10a3l9e/Cff9icTiCe0n6c3y08oKf
CN− were analyzed as functions of time. The above operations
were performed four times by the reversible addition of CN−
(1.0  10-3 M) and H2O2 (1.0  10-2 M) to test the repeatability
of the material.
Results and discussion
Synthesis and Characterization of Complex 1.
In this study, [BTPPC][FeII(tppz)(CN)3] was used as a building block
Scheme 1 Proposed ICDA mechanism of complex 1 for the
simultaneous detection and degradation of cyanide.
to construct
a multifunctional chemosensor/catalyst material
because of its advantages: (i) strong and low-energy UV-Vis
absorption, which is an ideal property for the signal-transducing
counterpart; (ii) the free N^N^N tridentate site, which is believed to
be a good coordination position for the reversible association and
dissociation of a metallic receptor/catalyst; and (iii) free CN
ligands, which can be exploited for adsorption on solid-supporting
materials.
Experimental section
Synthetic procedures of (CN)3FeII(tppz)CuIICl (1).
A
mixture
of
[BTPPC][FeII(tppz)(CN)3]
(BTPPC
=
benzyltriphenylphosphonium bromide; 437.5 mg, 0.5 mmol)
and CuCl2 (66.5 mg, 0.5 mmol) was stirred at 298 K in ethanol
(100 mL) for overnight. The blue solids precipitated out were
collected, washed with ethanol, and air-dried at room
temperature. (215.0 mg, 67.3%) IR (KBr): CN = 2092 cm−1.
High-resolution ESI-MS (positive mode): m/z 642.9438
{(Na)(CN)3FeII(tppz)CuIICl}+ (calculated mass: 642.9760 amu);
Anal. calcd. for C27ClCuFeH16N9·4.5H2O·CH3CH2OH: C, 46.54; H,
4.17; N, 16.84. Found C, 46.56; H, 4.13; N, 17.20.
Bimetallic complex
1 was synthesized by simply stirring
equivalent molar amounts of [BTPPC][FeII(tppz)(CN)3] to CuCl2 in
ethanol at 298 K and isolated as an air-stable compound with high
solubility in aqueous medium. The results of high-resolution ESI-MS
and elemental analysis confirmed the proposed bimetallic structure
of complex 1, where the tppz ligand is believed to act as a bridge
connecting the Fe(II) and Cu(II) metal ions (Scheme 1).
The UV-Vis absorption spectrum of [BTPPC][FeII(tppz)(CN)3]
featured a broad and low-energy band at 425–650 nm. According to
the literature, this low-energy absorption band originates from the
Chemosensing Selectivity of Complex 1 Toward Various Anions.
-
-
Various anions, including CN-, SO42-, HCO3 , HPO42-, N3 , CH3COO-,
NCS-, NO3 , NCO-, and Cl- (0–2.0  10−3 M) were titrated with
-
Fe(dπ)
→ tppz(π*) metal-to-ligand charge transfer (MLCT)
complex 1 solution (1.0  10−4 M). The titrations were carried out in
phosphate buffer (pH 7, 0.02 M) at 298 K. The spectroscopic
changes of resulting mixtures at 597 nm were plotted as a function
of the analyte mole ratio. The colorimetric responses of 1 by the
analytes were also obtained by digital photography. The binding
constants8 and method detection limits9 were evaluated from the
spectroscopic changes.
absorption.11 [BTPPC][FeII(tppz)(CN)3] appears purple in color when
dissolved in aqueous pH 7 phosphate buffer. Upon coordination of
a Cu(II) ion, the MLCT transition of Fe(II)-diimine chromophore in
complex 1 shows a red-shift from λmax at 532 to 597 nm, due to the
electron-withdrawing effect of Cu(II) in destabilizing the d-orbitals
of the Fe(II)-diimine chromophore (S.Figure 1a). The color of
complex 1 is blue in aqueous pH 7 phosphate buffer. The results of
the UV-Vis spectroscopic titration of [BTPPC][FeII(tppz)(CN)3] by
CuCl2 fitted the 1:1 Benesi–Hildebrand equation with a good linear
relationship (R2=0.999) for the plot of A0/(A–A0) at 597 nm versus
1/[CuCl2] (S.Figure. 1b). This further suggests that the free N^N^N
tridentate site in [FeII(tppz)(CN)3]- is associated with one Cu(II)
metallic counterpart to form the bimetallic complex. The overall
binding constant, log K, for this formation is estimated as 2.86 M-1.
Catalytic Degradation of Cyanide by Complex 1.
A 15.00 mL test solution (pH 7 phosphate buffer) containing 1, CN-,
and H2O2 (1.0  10−4, 1.0  10−3, and 2.0  10−3 M, respectively) was
stirred for 180 min at 298 K. The test solution was measured at
regular intervals using a Thermo Scientific™ Orion™ analyzer and
ion chromatography10 to evaluate the levels of CN− and NCO−,
respectively. All the samples were immediately analyzed to avoid
errors due to subsequent reactions.
Chemosensing Property of Complex 1 Toward Cyanide.
The formation of complex 1 through the binding of the indicator,
[FeII(tppz)(CN)3]-, to the Cu(II) receptor enables us to use this
bimetallic “indicator-receptor ensemble” to detect cyanide. Figure
1a shows the UV-Vis spectroscopic titration of 1 by the addition of
an increasing amount of cyanide in aqueous pH 7 buffer. Three
clear isosbestic points at 346, 471, and 558 nm were obtained
during the titrations, with a blue-shift of both π- π* and MLCT
absorptions from λmax at 393 to 333 nm and from 597 to 532 nm,
respectively. Figure 1b shows the mole ratio plot between 1 and
cyanide, revealing that the maximum UV-Vis spectroscopic
response occurs at a ratio of 1:4. The overall binding constant, log
K, and the method detection limit (MDL) calculated from the
titrations of 1 by cyanide ions were estimated as 12.27 ± 0.01 M-4
Solid-supported Complex
1 and its Repeatability of
Chemosensing and Catalytic degradation toward Cyanide.
The solid-supported complex 1 was fabricated by adding SiO2
(40–63 μm, 2.5 g) to complex 1 solution (1.0  10-4 M, 50 mL,
pH 7 phosphate buffer). The moist green powders obtained
were collected by filtration, washed with deionized water, and
air-dried at 298 K. IR (KBr): CN = 2145 cm−1. The green solid-
supported complex 1 material (2.5 g) was suspended in 50 mL
phosphate buffer. Initially, CN− (1.0  10-3 M) was added to
activate the chemosensing activity of the solid-supported
complex 1. H2O2 (1.0  10-2 M) was then added to initiate its
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and 1.16 × 10-4 M (3.02 mg/L), respectively (Figure 1c). The lethal
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dose (LD50) of cyanide is 0.5–3.5 mgkg-1 to body weight.12 Figure 1d
DOI: 10.1039/C9TC06308K
shows that the colorimetric responses from blue to purple of 1 with
increasing amounts of cyanide can be detected by naked eyes.
-
Upon the recognition of 10 different anions, CN-, CH3COO-, N3 ,
HCO3 , Cl-, NO3 , HPO42-, SO42-, SCN-, and OCN- by complex 1, only
cyanide could trigger UV-Vis spectroscopic changes (Figure 2a),
producing a sharp naked-eye colorimetric response from blue to
purple (Figure 2b).
-
-
The sensing mechanism of complex 1 toward cyanide ions is
proposed in Scheme 1. The clear isosbestic points obtained during
the titration of 1 by cyanide and the close resemblance of the UV-
Vis spectrum of the “complex 1 + cyanide mixture” to that of
[BTPPC][FeII(tppz)(CN)3] suggest that the N^N^N tridentate
coordination between Cu2+ and [FeII(tppz)(CN)3]- is cleaved in the
presence of cyanide ions. The results of UV-Vis spectroscopic
titration between 1 and cyanide fitted the 1:4 Benesi–Hildebrand
equation with a good linear relationship (R2=0.997; Figure 1c),
further suggesting that four molecules of cyanide led to Cu(II) ion
displacement. The dissociation of complex 1 into [FeII(tppz)(CN)3]-
and [Cu(CN)4]2- is due to the driving force for the formation of the
more stable [Cu(CN)4]2-. The Gibbs free energy changes (∆G°) for
complex 1 and [Cu(CN)4]2- are -16.3 (Fig. S1) and -125.5 kJ/mol13,
respectively, further supporting our explanation.14
Fig. 2 (a) Summary of UV-Vis spectroscopic titrations (A/A0 at 597
nm) of complex 1 (1 × 10-4 M) with ten different anions monitored
as a function of their concentration (0–1 × 10-3 M). (b) Photographs
of the colorimetric responses of the above titration with anion
concentration as 1 ×10-3 M: from left to right is blank, CN-, CH3COO-,
Fig. 1 (a) UV-Vis spectroscopic titrations of complex 1 (1 × 10-4 M)
with CN- (0–1 ×10-3 M), (b) mole ratio plot between 1 (3 × 10-4 M)
and cyanide (0–3 ×10-3 M) at 532 nm, (c) the slope and y-intercept
of the best-fitted plot of A0/(A-A0) at 532 nm versus 1/[cyanide]4 as
4.48 × 10-13 M4 and 0.83, respectively, log K = 12.27, and (d)
Photographs of the colorimetric responses of complex 1 (1 × 10-4 M)
in the presence of increasing concentration of CN- (0–1 × 10-3 M). All
the experiments were carried out in pH 7 phosphate buffer (0.02 M)
at 298 K.
-,
-
-
N3 HCO3 , Cl-, NO3 , HPO42-, SO42-, SCN-, and OCN-. All the
experiments were carried out in pH 7 phosphate buffer (0.02 M) at
298 K.
Catalytic Activity of Complex 1 Toward Cyanide.
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The advantages of exploiting the bimetallic functionalities of
complex 1 are not limited to the detection of cyanide but also to
degrade pollutants into harmless substances. Cu(II) complexes have
been studied as active metal catalysts to oxidize CN- to NCO- using
H2O2 as the oxidant.3g In this study, we attempted to demonstrate
the catalytic property of complex 1 in the presence of cyanide after
the abovementioned displacement. For this investigation, the
concentrations of CN- and NCO- in eight test solutions containing
CN-, H2O2, and 1 in a molar ratio of 10:20:1 in deionized water were
regularly measured at 30 min intervals.15 As seen in Figure 3a,
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DOI: 10.1039/C9TC06308K
complex
1 catalyzes the oxidative degradation of cyanide
quantitatively within 420 min. Control experiments conducted
without the complex or with [BTPPC][FeII(tppz)(CN)3] under the
given conditions revealed that less than 25% of cyanide was
oxidized during the experimental period. Even in the reaction using
CuCl2 instead of the bimetallic complex, cyanide was quantitatively
oxidized within 420 min.10 The catalytic activity of complex 1
originated from the displacement of the Cu(II) complex by cyanide.
[Cu(CN)4]2- was eventually formed as the active catalyst for this
oxidation (Scheme 1). Interestingly, the subsequent observation of
[Cu(OCN)(CN)3]2- (m/z 91.8; mass-to-charge ratio is 2) and [Cu(CN)3]
- (m/z 141.6) in the ESI-MS profile of the “complex 1+CN-” mixture
confirmed the degradation of not only the free cyanide but also the
Cu-bound cyanide.
Reversibility of Complex 1 Toward Cyanide.
As mentioned in the introduction, the formation of a more
thermodynamically stable “receptor-analyte ensemble” with
respect to the “indicator-receptor ensemble” makes IDAs
irreversible.4 However, the catalytic degradation property of
complex 1 has been demonstrated to destroy this stable “receptor-
analyte ensemble” to form a new “receptor-degradant ensemble”;
hence, we believe that the reversibility of system should be
changed. If a less stable “receptor-degradant ensemble” is formed
during the degradation, the receptor from the “receptor-degradant
ensemble” can be exchanged back to the free indicator, thus
restoring the original “indicator-receptor ensemble.”
Figure 3b shows the color changes in the test solution
containing CN-, H2O2, and 1 (molar ratio of 10:20:1) with time.
Unlike other traditional chemodosimeters and chemosensors,
complex 1 regained its original color after a complete detection and
degradation cycle. To investigate this reversibility, the cyanide and
cyanate levels as well as the UV−Vis spectroscopic changes of the
abovementioned test solution were regularly measured at 30 min
intervals (Figures 3b and 3c). At 0 h, the π- π* and MLCT
absorptions of the Fe(II)-diimine chromophore, which existed as an
intact bimetallic complex, were detected at λmax 383 and 597 nm,
respectively. The color of test solution was blue, and the level of
cyanide is full, indicating 100% cyanide concentration in the
solution.
Stage 1 (“indicator-receptor ensemble” + analyte → “receptor-
analyte ensemble” + indicator): From 0 to 30 min, cyanide rapidly
initiated the indicator displacement by dissociating complex 1 into
[FeII(tppz)(CN)3]- and [Cu(CN)4]2-. Thus, four equivalents of cyanide
were found to be decreased, and 60% of cyanide was left in the test
solution. The dissociation caused the original π-π* and MLCT
absorptions in complex 1 to be gradually suppressed and blue-
shifted to 333 and 532 nm, respectively (S.Figure 2b); thus, λmax at
383 nm was found to be decreased. At this stage, the color of the
test solution changed from blue to purple. No cyanate was found in
this stage.
Fig. 3 (a) Catalytic degradation of CN- by complex 1 (▲, 1 × 10-4 M),
CuCl2 (▼, 1 × 10-4 M) and [BTPPC][Fe(tppz)(CN)3] (, 1 × 10-4 M)
and control () in the presence of H2O2 as the oxidant; for the
degradation of CN- by complex 1: (b) photograph of its colorimetric
responses; (c) absorbance changes (383 nm); and (d) cyanide and
cyanate concentrations (c0 = initial concentration, c = concentration
after a given time). All the experiments were carried out in DI water
at 298 K with the concentrations of CN- and H2O2 set as 1 × 10-3 and
2 × 10-3 M, respectively.
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Stage 2 (analyte → degradant): During the next 4.5 h (30–300
min), [Cu(CN)4]2- formed served as the active catalytic center to
initiate the oxidative degradation of CN- to OCN- in the presence of
H2O2. During the catalytic oxidation, all the unbound cyanide anions
were completely degraded, while the concentration of cyanate
proportionally increased. Note that at this stage, the level of
cyanate reached only 60% with respect to the original level of
cyanide used, because 40% of the cyanide existed as [Cu(CN)4]2-. No
UV−Vis spectroscopic changes for the test solution were found, and
λmax at 383 nm was unchanged throughout this period. The color of
test solution remained purple. At the end of this stage, [Cu(CN)4]2-,
NCO-, and [FeII(tppz)(CN)3]- were formed and present in the test
solution.
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DOI: 10.1039/C9TC06308K
Stage 3 (“receptor-analyte ensemble” + indicator → “indicator-
receptor ensemble” + degradant): After complete degradation of
the free cyanide, during the next 3 h (300–480 min), the cyanide
ligands in [Cu(CN)4]2- were further degraded to cyanate. During this
degradation, the concentration of cyanate gradually increased, and
the quantitative amount of cyanate was reached at 19 h. The π-π*
and MLCT absorptions gradually increased and red-shifted to their
original wavelengths at 383 and 597 nm, respectively (S.Figure 2c).
Figure 3c shows a steep change in λmax at 383 nm from 300 to 360
min, with a steady change from 360–480 min. These UV−Vis
spectroscopic changes could be explained by the re-formation of
the [(CN)3FeII(tppz)CuII]+ ensemble due to the exchange of Cu2+ from
the [Cu(OCN)4]2- intermediate16, the so-called “receptor-degradant
ensemble”, to [FeII(tppz)(CN)3]-. The Gibbs free energy changes
(∆G°) for complex 1 and [Cu(OCN)4]2- were -16.3 (S. Figure 1) and -
14.1 kJ/mol,17 respectively, which confirmed that the driving force
for this exchange is due to the formation of the more stable
[(CN)3FeII(tppz)CuII]+ ensemble. Consequently, the system could be
restored to its initial stage, where the color of test solution was also
restored from purple to blue, indicating (i) the end of the
detoxification and (ii) the time for restarting a new sensing and
degradation cycle.
Fig. 4 (a) Repeatability of the detection and degradation of cyanide
by the solid-supported complex 1 material in the presence of H2O2.
The black line represents the λmax of the supernatant at 532 nm,
while the blue line is the ratio of [cyanide] in the supernatant (c0 =
initial concentration, c = concentration after a given time). (inset)
Photographic images of the solid and the supernatant solution. (b)
The removal efficiency of CN- by the material in different types of
water samples. All the experiments were carried at 298 K with the
Solid-supported Material 1: Fabrication, Reversibility, and
Repeatability, and Detection/Oxidation of Cyanide in Real Water
Samples.
solid-supported complex
1 material (63.8 mg/L, complex 1
component: 1 × 10-4 M), CN- (1 × 10-3M), and H2O2 (1 × 10-2 M).
To further apply and test the reversibility and repeatability of
complex 1 toward cyanide, a solid-supported material 1 was
fabricated by adsorbing complex 1 onto commercially available
silica gel (SiO2, 0.040–0.063 mm) in 1:780 w/w ratio. The red-shift of
the CN stretching frequencies from 2077 to 2145 nm in the FTIR
spectrum of solid-supported complex 1 with respect to the free
complex 1 suggested that the CN ligands in complex 1 acted as
bridges for this adsorption.
cycle of ICDA, the purple supernatant solution became colorless,
while the white-colored solid-supported material reverted to green
(Figure 4a inset). This was because the [(CN)3FeII(tppz)CuII]+
ensemble was re-formed as the mechanism stated above, and it re-
adsorbed onto the blank SiO2. Experiments were performed on the
material continuously for four cycles by the addition of a new
portion of cyanide and H2O2 after each round. Afterward, the
sensing signals were fully recovered, and the degradation efficiency
was >99%, thus indicating that the material showed repeatable
ICDA performance (Figure 4a).
Upon the addition of cyanide to the green solid-supported
material 1 in pH 7 buffer, the color of supernatant solution changed
from colorless to purple while the color of solid-supported material
1 changed from green to white (Figure 4a inset). Furthermore,
cyanide was found to be quantitatively degraded within 60 min
under the given conditions, in the presence of H2O2 (Figure 4a).
These results concurred with the ICDA mechanism, according to
which the adsorbed complex 1 dissociated into [Cu(CN)4]2- and
[FeII(tppz)(CN)3]-. The negatively charged Fe(II) and Cu(II) complexes
caused the desorption and imparted color to the supernatant
solution.
Finally, the application of solid-supported material 1 to detect
and detoxify cyanide ions in real water samples such as tap water,
river water, and underground water was investigated. The real
water samples were spiked with a constant amount of cyanide ions
at room temperature. The concentration of residual cyanide was
regularly analyzed every 30 min.3f,10 The complete oxidation (85%
oxidation) of cyanide to cyanate ions required approximately 180
min for all the water samples (Figure 4b). These results indicated
that the presence of organic and inorganic matter in the real water
Most importantly, the reversible property of complex 1 resulted
in repeatability to solid-supported material 1. One hour after the 1st
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Journal of Materials Chemistry C
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ARTICLE
Journal Name
Nau, Angew. Chem. Int. Ed. 2015, 54, 792; (d) R. Kaushik, R.
samples does not interfere with the operation of solid-supported
View Article Online
Sakla, A. Ghosh, G. T. Selvan, P. M.SDeOlvIa: k10u.m10a3r9,/CD9.TCA0.6J3o0s8eK,
ACS Sens. 2018, 3, 1142; (e) J. C. Chang, I. D. Tomlinson, M.
R. Warnement, H. Iwamoto, L. J. DeFelice, R. D. Blakely, S. J.
Rosenthal, J. Am. Chem. Soc., 2011, 133, 17528; (f) W. C. Tse,
D. L. Boger, Acc. Chem. Res., 2004, 37, 61; (g) C. F. Chow, P.
Y. Ho, W. L. Wong, Y. J. Lu, Q. Tang, C. B. Gong, Chem. Sci.,
2017, 8, 3812.
A. W. Czarnik, Fluorescent Chemosensors for Ion and
Molecular Recognition; ACS Press: Washington, D. C., 1992.
(a) C. F. Chow, B. K. W. Chiu, M. H. W. Lam, W. Y. Wong, J.
Am. Chem. Soc., 2003, 125, 7802; (b) C. F. Chow, P. Y. Ho, W.
L. Wong, C. B. Gong, Eur. Chem. J., 2015, 21, 12984; (c) C. F.
Chow, K. Y. F. Ho, C. B. Gong, Anal. Chem., 2015, 87, 6112.
(a) Z. Xu, X. Chen, H. N. Kim, J. Yoon, Chem. Soc. Rev., 2010,
39, 127; (b) P. Anbarasan, T. Schareina, M. Beller, Chem. Soc.
Rev., 2011, 40, 5049; (c) P. Anzenbacher Jr, D. S. Tyson, K.
Jursikova, F. N. Castellano, J. Am. Chem. Soc., 2002, 124,
6232.
material 1.
Conclusions
A
new bimetallic complex, (CN)3FeII(tppz)CuIICl, has been
synthesized and used to demonstrate the concept of ICDA for the
simultaneous detection and detoxification of cyanide. Two major
components are incorporated in the bimetallic design, a Fe(II)-
diimine indicator and a dual functional Cu(II) receptor/catalyst, in
order to achieve “SSDRRA”: selectivity, sensitivity, detoxification,
reversibility, repeatability, and applicability.
4
5
6
7
Complex 1 shows good selectivity and sensitivity by producing a
naked-eye colorimetric response to cyanide but not to the other
common anions. The log K and MDL values are 12.27 ± 0.01 M-4 and
1.16 × 10-4 M (3.02 mg/L), respectively. The complex also shows
catalytic activity for the oxidation of cyanide. This detoxification is
quantitative and can be achieved in 60−180 min. A silica gel-based
solid-supporting complex 1 material is fabricated and demonstrated
to be suitable for the detoxification of cyanide ions in real water
bodies, such as tap water, river water, and underground water
bodies, with 85% recovery.
(a) D. G. Cho, J. H. Kim, J. L. Sessler, J. Am. Chem. Soc. 2008,
130, 12163; (b) F. Wang, L. Wang, X. Chen, J. Yoon, Chem.
Soc. Rev. 2014, 43, 4312; (c) K. Xiao, H. M. Nie, C. B. Gong, X.
X. Ou, Q. Tang, C. F. Chow, Dyes Pigments 2015, 116, 82.
K. A. Connors, Binding Constants: The Measurement of
Molecular Complexes Stability, John Wiley and Sons: New
York, 1987.
8
9
The catalytic degradation is demonstrated as a necessary tool to
make the ICDA system reversible and repeatable. Through the
degradation of cyanide by complex 1 in the test solution, a free
Cu(II) complex, NCO-, [FeII(tppz)(CN)3]- is revealed to be formed. The
stability of complex 1 (∆G° = -16.3 kJ/mol) over that of [Cu(NCO)4]2-
(∆G° = -14.1 kJ/mol) is revealed and used to explain the reversibility
and repeatability offered by the system.
A. Hubaux, G. Vos, Anal. Chem., 1970, 42, 849.
10 Separation occurred at 35 °C on a Metrosep Carb 2 (250/4.0)
column. The eluent was 20 mM NaOH at a flow rate of 0.8
mL min−1. An ion chromatographic amperometric detector
(Metrohm) was used for detection of eluted components.
11 L. M. Toma, D. Armentano, G. De Munno, J.Sletten, F. Lloret,
M. Julve, Polyhedron, 2007, 26, 5263.
12 R. Koenig, Science 2000, 287, 1737.
13 M. T. Beck, Pure and Appl. Chem., 1987, 59, 1703.
14 (a) A. Mohammadi, F. S. Zabihi, N. Chaibakhsh, J. Photochem.
Photobiol. A., 2018, 367, 384; (b) A. Mohammadi, S.
Yaghoubi, Sens. Actuators B., 2017, 251, 264.
Conflicts of interest
There are no conflicts to declare.
15 (a) J. E. Erman, Biochemistry., 1974, 13, 39; (b) V. Garcia, P.
Hayrynen, J. Landaburu-Aguirre, M. Pirila, R. L. Keiski, A.
Urtiaga, J. Chem. Technol. Biotechnol., 2014, 89, 803.
16 A. H. Norbury, Advances in Inorganic Chemistry and
Radiochemistry, 1975, 17, 231.
Acknowledgements
The work described in this paper was funded by a grant from the
Education University of Hong Kong (Project No. R3444, R4175 and
R4201), and grants from the Research Grants Council of Hong Kong
SAR, China (GRF 18300415).
17 A. Lodzinska, Rocz. Chem., 1967, 41, 1437.
References
1
(a) T. Nguyen, D. Turp, D. Wang, B. Nolscher, F. Laquai, K.
Mullen, J. Am. Chem. Soc., 2011, 133, 11194; (b) Y. Zheng, A.
H. Soeriyadi, L. Rosa, S. H. Ng, U. Bach, J. J. Gooding, Nat.
Commun., 2015, 6, 8797; (c) M. E. Moragues, R. Martínez-
Máñez, Félix Sancenón, Chem. Soc. Rev., 2011, 40, 2593; (d)
L. E. Santos-Figueroa, M. E. Moragues, E. Climent, A.
Agostini, R. Martínez-Máñez, Félix Sancenón, Chem. Soc.
Rev., 2013, 42, 3489.
2
3
(a) D. Drahonovskly, J. M. Lehn, J. Org. Chem., 2009, 74,
8428; (b) N. Hafezi, J. M. Lehn, J. Am. Chem. Soc., 2012, 134,
12861; (c) J. M. Lehn, Science 2002, 295, 2400;(d) V. Berl, I.
Huc, R. G. Khoury, M. J. Krische, J. M. Lehn, Nature, 2000,
407, 720.
(a) B. T. Nguyen, E. V. Anslyn, Coord. Chem. Rev., 2006, 250,
3118; (b) T. Minami, Y. Liu, A. Akdeniz, P. Koutnik, N. A.
Esipenko, R. Nishiyabu, Y. Kubo, P. Anzenbacher Jr, J. Am.
Chem. Soc., 2014, 136, 11396; (c) A. Norouzy, Z. Azizi, W. M.
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