Rational design, green synthesis of reaction-based dual-channel chemosensors for cyanide anion

Article abstract of DOI:10.1016/j.tetlet.2013.07.022

Chemosensors CF1-CF3 were designed and synthesized via a simple green chemistry procedure. CF3 could instantly detect cyanide anion in aqueous solution by dual-channel model. The detection limit of CF3 for CN- is 10 nM. Test strips based on CF3 could act as a convenient and efficient CN^- test kit.

Full text of DOI:10.1016/j.tetlet.2013.07.022

Tetrahedron Letters 54 (2013) 5031–5034
Contents lists available at SciVerse ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Rational design, green synthesis of reaction-based dual-channel
chemosensors for cyanide anion
⇑
Qi Lin, Yong-Peng Fu, Pei Chen, Tai-Bao Wei, You-Ming Zhang
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
a r t i c l e i n f o
a b s t r a c t
Article history:
Chemosensors CF1–CF3 were designed and synthesized via a simple green chemistry procedure. CF3
could instantly detect cyanide anion in aqueous solution by dual-channel model. The detection limit of
CF3 for CN- is 10 nM. Test strips based on CF3 could act as a convenient and efficient CNÀ test kit.
Ó 2013 Elsevier Ltd. All rights reserved.
Received 26 April 2013
Revised 11 June 2013
Accepted 3 July 2013
Available online 10 July 2013
Keywords:
Green synthesis
Chemosensors
Cyanide anion
Colorimetric
Fluorimetric
Cyanide anion (CNÀ) is known to be an extremely toxic anion1
and can directly lead to the death of human beings in several min-
utes because it strongly binds cytochrome-c, disrupting the mito-
chondrial electron-transport chain and leading to decreased
oxidative metabolism and oxygen utilization.1,2 Therefore, the
maximum permissive level of cyanide in drinking water is set at
or fluorometric chemosensors5c–e become an excellent choice. Fur-
thermore, in biological and environmental systems, cyanide–sen-
sor interactions commonly occur in the aqueous solution,
therefore, much attention has been paid to develop CNÀ optical
chemosensors that work in the aqueous solution.7
Several chemosensor systems for cyanide anion detection re-
ported to date are based on the mechanism of coordination,7d,8
hydrogen-bonding interaction,7e,f nucleophilic addition reac-
tion,7a,c,9 and so on. Among these cyanide sensors, reaction-based
sensors display both specific selectivity and high sensitivity to
the cyanide anion. However, most of the reaction-based cyanide
anion sensors often employ sophisticated structures, require com-
plicated synthetic steps, high temperature or long reaction time for
detection of CNÀ, and can only be operated in the pure or mixed or-
ganic solvents. Therefore, simple and efficient CNÀ optical chemo-
sensors which could instantly detect CNÀ in the aqueous solution
at the room temperature are essential. On the other hand, the syn-
thesis procedures of most artificial sensors usually involve rather
harsh reaction conditions and often employ hazardous materials
like reaction raw materials, solutions, and catalysts which cause
a huge risk to the environment. To minimize the generation and
application of hazardous substances, a green synthetic procedure
should be encouraged in the synthesis of CNÀ chemosensors.
With these considerations and our interest in ion recognition,10
we here report a series of efficient optical chemosensors (Scheme 1)
which could sense CNÀ with specific selectivity and high sensitivity
in aqueous solutions. In addition, these sensors were synthesized
1.9 l
M by the World Health Organization (WHO).3 On the other
hand, large quantities of cyanide anions are widely used in indus-
try for the synthesis of fine chemicals, electroplating, and precious
metal mining.2a In addition, a higher level of cyanide could also be
accumulated through the consumption of certain foods and
plants.4 All things considered, the rational design and synthesis
of efficient sensors to selectively detect CNÀ at the environmental
and biological levels have attracted much attention. Although pre-
vious work has involved the development of a wide variety of
chemical and physical sensors for the detection of CNÀ,5 so far, it
is still a challenge to improve the detection selectivity and sensitiv-
ity in the contexÀt of interference from coexisting anions such as FÀ,
AcOÀ, and H2PO4 in the aqueous solution. Moreover, most of phys-
ical methods require expensive equipment, involve time-consum-
ing and laborious procedures that can be carried out only by
well-trained professionals, and seriously restrict the practical
application of these CNÀ sensors.5a,b,6 For purposes of simplicity,
convenience, and low-cost, easily-prepared CNÀ colorimetric and/
⇑
Corresponding author. Tel.: +86 931 7973120.
E-mail address: zhangnwnu@126.com (Y.-M. Zhang).
0040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2013.07.022

5032
Q. Lin et al. / Tetrahedron Letters 54 (2013) 5031–5034
Ha
Hb
NC
CN
O
O2N
O
CN
O
O2N
CH2(CN)2
H2O; 90 o
O
CN-
O2N
CN
C
CN
M1~3
CF1: o-nitryl; CF2: m-nitryl; CF3: p-nitryl
CF1~CF3-CN
Scheme 1. The green synthesis of CF1–CF3 and the CNÀ sensing mechanism.
via a simple, efficient, and environmentally friendly route in pure
water without using any catalyst.
Guest recognition experiments. The colorimetric and fluorimetric
sensing abilities were primarily investigated by adding pure water
solution of various anions to the DMSO/H2O (7/3, v/v; pH 7.0) solu-
tions of sensor CF3 respectively. As shown in Figure 2a, the sensor
immediately responded with dramatic color changes from yellow-
green to pale pink when water solution of CNÀ was added to the
solution of CF3 in room temperature. In the corresponding UV–
vis spectra, the absorption peak at 410 nm decreased and shifted
to 358 nm. However, as shown in Figure 2b, a green fluorescence
with one emission band centered at 510 nm appeared when the
solution of sensor CF3 was excited at 437 nm. Upon addition of
water solution of CNÀ, the fluorescence color instantly changed
from green to orange and the emission band decreased remarkably
and shifted to 536 nm. However, when waterÀsolutions of other an-
ions FÀ, ClÀ, BrÀ, IÀ, AcOÀ, H2PO4À, HSO4À, ClO4 , N3À, SCNÀ, NOÀ3 and
ClOÀ4 were added to the solution of sensor CF3 respectively, neither
significant color nor fluorescence changes were observed. It was
confirmed that CF3 could selectively dual-channel instantly detect
CNÀ in DMSO/H2O binary solution.
The strategies for the design of these sensors are as follows.
Firstly, we introduced the nitrophenyl furan moiety as the signal
groups to achieve ‘naked-eye’ colorimetric and fluorimetric recog-
nition. It is noteworthy that the nitrophenyl furan moiety has sel-
dom been utilized as the signal group for chemosensors. However,
this moiety possesses the dual-channel response ability for chem-
ical stimulation. In this moiety, the nitro group is a chromophore
and the phenyl furan group is a fluorophore. Moreover, the nitro
group is an electron-withdrawing group, which could strengthen
the sensitivity of the nucleophilic addition reaction. Secondly, in
order to achieve the instantaneous detection of cyanide, a dicyano-
vinyl group was introduced as the binding site. According to liter-
atures,9d,f vinyl-substituted derivates display both selective and
sensitive responses to various concentrations of the cyanide anion.
Additionally, the dicyano substitution on the vinyl group could sig-
nificantly enhance the sensitivity of the nucleophilic addition reac-
tion between the vinyl group and CNÀ. Finally, the sensors were
designed to be easily synthesized via a green chemistry method.
In order to estimate the effect of the signal group on the sensor’s
colorimetric and fluorimetric sensing abilities for CNÀ, the o, m,
and p-nitro substituted compounds were synthesized respectively.
Sensors CF1–CF3 were synthesized by the Knöevenagel reaction
as depicted in Scheme 1.11 Usually, the Knöevenagel reaction is
carried out in dipolar aprotic solvents like DMF or CH3CN and cat-
alyzed by bases such as piperidine, or sodium hydroxide.9d We,
however, attempt to synthesize the sensors CF1–CF3 in pure water
under the catalyst free condition to avoid the use of organic sol-
vents and catalyst and prevent environmental contamination. It
is exciting that 5-nitrophenylfuran-2-carbaldehydes (M1–M3)
could carry out the Knöevenagel reaction with malononitrile in
pure water without using any catalyst to give 5-(nitrophenyl)-2-
dicyanovinyl-furan (CF1–CF3) with high yields. These compounds
are characterized by 1H NMR, 13C NMR, IR, EA, and MS, the single
crystal structure of CF2 also confirmed the synthesis results
(Fig. 1, CCDC 924675). This is an excellent green chemistry method
for the preparation of these kinds of fine chemicals.
(a)
0.8
0.7
0.6
CF3 and CF3 + others
0.5
0.4
0.3
0.2
-
CF3+CN
0.1
0.0
300
400
500
600
700
Wavelength/nm
In order to investigate the CNÀ recognition abilities of the sen-
sors CF1–CF3 in aqueous solution, we carried out a series of Host–
(b)
CF3 and CF3+others
800
600
400
200
CF3
CF3
-
+CN
-
CF3+CN
0
400
500
600
700
Wavelength/nm
Figure 2. (a) UV–vis spectra of CF3 with various anions in DMSO/H2O (7/3, v/v;
pH = 7.0) solutions. Inset: color changes of CF3 with various anions; (b) fluores-
cence responses of CF3 with various anions in DMSO/H2O solution (kex = 437 nm).
Inset: Fluorescent photograph of CF3 and CF3 + CNÀ. Concentration of CF3:
2.0 Â 105 M; CNÀ: 1 Â 103 M.
Figure 1. Single crystal structure of CF2.

Q. Lin et al. / Tetrahedron Letters 54 (2013) 5031–5034
5033
The same tests were applied to CF2 and CF1. In this case, when
700
600
500
400
300
200
100
water solution of CNÀ was added to the DMSO/H2O solution of CF2
and CF1, respectively, the colors of the solutions changed from yel-
low–green to pale pink. In corresponding UV–vis spectra, the
absorption peaks at 396 nm (for CF2) and 383 nm (for CF1) de-
creased (Fig. S1 in the Supplementary data). While other anions
could not cause such color and spectra changes, therefore, the
CF2 and CF1 could colorimetrically detect CNÀ selectively. How-
ever, in the corresponding fluorescence spectra of CF2 and CF1,
the meta or ortho position of the phenyl groups of CF2 and CF1 is
substituted respectively by the nitro group, therefore the fluores-
cent intensities of CF2 and CF1 are very weak (Fig. S2 in the Sup-
plementary data). The addition of CNÀ caused very slight
responses in the fluorescence emission intensity, which indicated
that CF2 or CF1 could not fluorescently sense CNÀ.
0
1
2
3
4
5
6
7
8
9
10 11 12 13
Anions
Because CF3 has properties of dual-channel specific selectivity
for CNÀ, a series of experiments were carried out to investigate
the CNÀ recognition capability and mechanism of CF3. To gain an
insight into the stoichiometry of the CNÀ–CF3 addition reaction,
the method of UV–vis titration was used. As shown in Figure 3,
upon addition of 1 equiv of cyanide, the UV–vis absorbance of
the solution at 410 nm experiences a ca. 4.2-fold (A0/A) decrease
in a manner, that is, inversely proportional and 1:1 stoichiometri-
cally related to the cyanide concentration.
Figure 4. Selectivity of CF3. The black bars represent the fluorescence intensity of
CF3 in the presence of other anions (1 mM). The red bars represent the fluorescence
intensity that occurs upon the subsequent addition of 1 mM of CNÀ to the above
solution. From 1 to 13: none, FÀ, ClÀ, BrÀ, IÀ, AcOÀ, H2POÀÀ, HSO4À, ClOÀ4 , N3À, SO24À
4
and NOÀ3 , SCNÀ.
An important feature of the sensor is its specific selectivity to-
ward the analyte over other competitive species. The variations
of UV–vis absorbance, fluorescence, and visual color changes of
sensor CF3 in DMSO/H2O binary solutions caused by the anions
FÀ, ClÀ, BrÀ, IÀ, AcOÀ, H2PO4À, HSO4À, ClOÀ4 , CNÀ, N3À, SCNÀ, NOÀ3 ,
and ClOÀ4 , were recorded in Figure 4 and Figure S3 in the Supple-
mentary data. It is noticeable that the miscellaneous competitive
anions did not lead to any significant interference. In the presence
of these ions, the CNÀ still produced similar color and optical spec-
tral changes. These results showed that the selectivity of sensor
CF3 toward CNÀ was not affected by the presence of other anions.
The colorimetric and fluorimetric detection limits of sensor CF3
for CNÀ were also tested. As shown in Figure 3, with the gradual
addition of CNÀ, a sharp decrease in the absorbance at 410 nm
and an obvious increase in the absorbance at 480 nm were ob-
served. Simultaneously, the ratio of A480/A410 rises along with
the increase in CNÀ concentrations, which allows the CNÀ concen-
tration to be determined ratiometrically. The detection limit using
Figure 5. (a) Color changes observed upon the addition of various concentrations of
CNÀ water solution to the solutions of CF3 in DMSO/H2O (v/v, 7/3); (b) photographs
of test strips of CF3 and CF3 + CNÀ under an UV lamp at 360 nm; (c) under nature
light.
(0.1 lM) while the detection limit of the fluorescence spectra
changes calculated on the basis of 3sB/S12 was 1.0 Â 10À8
M
(0.01
line of 1.9
l
M) for CNÀ anion, which is far lower than the WHO guide-
l
M cyanide.
To investigate the practical application of chemosensor CF3, test
strips were prepared by immersing filter papers into a DMSO solu-
tion of CF3 (0.1 M) and then drying in the air. The test strips con-
taining CF3 were utilized to sense different anions. As shown in
Figure 5b and c, the obvious color and fluorescence changes were
observed only with CNÀ water solution when different anion solu-
tions were added to the test kits respectively. Therefore, the test
strips could conveniently detect CNÀ in water solutions.
visual color changes (Fig. 5a) was a concentration of 1.0 Â 10À7
M
The further CF3–CNÀ reaction mechanism was observed from
1H NMR titration experiments (Fig. S4 in the Supplementary data)
in DMSO-d6/D2O. It was obvious that the resonance signal corre-
sponding to the vinyl proton (Ha) at 8.39 ppm completely disap-
peared, whereas a new signal grew at 6.30 ppm corresponding to
0.8
0.8
0.6
0.6
0.4
0.2
0.0
0.4
0.2
the a
-proton (Hb). Meanwhile, the furan protons and aromatic pro-
0.0
0.5
1.0
1.5
tons displayed upfield shift compared to those of CF3 due to the
breaking of the conjugation. These observations obviously indi-
cated that the cyanide anion was added to the vinyl group.
The results of EI-MS experiments also support this presump-
tion. In the EI-MS spectra of CF3, the [CF3 + H]+ peak appeared at
266.2 (m/zcalcd = 266.1). However, when 1 equiv of CNÀ was added
to the solution of CF3, the [CF3 + H]+ peak at 266.2 disappeared and
a new peak appeared at 291.2, coinciding well with that for the
species [CF3 + CNÀ] (m/zcalcd = 291.1) and indicating the formation
of the stabilized anionic species CF3–CNÀ.
-
CN ]/[CF3]
[
250 300 350 400 450 500 550 600 650 700
Wavelength/nm
In summary, an easy-to-make CNÀ sensor CF3 was designed
and synthesized via a green chemistry method. This sensor could
dual-channel instantly detects CNÀ in water solutions at room
Figure 3. UV–vis titration spectra of CF3 (20
lM in DMSO/H2O) upon the addition
of CNÀ water solution. [CNÀ] = 0, 2, 2.4, 4.8, 7.2, 9.6, 12, 14.4, 16.8, 19.2, 20.8, 24, 28,
32, 36
CNÀ.
lM. Inset: Plot of absorbance at 410 nm versus number of equivalents of

5034
Q. Lin et al. / Tetrahedron Letters 54 (2013) 5031–5034
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Acknowledgments
9
11978–11986; (m) Gomez, T.; Moreno, D.; Díaz de Greñu, B.; Fernández, A. C.;
This work was supported by the National Natural Science Foun-
dation of China (NSFC) (Nos. 21064006; 21161018; 21262032), the
Natural Science Foundation of Gansu Province (1010RJZA018) and
the Program for Changjian Scholars and Innovative Research Team
in University of Ministry of Education of China (IRT1177).
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Supplementary data
Supplementary data associated with this article can be found, in
11. General procedure for the synthesis of CF1–CF3: 5-(4-nitrophenyl)furan-2-
carbaldehydes (2.17 g, 10 mmol) (M3) and malononitrile (0.66 g, 10 mmol)
were combined in 30 mL pure water. The solution was stirred under 90 °C for
2 h, after cooling to room temperature, the yellow precipitate was filtrated,
washed with 75% ethanol three times, then recrystallized in ethanol to get
yellow powdery product CF3 (2.35 g, 8.9 mmol) 89% yield. The other
compounds CF1 and CF2 were prepared by the similar procedure.
the
online
version,
at
http://dx.doi.org/10.1016/j.tet-
let.2013.07.022. These data include MOL files and InChiKeys of
the most important compounds described in this article.
References and notes
CF1: yield: 75%; mp 155–156 °C; 1H NMR (DMSO-d6, 400 MHz) dH 8.32 (d,
J = 2 Hz, 1H, HC = N), 8.07–8.10 (m, 1H, Ph), 7.95–7.98 (m, 1H, Ph), 7.86–7.91
(m, 1H, Ph), 7.75–7.80 (m, 1H, Ph), 7.56–7.58 (m, 1H, Furan), 7.22–7.23 (m, 1H,
Furan); 13C NMR (DMSO-d6, 100 MHz) dC 155.26, 149.12, 147.81, 144.12,
133.90, 132.11, 130.77, 127.85, 125.47, 122.12, 114.98, 114.68, 113.73, 76.18;
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IR (KBr, cmÀ1
) v: 2222 (CN); Anal. Calcd for C14H7N3O3: C, 63.40; H, 2.66; N,
15.84. Found: C, 63.45; H, 2.62; N, 15.78. ESI-MS: Calcd for C14H8N3O3 [M+H]+
266.1; Found 266.2.
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CF2: yield: 87%; mp 240–241 °C; 1H NMR (DMSO-d6, 400 MHz) dH 8.67 (d,
J = 2.0 Hz, 1H, Ph), 8.33 (d, J = 1.6 Hz, 1H, HC = N), 8.27–8.29 (m, 2H, Ph), 7.81–
7.85 (m, 1H, Ph), 7.71–7.72 (m, 1H, Furan), 7.56–7.57 (m, 1H, Furan); 13C NMR
(DMSO-d6, 100 MHz) dC 157.73, 149.02, 148.64, 143.96, 131.50, 131.43,
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130.02, 128.53, 124.94, 120.02, 115.13, 114.48, 113.08, 75.61; IR (KBr, cmÀ1
)
v
: 2222 (CN); Anal. Calcd for C14H7N3O3: C, 63.40; H, 2.66; N, 15.84. Found: C,
63.44; H, 2.69; N, 15.90. ESI-MS: calcd for C14H8N3O3 [M+H]+ 266.1; Found
266.2.
CF3: yield: 89.5%; mp 219–221 °C; 1H NMR (DMSO-d6, 400 MHz) dH 8.42 (d,
J = 2.8 Hz, 1H, Ph), 8.39 (d, J = 2.0 Hz, 1H, HC = N), 8.37 (d, J = 2.8 Hz, 1H, Ph),
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8.12–8.16 (m, 2H, Ph), 7.74–7.75 (m, 1H, Furan), 7.59–7.61 (m, 1H, Furan); 13
C
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NMR (DMSO-d6, 100 MHz) dC 157.64, 149.26, 148.23, 144.06, 134.12, 128.46,
126.46, 125.16, 115.03, 114.38, 76.23; IR (KBr, cmÀ1
)
v
: 2220 (CN); Anal. Calcd
for C14H7N3O3: C, 63.40; H, 2.66; N, 15.84. Found: C, 63.47; H, 2.62; N, 15.81.
ESI-MS: Calcd for C14H8N3O3 [M+H]+ 266.1; Found 266.2.
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