A turn-on fluorescent chemosensor selectively detects cyanide in pure water and food sample

Article abstract of DOI:10.1016/j.tetlet.2016.05.028

A turn-on fluorescent chemosensor (H-1) for cyanide anions based on dihydroxy phenazine was designed and synthesised. The sensor H-1 exhibits high sensitivity and good selectivity for cyanide in pure water. The CN^- response mechanism involves a hydrogen bonding and deprotonation process in the sensor, which induced prominent fluorescence enhancement. The detection limit of the sensor toward CN^- is 5.65 × 10^-7 M, and other anions had nearly no influence on the probing behavior. In addition, test strips based on the sensor were fabricated, which also exhibit a good selectivity to CN^- in water. Notably, this sensor was successfully applied to detect CN^- in food samples, which proves a very simple and selective platform for on-site monitoring of CN^- in agriculture samples.

Full text of DOI:10.1016/j.tetlet.2016.05.028

Accepted Manuscript
A turn-on fluorescent chemosensor selectively detects cyanide in pure water and
food sample
Tai-Bao Wei, Wen-Ting Li, Qiao Li, Jun-Xia Su, Wen-Juan Qu, Qi Lin, Hong
Yao, You-Ming Zhang
PII:
S0040-4039(16)30542-1
DOI:
http://dx.doi.org/10.1016/j.tetlet.2016.05.028
TETL 47647
Reference:
To appear in:
Tetrahedron Letters
Received Date:
Revised Date:
Accepted Date:
5 April 2016
6 May 2016
9 May 2016
Please cite this article as: Wei, T-B., Li, W-T., Li, Q., Su, J-X., Qu, W-J., Lin, Q., Yao, H., Zhang, Y-M., A turn-
on fluorescent chemosensor selectively detects cyanide in pure water and food sample, Tetrahedron Letters (2016),
doi: http://dx.doi.org/10.1016/j.tetlet.2016.05.028
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Tetrahedron Letters
A turn-on fluorescent chemosensor selectively detects cyanide in pure water and food
sample
Tai-Bao Wei*, Wen-Ting Li, Qiao Li, Jun-Xia Su, Wen-Juan Qu, Qi Lin, Hong Yao, 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
ARTICLE INFO
ABSTRACT
Article history:
Received
Revised
Accepted
Available online
A turn-on fluorescent chemosensor (H-1) for cyanide anions based on dihydroxy phenazine was
designed and synthesised. The sensor H-1 exhibits high sensitivity and good selectivity for cyanide in
pure water. The CN response mechanism involves a hydrogen bonding and deprotonation process in
−
the sensor, which induced prominent fluorescence enhancement. The detection limit of the sensor
−
−7
towards CN is 5.65 × 10 M, and other anions had nearly no influence on the probing behavior. In
Keywords:
Dihydroxy phenazine
Cyanide
−
addition, test strips based on the sensor were fabricated, which also exhibit a good selectivity to CN in
−
water. Notably, this sensor was successfully applied to detect CN in food samples, which proves a
−
very simple and selective platform for on-site monitoring of CN in agriculture samples.
Test strips
Food samples
−
The cyanide (CN ) has been continuously of concern all over the
cyanide anions in pure water. The recognition progress occurred via
deprotonating between the hydroxyl of H-1 and cyanide. When
exposed H-1 to the low concentration solution of cyanide anion
there was a dramatically increase of the emission maximum of H-1,
and the color of the solution changed from dim orange to bright
yellow, which can be seen by naked-eyes under the UV lamp (365
nm). As practical applications, the chemosensor was successfully
world due to its extreme toxicity and widespread use in metallurgy,
1
plastics
production,
and silver
or
gold
extraction.
Cyanide-containing substance, found in foods, plants, water, soil,
polluted air, vehicle exhaust, and even cigarette burning gas, are
extremely detrimental to living organisms and most animals by
causing lethal effect to their central nervous system. Uptake of toxic
cyanide could occur through absorption by lungs and skin, and also
from contaminated food and drinking water. Therefore, much
interest has been sparked in the design of new methods to monitor
CN in biological and environmental samples.
Thanks to the enthusiastic efforts of scientists, a large number of
2
−
applied to the detection of CN in sprouting potatoes and bitter seeds,
3
which prove a very simple and selective platform for on-site
−
monitoring of CN in agriculture samples.
−
The 2, 5-dihydroxy-p-benzoquinone (2) was reacted with
o-diaminobenzenes (1.1 equiv) in water to afford high yields of 2,
4
10
good sensors for cyanide have been invented. Among the various
sensors, fluorescent chemosensors present numerous advantages,
including high sensitivity, low cost, and easy operation. Moreover,
3-dihydroxyphenazines H-1 (Scheme S1). It was characterized by
1
H NMR, IR and ESI-MS (Fig. S5, S8, and S9 in SI).
In order to investigate the CN recognition abilities of the sensor
5
−
phenazine derivatives, which have dramatic fluorescent emissions,
have been synthesized for a long time, but they were seldom been
H-1 in water, we carried out a series of host-guest recognition
experiments. The recognition profiles of the chemosensor H-1
6
−
−
−
−
−
−
used in ions recognition field. On the other hand, in biological and
toward various anions, including F , Cl , Br , I , AcO , H
2 4
PO ,
−
−
−
−
−
environmental systems, CN sensors interactions commonly occur in
HSO , ClO , CN and SCN , were primarily investigated using
4 4
aqueous solution, therefore, much attention has been paid to develop
the cyanide sensors that work in water. However, few, if any, CN
fluorescence and UV-vis spectroscopy in water. When 50 equiv. of
−
−
CN were added to the sensor H-1 (20 µM), there was not a
−
sensors are able to display high selectivity over other anions such as
significant color change. Interaction of H-1 with 50 equiv. of CN
−
−
−
4
7
F , AcO , and H
2
PO
in pure water. Recently, we have also
resulted in a negligible red shift in the absorption spectrum, which
was not visible to the naked eye (Fig. S1 in SI).
As shown in Figure 1, in the fluorescence spectrum, the maximum
reported 4-amino-3-hydroxynaphthalene-1-sulfonic acid (Scheme S2)
and 2, 4-dimethyl-7-amino-1, 8-naphthyridine as the fluorescent
8
cyanide sensors in pure water.
emission of H-1 appeared at 548 nm in water when excited at λex =
−
In view of this requirement and as a part of our research interest in
415 nm. On the addition of 50 equivalents of CN , the fluorescence
intensity of sensor H-1 (20 µM) increased rapidly, and the maximum
emission shifted to 568 nm. The color change from dim orange to
bright yellow could be distinguished by the naked eye on UV lamp
9
ion recognition. Herein, we report a rationally designed, simple, and
efficient fluorescent sensor H-1 based on dihydroxy phenazine. The
chemosensor H-1 could act as a turn-on fluorescent sensor for

Corresponding author. Tel: +086 931 7973120;
E-mail address: weitaibao@126.com (T.-B. Wei); zhangnwnu@126.com (Y.-M. Zhang).

−
(
365 nm). To validate the selectivity of sensor H-1, the same tests
of sensor H-1 with CN was not influenced by the subsequent
−
−
−
−
−
−
−
were also conducted using F , Cl , Br , I , AcO , H
ClO
2
PO
4
, HSO
4
,
addition of competing anions, which indicated that H-1 has specific
selectivity to CN (Fig. 3).
−
−
−
4
, and SCN , and none of these anions induced any significant
changes in the fluorescent spectrum of the sensor (Fig. S3 in SI).
Therefore, in water solution, H-1 showed specific fluorescent
selectivity to CN .
−
H-1
H-1+other anions
-
-
6
00
H-1 + CN
H-1 + CN +other anions
-
H-1 CN
4
3
2
1
00
00
00
00
0
400
-
H-1 +50 equiv.CN
Only H-1
2
00
0
-
-
-
-
-
-
-
-
-
-
H-1 CN
F
Cl
Br
I
AcO H PO HSO ClO SCN
2
4
4
4
Figure 3. Fluorescence intensity changes of H-1 (20 µM) in the presence of
CN (50 equiv.) and additional anions (50 equiv.) in water (λex = 415 nm, λem
−
4
50
500
550
600
650
700
=
568 nm).
Wavelength (nm)
Figure 1. Fluorescence spectral response of H-1 (20 µM) in water upon
−
1
addition of 50 equiv. of CN (λex = 415 nm). Inset: photograph of H-1 (20
In addition, the recognition mechanism was investigated by H
−
µM) upon addition of 50 equiv. of CN , which was taken under a UV-lamp
−
1
NMR titration of the sensor H-1 with CN . H NMR titration
displayed the chemical shift changes of H-1 upon the addition of
CN , as shown in Fig. 4, sensor H-1 showed a peak at 10.94 ppm in
6
, we confirmed that which correspond to the protons of
OH. Cyanide could take the protones away via deprotonating
(365 nm).
−
−
To get further insight into the sensing behavior of H-1 to CN ,
DMSO-d
fluorescence titration experiment was performed (Fig 2). Upon
−
−
1
incremental addition of CN to solution H-1, the emission peak at
during the −OH moieties of H-1, in the corresponding H NMR
spectra, upon addition of 1.0 equiv. CN by deuterium water solution,
−
548 nm gradually enhanced intensity and blue-shifted maximum
emission, as well as the fluorescence of H-1 was essentially reached
the signal at 10.94 ppm (−OH) disappeared. At the same time, the
phenazine signals from 7.20 to 8.10 ppm have a significant upfield
shift, indicating that the density of intramolecular charge increased
through deprotonating.
−
saturation by 10.16 equivalents of CN . Meanwhile, the fluorescence
11
quantum yields increased from 0.24 to 0.68 (in SI). The binding
9
-2
12
constant K
a
was determined to be 2.65 × 10
M
(in SI).
Furthermore, the detection limit of the fluorescent spectrum changes
16
−7
−
calculated on the basis of 3σ/m is 5.65 × 10 M for CN , which is
Hc
Hb
Hc
Hb
far lower than the WHO guideline of 1.9 µM cyanide (Fig. S4 in
SI).
H
13
Ha
N
N
O
N
N
O
O
Hd
Hd
H
H
O
Ha
Hc
Hb
Hc
Hb
H
500
1
0.16 equiv.
400
4
3
2
1
00
00
00
00
0
Hc
Hd
Hb
3
00
-
CN
H-1+1.00 equiv. CN
-
200
Hc
Hd
Hb
100
H-1+0.50 equiv. CN
-
0
.00 equiv.
0
2
4
6
8
10
Hc
Hd
Hb
Hb
[
CN-]/[H-1]
H-1+0.10 equiv. CN
-
Hc
Hc
Hd
Hd
H-1+0.05 equiv. CN
-
Ha
Hb
Only H-1
4
50
500
550
600
650
700
Wavelength(nm)
1
Figure 4. H NMR spectra (400 MHz, DMSO-d
6
) of free H-1 and in the
−
presence of CN .
Figure 2. Fluorescence spectra of H-1 in the presence of different
−
concentrations of CN in water (λex = 415 nm). Inset: a plot of fluorescence
−
intensity depending on the concentration of CN in the range from 0.00 to
−
In order to quantify the reaction ratio between H-1 and CN ion,
besides the fluorescence Job’s plot measurement (Fig. 5) was
conducted by varying the concentration of both the receptor and
the CN ion with a total concentration of 4 × 10 M. The
maximum point appears at the mole fraction of 0.75, which
indicates the reaction ratio of H-1 and CN is 1:2. It was further
confirmed by the appearance of a peak at m/z 257.00 assignable to
H-1 + 2Na ] (m/z = 256.99) in the ESI-MS spectrum (Fig. S10 in
1
0.16 equivalents (λex = 415 nm, λem = 568 nm).
To further explore the utility of sensor H-1 as an ion-selective
−
−5
−
chemosensor for CN , competitive experiments were carried out in
−
the presence of 50 equiv. of CN and 50 equiv. of various other
−
−
−
−
−
−
−
−
−
−
anions (F , Cl , Br , I , AcO , H
2 4 4 4
PO , HSO , ClO , and SCN ) in
a water solution of sensor H-1. The fluorescent emission spectrum
+
[

SI).
600
5
00
CN-
CN-
CN-
CN-
CN-
3
2
1
00
00
00
0
400
3
2
00
00
HCl
100
H-1
HCl
HCl
HCl
2
4
6
8
10
Cycle index
Figure 8. Reversible switching cycles of fluorescence intensity (λex = 415 nm,
λem = 568 nm) by the alternating addition of CN and HCl in water. Above
are the vials showing visual fluorescent color.
0
.0
0.2
0.4
0.6
0.8
1.0
−
-
-
CN ]/[H-1+CN ]
[
−
Figure 5. Job’s plot examined between H-1 and CN , indicating the 1:2
stoichiometry.
Generally, chemosensors suffer from a long response time. In our
−
case, the response of H-1 toward CN was found to be very fast (Fig.
Based on the above findings, we propose that the mechanism is
the deprotonation process between the probe H-1 and cyanide in this
system may proceed through the route depicted in Figure 6.
−
9). After addition of a solution of CN (50 equiv.), the fluorescence
emission intensity of H-1 in water at 568 nm increased rapidly and
reached a plateau in about 30 s at room temperature.
NaCN
525
H
N
N
O
N
N
ONa
ONa
Recycle
On
+
2HCN
H
H
4
50
O
N
N
HCl
H-1
N
N
O
O
375
300
CN
-
HCl
HO
OH
H
H-1
−
Figure 6. The proposed mechanism of H-1 for CN .
2
25
Off
−
The selectivity of H-1 to CN was also examined over a wide
range of pH values. The detection of CN can work well in the pH
0
10
20
30
40
50
60
−
Time (s)
range of 3.0 ~ 8.0 in HEPES buffered solution in water (Fig. 7).
Figure 9. Fluorescence intensity (λex = 415 nm, λem = 568 nm) for H-1 (20
μM) in water after addition of pure water solution of 50 equiv. of CN (0.01
−
M).
6
4
3
1
00
50
00
50
0
H-1
-
H-1+CN
To investigate the practical application of chemosensor H-1, test
strips were prepared by immersing filter papers into a water solution
of H-1 (0.1 M) and then drying them in air. The test strips containing
−
H-1 were utilized to sense CN and other anions. As shown in
−
Figure 10, when CN and the other anions were added on the test
−
strips, the obvious color change was observed only with CN
solution under irradiation at 365 nm by a UV lamp. And potentially
−
competitive ions exerted no influence on the detection of CN by the
−
test strips. Therefore, the test strips could conveniently detect CN in
2
4
6
8
10
12
pH
solutions.
−
Figure 7. Influence of pH on the fluorescence of H-1 and H-1+CN in
HEPES buffered solution in water (λex = 415 nm, λem = 568 nm).
A
B
C
D
The reversibility of sensor H-1 has been measured by alternating
−
addition of hydrochloric acid to the solution of H-1+CN , which
induced the opposite trend in the fluorescent spectra to that observed.
Upon addition of 1.0 equivalent of hydrochloric acid, the optical
fluorescence intensity returned to the levels observed for the free
compound H-1, and the solution became orange under the UV lamp
Figure 10. Photographs of H-1 on test strips (A) only H-1, (B) after
immersion into water solutions with CN , (C) after immersion into water
−
solutions with other anions, (D) after immersion into water solutions with
(
365 nm) again. This cycle could be repeated more than several
times without considerable loss of sensing ability of the sensor (Fig.
).
−
CN and other anions under irradiation at 365 nm.
8

In order to further investigate the practical utilities of probe in our
lives, one hundred grams of bitter seeds must be crushed and
pulverized. Then the mixture must be introduced into a flask. This is
followed by addition of 300 mL of water and 0.5 g of NaOH. The
obtained mixture must be vigorously stirred for 15 min. Then the
mixture was filtered to obtain the cyanide-containing solution
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into H-1 (20 µM), the fluorescence intensity of sensor H-1 increased
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In summary, a simple sensor (H-1) for highly selective and
sensitive detection of cyanide anions based on dihydroxy phenazine
was designed and synthesized, which can be used as a turn-on
fluorescent sensor for cyanide in pure water. The detection limit of
−
−7
the sensor towards CN is 5.65 × 10 M, and other anions,
−
−
−
−
−
−
−
−
−
2 4 4 4
including F , Cl , Br , I , AcO , H PO , HSO , ClO , and SCN
2
0, 11457; (f) Wu, G. Y.; Shi, B. B.; Lin, Q.; Li, H.; Zhang, Y. M.; Yao, H.;
had nearly no influence on the probing behavior. In addition, test
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J.; Gao, G. Y.; Lin, Qi.; Yao, H.; Zhang, Y. M.; Wei, T. B. Tetrahedron 2015,
strips based on H-1 were fabricated, which also exhibited a good
−
selectivity to CN in water. Notably, the chemosensor was
7
1
1, 857.
successfully applied to the detection of cyanide in sprouting potatoes
and bitter seeds. Thus, it will be regarded as an environmental
friendly material which can sense cyanide anion in water and make
great contribution to the development of cyanide anion sensors.
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Acknowledgment
1
This work was supported by the National Natural Science
Foundation of China (Nos. 21161018; 21262032; 21574104), the
Program for Chang Jiang 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.

Graphical abstract: In this work, a turn-on fluorescent chemosensor (H-1) for
cyanide anions based on dihydroxy phenazine was designed and synthesised. The
sensor H-1 exhibits high sensitivity and good selectivity for cyanide in pure water.
NaCN
Recyclable
HCl
H
O
N
Na
H-
1
6
5
00
00
-
H-1 CN
4
3
2
1
00
00
00
00
0
CN-
CN-
CN-
CN-
CN-
-
400
H-1 +50 equiv.CN
Only H-1
3
2
1
00
00
00
HCl
H-1
HCl
HCl
HCl
4
50
500
550
600
650
700
2
4
6
8
10
Wavelength (nm)
Cycle index

Highlights
1
. A structurally simple anion sensor for highly selective and sensitive detection of
−
CN anions via fluorescent OFF-ON mechanism.
2
3
4
. Taking advantage of a simple mechanism of deprotonation.
−
. This sensor was successfully applied to detect CN in pure water and food samples.
. H-1 could serve as a potential recyclable component by fluorescent changes in
sensing materials.