A carbonothioate-based highly selective fluorescent probe with a large Stokes shift for detection of Hg2+

Article abstract of DOI:10.1002/bio.3404

Mercury (Hg) is one of the heavy metal pollutants in the environment. Even a very small amount of mercury can cause serious harm to human beings. Herein, we reported a new carbonothioate-based fluorescent probe for the detection of Hg²⁺ without interference from other metal ions. This probe possessed a very large Stokes shift (192?nm), which could improve the detection sensitivity by minimizing the interferences resulted from self-absorption or auto-fluorescence. With the addition of Hg²⁺ to the probe solution, considerable fluorescence enhancement was observed. Additionally, the Hg²⁺ concentration of 0–16?μM and fluorescence intensity showed a good linear relationship (y?=?22106×?+?53108, R²?=?0.9955). Finally, the proposed probe was used to detect Hg²⁺ in real water samples, and its result was satisfactory. Therefore, our proposed probe would provide a promising method for the determination of Hg²⁺ in the environment.

Full text of DOI:10.1002/bio.3404

Received: 3 May 2017
DOI: 10.1002/bio.3404
Revised: 21 July 2017
Accepted: 1 August 2017
R E S E A R C H A R T I C L E
A carbonothioate‐based highly selective fluorescent probe with
2
+
a large Stokes shift for detection of Hg
1
2
2
2
2
1
|
|
|
|
|
|
Jing Xu
Zhenghe Xu
Zuokai Wang
Caiyun Liu
Baocun Zhu
Xiuru Wang
2
2
2
|
|
Kun Wang
Jiangting Wang
Guoqing Sang
1
School of Water and Soil Conservation,
Beijing Forestry University, Beijing, China
Abstract
2
Mercury (Hg) is one of the heavy metal pollutants in the environment. Even a very small amount
School of Resources and Environment,
University of Jinan, Shandong Provincial
Engineering Technology Research Center for
Ecological Carbon Sink and Capture
Utilization, Jinan, China
of mercury can cause serious harm to human beings. Herein, we reported a new
2+
carbonothioate‐based fluorescent probe for the detection of Hg without interference from
other metal ions. This probe possessed a very large Stokes shift (192 nm), which could improve
the detection sensitivity by minimizing the interferences resulted from self‐absorption or auto‐
Correspondence
2+
Xiuru Wang, School of Water and Soil
Conservation, Beijing Forestry University,
Beijing 100083, China.
fluorescence. With the addition of Hg to the probe solution, considerable fluorescence
2+
enhancement was observed. Additionally, the Hg concentration of 0–16 μM and fluorescence
2
intensity showed a good linear relationship (y = 22106× + 53108, R = 0.9955). Finally, the pro-
Email: wang‐xr@163.com
2+
posed probe was used to detect Hg in real water samples, and its result was satisfactory.
Funding information
Therefore, our proposed probe would provide a promising method for the determination of
Ministry of Water Resources Public Welfare
Industry Research Special Project, Grant/
Award Number: 201401001; Major Livelihood
Projects of Jinan, Grant/Award Number:
SHMS2015‐3‐01; Shandong Province Key
Research and Development Project, Grant/
Award Number: 2016GSF117010; Outstand-
ing Young Scientists Award Fund of Shandong
Province, Grant/Award Number:
2+
Hg in the environment.
KEYWORDS
carbonothioate, excited‐state intramolecular proton transfer (ESIPT), fluorescent probe, mercury
2+
ions (Hg ), Stokes shift
BS2013HZ007
[
11–15]
1
|
INTRODUCTION
coupled plasma mass spectrometry, optical probes and so on.
Among these methods, optical probes might be the most attractive
Currently, heavy metal ion pollution has become a critical worldwide
issue, and attracted more and more attention. Mercury is a highly toxic
heavy metal pollutant in the environment, and can cause serious dam-
age to human health due to its bioaccumulation, durability and long
method due to their high selectivity, sensitivity, quick response and rel-
[
16–22]
2+
atively low‐cost.
Despite reports on Hg detection, some short-
comings still existed, such as longer response time, bad water
[
23–29]
solubility, a smaller Stokes shift, and poor selectivity (Table 1).
[
1–4]
residence.
Once it has entered the organism, it is difficult to be
Especially, the small Stokes shift of the probe will pose potential
difficulties for quantitative determination and bioimaging, and
reabsorption of emitted photons leads to undesired background
excreted, and will have a serious effect on the central nervous, endo-
[5–7]
crine systems, kidney, respiratory system, blood, etc.
Based on
[
30–32]
the standard 2 ppb (0.01 μM) of mercury contamination in water which
interferences.
In contrast, a large Stokes shift could improve
[8,9]
was set by the Environment Protection Agency (EPA),
very small
the detection sensitivity by minimizing interferences caused by self‐
absorption or auto‐fluorescence. Thus, considerable efforts have been
amount of mercury will cause serious harm to human, so it is very
important to develop simple and effective methods for sensitive and
devoted to designing new and practical fluorescent probes with large
2+
2
+ [10]
selective detection of Hg
.
Stokes shift to detect Hg .
2+
Many methodologies have been used to detect Hg , such as
atomic absorption spectroscopy, electrochemical analysis, inductively
Recently, we have designed and synthesized a series of fluores-
2+
cent probes to detect Hg . One of these is a tricyanoethylene moiety
2+
that was used to design a colorimetric probe for Hg
detec-
N‐butyl‐4‐hydroxy‐1,8‐naphthalimide was chosen as the
fluorophore, and carbonothioate moiety was used as the
[
33]
tion.
Abbreviations used: ESIPT, excited‐state intramolecular proton transfer; HBT,
2
‐(2′‐hydroxyphenyl) benzothiazole; TFA, trifluoroacetic acid.
a
Luminescence. 2017;1–6.
wileyonlinelibrary.com/journal/bio
Copyright © 2017 John Wiley & Sons, Ltd.
1

2
XU ET AL.
2+
TABLE 1 Comparison of fluorescent probes for Hg
Stokes
shift (nm)
Reaction
time (min)
Real water
sample
Probe
LOD (nM)
References
[
21]
5
0
30
No
100
[
22]
6
3
30
Yes
300
[
23]
4
9
–
No
38
[
24]
6
2
20
No
350
[
25]
8
0
15
Yes
230
[
26]
7
5
–
Yes
230
(Continues)

XU ET AL.
3
TABLE 1 (Continued)
Probe
Stokes
shift (nm)
Reaction
time (min)
Real water
sample
LOD (nM)
References
[27]
1
35
30
No
100
1
92
15
Yes
55
This work
[34]
recognition receptor for the first time.
These both showed high
reaction mixture was filtered to obtain the pure colorless solid
selectivity, quick response and excellent water solubility. In connec-
tion with our continuing research, we here report a carbonothioate‐
based fluorescent probe, and chose the 2‐(2′‐hydroxyphenyl)
benzothiazole (HBT) as the fluorophore for its outstanding excited‐
state intramolecular proton transfer (ESIPT) structure to obtain a large
Stokes shift. The experimental results demonstrated that this probe
possessed the advantages of: (1) a very large Stokes shift (192 nm);
product 2 (2.7206 g, yield: 85%).
[37]
2
.3
|
Synthesis of compound 3
Compound 2 (460.5 mg, 2.8 mol) was dissolved in 20 ml absolute alco-
hol. Then 2‐aminothiophenol (1050 mg, 8.4 mol) was added and
stirred. Hydrochloric acid 37% (830.2 mg, 22.7 mol) and hydrogen per-
oxide 30% (1903.5 mg, 56.1 mol) were added in turn. The reaction
needed to stir for 30 min at room temperature (25°C). The reaction
mixture was filtered to acquire the pure yellow solid product 3
(
2) excellent water solubility, selectivity and anti‐interference; (3)
practical applicability in real water samples; and (4) a low detection
[35]
limit of 55 nM (on the basis of 3σ/slope).
(
918.2 mg, yield: 87%).
2
2
|
EXPERIMENTAL
Materials and general methods
2
.4
|
Synthesis of probe 1
Phenyl chlorothionocarbonate (1400.6 mg, 8.1 mol) was added to the
solution of compound 3 (500.3 mg, 1.3 mol) and DIPEA (1660.4 mg,
12.9 mol) in 10 ml dry dichloromethane. Then the reaction was
stirred at 50°C for 10 h. The pure faint‐yellow solid probe 1
(45.6 mg, yield: 7%) was obtained through a silica column chromatog-
raphy with dichloromethane and petroleum ether as eluant (2:1, v/v)
.1
|
All chemicals were bought from commercial suppliers and none of
these needed to be further purified for use. The Sartorius Arium
6
11DI system produced ultra‐pure water that was used in the experi-
ment. Column chromatography using silica gel 200–300 mesh from the
Qingdao Haiyang Chemical Co was used to purify the reaction prod-
(Scheme 1).
1
1
uct. The Bruker AV‐400 spectrometer was used to record the
H
6
H–NMR (400 MHz, DMSO‐d ) δ (ppm): 2.59(s, 3H), 7.21(d,
13
NMR and C NMR with chemical shifts reported as ppm (in DMSO‐
, TMS as internal standard). Fluorescence spectra were gained from
J = 8.0 Hz, 2H), 7.35(t, J = 8.0 Hz, 1H), 7.49(t, J = 8.0 Hz, 2H), 7.57(t,
d
6
J = 8.0 Hz, 2H), 7.65(t, J = 8.0 Hz, 2H), 8.19(d, J = 8.0 Hz, 2H),
13
a HoribaFluoroMax‐4 spectrophotometer.
8.33(d, J = 8.0 Hz, 2H), 8.34 (s, 2H). C–NMR (100 MHz, DMSO‐d6)
δ (ppm): 20.90, 115.69, 121.94, 122.97, 123.63, 126.55, 127.48,
1
27.73, 129.82, 130.55, 133.46, 135.56, 138.70, 145.61, 152.86,
[36]
2
.2
|
Synthesis of compound 2
2 2 3
153.62, 161.72, 193.28. ESI‐MS calcd for C28H19N O S [M + H]
+
5
11.1, found 511.1.
Hexamethylenetetramine (11.2012 g, 80 mol) was dissolved in 15 ml
trifluoroacetic acid (TFA). Then, 4‐hydroxytoluene (2.1608 g, 20 mol)
was added and heated at 100°C for 6 h under a nitrogen atmo-
sphere. After the reaction was completed, 10 ml ultra‐pure water
was added to the product of the reaction, and then continued
heating reflux was performed for 10 min. The reaction product was
mixed into 400 ml ice ultra‐pure water, drop by drop, as soon as
the temperature dropped to the room temperature. Finally, the
3
3
|
RESULTS AND DISCUSSION
Characteristic spectra
.1
|
2+
The recognition of Hg with probe 1 was tested under the system of
ultra‐pure water and ethanol (5:5, v/v) containing HEPES (5 mM,

4
XU ET AL.
Cl
S
NH2
SH
O
OH
OH
O
S
C H12N
6
4 OHC
CHO
N
OH N
N
O
N
S
S
TFA 100
S
S
C H OH 25
2
5
CH Cl2 50
2
HCl H O2
2
DIPEA
2
3
1
SCHEME 1 Synthesis of probe 1
pH 7.4). The free probe solution showed weak fluorescence (Figure 1)
2+
and, when Hg was added, a large fluorescence intensity enhance-
ment was observed at 562 nm. Probe 1 shows the excitation spectra
around 370 nm, and the emission spectra at 562 nm. The result
showed that probe 1 possessed a large Stokes shift (192 nm). In other
2+
words, our probe can detect Hg by fluorescence spectra.
2
+
3
.2
|
Reaction time on detecting Hg
As a significant element to test the effect of the probe, the response
time of probe 1 was investigated under the analytical conditions that
were mentioned above. As shown in Figure 2, the fluorescence inten-
2+
sity at 562 nm was increased as soon as Hg was added, and remained
2+
FIGURE 2 Reaction time for probe 1 (5 μM) in the presence of Hg
20 μM)
when the reaction time exceeded 15 min. The results showed that
(
2+
probe 1 could provide a rapid analytical method for detecting Hg
.
2
+
3
.3
|
Quantification of Hg
A new peak at 562 nm can be seen with the continuous addition of
2+
2+
Hg (Figure 3). There was a good linearity between the Hg concen-
trations of 0–16 μM and the fluorescence intensity at 562 nm, and the
detection limit was 55 nM (3σ/slope). The results showed that the
2+
probe 1 had good sensitivity for detecting Hg , and provided a sensi-
tive detection method.
FIGURE 3 Fluorescence spectra of probe 1 (5 μM) with the addition
2+
of different concentrations Hg (final concentration: 0, 1, 2, 4, 6, 7,
9
, 12, 14, 16, 18, 20, 25, 30, 35, 40 μM). The fluorescence intensity at
62 nm of probe 1 increased with the increasing concentrations of
5
2+
Hg . Excitation wavelength = 370 nm, emission wavelength = 562 nm,
so the Stokes shift = 192 nm. Conditions: In HEPES (5 mM, pH 7.4).
Solution: Ultra‐pure water /ethanol = 5:5, v/v
2
+
3
.4
|
Selectivity to Hg
2+
Selectivity is also an important factor of probes. Hg and other rele-
FIGURE 1 Fluorescence spectra of probe 1 (5 μM) in the presence
and absence of Hg (20 μM) under the ultra‐pure water and ethanol
system (5:5, v/v) containing HEPES (5 mM, pH 7.4)
2+
2+
2+
3+
2+
3+
3+
2+
vant metal ions, including Cd , Pb , Mg , Al , Fe , Fe , Cr
,
2+
2+
+
+
2+
2+
Ca , Zn , Na , K , Co , Ni were respectively added to the

XU ET AL.
5
2
+
solution, and only Hg resulted in a fluorescence enhancement
In other words, due to the carbonothioate moiety, it is a good recep-
2+
(
Figure 4). The interference of the metal ions on the detection of
tor for detecting Hg , probe 1 can provide more accurate detection
2+
Hg was also studied (Figure 4). The final results showed that a
results in real samples.
2+
new peak emerged only after the addition of Hg and relevant metal
2+
ions cannot disturb the reaction of probe 1 with Hg . Moreover,
2
+
probe 1 also had a good response to Hg . Thus it can be seen that
|
3
.5
3.5 Analytical application
2+
probe 1 had excellent selectivity and anti‐interference toward Hg
.
2+
We tried to use the probe 1 to detect Hg in real water samples which
were obtained from Jia Zi Lake and Xiu Jiang river in Jinan, Shandong
Province, China. All the water samples needed to be filtered before
2+
analysis. Initially, there were no Hg ions in the four water samples,
2+
then 10 μM, 15 μM, or 20 μM Hg was respectively added to the
solution of real water/ethanol = 5:5, v/v (5 mM, HEPES, pH 7.4) con-
taining 5 μM probe 1, and every sample were tested three times. The
results are shown in Table 2. Therefore, we obtained a good method
2+
for detecting Hg in the environment.
2
+
3
.6
|
Mechanism of probe 1 in sensing Hg
2+
The reaction products of probe 1 and Hg were subjected to
electrospray ionization mass spectral analysis to fully explore the sens-
2+
2+
ing mechanism of probe 1 for Hg . With the addition of Hg , the
FIGURE 4 The selectivity of probe 1 (5 μM) to different analytes
containing Hg (20 μM), and it with the Hg in addition and in
+
peak of probe 1 (m/z 511.1 [M + H] ) disappeared, while a new peak
2+
2+
+
emerged at m/z 375.1 [M + H] , which represented the formation of
2
+
2+
2+
absence of other relevant metal ions. (1) Hg ; (2) Cd ; (3) Pb ; (4)
2+
3+
2+
3+
3+
2+
2+
+
compound 3. Therefore, we propose that the fluorescence turn‐on
reaction process most likely undergoes the mechanism proposed in
Scheme 2.
Mg ; (5) Al ; (6) Fe ; (7) Fe ; (8) Cr ; (9) Ca ; (10) Zn ; (11) Na ;
+
2+
2+
(
12) K ; (13) Co ; (14) Ni . Solution: Ultra‐pure water / ethanol =
:5, v/v
5
2+
a
TABLE 2 Analysis results of Hg in four real water samples
Addition
Hg (μM)
2
+
2+
Real water sample
Found Hg
Found (μM)
Recovery (%)
RSD (n = 3) (%)
Sample A
no
10
10.88 ± 0.63
16.13 ± 0.45
20.77 ± 1.21
10.79 ± 0.49
14.14 ± 0.24
20.57 ± 0.82
9.73 ± 0.38
13.74 ± 0.59
20.40 ± 0.53
9.24 ± 0.21
16.29 ± 0.42
19.25 ± 1.03
108.84
107.53
101.16
107.88
94.29
6.33
3.01
1.67
4.93
1.60
4.11
3.79
3.93
2.63
2.09
2.79
5.14
1
2
5
0
Sample B
Sample C
Sample D
no
no
no
10
1
2
5
0
102.87
97.26
10
1
2
5
0
91.58
101.98
92.38
10
1
2
5
0
108.61
96.27
a
Sample A, lake water from JiaZi Lake, University of Jinan; samples B,C,D, from the upper, middle and lower reach of the Xiu Jiang River, at Jinan, China.
SCHEME 2 Reaction mechanism of probe 1
2+
for Hg

6
XU ET AL.
4
|
CONCLUSION
[
[
12] D. Dinda, B. Shaw, S. Saha, Mater. Interfaces 2015, 7, 14743.
13] L. Chen, J. Li, L. Chen, ACS Appl. Mater. Interfaces 2014, 6, 15897.
In summary, a long‐wavelength fluorescent probe has been success-
fully designed and synthesized in this work. Compared with other
probes, our new probe has the advantages of large Stokes shifts, excel-
lent selectivity and anti‐interference, practical applicability in real
water samples, and a low detection limit of 55 nM (on the basis of
[14] Y. Du, R. Liu, B. Liu, S. Wang, M. Han, Z. Zhang, Anal. Chem. 2013, 85,
160.
3
[
[
[
15] H. Agarwalla, P. Mahajan, D. Sahu, N. Taye, B. Ganguly, S. Mhaske,
Inorg. Chem. 2016, 55, 12052.
16] Q. Mei, R. Tian, Y. Shi, Q. Hua, C. Chen, B. Tong, New J. Chem. 2016,
4
0, 2333.
3
0
1
σ/slope). There was a good linear relationship in the range
17] X. Wang, Z. Gao, J. Zhu, Z. Gao, F. Wang, Polym. Chem. 2016, 7,
–18 μM. Importantly, the Stokes shift of the probe can reach
5217.
92 nm, which could improve the detection sensitivity by minimizing
[18] H. Lu, W. Wang, X. Tan, X. Luo, M. Zhang, M. Zhang, S. Zang, Dalton
Trans. 2016, 45, 8174.
the interferences caused by self‐absorption or auto‐fluorescence.
More importantly, it was shown that probe 1 can provide an excellent
[
19] R. Bhowmick, R. Alam, T. Mistri, D. Bhattacharya, P. Karmakar, M. Ali,
ACS Appl. Mater. Interfaces 2015, 7, 7476.
2+
method for the determination of Hg in the environment through the
results of testing the real water samples. All these marked advantages
of this new probe suggest that the probe 1 will have potential applica-
tion in the detection of mercury ions.
[
20] M. Formica, V. Fusi, L. Giorgi, M. Micheloni, Coord. Chem. Rev. 2012,
2
56, 170.
[
21] L. Zhang, H. Zhu, C. Zhao, X. Gu, Chinese Chem. Lett 2017, 28, 218.
22] L. Zhu, J. Xu, Z. Sun, B. Fu, C. Qin, L. Zeng, X. Hu, Chem. Comm 2015,
[
5
1,1154.
[23] T. Zhang, B. Wu, Z. Zou, Y. Wu, J. Zheng, W. Wong, K. Wong, J. Lumin.
016, 170, 187.
ACKNOWLEDGEMENTS
2
This work was supported by the Ministry of Water Resources Public
Welfare Industry Research Special Project (201401001), Major
Livelihood Projects of Jinan (SHMS2015–3‐01), Shandong Province
Key Research and Development Project (2016GSF117010), Outstand-
ing Young Scientists Award Fund of Shandong Province
[
24] M. Hong, S. Lu, F. Lv, D. Xu, Dyes Pigm. 2016, 127, 94.
[
25] S. Maity, S. Banerjee, K. Sunwoo, J. Kim, P. Bharadwaj, Inorg. Chem.
2
015, 54, 3929.
26] F. Yan, D. Cao, N. Yang, Q. Yu, M. Wang, L. Chen, Sens. Actuators, B
012, 162, 313.
[
2
(
BS2013HZ007).
[
27] R. Zhang, W. Chen, Biosens. Bioelectron. 2014, 55, 83.
[
28] K. Tayade, B. Bondhopadhyay, A. Basu, G. Chaitanya, S. Sahoo, N.
ORCID
Singh, S. Attarde, A. Kuwar, Talanta 2014, 122, 16.
[
[
[
[
29] M. Santra, B. Roy, K. Ahn, Org. Lett. 2011, 13, 3422.
30] L. Xue, C. Liu, H. Jiang, Chem. Commun. 2009, 1061.
31] Z. Gao, Y. Hao, M. Zheng, Y. Chen, RSC Adv. 2017, 7, 7604.
Caiyun Liu http://orcid.org/0000-0001-6506-4783
Baocun Zhu http://orcid.org/0000-0002-6221-2071
32] C. Zhao, X. Zhang, K. Li, S. Zhu, Z. Guo, L. Zhang, F. Wang, Q. Fei, S.
REFERENCES
Luo, P. Shi, H. Tian, W. Zhu, J. Am. Chem. Soc. 2015, 137, 8490.
[1] K. Foster, G. Stern, M. Pazerniuk, B. Hickie, W. Walkusz, F. Wang, R.
[
33] J. Liu, Z. Xu, L. Xu, Z. Bian, G. Sang, B. Zhu, Anal. Sci. 2016, 32, 361.
Macdonald, Environ. Sci. Technol. 2012, 46, 12952.
[
34] W. Shu, Y. Wang, L. Wu, Z. Wang, Q. Duan, Y. Gao, C. Liu, B. Zhu, L.
[
[
2] X. Xu, B. Yan, J. Mater. Chem. C 2016, 4, 1543.
Yan, Ind. Eng. Chem. Res. 2016, 55, 8713.
3] B. Zhu, W. Wang, L. Liu, H. Jiang, B. Du, Q. Wei, Sens. Actuators, B
[
35] J. Xu, J. Pan, X. Jiang, C. Qin, L. Zeng, H. Zhang, J. Zhang, Biosens.
Bioelectron. 2016, 77,725.
2
014, 191, 605.
[
4] K. Lambert, D. Evers, H. Hintelmann, H. Yan, T. He, G. Qiu, Environ. Sci.
[
36] T. Kumagai, S. Itsuno, Macromolecules 2001, 34, 7624.
Technol. 2010, 44, 3363.
[
37] L. Tang, Y. Zou, K. Zhong, Y. Bian, RSC Adv. 2016, 6, 48351.
[
[
[
[
5] G. Chen, Z. Guo, G. Zeng, L. Tang, Analyst 2015, 140, 5400.
6] Q. Wang, Y. Xu, Y. Hou, H. Wang, RSC Adv. 2016, 6, 114685.
7] R. Roy, S. Rakshit, S. Bhar, S. Bhattacharya, RSC Adv. 2015, 5, 67833.
How to cite this article: Xu J, Xu Z, Wang Z, et al. A
carbonothioate‐based highly selective fluorescent probe with
8] W. Shu, L. Yan, J. Liu, Z. Wang, S. Zhang, C. Tang, C. Liu, B. Zhu, B. Du,
Ind. Eng. Chem. Res. 2015, 54, 8056.
2+
a large Stokes shift for detection of Hg . Luminescence.
017;1–6. https://doi.org/10.1002/bio.3404
[9] H. Kim, W. Ren, J. Kim, J. Yoon, Soc. Rev. 2012, 41, 3210.
2
[
10] H. Wang, Y. Chen, Y. Li, H. Zhang, J. Cao, RSC Adv. 2015, 5, 94099.
11] W. Shi, S. Zhao, Y. Su, Y. Hui, Z. Xie. New J. Chem. 2016, 40, 7814.
[