Synthesis and fluorescent properties of a novel dansyl-based fluorescent probe for Hg2+

Article abstract of DOI:10.3184/174751914X13895467018450

A novel turn-off fluorescent probe containing a dansyl fluorophore has been synthesised. Its recognition properties towards various metal ions have been studied by fluorescence spectrometry. The compound showed a high sensitivity and selectivity to Hg²⁺ ion and a complexation ratio towards Hg ²⁺ of 2 : 1. Its fluorescence intensity varied almost linearly versus the concentration of Hg²⁺ (0.8-8.4 μmol L^-1), and the detection limit of Hg²⁺ was estimated to be 0.88 μmol L ^-1.

Full text of DOI:10.3184/174751914X13895467018450

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
108 RESEARCH PAPER
FEBRUARY, 108–110
JOURNAL OF CHEMICAL RESEARCH 2014
Synthesis and fluorescent properties of a novel dansyl-based fluorescent
probe for Hg2+
Xiao Zuo-An*, Zhan Dan and Yang Xiao
College of Chemical Engineering and Food Science, Hubei University of Arts and Science, Xiangyang 441053, P.R. China
A novel turn-off fluorescent probe containing a dansyl fluorophore has been synthesised. Its recognition properties towards
various metal ions have been studied by fluorescence spectrometry. The compound showed a high sensitivity and selectivity to
Hg2+ ion and a complexation ratio towards Hg2+ of 2:1. Its fluorescence intensity varied almost linearly versus the concentration
of Hg2+ (0.8–8.4 µmol L–1), and the detection limit of Hg2+ was estimated to be 0.88 µmol L–1.
Keywords: dansyl, fluorescent probe, Hg2+, selectivity
The selective and sensitive detection of transition and
heavy metal ions is very important for medical diagnostics,
environmental, and biological applications.1,2 Hg2+ is considered
the most toxic heavy metal ion and its pollution has attracted
much attention. It is commonly spread into the environment
by anthropogenic and industrial releases and is converted into
toxic methylmercury by bacterial and chemical actions. The
bioaccumulation of such toxic material in the human body via
the food chain can lead to digestive, kidney and neurological
diseases even at very low concentration.3,4 The Environmental
Protection Agency has set the maximum allowable level of
inorganic mercury in drinking water at 2 ppb.5 Therefore, the
development of convenient and rapid methods for detection of
Hg2+ has attracted considerable interest. Consequently, great
efforts have been made to design efficient fluorescent probes to
detect Hg2+ either by fluorescence enhancement or quenching
and colour changes.6–9 However, only a few examples of Hg2+-
selective fluorescent probes have been found to be effective.10–13
Therefore, designing a highly selective sensor for Hg2+ remains
a challenge. We now report a novel and selective fluorescent
probe for Hg2+.
exhibited highly selective fluorescence quenching toward Hg2+
in a aqueous EtOH solution.
The maximum excitation (λex) and emission (λem)
wavelengths of 4 are 368 and 552 nm, respectively. The
+
fluorescence response of 4 to various metal ions (K , Ca2+, Na+,
Mg2+, Mn2+, Fe2+, Fe3+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Ag+, Pb2+
and Hg2+) is illustrated in Fig. 1. The results show that Hg2+
produced significant quenching in the fluorescent emission of
4, while other metal ions did not exhibit significant changes
under identical conditions, except that Cu2+ showed relatively
The dansyl group has often been chosen to be incorporated
into fluorescent probes due to its good fluorescent properties.
14,15
We have designed (Scheme 1) a dansyl-based fluorescent
probe 4, in which the dansyl group is linked to a chelating
moiety [bis(2-(ethylthio)ethyl)amine, 3]. Scheme 1 shows
how the intermediates 2 and 3 were prepared according to
the literature method.16,17 The reaction of dansyl chloride with
2 equiv. of 3 in acetone afforded 4 in 76% yield. Compound 4
1
was fully characterised by H NMR, 13C NMR, IR, MS and
Fig. 1 The effect of metal ions (10 µM) on the fluorescent properties of
probe 4 (10 µM) in 100 mM Tris-HCl buffer (pH 7.4) (H2O:EtOH=9:1, v/v)
with an excitation at 368 nm. The samples were incubated for 10 min at
room temperature prior to measurements.
elemental analysis, and its response to Hg2+ was studied through
fluorescent spectrometry. The primary test showed that 4
HCl
.
H
H
SOCl CH Cl
,
N
N
HS
2
3
l
C
l
C
HO
OH
Na
EtOH
,
0°C
1
2
O
S
O
S
S
S
S
l
C
N
N
O
NH
N
O
acetone
NEt
0°C
S
,
3
,
4
3
Scheme 1 Synthesis of fluorescent probe 4.
* Correspondent. E-mail: blueice8250@aliyun.com
JCR1302273_FINAL.indd 108
30/01/2014 11:43:16

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
JOURNAL OF CHEMICAL RESEARCH 2014 109
small fluorescence intensity changes. To further estimate
the selectivity for Hg2+ over other metal ions, competition
experiments of Hg2+ mixed with other metal ions were carried
out by fluorescence spectra and the results are shown in Fig. 2.
The fluorescence intensity of 4 (10 µmol L–1) in the presence
of 1 equiv. of Hg2+ was almost unaffected by the addition of
10 equiv. of competing metal ions. Thus it can be concluded
that 4 has a high selectivity for recognition of Hg2+.
The sensitivity of the fluorescence emission response of 4
towards Hg2+ was also examined by fluorescent titration (Fig. 3).
The fluorescence intensity of 4 was decreased continually upon
addition of Hg2+. When the concentration of Hg2+ increased
to 3 equiv., the fluorescence of 4 was nearly quenched. At a
very high concentration of Hg2+, the fluorescence of 4 was
completely quenched. This clearly indicates that the Hg2+–4
complex is non-fluorescent in nature. Moreover, as depicted in
the inset in Fig. 3, an obvious fluorescence change from bright
yellow to dark can be observed under irradiation at 365 nm after
the addition of 3 equiv. of Hg2+ to the solution of 4. It was found
that a linear regression curve (linear correlation coefficient
R2 =0.9947) of the Hg2+–4 complex fitted the relationship
between the fluorescence of 4 and the concentration of Hg2+
(0.8–8.4 µmol L–1) (Fig. 4). The detection limit of 4 to Hg2+ was
determined to be 0.88 µmol L–1 according to the calculation
method reported in the literature.18 The above results indicate a
high sensitivity of 4 to Hg2+.
To determine the stoichiometry of 4 and Hg2+ in the complex,
Job’s plot method was employed using the emission changes at
552 nm as a function of the molar fraction of 4. As shown in
Fig. 5, the maximum point was observed at the mole fraction
between 0.6 and 0.7, indicating that Hg2+ forms a 1:2 complex
with 4.
Based on above experiments and a recent report, 19 a possible
complexation mechanism seemed to be reasonable for the
binding site of 4 with Hg2+. In the chelating moiety of 4, there
are two sulfur atoms and one nitrogen atom, which probably
form a suitable binding site for Hg2+. When Hg2+ is added, the
sulfur and nitrogen atoms donate their lone pair of electrons
to the empty orbital of Hg2+. The capture of Hg2+ causes the
electron or energy transfer between the chelating unit and the
dansyl group, thus resulting in the fluorescence quenching of
the dansyl group. Therefore we propose that the reaction of 4
with Hg2+ would yield the 1:2 complex shown in Scheme 2.
In summary, we have synthesised a novel dansyl-based
fluorescent probe 4. A fluorescent study has shown that 4 is
selective and sensitive to Hg2+, and it formed a 2:1 complex
with Hg2+. The detection limit of 4 to Hg2+ was determined to
be 0.88 µmol L–1.
Fig. 2 The effect of Hg2+ on 4 (10 µmol L–1) in the presence of different
Fig. 4 Fluorescence intensity of 4 as a function of concentration of Hg2+
metal ions (100 µmol L–1).
(0.8–8.4 µmol L–1).
Fig. 3 The emission intensity of 4 (10 µmol L–1) changes with increasing
concentrations of Hg2+ (0–30 µmol L–1), the inset shows photograph of 4
(10 µmol L–1) in the absence and presence of Hg2+ under UV light (365 nm).
Fig. 5 Job’s plot of 4 and Hg2+ ([4]+[Hg2+]=10 mmol L–1).
JCR1302273_FINAL.indd 109
30/01/2014 11:43:16

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
110 JOURNAL OF CHEMICAL RESEARCH 2014
O
S
O
S
S
N
O
S
S
S
2+
2+
H
g
N
N
H
g
S
N
N
O
O
S
S
N
O
ON
FF
O
Scheme 2 Proposed binding model of fluorescent probe 4 with Hg2+.
This work was supported by the Science Technology Research
Programme of the Education Office of Hubei Province (grant
no. 20092503).
Experimental
All reagents were purchased from commercial companies and directly
used unless stated otherwise. Solvents were purified by standard
methods. The 1H NMR spectra were recorded on a Mercury Plus-400
spectrometer in CDCl3. Mass spectra were obtained with a Finnigan
Trace MS instrument using the EI method. The IR spectra were
measured on a Perkin-Elmer Spectrum BX FT-IR instrument in tablets
with potassium bromide. Elemental analyses were carried out on a
Perkin-Elmer 2400 instrument. Fluorescence spectra were performed
on a FluoroMax-P spectrofluorimeter.
Received 23 September 2013; accepted 23 December 2013
Paper 1302273 doi: 10.3184/174751914X13895467018450
Published online: 5 February 2014
References
5-(Dimethylamino)-N, N-bis(2-(ethylthio)ethyl)naphthalene-1-
sulfonamide (4): The intermediate 3 (0.77 g, 0.4 mol) and triethylamine
(0.40 g, 0.4 mol) were added to a solution of dansyl chloride (0.54 g,
0.2 mol) in acetone (100 mL). The mixture was stirred in an ice bath for
2 h. Then the ice bath was removed and the resulting yellow suspension
was stirred at room temperature for another 3 h. The progress of the
reaction was monitored by TLC until complete disappearance of
dansyl chloride. After filtration and rotary evaporation, the residue
was purified by flash chromatography (silica, petroleum ether/AcOEt,
5/1, v/v) to give a yellow compound 4; yield: 76%. IR (KBr): 2948,
1542, 1476, 1422, 1380, 1248, 1152 cm−1. 1H NMR (400 MHz, CDCl3,
ppm): δ 1.28 (t, 6H, J 7.2 Hz, –CH3), 2.45–2.58 (m, 8H, –CH2), 2.88 (s,
6H, –CH3), 3.52 (t, 4H, J 7.6 Hz, –CH2), 7.22–7.62 (m, 3H, ArH), 8.22–
8.65 (m, 3H, ArH). 13C NMR (100 MHz, CDCl3, ppm): δ 152.4, 145.2,
1334.6, 129.2, 127.4, 126.8, 124.3, 123.2, 118.9, 116.8, 48.7, 45.8, 29.8,
27.2, 15.4. EI-MS: m/z 578. Anal. calcd for C20H30N2O2S3:C, 56.30; H,
7.09; N, 6.57; found: C, 56.48; H, 7.28; N, 6.42%.
1
A.P. de Silva, H.Q.N. Gunaratne, T. Gunnlaugsson, A.J.M. Huxley, C.P.
McCoy, J.T. Rademacher and T.E. Rice, Chem. Rev., 1997, 97, 1515.
B. Valeur and I. Leray, Coord. Chem. Rev., 2000, 205, 3.
R.K. Zalups, Pharmacol. Rev., 2000, 52, 113.
2
3
4
5
6
M. Harada, Crit. Rev. Toxicol., 1995, 25, 1.
E.M. Nolan and Stephen J. Lippard, Chem. Rev., 2008, 108, 3443.
Y. Liu, X. Lv, Y. Zhao, M. Chen, J. Liu, P. Wang and W. Guo, Dyes Pigm.,
2012, 92, 909.
Y.J. Gong, X.B. Zhang, Z. Chen, Y. Yuan, Z. Jin, L. Mei, J. Zhang, W. Tan,
G.L. Shen and R.Q. Yu, Analyst, 2012, 137, 932.
Y.K. Yang, K.J. Yook and J. Tae, J. Am. Chem. Soc., 2005, 127, 16760.
P. Srivastava, R. Ali, S.S. Razi, M. Shahid, S. Patnaik and A. Misra,
Tetrahedron Lett., 2013, 54, 3688.
7
8
9
10 Q. Zou and H. Tian, Sens. Actuators B: Chem., 2010, 149, 20.
11 X. Li. Wu, J.P. Lai and Y.B. Zhao, Chem. J. Chin. Univ., 2012, 33, 695.
12 Z.H. Xu, X.F. Hou, W.L. Xu, R. Guo and T.C. Xiang, Inorg. Chem.
Commun., 2013, 34, 42.
13 K. Wang, L. Yang and C. Zhao, Spectrochim. Acta A: Mol. Biomol.
Spectrosc., 2013, 105, 29.
14 K. Kavallieratos, J.M. Rosenberg, W.Z. Chen and T. Ren, J. Am. Chem.
Soc., 2005, 127, 6514.
Fluorescence experiment studies:
A stock solution of 4 was prepared by dissolution in ethanol/water
(8:2, v/v) containing 100 mmol L–1 Tris-HCl buffer (pH 7.4). Solutions
of various metal ions (K+, Ca2+, Na+, Mg2+, Mn2+, Fe2+, Fe3+, Co2+, Ni2+,
Cu2+, Zn2+, Cd2+, Pb2+ and Hg2+) were prepared in water (1 mmol L–1).
Fluorescence titration was performed on 3 mL solutions of 4 in a quartz
cell, by adding different stock solutions of cations into the quartz cell
portionwise using a microsyringe each time. After mixing well, the
fluorescence spectrum of the solution was monitored.
15 T. Koike, T. Watanabe, S. Aoki, E. Kimura and M. Shiro, J. Am. Chem.
Soc., 1996, 118, 12696.
16 Z.R. Liao, D.F. Xiang, D.F. Li, F.S. Mei and F. Yun, Synth. React. Inorg.
Met.-Org. Chem., 1998, 28, 1327.
17 H. Sakamoto, J. Ishikawa, H. Osuga, K. Doib and H. Wadab, Analyst, 2010,
135, 550.
18 M. Shortreed, R. Kopelman, M. Kuhn and B. Hoyland, Anal. Chem., 1996,
68, 1414.
19 S. Park, S.Y. Lee and S.S. Lee, Inorg. Chem., 2010, 49, 1238.
JCR1302273_FINAL.indd 110
30/01/2014 11:43:16

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
Copyright of Journal of Chemical Research is the property of Science Reviews 2000 Ltd. and
its content may not be copied or emailed to multiple sites or posted to a listserv without the
copyright holder's express written permission. However, users may print, download, or email
articles for individual use.