A novel azobenzene-based fluorescent sensor for selective detection of mercury ion

Article abstract of DOI:10.2174/157017811799304223

A highly sensitive fluorescent probe (3) for selective detection of mercury based on an azobenzene derivative with 1,3,4-triazole units has been designed, synthesized, and examined for their cation recognition abilities toward various cations by UV-vis, f

Full text of DOI:10.2174/157017811799304223

Letters in Organic Chemistry, 2011, 8, 749-751
749
A Novel Azobenzene-Based Fluorescent Sensor for Selective Detection of
Mercury Ion
Yan Gaoa,b, Jian Song*,a and Wei Wang*,c
aSchool of Chemical and Technology, Tianjin University, Tianjin, 300072, P.R. China
bDepartment of Chemical Engineering, Liaoning University of science and Technology, Anshan, 114004, P.R. China
cSchool of Perfume and Aroma Technology, Shanghai Institute of Technology, Shanghai 200235, P.R. China
Received September 16, 2010: Revised March 27, 2011: Accepted August 25, 2011
Abstract: A highly sensitive fluorescent probe (3) for selective detection of mercury based on an azobenzene derivative
with 1,3,4-triazole units has been designed, synthesized, and examined for their cation recognition abilities toward various
cations by UV-vis, fluorescence. The fluorescent probe (3) exhibits a highly selective response of fluorescence
enhancement toward mercury in DMF aqueous media (DMF: H2O, v/v=1:1).
Keywords: 1,3,4-triazole, azobenzene, fluorescence, mercury, recognition, selectivity.
INTRODUCTION
Scheme 1. (E)-4,4ꢀ-bisbromomethyl azobenzene (2) (2mmol)
was added to a mixture of 1,2-diphenyl-5-mercapto-1,3,4-
triazole (4mmol), KOH (4mmol) in DMF (20ml) and the
mixture was stirred for 24h at room temperature, the mixture
was filtered and washed with water, the resulting residue was
then dried. The crude product was purified by column
chromatography and an orange solid was obtained. The
target compound was characterized by the spectra.
Among heavy and soft metal ions, mercury is considered
as a highly toxic element, the toxicity of Hg2+, even at very
low concentration, has long been recognized as a problem of
primary concern [1]. Our increased understanding of the
deleterious effects of mercury exposure has sparked the
interest in the development of new tools for detecting Hg2+
in the environment [2, 3]. Because of great sensitivity,
fluorescent chemosensor combining ionophores and
fluorophores are commonly considered superior [4, 5].
BINDING STUDIES
Azobenzene, as a molecular scaffold for the construction
of selective ionophores, has been incorporated into
fluorescent ion sensors. A few fluorescent chemosensors
based on azobenzene that display selectivity to heavy and
transition metal cations have been reported [6-9]. However,
there are limited reports about recognition of heavy metal
cations, such as Hg2+ [10, 11], and there still is a need for
alternative systems to selectively recognize heavy metal
cations for environmental or biological applications [12].
Complexation properties of compound (3) were
investigated toward various heavy and transition metal
cations(Ca2+,Cd2+, Cu2+, Hg2+, Mn2+, Ni2+, Pb2+, Zn2+, Mg2+,
Na+, Al3+, Fe3+, Ag+) by UV-vis spectroscope. As shown in
Fig. (1), maximum band of compound (3) was observed at
340nm. When Hg2+ was added, the original peak was
significantly increased, whereas the negligible changes were
observed with the other metal ions. Thus, it may be
concluded that compound (3) has special selectivity and
sensitivity to Hg2+.
Herein, we report the synthesis of a new fluorescent
chemosensor based on the azobenzene framework with azo
group as ionophore and substituted phenyl 1, 3, 4-triazole as
fluorophore and the metal-binding properties toward Hg2+.
The results show that (3) displays a highly selective and
sensitive response toward Hg2+ in DMF aqueous media.
The fluorescence enhancement effects of various metal
ions on compound (3) in DMF solution were investigated
(Fig. 2).
In the fluorescence spectrum, compound (3) exhibited
weak fluorescence emission at 448nm in DMF aqueous
media. When Hg2+ was added to compound (3), the
fluorescence intensity was enhanced remarkably. Emission
change of 18-fold was observed for Hg2+. Fluorescence
enhancement observed for (3) is attributed to the formation
of the (3)-Hg2+ complex as a result of which the PET from
sulfur atoms to the substituted phenyl 1, 3, 4-triazole moiety
is suppressed, resulting in the fluorescent enhancement.
Addition of Cu2+ also resulted in a modest emission
enhancement, whereas no change in fluorescence occurred in
the presence of the other cations (Ca2+, Cd2+, Mn2+, Ni2+,
Pb2+, Zn2+, Mg2+, Na+, Al3+, Fe3+, Ag+ ).
RESULTS AND DISCUSSION
Compound (2) [13-14], 1, 2-diphenyl-5-mercapto-1,3,4-
triazole [15] was prepared according to the literatures. The
synthesis of the target compound (3) was illustrated in
*Address correspondence to these authors at the School of Chemical and
Technology, Tianjin University, Tianjin, 300072, P.R. China; Tel: +86-22-
27401450; Fax: +86-22-27401450; E-mail: songjian@tju.edu.cn
School of Perfume and Aroma Technology, Shanghai Institute of
Technology, Shanghai 200235, P.R. China; Tel: +86-21-64688236; Fax:
+86-21-64086167; E-mail: wangweittg@yahoo.com.cn
1875-6255/11 $58.00+.00
© 2011 Bentham Science Publishers

750 Letters in Organic Chemistry, 2011, Vol. 8, No. 10
Gao et al.
a
N
N
b
BrH2C
N
N
CH2Br
1
2
N
N
S
Ph
N
N
N
N
N
Ph
S
Ph
N
3
Ph
Scheme 1. (a) zinc power, methanol, ammonium water; N-bromosuccinimide, CCl4; (b) 1,2-diphenyl-5-mercapto-1,3,4-triazole, KOH,
DMF.
300
250
200
150
100
50
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
Hg2+
Hg2+/10-5M
3.0
2.0
1.8
1.5
1.2
1.0
0.8
0.6
0.4
0.2
0
3, Ca2+, Cd2+, Cu2+, Mn2+
Ni2+, Pb2+, Zn2+, Mg2+
Na+, Al3+, Fe3+, Ag+
0
300 350 400 450 500 550 600 650 700 750
270
300
330
360
390
420
450
480
510
Wavelength/nm
Wavelength/nm
Fig. (1). UV-vis spectra of compound (3) (10uM) upon addition of
300
various metal ions (10 uM) in DMF and H2O (v/v=1:1).
250
200
150
100
50
The titration of compound (3) by Hg2+ with an excitation
at ꢀex=373nm, given in Fig. (3) as an example, exhibited an
increase of its emission intensity at 448nm. From the
titrations, we determined association constants of compound
(3) (Ka= 1.1ꢁ105) for Hg2+.
250
225
0
0.0
Hg2+
0.5
1.0
1.5
2.0
2.5
3.0
3.5
200
Hg2+/10-5M
175
150
125
100
Fig. (3). Fluorescence emission spectra of compound (3) (10uM)
for Hg2+ ion titration in a mixture of DMF/H2O (v/v=1:1).
3, Ca2+, Cd2+, Mn2+
,
Cu2+
75
50
25
0
Ni2+, Pb2+, Zn2+, Mg2+
Na+, Al3+, Fe3+, Ag+
CONCLUSION
In conclusion, we have synthesized a novel fluorescent
azobenzene derivative bearing substituted phenyl 1, 3, 4-
triazole units, the complexation properties of compound (3)
were described, which can selectively recognize Hg2+.
Compound (3) may provide a potential fluorescent probe for
Hg2+.
360
400
440
480
520
560
600
640
680
Wavelength/nm
Fig. (2). Fluorescence emission spectra of compound (3) upon
addition of various metal ions (10uM) in DMF and H2O (v/v=1:1).
Fitting the changes in fluorescence spectra of compound
(3) with Hg2+ ions, we applied the method of continuous
variation(Job’s plot) to prove the complexation ratio between
compound (3) and Hg2+ ions. As shown in Fig. (4), the
maximum point at the mole fraction of 0.65 indicates the
complexation ratio of compound 3 and Hg2+ is 1:2.
EXPERIMENTAL
All reagents were purchased from Aladdin and were used
without further purification. Thin layer chromatography
(TLC) was carried out on alumina backed plates coated with
Merck gel F254. IR spectra (KBr) were recorded on a Perkin

A Novel Azobenzene-Based Fluorescent Sensor for Selective Detection
Letters in Organic Chemistry, 2011, Vol. 8, No. 10
751
REFERENCES
250
200
150
100
50
[1]
Benoit, J. M.; Fitzgerald, W. F.; Damman, A. W. The
biogeochemistry of an ombrotrophic bog: evaluation of use as an
archive of atmospheric mercury deposition. Environ. Res., 1998,
78(2), 118-133.
[2]
He, X. L.; Wang, Y. Q.; Ling, K.Q. Synthesis of a novel bistriazene
reagent 4,4ꢀ-bis [3-(4-phenylthiazol-2-yl) triazenyl]
biphenyl
and its highly sensitive color reaction with mercury(II). Talanta.,
2007, 72(2), 747-754.
[3]
[4]
[5]
[6]
Nolan, E. M.; Racine, M. E.; Lippard, S. J. Selective Hg(II)
detection in aqueous solution with thiol derivatized fluoresceins.
Inorg. Chem., 2006, 45(6), 2742-2749.
0
0.0
Liu, B.; Tian, H.
A
selective fluorescent ratiometric
0.2
0.4
0.6
0.8
1.0
chemodosimeter for mercury ion. Chem. Commum., 2005, 25,
3156-3158.
Mole Fraction of Hg2+
Wang, J.; Qian, X.; Cui, J. Detecting Hg2+ ions with an ICT
fluorescent sensor molecule: remarkable emission spectra shift and
unique selectivity. J. Org. Chem., 2006, 71(11), 4308-4311.
Lahiri, G. K.; Bhattacharya, S.; Mukherjee, M.; Mukhejee, A. K.;
Chakravorty, A. Directed metal oxidation levels in azo ruthenium
cyclometalates: synthesis and structure of a trivalent family. Inorg.
Chem., 1987, 26(20), 3359-3365.
Fig. (4). Job’s plot for determining the stoichiometry of receptor (3)
and Hg2+ ion in DMF and H2O(v/v=1/1), I and I0 are the
fluorescence intensity of (3) in the presence and absence of Hg2+,
respectively, the total concentration of (3) and Hg2+ ion is 0.1 mM
( ꢃex=373nm).
[7]
Besslera, K. E.; Santosa, J. A.; Deflona, V. M.; Lemosa, S. S.;
Niquet, E. Organotin dyes: synthesis and structural characterization
of dibutyltin and dimethyltin complexes with 2, 2ꢀ-
dihydroxyazobenzene. Z. Anorg. Allg. Chem., 2004, 630, 742-745.
Adams, H.; Bucknall, R. M.; Fenton, D. E.; Garcia, M.; Oakes, J.
Self association in the structures of two copper (II)–azo-dye
complexes. Polyhedron., 1998, 17, 4169-4177.
Nag, J. K.; Chattopadhyay, P.; Mishra, T. K.; Sinha, C.
Dioxouranium complexes of 2,2-dihydroxyazobenzene:binding of
mono-and bidentate lewis bases. J. Indian Chem. Soc., 2000, 77(6),
270-272.
Cuny, G. D.; Landgrebe, K. D.; Smith, T. P. Photoactivated
virucidal properties of tridentate 2,2ꢀ-dihydroxyazobenzene and 2-
salicylideneaminophenol platinum pyridine complexes. Bioorg.
Med. Chem. Lett., 1999, 9, 237-240.
Guo, M.; Xue, W.; Guan, M. Y.; Sun, J. H.; Yin, G. New
azobenzene dye colorimetric and ratiometric chemosensors for
mercury(II) ion. Chin. J. Chem., 2009, 27(9), 1773-1776.
Kim, J. S.; Quang, D. T. Calixarene-derived fluorescent probes.
Chem. Rev., 2007, 107(9), 3780-3799.
Husain, M.; Bhattacharjee, S. S.; Lal, R. A.; Askari, H. Zinc-
ammonia reduction of nitrobenzenes: a simple method for the
synthesis of azobenzenes. Indian J. Chem., 1989, 28B,1077–1078.
Jousselme, B.; Blanchard, P.; Gallego-Planas, N.; Levillain, E.;
Delaunay, J.; Allain, M.; Richomme, P.; Roncali, J.
Photomechanical control of the electronic properties of linear ꢂ-
conjugated systems. Chem. Eur. J., 2003, 9(21), 5297–5306.
Wang, L. C.; Tang, J.; Wei, T. Synthesis and biological activity of
Elmer FTIR. 1H NMR spectra were recorded at room
temperature on a Bruker Avance-500 NMR spectrometer.
Chemical Ionization (CI) Mass-Spectrometry was performed
using Agilent 1100 LC/MS. Elemental analyses were made
with a CHN Analyzer .The UV-vis spectra were measured
[8]
[9]
using
a Lambda-900 spectrometer. The fluorescence
emission spectra were measured using a LS-55 spectrometer.
Synthesis of 4,4'-Bis (1,2-diphenyl-1,3,4-triazolyl-5-
ylmethylthio) azobenzene (3)
[10]
[11]
To a DMF solution (10mL) of the 1,2-diphenyl-5-
mercapto-1,3,4-triazole (4 mmoL), KOH (0.22g, 4 mmoL)
was added. The suspension was stirred until the solution was
clarified. Then, the solution (10 ml) of (E)-4,4ꢀ-
bisbromomethyl azobenzene (2) (2 mmoL) was slowly
added and an orange precipitate was obtained gradually,
continued to stir for 24h at room temperature, the mixture
was filtered and washed with water, the resulting residue was
then dried. The crude product was purified by column
chromatography and eluted with a solvent gradient ranging
from 15/1 to 5/1 petroleum ether in ethyl acetate and an
orange product was obtained (3). Yield：52.6%; m.p. 213-
215ºC; IR (KBr, cm-1): 3048, 2936, 2878, 1592, 1488, 1419,
[12]
[13]
[14]
[15]
2-(3-phenoxymethyl-4-phenyl-[1,2,4]triazole-5-thio)acetic
acid.
Chin. J. Org. Chem., 2008, 28, 343-347.
1
1235, 838, 775; H NMR (500MHz, DMSO-d6): ꢁ 7.81 (d,
4H, Ph-H), 7.57(d, 4H, Ph-H), 7.49-7.37 (t, 20H, Ph-H), 4.49
(s, 4H, CH2); MS, m/z: 713(M+H+); Anal. Calcd. for
C42H32N8S2(%): C, 70.77; H, 4.55; N, 15.70; S, 8.97. Found:
C,70.84; H, 4.53; N, 15.73; S, 9.00.
ACKNOWLEDGEMENTS
The project was supported by the Key Laboratory Project
(2008S127) and the Initial Fund for Young Teachers of
Liaoning University of science and Technology (008131).