Synthesis and mercury ion recognition of a novel azobenzene derivative bearing naphthalene units

Article abstract of DOI:10.3184/174751913X13795955735210

A fluorescent probe for selective detection of mercury based on an azobenzene derivative bearing naphthalene units has been synthesised and its cation recognition abilities examined by UV-Vis and fluorescence spectroscopy. The fluorescent probe exhibits a

Full text of DOI:10.3184/174751913X13795955735210

6
62 RESEARCH PAPER
NOVEMBER, 662–664
JOURNAL OF CHEMICAL RESEARCH 2013
Synthesis and mercury ion recognition of a novel azobenzene derivative
bearing naphthalene units
a
b
Wei Wang , Xiaoyu Jiang, Qiang Zhang, Mingzhu Li, Xiaolong Yu, Junwu Wang and Yan Gao *
aSchool of Perfume and Aroma Technology, Shanghai Institute of Technology, Shanghai 200235, P.R. China
bDepartment of Chemical Engineering, Liaoning University of Science and Technology, Anshan, 114051, P.R. China
A fluorescent probe for selective detection of mercury based on an azobenzene derivative bearing naphthalene units has been
synthesised and its cation recognition abilities examined by UV-Vis and fluorescence spectroscopy. The fluorescent probe
exhibits a highly selective response of fluorescence enhancement toward mercury in DMF aqueous media (DMF: H O, v/v=1:1).
2
Keywords: azobenzene, naphthalene, recognition, mercury, UV-Vis spectroscopy, fluorescence spectroscopy
The design of optical sensors for selective recognition and
sensing of desired metal ions is an important and contemporary
research area. In this regard, metal ions that are known to have
detrimental effects on living organisms or the environment are
1,2
generally more common as target metal ions for such studies.
Mercury is a prevalent toxic metal in the environment because
both elemental and ionic mercury can be converted by bacteria
in the environment to methyl mercury, which subsequently
bioaccumulates through the food chain. When absorbed in the
human body, mercury causes damage to the central nervous,
3
–5
DNA, mitosis, and endocrine systems. Therefore, developing
2+
new and practical multi-signalling chemosensors for Hg is
still a challenge.
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
6
–9
have been reported. However, since there are only limited
reports about recognition of heavy metal cations, such as
Fig. 1 UV-Vis spectra of compound 3 (10 μM) upon addition of various
ions (20 μM) in DMF and H O (v/v=1/1).
2+ 10,11
2
Hg , there is a need for good sensors and further efforts are
required to develop them. Here we describe a new fluorescent
chemosensor, based on the azobenzene framework with the
azo group as ionophore and naphthyl as fluorophore, which has
metal-binding properties and shows a selective and sensitive
column chromatography and a pink solid was obtained. The
1
target compound was characterised by elemental analysis, H
13
NMR, C NMR, IR, and MS, the spectral data are in agreement
with the desired structure.
2+
fluorescence enhancement response to the Hg ion.
Thecomplexationpropertiesofcompound3were investigated
Results and discussion
2+
2+
toward various heavy and transition metal cations (Ca , Cd ,
2
+
2+
2+
2+
2+
2+
2+
+
3+
3+
+
The target products were synthesised using a three-step
procedure as shown in Scheme 1: (i) synthesis of (E)-4,4′-
dicarboxyl azobenzene 1 using the reduction reaction of
Cu , Hg , Mn , Ni , Pb , Zn , Mg , Na , Al , Fe , Ag ) by
UV-Vis spectroscopy. As show in Fig. 1, the UV-Vis absorption
2+
band of compound 3 was observed at 337 nm. When Hg
4
-nitrobenzoic acid D-(+)-glucose; (ii) synthesis of the (E)-
was added, the original peak decreased and new absorption
bands at 324 nm and 379 nm were formed, whereas negligible
changes were observed with the other metal ions. Thus, it
may be concluded that compound 3 has special selectivity and
4,4′-bischloroformyl azobenzene 2 by chlorination reaction
of 1 with thionyl chloride; (iii) azobenzene derivative 3 was
synthesised by nucleophilic addition-elimination reaction of
2
2+
with 1-naphthylamine. The crude product was purified by
sensitivity to Hg .
NaOH/gluocose
SOCl2
HOOC
NO2
HOOC
N
N
H O, O2
COOH
2
1
NH2
O
ClOC
N
O
C
HN
C
N
N
COCl
Et N/CH CN
3
3
N
NH
2
3
Scheme 1 Synthesis of azobenzene derivative 3.
*
Correspondent. E-mail: gys20080901@126.com
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JOURNAL OF CHEMICAL RESEARCH 2013 663
Fig. 2 Fluorescence emission spectra of compound 3 (10 μM) upon
2+
2+
Fig. 4 Job’s plot for determining the stoichiometry of receptor 3 and Hg2+
ion in DMF and H O(v/v=1/1), I and I are the fluorescence intensity of 3 in
addition of Hg and Cu (20 μM) in DMF and H O (v/v=1/1).
2
2
0
2+
2+
the presence and absence of Hg , respectively; the total concentration of 3
The fluorescence enhancement effects of Hg ion on
compound 3 in DMF aqueous media were investigated, as
shown in Fig. 2.
2+
and Hg ion is 0.1 mM (λ =396 nm).
ex
In the fluorescence spectrum, compound 3 exhibited weak
fluorescence emission at 461 nm in DMF/aqueous media. When
Hg was added to compound 3, the fluorescence intensity was
Experimental
2+
12
(E)-4,4’-bischloroformyl azobenzene was prepared according to
procedures described in the literature; other reactants and chemicals
were purchased from Aladdin. Solvents were of analytical grade. NMR
spectra were recorded at room temperature on a Bruker Avance-500
enhanced nine-fold. The fluorescence enhancement observed
2+
for 3 is attributed to the formation of the 3–Hg complex, as a
result of which the PET from nitrogen atoms to the naphthalene
moiety is suppressed, resulting in the fluorescent enhancement.
NMR spectrometer. DMSO-d6 and CDCl were used as solvents and
3
2+
The titration of compound 3 by Hg with an excitation at
λex =396 nm, given in Fig. 3 as an example, exhibited an
increase of its emission intensity at 461 nm. From the titrations,
tetramethylsilane (TMS) as internal standard. Mass spectral data
were obtained on an Agilent 1100 LC/MS instrument. IR spectra were
obtained with a Perkin Elmer spectrophotometer. Elemental analyses
were made with a CHN analyser. (Thermo Finnigan Company). UV-
Vis absorption spectra were recorded at room temperature using a
Lambda-900 spectrometer. The fluorescence emission spectra were
measured using a LS-55 spectrometer.
2
+
we determined the association constant of compound 3 for Hg
(
6
–2
Ka=1.25×10 M ).
Using the changes in the fluorescence spectra of compound 3
with Hg ions, we applied the method of continuous variation
2+
(
3
Job’s plot) to prove the complexation ratio between compound
and Hg ions. As shown in Fig. 4, the maximum point at
2+
Synthesis of compound 3; general procedure
(E)-4,4′-bischloroformyl azobenzene 2 (0.98 mmol) was added to a
the mole fraction of 0.67 indicates the complexation ratio of
compound 3 and Hg is 1:2.
In conclusion, we have synthesised a novel azobenzene
derivative bearing naphthalene units 3. The structure of the
target compound was clearly identified by H NMR, C NMR
spectroscopy and elemental analysis. The UV and fluorescence
spectra data indicate that compound 3 could recognise Hg and
a 1:2 stoichiometric complex was formed between the receptor
and cation.
2+
mixture of 1-naphthylamine (1.96 mmol), Et N (1.98 mmol) in ClCH Cl
3
2
(20 mL) and the mixture was stirred for 8 h at room temperature. The
resulting solid was filtered and the crude product was purified on a
silica gel column using petroleum: the product was obtained as salmon
pink powder. Yield 69%; m.p. >300 °C; IR (KBr, cm ): 3283, 3063,
2945, 1646, 1597, 1529, 1439, 1344, 1147, 858, 763; H NMR (500 MHz,
DMSO-d6): δ 10.693(s, 1H, NH), 10.679(s, 1H, NH), 8.366 (t, 3H,
1
13
–1
1
2+
J=8.5, PhH), 8.205 (d, 1H, J=8.5, PhH), 8.153 (m, 2H, PhH), 8.066
Fig. 3 Fluorescence emission spectra of compound 3 (10 μM) for Hg2+ ion: titration in a mixture of DMF/H O (v/v=1/1) (λ =396 nm).
2
ex
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64 JOURNAL OF CHEMICAL RESEARCH 2013
(m, 4H, PhH and naphthalene-H), 8.016 (m, 2H, naphthalene-H), 7.918
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Received 9 July 2013; accepted 9 August 2013
Paper 1302054 doi: 10.3184/174751913X13795955735210
Published online: 11 November 2013
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