A selective, sensitive probe for mercury(II) ions based on oxazine-thione

Article abstract of DOI:10.1016/j.tetlet.2010.11.130

A selective, sensitive probe for Hg(II) ions, 7-(diethylamino)-3-methyl-2H- benzo[b][1,4] oxazine-2-thione (1), is developed. Compound 1 behaves as a ratiometric probe, exhibiting a large blue shift of 100 nm in its absorption spectra upon exposure to Hg(

Full text of DOI:10.1016/j.tetlet.2010.11.130

Tetrahedron Letters 52 (2011) 595–597
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Tetrahedron Letters
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A selective, sensitive probe for mercury(II) ions based on oxazine-thione
⇑
⇑
Qian-Qian Zhang, Jian-Feng Ge , Qing-Feng Xu, Xue-Bo Yang, Xue-Qin Cao, Na-Jun Li, Jian-Mei Lu
Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A selective, sensitive probe for Hg(II) ions, 7-(diethylamino)-3-methyl-2H-benzo[b][1,4] oxazine-2-thi-
one (1), is developed. Compound 1 behaves as a ratiometric probe, exhibiting a large blue shift of
100 nm in its absorption spectra upon exposure to Hg(II) ions. The dramatic color change of the solution
made ‘naked-eye’ detection of Hg(II) ions possible. Emission spectra of 1 displayed a selective enhance-
ment in intensity in the presence of Hg(II) ions. ESI+-MS analysis indicated that Hg2+-induced desulfur-
ization caused the large absorption response.
Received 27 September 2010
Revised 16 November 2010
Accepted 26 November 2010
Available online 2 December 2010
Keywords:
Ó 2010 Elsevier Ltd. All rights reserved.
Mercury(II) ion probe
Oxazine thione
Naked-eye detection
Chemosensor
1. Introduction
7-(Diethylamino)-3-methyl-2H-benzo[b][1,4]oxazin-2-one (2)
was prepared from 5-(diethylamino)-2-nitrosophenol hydro-chlo-
Because of the high toxicity, wide distribution, bio-accumula-
tion, and serious effects on human health and environment result-
ing from mercury contamination, Hg(II) detection is attracting a
significant amount of attention.1 In recent years, small-molecule-
based Hg(II) sensors3–5 have been focused on because they possess
advantages such as simple operation, low cost, real time monitor-
ing, high sensitivity, and do not require sophisticated instruments
or complex sample preparation for testing by traditional quantita-
tive approaches.2,1a
ride following a reported procedure,7 with a modification in the
reduction step. The resulting 2-amino-5-(diethylamino)phenol
was used directly in the next step. Compound 2 was reacted with
Lawesson’s reagent in refluxing dry toluene, and the resulting
material was purified by column chromatography with silica gel
using chloroform as the eluent. Compound 1 was obtained as red
solid with a yield of 19% (Scheme 1). The structures of 1 and 2 were
fully confirmed by NMR spectroscopy and mass spectrometry
(MS).
The probes reported for Hg(II) generally consist of a chromo-
phore and a reactive region that can be chelated3a–c,f–h,k–m or
reacted3n–x with Hg(II) ions. The absorption or emission properties
of the probes change with the interactions between the reactive
region and Hg(II) ions. The development of novel chromophores
with appropriate reactive regions for selective, sensitive detection
remains an important goal for ion sensors.
Current research on Hg(II) probes is focused on rhodamine
derivatives,3s,u–w coumarin derivatives,3l and other species.3g,h
Herein, we report the synthesis and application of a probe based
on oxazine-thione, (7-(diethylamino)-3-methyl-2H-benzo[b][1,4]
oxazine-2-thione (1), for the selective, sensitive detection of Hg(II)
ions. The desulfurization reaction3n–p,r,t of carbonyl sulfide takes
advantage of the high affinity of Hg(II) for sulfur.3n–p,r,t A simple
substitution of the oxygen atom with sulfur results in a significant
change in the optical properties of the compounds.6,3u
Figure 1 shows the absorption spectra of 1 in CH3CN/H2O
(v/v = 1/1) containing various concentrations of Hg2+ at room
temperature. The absorption spectrum of 1 in the absence of Hg(II)
has a peak with a maximum at 514 nm (Table S1 and Fig. S1,
Supplementary data), which is responsible for the red color of
the solution. Addition of 2 equiv of Hg(II) causes a dramatic blue
shift of the maximum absorption from 514 nm to 414 nm, with
an isosbestic point appearing at about 460 nm. The color of the
NH2
NO
1) NaHCO3, H2O;
2) H2, Pd-C.
CH3COCOOEt
Et
Et
N
Et
OH
N
Et
OH
HCl
N
O
CH
N
O
CH3
S
3 Lawesson's reagent
toluene, reflux
Et
Et
N
Et
O
N
Et
⇑
Corresponding authors. Address: 199 Ren’ai Road, Suzhou Industrial Park,
Suzhou 215123, China (J.-M.L.). Tel.: +86 512 6588 0368; fax: +86 512 6588 0367.
2
1
E-mail addresses: gejianfeng@suda.edu.cn (J.-F. Ge), lujm@suda.edu.cn (J.-M. Lu).
Scheme 1. Synthesis of oxazine-thione 1.
0040-4039/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2010.11.130

596
Q.-Q. Zhang et al. / Tetrahedron Letters 52 (2011) 595–597
Hg2+
H2O
N
O
CH3
O
N
O
CH3
S
Et
Et
N
N
Et
Et
2
1
Scheme 2. Hg2+-induced desulfurization of 1.
Figure 1. UV–vis absorption spectra of
1 (10 lM) in CH3CN/H2O (v/v = 1/1)
containing different concentrations of Hg2+ (0, 0.2, 0.4, 0.8, 1.0, 2.0, 4.0, 8.0, 10,
20, 40, 80 lM).
Figure 3. (a) Emission spectra of 1 (10
and 100
M of each of Ag+, Ba2+, Ca2+, Cd2+, Co2+, Cu2+, Fe3+, K+, Mg2+, Mn2+, Na+, Ni2+
Pb2+, and Zn2+ ions. The excitation wavelength was 460 nm. (b) The ratio of A(414)/
lM) in the presence of 40 l
M of Hg2+ ions
l
,
A(514) in the absorption spectra of 1 (10 lM) upon the addition of different metal
ions (10 equiv of each).
To examine the sensitivity of 1, fluorescence emission spectra
were recorded as the concentration of Hg(II) was increased from
0 to 80 lM. As shown in Figure 2a, 1 displays relatively weak fluo-
rescence centered at about 556 nm in the absence of Hg(II) with
kex = 460 nm. Upon the addition of Hg(II), a gradual increase in
the intensity of fluorescence was observed. The fluorescence titra-
tion profile of 1 versus Hg(II) revealed that the maximum enhance-
ment of the emission from 1 was obtained when 40
added to the solution (Fig. 2b). The sensitivity curve indicated that
the probe 1, maintained at a concentration of 10 M, can be used
for the analysis of micromolar concentrations of Hg(II) ions. The
‘off-on’-type enhancement in fluorescence may result from the
desulfurization reaction depicted in Scheme 2.
lM Hg(II) was
Figure 2. (a) Fluorescence emission spectra and (b) fluorescence intensity of a
solution of 1 (10 lM) in CH3CN/H2O (v/v = 1/1) containing different concentrations
l
of Hg2+ at kex = 460 nm, kem = 556 nm (I0 indicates the fluorescence intensity of free
1 and I indicates the fluorescence intensity upon the introduction of different
amounts of Hg2+).
To explore the mechanism of the change in absorption, the
complexes were detected by electrospray ionization (ESI+)-MS
analysis. In the absence of Hg(II), a peak was observed at m/z
249.1062 corresponding to [1+H]+. After the addition of 2 equiv
of HgCl2 to the solution of 1, the peak at m/z 249.1062 disappeared.
solution changes simultaneously from red to yellow, which is per-
ceptible to the naked eye. Meanwhile, the addition of other metal
ions does not affect the absorption maxima (Fig. S2, Supplemen-
tary data).

Q.-Q. Zhang et al. / Tetrahedron Letters 52 (2011) 595–597
597
Acknowledgments
We thank Professor Masataka Ihara (Hoshi University, Japan)
for encouragement and helpful discussion regarding the synthesis
of 1. We are also grateful for the financial support from the Na-
tional Environmental Community Project of China (200909044),
the Natural Science Fund (SBK200930379), and the Natural Science
Fund for Colleges and Universities (08KJB430013) in Jiangsu
Province.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tetlet.2010.11.130.
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2. Conclusion
An oxazine-thione (1) was synthesized as a highly selective and
sensitive probe for the detection of Hg(II) ions in water-compatible
solvents with different pH values using UV/vis and fluorescent re-
sponses. Moreover, the dramatic color change of the solution made
the detection of Hg(II) ions possible by the naked eye. ESI+-MS data
indicated that the high selectivity of 1 was due to an Hg2+-induced
desulfurization reaction. It is anticipated that 1 could contribute to
the development of mercury ion sensors.