Colorimetric chemosensors designed to provide high sensitivity for Hg 2+ in aqueous solutions

Article abstract of DOI:10.1016/j.dyepig.2012.06.023

The specific colorimetric detection of Hg²⁺ in the context of interference from coexisting metal ions in aqueous solutions is a challenge. Therefore, a series of easy-to-make Hg²⁺ colorimetric chemosensors S1～S3, bearing thiourea moi

Full text of DOI:10.1016/j.dyepig.2012.06.023

Dyes and Pigments 96 (2013) 1e6
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Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Colorimetric chemosensors designed to provide high sensitivity
for Hg2þ in aqueous solutions
*
Qi Lin, Yong-Peng Fu, Pei Chen, Tai-Bao Wei, You-Ming Zhang
Key Laboratory of Eco-Environment-Related Polymer Materials, Ministry of Education of China, Key Laboratory of Polymer Materials of Gansu Province, College of Chemistry and
Chemical Engineering, Northwest Normal University, Lanzhou, Gansu 730070, PR China
a r t i c l e i n f o
a b s t r a c t
The specific colorimetric detection of Hg2þ in the context of interference from coexisting metal ions in
aqueous solutions is a challenge. Therefore, a series of easy-to-make Hg2þ colorimetric chemosensors
S1wS3, bearing thiourea moiety as binding site and nitrophenyl moiety as signal group, were designed
and synthesized. Among these sensors, S3 showed excellent colorimetric specific selectivity and high
sensitivity for Hg2þ in DMSO and DMSO/H2O binary solutions. When Hg2þ was added to the solution of
Article history:
Received 25 January 2012
Received in revised form
28 June 2012
Accepted 29 June 2012
Available online 25 July 2012
S3, a dramatic color change from brown to colorless was observed, while the cations Ca2þ, Mg2þ, Cd2þ
,
.
Fe3þ, Co2þ, Ni2þ, Cu2þ, Zn2þ, Pb2þ, Agþ and Cr3þ did not interfere with the recognition process for Hg2þ
Keywords:
The detection limits were 5.0 ꢀ 10ꢁ6 and 1.0 ꢀ 10ꢁ7 M of Hg2þ using the visual color changes and UVevis
Mercury cation
Colorimetric sensor
Specific selectivity
High sensitivity
Aqueous solutions
Easy-to-make
changes respectively.
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
attention has been paid to developing mercury sensors that work in
the aqueous phase [17,23e26,32,34,49e52].
As mercury has an extremely toxic impact on the environment
and human health [1e5], the development of chemosensors for the
mercury cation (Hg2þ) has received considerable attention [6e10].
As is well known, mercury can lead to dysfunctions of the brain,
kidney, stomach, and central nervous systems [1e5,11,12]. There-
fore, the rational design and synthesis of efficient sensors to
selectively recognize mercury cations is an important topic in
supramolecular chemistry [6e10]. Although previous work has
involved the development of a wide variety of chemical [13e43]
and physical [44e48] sensors for the detection of Hg2þ, so far,
improving the detection selectivity in the context of interference
from coexisting metal ions has been challenging. Moreover, most of
these methods require expensive equipment and involve time-
consuming and laborious procedures that can be carried out only
by trained professionals [44e48], which significantly restricting
the practical application of these Hg2þ sensors. For simplicity,
convenience and low cost, easily-prepared Hg2þ colorimetric
sensors [15e23,30,38] are needed. On the other hand, in biological
and environmental systems, mercuryesensor interactions
commonly occur in aqueous solution [23e26], therefore, much
In view of this requirement and as part of our research effort
devoted to ion recognition [53e60], an attempt was made to obtain
efficient colorimetric sensors which could sense Hg2þ with specific
selectivityandhighsensitivityinaqueoussolutions. Thispaperdetails
the design and synthesis of a series of Hg2þ colorimetric sensors
S1wS3 bearing thiourea and nitrophenyl groups (Scheme 1). The
strategies for the design of these sensors were as follows. Firstly,
a thiourea group was introduced as the binding site. The C¼S moiety
onthethioureagrouppossesses ahighaffinitywithHg2þ. Secondly, in
order to achieve “naked-eye” colorimetric recognition, we introduced
nitrophenyl groups as the signal group. Finally, the sensor was
designed to be easy to synthesize. In order to establish the signal
group’s contribution to the sensor’s colorimetric sensing abilities for
Hg2þ, compound S1 which without containing the nitro-group was
also synthesized.
2. Experimental section
2.1. Materials and physical methods
1H NMR spectra were recorded with a Mercury-400BB spec-
trometer at 400 MHz 1H chemical shifts are reported in ppm
* Corresponding author. Tel.: þ86 931 7970394.
E-mail address: zhangnwnu@126.com (Y.-M. Zhang).
downfield from tetramethylsilane (TMS,
d scale with the solvent
0143-7208/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.dyepig.2012.06.023

2
Q. Lin et al. / Dyes and Pigments 96 (2013) 1e6
Scheme 1. Synthetic procedures for sensors S1wS3.
Fig. 1. Color changes observed upon the addition of various cations (5 equiv.) to the solutions of sensor S3 (2 ꢀ 10ꢁ5 M) in DMSO solutions.
resonances as internal standards). High-resolution mass spectra
were recorded on a Bruker APEXII Fourier transform ion cyclotron
resonance (FTICR) MS instrument. Ultravioletevisible (UVevis)
spectra were recorded on a Shimadzu UV-2550 spectrometer.
Melting points were measured on an X-4 digital melting-point
apparatus (uncorrected). The infrared spectra were performed on
a Digilab FTS-3000 Fourier transform-infrared spectrophotometer.
The inorganic salts Ca(ClO4)2$6H2O, Mg(ClO4)2$6H2O,
Cd(ClO4)2$6H2O, Fe(ClO4)3$6H2O, Co(ClO4)2$6H2O, Ni(ClO4)2$6H2O,
Cu(ClO4)2$6H2O, Zn(ClO4)2$6H2O, Pb(ClO4)2$3H2O, AgClO4$H2O
and Cr(ClO4)3$6H2O were purchased from Alfa Aesar Chemical
Reagent Co. (Tianjin, China). All solvents and other reagents were of
analytical grade.
2.3. General procedure for 1H NMR
For 1H NMR titrations, two stock solutions were prepared in
DMSO-d6: one of them contained the host only and the second one
contained an appropriate concentration of guest. Aliquots of the
two solutions were mixed directly in NMR tubes.
2.4. Synthesis and characterization of sensors S1wS3
Benzoyl chloride (3 mmol), dry and powdered KSCN (4 mmol) and
PEG-400 (0.1 mL, as phase transfer catalyst) were added to dry
dichloromethane (15 mL). Then the reaction mixture was stirred at
room temperature for 2 h, and the inorganic salts were filtered out. The
filtrate was a solution of the corresponding benzoyl isothiocyanate,
which did not need separating. Then 2.8 mmol of phenylhydrazine was
added to the filtrate solution and stirred at room temperature for 3 h,
yielding the precipitate of S1. After evaporating the solvent in avacuum,
the precipitate was filtered, washed with 75% ethanol three times, and
recrystallized with ethanol to get white crystal of S1. The other
compounds S2 and S3 were prepared by similar procedures.
2.2. General procedure for UVevis spectroscopy
All the UVevis experiments were carried out in DMSO solution
on a Shimadzu UV-2550 spectrometer. Any changes in the UVevis
spectra of the synthesized compound were recorded on the addi-
tion of perchlorate metal salts while the ligand concentration was
kept constant in all experiments.
S1: yield: 80.5%; m.p. 138e140 ꢂC; 1H-NMR (DMSO-d6,
400 MHz)
d 12.61 (s, 2H, NH), 11.59 (s, 1H, NH), 7.99e7.97 (m, 2H,
0.9
ArH), 7.71e7.65 (m, 2H, ArH), 7.57e7.53 (m, 2H, ArH), 7.45e7.41 (m,
3+
2H, ArH), 7.30e7.26 (m, 2H, ArH); 13C NMR (DMSO-d6, 100 MHz)
Fe
0.8
d
179.18, 168.37, 138.02, 133.20, 132.18, 128.75, 128.69, 128.53,
2+
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
Cu
126.42, 124.37; IR (KBr, cmꢁ1) v: 3444 (mb, NeH), 3310 (m, NeH),
3235 (m, NeH), 1678 (s, C¼O), 1601 (s, C¼C), 1525 (s, C¼C), 1474
(s, C¼C), 1276 (s, C¼S); Anal. calcd. for C14H13N3OS: C, 61.97; H,
4.83; N, 15.49; Found: C, 61.85; H, 4.74; N, 15.58.
S3, S3+other cations,
2+
+
Ag
other cations are Ca
2+ 2+ 2+
,
S2: yield: 95.7%; m.p. 199e201 ꢂC; 1H-NMR (DMSO-d6,
Mg , Cd , Co
,
2+
2+
2+
3+
400 MHz)
d 12.02 (s, 2H, NH), 9.77 (s, 1H, NH), 8.15e8.12 (m, 1H,
Ni , Zn , Pb , and Cr
ArH), 7.95e7.92 (m, 2H, ArH), 7.72e7.69 (m, 2H, ArH), 8.15e8.12 (m,
2H, ArH), 6.98e6.94 (m, 2H, ArH); 13C NMR (DMSO-d6, 100 MHz)
2+
Hg
d
182.07, 167.02, 159.06, 138.56, 133.11, 132.07, 128.94, 126.42,
125.86, 111.14; IR (KBr, cmꢁ1) v: 3441 (mb, NeH), 3259 (m, NeH),
3065 (m, NeH), 1648 (s, C¼O), 1609 (s, C¼C), 1571 (s, C¼C), 1470
(s, C¼C), 1292 (s, C¼S); ESI-HRMS calcd. for [M þ H] þ: m/z
316.0630, Found: 317.0710; Anal. calcd. for C14H12N4O3S: C, 53.16;
H, 3.82; N, 17.71; Found: C, 53.37; H, 3.65; N, 17.59.
300
400
500
600
700
Wavelength/nm
S3: yield: 85.4%; m.p. 216e219 ꢂC; 1H-NMR (DMSO-d6, 400 MHz)
d
11.77 (s, 2H, NH), 10.65 (s, 1H, NH), 8.90 (s, 1H, ArH), 8.37 (d, 1H,
Fig. 2. UVeVis absorption spectra of S3 in the presence of 5 equiv. of various cations in
DMSO solution at room temperature.
J ¼ 7.2, ArH), 8.00 (d, 2H, J ¼ 8.0, ArH), 7.67 (t,1H, J ¼ 7.2, ArH), 7.55 (t,

Q. Lin et al. / Dyes and Pigments 96 (2013) 1e6
3
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
b
a
1.4
3+
Fe
1.2
S1, S1+Other cations
Other cations are: Ca
3+
Fe
2+
,
1.0
0.8
0.6
0.4
0.2
0.0
2+
Cu
2+ 2+
2+
2+
3+
Cr
2+
Mg , Cd , Co , Ni ,
Hg
+
Ag
2+
2+
3+
S2+other cations
Other cations are:
Zn , Pb , and Cr
S2
2+
Cu
2+
Ca
2+ 2+
2+
Cd , Ni , Mg ,
2+ 2+ 2+
Pb , Co , Zn
+
Ag
2+
Hg
250
250 300 350 400 450 500 550 600 650 700 750
300
350
400
450
500
550
600
Wavelength/nm
Wavelength/nm
Fig. 3. UVevis absorption of sensor (a) S2, (b) S1 (2.0 ꢀ 10ꢁ5 M) in the presence of 5 equiv. of various cations in DMSO solution at room temperature.
2H, J ¼ 7.6, ArH), 7.33 (d, 1H, J ¼ 9.6, ArH); 13C NMR (DMSO-d6,
therefore, in DMSO solution, S3 showed specific colorimetric
selectivity to Hg2þ
100 MHz)
d
181.35,167.07,162.32,147.00,137.25,133.18,132.01,129.99,
.
128.78, 128.50, 123.07, 116.17; IR (KBr, cmꢁ1) v: 3367 (m, NeH), 3265
(m, NeH), 3143 (m, NeH),1682 (s, C¼O),1618 (s, C¼C),1596 (s, C¼C),
1490 (s, C¼C), 1275 (s, C¼S); ESI-HRMS calcd. for [M þ H]þ: m/z
362.0481, Found: 362.0554; Anal. calcd. for C14H11N5O5S: C, 46.54; H,
3.07; N, 19.38; Found: C, 46.83; H, 3.28; N, 19.27.
The same tests were applied to S2 and S1. In this case, when
various cations were added to the DMSO solutions of S2 respec-
tively, it was not only Hg2þ that induced a large blue shift from
495 nm to 372 nm (corresponding to a distinct color change from
brown to colorless), but Fe3þ and Cr3þ caused similar spectra and
color changes also (Fig. 3(a)). So sensor S2 produced a colorimetric
response to Hg2þ, Fe3þ and Cr3þ in DMSO solutions, however,
owing to the color and UVevis spectra changes were very similar,
sensor S2 could not selectively recognize Hg2þ, Fe3þ and Cr3þ. In
addition, when various cations were added to the DMSO solutions
of S1 respectively, no obvious color or spectra changes were
observed (Fig. 3(b)). Which indicated that S1 couldn’t colorimetric
sense any cations under these conditions.
In order to investigate the mercury recognition abilities of S3 in
aqueous solution, we carried out the similar experiments in DMSO/
H2O (9:1/v:v) HEPES buffered solution at pH 7.40. When adding
5 equiv. of Hg2þ to the DMSO/H2O HEPES buffered solution of S3
(2.0 ꢀ 10ꢁ5 M), the sensor responded with dramatic color changes
from brown to colorless, meanwhile, in the corresponding UVevis
spectra, the absorption at 470 nm disappeared (Fig. 4). While other
cations couldn’t cause such distinct color and spectra changes,
therefore, the sensor S3 could colorimetric recognition Hg2þ in
DMSO/H2O binary solutions with specific selectivity.
3. Results and discussion
The colorimetric sensing abilities were primarily investigated by
adding various cations (Ca2þ, Mg2þ, Cd2þ, Fe3þ, Co2þ, Ni2þ, Cu2þ
,
Hg2þ, Zn2þ, Pb2þ, Agþ and Cr3þ) to the DMSO solutions of sensor S3.
When 5 equivalent (equiv.) of Hg2þ was added to the solution of S3
(2.0 ꢀ 10ꢁ5 M), the sensor responded with dramatic color changes
from brown to colorless (Fig. 1). In the corresponding UVevis
spectrum, the absorption at 470 nm disappeared (Fig. 2). When
adding 5 equiv. of Cu2þ, the DMSO solution of S3 showed color
changes from brown to green. Meanwhile, the addition of Agþ and
Fe3þ also lead to slight color and UVevis spectrum changes.
Whereas when adding the cations Ca2þ, Mg2þ, Cd2þ, Co2þ, Ni2þ
,
Zn2þ, Pb2þ, or Cr3þ into the DMSO solutions of sensor S3, no
significant color or spectra changes were observed. Even though
sensor S3 showed colorimetric response toward Cu2þ, Agþ and Fe3þ
in DMSO solutions, owing to only Hg2þ could bleaches the solution,
Simultaneously, the same tests were applied to S2 and S1 also.
As shown in Fig. S-1 in Supplementary data, the compound S2
could response a lot of cations such as Hg2þ, Cu2þ, Co2þ, Cr3þ and
Fe3þ in DMSO/H2O (9:1/v:v) HEPES buffered solution, however, S2
could not selectively recognize these cations. Similarly, S1 couldn’t
colorimetric response any cations in DMSO/H2O binary solutions as
well (Fig. S-2 in Supplementary data).
1.0
Host S3, other cations
2+
2+
2+
are Ca , Mg , Cd
3+
,
0.8
0.6
0.4
0.2
0.0
2+
2+
2+
Fe , Co , Ni , Cu
2+ 2+ 3+
,
Therefore, according to these results we can find that, on the one
hand, the nitrophenyl moiety acted as a signal group and played
a crucial role in the process of colorimetric recognition. Because the
S1 doesn’t employ nitrophenyl as signal group, it could not color-
imetric sense any cations. On the other hand, S2 and S3 employ 4-
nitrophenyl and 2,4-dinitrophenyl as signal groups respectively,
they all possess colorimetric response abilities for above mentioned
cations. However, due to the steric effects of ortho-nitro group on
S3, other cations except Hg2þ couldn’t coordinate with S3, thus the
sensor S3 showed specific selectivity toward Hg2þ. Owing to the
compound S2 does not contain ortho-nitro group, there are no
steric effects, many cations could coordinate with S2, hence the S2
could not show selectivity toward those cations.
Zn , Pb , and Cr
Hg2+
300 350 400 450 500 550 600 650 700 750
As S3 showed specific selectivity for Hg2þ, a series of experi-
ments was carried out to investigate the Hg2þ recognition capa-
bility and mechanism of S3. To gain an insight into the
stoichiometry of the S3-Hg2þ complex, the method of continuous
Wavelength/nm
Fig. 4. UVeVis absorption spectra of S3 (2.0 ꢀ 10ꢁ5 M) in the presence of 5 equiv. of
various cations in (9:1/v:v) DMSO/H2O HEPES buffered solution at pH 7.40, room
temperature.

4
Q. Lin et al. / Dyes and Pigments 96 (2013) 1e6
Fig. 5. (a) A Job plot of S3 and Hg2þ, which indicated that the stoichiometry of S3-Hg2þ complex was 1:1. (b) UVevis spectral titration of sensor S3 with Hg2þ in DMSO solution. The
non-linear fitting curve of the change in absorbance of S3 with respect to the amounts of Hg2þ is shown in the inset.
Fig. 6. The proposed reaction mechanism of the sensor S3 with Hg2þ
.
variations (Job’s method) was used (Fig. 5a). As expected, when the
molar fraction of sensor S3 was 0.50, the absorbance value
approached a maximum, which demonstrated the formation of
shift led to the solution color changing from brown to colorless. Two
clear isosbestic points were observed at 434 and 337 nm, which indi-
cated the formation of an S3-Hg2þ complex. By nonlinear least-squares
fitting [61] at lmax ¼ 469 nm, the association constant Ka of the sensor
a 1:1 complex between the sensor S3 and Hg2þ
.
The binding properties of sensor S3 with Hg2þ were further studied
by UVevis titration experiments (Fig. 5b). It turned out that in DMSO
solution of S3, with an increasing amount of Hg2þ, the absorbance at
470 nm decreased while a new band appeared at 398 nm. Such a blue
S3 toward Hg2þ was obtained as 6.04 ꢀ 104 Mꢁ1
.
To further elucidate the binding mode of the sensor S3 with
Hg2þ, 1H NMR-titration were carried out by gradually adding Hg2þ
into DMSO-d6 solution of S3. As shown in Fig. 6, before the addition
of Hg2þ, there were two intramolecular hydrogen bonds in the
molecular structure of S3: one was NeHb.O¼C, and the other was
NeHc.O¼N. The formation of these hydrogen bonds led to the 1H
NMR chemical shifts of NeHb and NeHc appearing at low-field.
Owing to the fact that NeHb.O¼C is a very strong intra-
molecular hydrogen bond, as shown in Fig. 7, the 1H NMR chemical
shift of NeHb appeared at the lowest field of the molecular S3 at
d
11.77 ppm, which overlapped the proton signal of NeHa. The 1H
NMR chemical shift of NeHc appeared at
10.65 ppm. After the
d
addition of 0.2 equivalent of Hg2þ, an intergradation was formed
between S3 and Hg2þ(Fig. 6), which caused the 1H NMR chemical
shifts of the NeHa, NeHb and NeHc to appear as two very broad
peaks. For the same reason, the proton signals of NeHe and NeHf
shifted downfield and broadened (Fig. 7). With the continuous
addition of Hg2þ, as shown in Fig. 6 the molecular structure
underwent an intramolecular rotation, which induced the breaking
of NeHb.O¼C and NeHc.O¼N; simultaneously, the interactions
between the Hg2þ.HeeC and Hg2þ.HfeC were interrupted also.
Fig. 7. Partial 1H NMR of sensor S3 (2.5 mM) in DMSO-d6 upon the addition of Hg2þ
(a) S3 alone, then after adding (b) 0.1, (c) 0.2, (d) 0.5, (e) 0.7, (f) 0.9 and (g) 1 equiv. of
Hg2þ
:
.

Q. Lin et al. / Dyes and Pigments 96 (2013) 1e6
5
Fig. 8. (a) UVeVis absorption spectra, (b) photographs and UVeVis absorption at 470 nm of sensor S3 (2.0 ꢀ 10ꢁ5 M) in DMSO solutions in the presence of Hg2þ (5 equiv.) and the
miscellaneous cations Ca2þ, Mg2þ, Cd2þ, Fe3þ, Co2þ, Ni2þ, Cu2þ, Zn2þ, Pb2þ, Agþ and Cr3þ (5 equiv., respectively).
An important feature of the sensor is its high selectivity toward
the analyte over other competitive species. The variations of
UVevis spectral and visual color changes of sensor S3 in DMSO
solutions caused by the metal ions Ca2þ, Mg2þ, Cd2þ, Fe3þ, Co2þ
,
Ni2þ, Cu2þ, Zn2þ, Pb2þ, Agþ and Cr3þ were recorded in Fig. 8. It is
noticeable that the miscellaneous competitive metal ions did not
lead to any significant interference. In the presence of these ions,
the Hg2þ still produced similar color (Fig. 8(b)) and absorption
changes (Fig. 8(a): the absorption at 470 nm disappeared). These
results shown that the selectivity of sensor S3 toward Hg2þ was not
affected by the presence of other cations and suggested that it could
be used as a colorimetric chemosensor for Hg2þ
.
The colorimetric and UVevis limits of sensor S3 for Hg2þ cation
were also tested and are presented in Fig. 9. The detection limit using
visual color changes was a concentration of 5.0 ꢀ10ꢁ6 Mof Hg2þ cation
in 1.0 ꢀ 10ꢁ6 M solution of sensor S3, while the detection limit of the
UVevis changes calculated on the basis of 3sB/S [62] is 1.0 ꢀ 10ꢁ7 M for
Hg2þ cation, which pointing to the high detection sensitivity.
Fig. 9. Color changes observed upon the addition of 5 equiv. of Hg2þ to the solutions of
sensor S3 (from right to left, 1 ꢀ 10ꢁ4 M, 1 ꢀ 10ꢁ5 M, 1 ꢀ 10ꢁ6 M) in DMSO solutions.
As a result, the stable Hg2þ-S3 1: 1 complex was formed via the
coordination of Hg2þ with S¼C and O¼C groups on S3. The breaking
of the hydrogen bonds led to an obvious up field shift of NeHb and
NeHc(Fig. 7def). On the other hand, owing to the interactions
between the Hg2þ.HeeC and Hg2þ.HfeC were broken, the
signals of NeHe and NeHf returned to their original positions
(Fig. 7def). Namely, before all the 1 equiv. of Hg2þ was added, the
intergradations and the stable Hg2þ-S3 complex coexisted in the
solution. Therefore, every proton signal of NeHa, NeHb, NeHc,
CeHe and CeHf displayed two signals, for the intergradations
state and the stable Hg2þ-S3 complex state respectively (Fig. 7def).
After 1 equiv. of Hg2þ had been added, the intergradations
completely changed into stable Hg2þ-S3 complex. Accordingly, in
the whole titration process, the signals of NeHc, NeHb and NeHa
4. Conclusion
An easy-to-make Hg2þ colorimetric sensor S3, bearing thiourea
moiety as the binding site and nitrophenyl moiety as the signal group,
was designed and synthesized. This sensor showed specific selectivity
for Hg2þ in DMSO and DMSO/H2O binary solutions. Comparison with
sensor S1 indicated that the nitrophenyl moiety acted as a signal group
and played a crucial role in the process of colorimetric recognition.
Investigation of the recognition mechanism indicated that the sensor
S3 recognized Hg2þ by forming a stable 1:1 S3-Hg2þ complex. The
coexistence of other cations did not interfere with the Hg2þ recognition
process. Moreover, the detection limitof the sensor S3 toward Hg2þ was
1.0 ꢀ 10ꢁ7 M, which indicated that the sensor S3 may be useful as
a colorimetric sensor for monitoring Hg2þ levels in physiological and
environmental systems.
shifted to
d 11.22, 10.49 and 10.24 ppm, respectively, and the
proton signals of CeHe and CeHf were back to their original posi-
tions (Fig. 7g). In summary, according to the 1H NMR-titration
experiments, the Hg2þ ions and S3 formed a stable 1: 1 complex
by the coordination of Hg2þ with S¼C and O¼C groups on S3.
The recognition mechanism of the sensor S3 with Hg2þ were
investigated by IRspectra(Fig. S-3inSupplementary data)also.IntheIR
spectra of S3, the stretching vibration absorptionpeaks of C¼OandC¼S
appeared at 1682 and 1275 cmꢁ1 respectively. However, when S3
coordinated with Hg2þ (1:1, solid complex, KBr), an electron transfer
effect occurred from C¼S and C¼O to Hg2þ, which induced the
stretching vibration absorption peaks of C¼O and C¼S shifted to 1643
and 1262 cmꢁ1 accordingly. At the same time, owing to the influence of
above mentioned electron transfer effect and the rupture of intra-
molecular hydrogen bonds NeHb.O¼C and NeHc.O¼N, stretching
vibration absorption peaks of NeHb and NeHc shifted from 3265 and
3143 to 3225 and 3100 cmꢁ1 respectively. Which confirmed that S3
coordinated with Hg2þ by C¼O and C¼S groups as shown in Fig. 6.
Acknowledgment
This work was supported by the National Natural Science
Foundation of China (NSFC) (Nos. 21064006 and 21161018), the
Natural Science Foundation of Gansu Province (1010RJZA018) and
the Program for Changjian Scholars and innovative Research Team
in University of Ministry of Education of China (IRT1177).
Appendix A. Supplementary data
Supplementary data related to this article can be found online at
http://dx.doi.org/10.1016/j.dyepig.2012.06.023.

6
Q. Lin et al. / Dyes and Pigments 96 (2013) 1e6
[35] Aksuner N, Basaran B, Henden E, Yilmaz I, Cukurovali A. A sensitive and
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