A novel 5-mercapto triazole Schiff base as a selective chromogenic chemosensor for Cu2+

Article abstract of DOI:10.1016/j.saa.2011.05.068

A novel colorimetric cation sensor bearing phenol, thiol and HCN groups was designed and synthesized. In a DMSO/H₂O (9:1, v/v) solution, the sensor exhibited highly selective recognition of Cu²⁺ among a range of metal ions tested. In the presence of Cu²⁺, solutions of the sensor underwent a dramatic color change from colorless to yellow, while the presence of other metal cations such as Zn²⁺, Pb²⁺, Cd²⁺, Ni²⁺, Co²⁺, Fe³⁺, Hg ²⁺, Ag⁺ and Ca²⁺ had no effect on the color. The detection limit of the sensor toward Cu²⁺ is 8.0 × 10 ^-7 M and an association constant K_a of 4.3 × 10 ⁵ M^-1 was measured. The sensing of Cu²⁺ by this sensor was found to be reversible, with the Cu²⁺-induced color being lost upon addition of EDTA.

Full text of DOI:10.1016/j.saa.2011.05.068

Spectrochimica Acta Part A 79 (2011) 1837–1842
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
A novel 5-mercapto triazole Schiff base as a selective chromogenic chemosensor
for Cu2+
Ming-Xia Liu, Tai-Bao Wei, Qi Lin, 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
Article history:
A novel colorimetric cation sensor bearing phenol, thiol and HC N groups was designed and synthesized.
In a DMSO/H2O (9:1, v/v) solution, the sensor exhibited highly selective recognition of Cu2+ among a range
of metal ions tested. In the presence of Cu2+, solutions of the sensor underwent a dramatic color change
Received 20 February 2011
Received in revised form 18 May 2011
Accepted 24 May 2011
from colorless to yellow, while the presence of other metal cations such as Zn2+, Pb2+, Cd2+, Ni2+, Co2+, Fe3+
,
Hg2+, Ag+ and Ca2+ had no effect on the color. The detection limit of the sensor toward Cu2+ is 8.0 × 10−7
M
Keywords:
Copper ion
Colorimetric sensor
Schiff base
and an association constant Ka of 4.3 × 105 M−1 was measured. The sensing of Cu2+ by this sensor was
found to be reversible, with the Cu2+-induced color being lost upon addition of EDTA.
© 2011 Elsevier B.V. All rights reserved.
Cation recognition
1. Introduction
soft heteroatoms, such as nitrogen and sulfur, as electron donors to
coordinate with the metal cation [17–21]. However, to date, only
The development of highly selective and sensitive chromogenic
chemosensors for the sensing of heavy and transition metal (HTM)
ions is a very active research field [1,2] in supramolecular chem-
istry. In particular, Cu2+-sensitive systems have attracted much
interest, as the copper ion (II) is a significant environmental pol-
lutant and also plays a critical role in various biological processes
[3,4]. While copper ions (II) are an essential biological trace ele-
ment, they are toxic to organisms when present in high levels.
Excess levels of copper ion (II) in the human body can cause kidney
damage, gastrointestinal problems and Wilsons’s disease [5], and
are associated with brain diseases such as Parkinson’s, Alzheimer’s
and prion diseases, when present even in trace amounts [6,7]. Thus,
the rational design and synthesis of efficient sensors to selectively
recognize Cu2+ analytes is a fundamental goal for supramolecular
chemistry.
very few examples of colorimetric probes using phenols and thiols
as the copper ion binding site have been reported. While phenols
commonly play an important role in the cation binding sites of bio-
logical systems [22], very little investigation has been carried out
to develop copper (II) sensors bearing phenol groups [23–25].
Our research group has a longstanding interest in molecular
recognition [26–28]. Here, we report the synthesis, characteriza-
tion and cation coordination properties of colormetric sensors 1
and 2 which bear phenol and thiol groups (Scheme 1). Only sensor
1 showed colorimetric selectivity for Cu2+ in DMSO/H2O (9:1, v/v)
solution. The strategy employed in the design of these sensors is
as follows. Firstly, we introduced thiol and phenol groups into the
same sensor molecule, to allow the coordination capacity required
to coordinate a copper ion. Secondly, to achieve “naked-eye” recog-
nition upon binding of Cu2+, we introduced nitrophenyl groups as
a chromophore. Thirdly, a Schiff base structure was used to signifi-
cantly enhance intramolecular charge transfer (ICT) [29,30]. Finally,
these sensors were designed with ease of synthesis in mind. In
order to clarify the phenol group’s contribution to the Cu2+ binding
ability of sensor 1, an analogous compound (2) which lacked a phe-
nol group was also synthesized. Compound 1 was found to exhibit
Cu2+-selective and sensitive chromogenic signaling behavior over
other common physiologically important metal ions. The associa-
tion constant Ka measured for coordination of sensor 1 with Cu2+
was 4.3 × 105 M−1, and the detection limit of the sensor 1 toward
Cu2+ was 8.0 × 10−7 M.
Accordingly, a variety of sensing devices, involving Schiff bases
[6,8,9], polythiacrown ethers [10–12], calix[n]arenes [13,14] and
tripodal derivatives [15,16] have been employed for the selective
detection of Cu2+. In general, such neutral copper ion sensors use
∗
Corresponding author at: 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. Tel.: +8609317973191.
E-mail address: zhangnwnu@126.com (Y.-M. Zhang).
1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2011.05.068

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M.-X. Liu et al. / Spectrochimica Acta Part A 79 (2011) 1837–1842
H2SO4
CH3OH
O
3
COOH
COOCH3
NH2
SH
NH2NH2 H2O
N
H
R
R
R
R
F
N N
N
O
CS2, ClCH2COONa
C2H5OH
H
N
NH2NH2
H2O
SCH2COONa
N
H
NH2
R
S
4
N N
SH
OH
EtOH
reflux
OH
N
N
CH
N N
CHO
SH
N
NH2
F
1
N N
N N
CHO
SH
EtOH
reflux
SH
N
N
CH
N
F
NH2
F
NO2
NO2
2
Scheme 1. Synthetic procedures for sensors 1 and 2.
2. Experimental
the residue was purified by recrystallization from hot anhydrous
ethanol to get 1 and 2.
2.1. Materials and physical methods
2.3.
1H NMR spectra were recorded on a Mercury-400BB spectrom-
eter at 400 MHz. 1H chemical shifts are reported in ppm downfield
from tetramethylsilane (TMS, ı scale with solvent resonances as
internal standards) UV–vis spectra were recorded on a Shimadzu
UV-2550 spectrometer. Melting points were measured on an X-
4 digital melting-point apparatus (uncorrected). Infrared spectra
were performed on a Digilab FTS-3000 FT-IR spectrophotometer.
All reagents used were of analytical grade.
2-((3-(4-Fluorophenyl)-5-mercapto-4H-1,2,4-triazol-4-ylimino)
methyl) phenol 1
Yield 69%, m.p. 228–230 ◦C, 1H NMR (DMSO-d6, 400 MHz) ı
12.13 (s 1H, OH), ı 11.25 (s 1H, SH), 8.64 (s 1H, CH). 6.93–7.58
(m 8H, ArH). IR (KBr, cm−1) v: 1522.27 (C C), 1654.17 (CH N),
1284.57 (C–N), 2864.36 (S–H), 3213.40 (O–H) cm−1. Anal. Calcd.
For C15H11FN4OS: C 57.31, H 3.53, N 17.82; Found C, 57.34; H, 3.55;
N, 17.88.
2.2. Synthesis of sensors 1 and 2
2.4. 4-(4-Nitrobenzylideneamino)-5-(4-fluorophenyl)-4H-1,2,4-
triazole-3-thiol
2
The synthesis of chemosensors 1 and 2 is outlined in Scheme 1.
The compound 3 (4-fluorobenzohydrazide) was synthesized via
four steps, starting from 4-fluorobenzoic acid, according to lit-
erature procedures [31]. Compound 3 (0.01 mol), distilled water
(2 mL), ethanol (2 mL) and concentrated ammonia were mixed at
0 ◦C, the solution was then stirred for 3 h at room temperature with
dropwise addition of carbon disulfide (1.2 mL). An ethanol solution
(2 mL) of sodium chloroacetate (1.2 g) and hydrazine hydrate (1 mL)
was added to the above solution and the mixture was refluxed for
2 h at 90 ◦C. The organic solvent was removed to give 4. Finally, com-
pound 4 and an equivalent of the appropriate benzaldehyde were
mixed in absolute ethanol. The solution was stirred under refluxing
conditions for 6 h at 80 ◦C. After cooling, and removing the solvent,
Yield 90%, m.p. 280–282 ◦C, 1H NMR (DMSO-d6, 400 MHz) ı
12.20 (s 1H, SH), ı 8.54 (s 1H, CH). 8.31–7.38 (m 8H, ArH). 1522.27
(C C), 1654.73 (CH N), 1287.37 (C–N), 2446.31 (S–H) cm−1. Anal.
Calcd. For C15H10FN5O2S: C 52.47, H 2.94, N 20.40; Found C, 52.41;
H, 2.89; N, 20.47.
2.5. General procedure for UV–vis experiments
All UV–vis spectroscopy was carried out just after the addition
of perchlorate metal salts in DMSO or a DMSO/H2O binary solution,

M.-X. Liu et al. / Spectrochimica Acta Part A 79 (2011) 1837–1842
1839
Fig. 1. (a) Solutions of sensor 1 upon addition of Cu2+. (b) Absorption changes of sensor 1 (c = 4.0 × 10−5 M) in DMSO upon addition of 1 equiv. of different perchlorate salts
(4.0 × 10−5 M). (c) Absorption changes of sensor 1 in DMSO upon addition of 1 equiv. of Cu2+
.
while keeping the ligand concentration constant (4.0 × 10−5 M) on
3. Results and discussion
a Shimadzu UV-2550 spectrometer. The solution of metal ions was
prepared from the perchlorate salts of Zn2+, Pb2+, Cd2+, Ni2+, Co2+
,
The recognition profiles of both 1 and 2 toward various metal
cations, Zn2+, Pb2+, Cd2+, Ni2+, Co2+, Fe3+, Hg2+, Ag+, Ca2+ and Cu2+
,
Fe3+, Hg2+, Ag+, Ca2+ and Cu2+
.
were primarily investigated by UV–vis spectroscopy in DMSO solu-
tions. When 1 equiv. of Cu2+ was added to the DMSO solutions of
sensors 1 and 2, only sensor 1 responded with a dramatic color
change, from colorless to yellow (Fig. 1a). In the corresponding
UV–vis spectrum, a strong and broad absorption band from 390
to 407 nm was observed for sensor 1 (Fig. 1). To validate the selec-
2.6. General procedure for 1H NMR experiments
For 1H NMR titrations, two stock solutions were prepared in
DMSO-d6, one containing the sensor only and the second contain-
ing an appropriate concentration of the metal. Aliquots of the two
solutions were mixed directly in NMR tubes.
tivity of sensor 1, the same tests were applied using Zn2+, Pb2+
,
Cd2+, Ni2+, Co2+, Fe3+, Hg2+, Ag+ and Ca2+ metal ions, and none of
these ions induced any significant changes in the UV–vis spectrum
1.0
0.9
0.8
0.7
0.6
0.5
3+
Fe
0.4
Host
0.3
0.2
0.1
0.0
2+
Cu
2+
Ni
2+
Hg
250
300
350
400
450
500
Wavelength/nm
Fig. 2. Absorption changes of sensor 2 (c = 4.0 × 10−5 M) in DMSO upon addition of
1 equiv. of different perchlorate salts (4.0 × 10−5 M).
Fig. 3. UV–vis absorption of sensor 1 (c = 4.0 × 10−5 M) in the presence of 1 equiv. of
various cations in H2O/DMSO (1:9, v/v) binary solution at room temperature.

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M.-X. Liu et al. / Spectrochimica Acta Part A 79 (2011) 1837–1842
0.85
of the sensor. Meanwhile, the absorbance changes of sensor 2 with
different metal ions are also shown in Fig. 2. No obvious changes
were observed in the UV–vis spectrum upon addition of any metal,
indicating that 2 is not a sensor for these metals.
0.80
0.75
0.70
0.65
0.60
To establish sensor 1’s utility in practice, the response of the
sensor toward various metal cations was investigated by UV–vis
spectroscopy in DMSO/H2O binary solutions. This showed that 1 is
a remarkably selective and sensitive sensor for Cu2+. As shown in
Fig. 3, in DMSO/H2O (9:1, v/v) solution, sensor 1 showed an obvious
color change from colorless to yellow upon addition of 1 equiv. of
Cu2+, accompanied by the appearance of a peak at 379–405 nm in
the UV–vis spectrum. On the other hand, a variety of other cations,
such as Zn2+, Pb2+, Cd2+, Ni2+, Co2+, Fe3+, Hg2+, Ag+ and Ca2+, did
not induce any significant change, indicating that sensor 1 is highly
selective for Cu2+. This is attributable to the strong binding capacity
of thiol and phenol groups toward Cu2+. Accordingly, sensor 1 still
showed high selectivity and sensitivity toward Cu2+ in DMSO/H2O
(9:1, v/v) solution.
1
2
3
4
5
6
7
8
9
10
PH
Fig. 4. The effect of the PH for sensor 1 in DMSO/H2O (9:1, v/v) (c = 4.0 × 10−5 M)
(10 mM NaH2PO4–Na2HPO4) toward 1–Cu2+
.
The formation of a complex between a ligand and a metal ion
is often pH-dependent, so the loading solution pH was optimized.
Change in the absorption of the 1–Cu2+ complex were studied in
the pH range of 2.21–9.16 by adjusting the pH using concentrated
NaH2PO4–Na2HPO4 aqueous buffering solutions. As shown in Fig. 4,
at low pH (<5.24), absorbance was lower than at high pH, indicating
that the protonated ionic group coordinates Cu2+ less effectively
in acidic solutions. In the pH range of 6.21–8.97, the absorbance
was significantly higher, as the non-protonated ionic group more
readily forms a complex with Cu2+
.
To further exploit the utility of sensor 1 as ion-selective sensor
for Cu2+, competitive experiments were carried out in the pres-
ence of 1.0 equiv. of Cu2+ and 1.0 equiv. of various metal ions in the
DMSO/H2O (9:1, v/v). As shown in Fig. 5, the optical absorbance
of the 1–Cu2+ complex at 398 nm was largely uninfluenced by the
addition of other cations, such as Zn2+, Pb2+, Cd2+, Ni2+, Co2+, Fe3+
,
Hg2+, Ag+ and Ca2+. This represents a significant advantage for this
sensor over other reported sensors of Cu2+, which generally lack
selectivity for Cu2+ over Hg2+ or Zn2+ [32–34].
Fig. 5. Optical absorbance of sensor 1 (4.0 × 10−5 M) in (9:1, v/v) DMSO/H2O solution
in the presence of Cu2+ (4.0 × 10−5 M) and miscellaneous cations including Zn2+, Pb2+
,
Cd2+, Ni2+, Co2+, Fe3+, Hg2+, Ag+ and Ca2+ (1 equiv., respectively, at 398 nm).
0.8
0.07
(b)
(a)
0.06
0.05
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
0.04
obs
calc
0.03
R=0.999
0.02
0.01
0.0002 0.0004 0.0006 0.0008 0.0010 0.0012 0.0014
[Cu2+]/[1]
260
280
300
320
340
360
380
400
420
440
460
480
500
Wavelength/nm
Fig. 6. (a) UV–vis titration of sensor 1 (c = 2.0 × 10−5 M) with Cu2+ (0–0.4 equiv.) in DMSO solution. (b) The nonlinear fitting curve of change in absorbance of sensor 1 at
354 nm with respect to amounts of Cu2+ in DMSO/H2O (9:1, v/v) solution.

M.-X. Liu et al. / Spectrochimica Acta Part A 79 (2011) 1837–1842
1841
0.6
0.5
0.4
0.3
0.2
0.1
0.0
protons, with the peaks shifted to ı 12.18, 11.75 and 9.87 ppm,
respectively. With the further addition of Cu2+ up to 1.0 equiv., the
peak of the thiol almost completely disappeared, and the peak of
the phenol shifted downfield and broadened. These results sug-
1-Cu2+
0.1
0.2
0.3
0.4
0.5
0.6
0.7
gested a possible interaction mode between the sensor 1 and Cu2+
,
in which Cu2+ coordinates with the sulfur of the thiol group and
the oxygen of the phenol group. Therefore, the color change was
observed for the sensor 1 in the presence of Cu2+ from colorless to
yellow and accounted for the appearance of the new absorbance
band at 398 nm, which were due to the coordination of Cu2+
.
0.8
0.9
1.0
4. Conclusion
In conclusion, a novel colorimetric chemosensor 1 was designed
and synthesized by coupling compound 4 with an equivalent of
an aldehyde, to form a Schiff base structure which has enhanced
intramolecular charge transfer. The sensor showed colorimetric,
selective recognition for Cu2+ in DMSO/H2O (9:1, v/v) solutions and
formed a stable complex with Cu2+. The excellent selectivity and
strong affinity for Cu2+ is due to the coordination of Cu2+ to the
sensor via the thiol and phenol groups. In addition, the detection
limit of the sensor 1 toward Cu2+ is 8.0 × 10−7 M which indicates
that this sensor could potentially be useful as a probe for moni-
toring Cu2+ levels in physiological and environmental systems. In
addition, the sensor also displayed a Cu2+-induced off-on-off type
of signaling pattern, which means the sensor could be used as a
supramolecular switching system.
250
300
350
400
450
500
Wavelength/nm
Fig. 7. (a) UV–vis spectra of sensor 1 Cu2+ (c = 2.0 × 10−5 M) in DMSO/H2O (9:1, v/v)
solution upon addition of EDTA (0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 and 1.0 equiv.).
To further investigate the interaction between sensor
and Cu2+
UV–vis absorption spectral variation of sensor
1
1
,
(c = 2.0 × 10−5 M) in DMSO/H2O (9:1, v/v) solution was monitored
during titration with different concentrations of Cu2+ from 0 to
8.1 × 10−5 M. As shown in Fig. 6, an isosbestic point at 354 nm is
clearly observed with increasing concentrations of Cu2+, indicat-
ing that sensor 1 reacts with Cu2+ to form a stable complex. The
association constant, Ka, of sensor 1 toward Cu2+ was calculated
as 4.3 × 105 M−1 (R = 0.999). Taken together, these results illustrate
that sensor 1 is a Cu2+-specific chemosensor. Furthermore, with the
probe concentrations employed in our studies, interactions of sen-
sor 1 with Cu2+ could be detected down to at least concentrations
of 8.0 × 10−7 M in DMSO/H2O (9:1, v/v), showing that this sensor
could potentially be used as a probe for monitoring Cu2+ levels in
physiological and environmental systems.
Acknowledgments
This work was supported by the NSFC (No. 21064006) and the
Natural Science Foundation of Gansu (1010RJZA018).
References
[1] V. Amendola, L. Fabbrizzi, F. Foti, M. Licchelli, A. Poggi, D. Sacchi, A. Taglietti,
Coord. Chem. Rev. 250 (2006) 273–299.
[2] A.P. de Silva, H.Q.N. Gunaratne, T. Gunnlaugsson, Chem. Rev. 97 (1997)
1515–1566.
[3] E.L. Que, D.W. Domaille, C.J. Chang, Chem. Rev. 108 (2008) 1517–1548.
[4] E. Pontiki, D. Hadjipavlou-Litina, A.T. Chaviara, C.A. Bolos, Bioorg. Med. Chem.
Lett. 16 (2006) 2234–2237.
[5] M. Schaefer, J.D. Gitlin, Am. J. Physiol. Gastrointest. Liver Physiol. 276 (1999)
311–314.
[6] R.-L. Sheng, P.-F. Wang, Y.-H. Gao, Y. Wu, W.-M. Liu, Org. Lett. 10 (2008)
5015–5018.
[7] E. Gaggelli, H. Kozlowski, D. Valensin, G. Valensin, Chem. Rev. 106 (2006)
1995–1999.
[8] A.K. Jain, R.K. Singh, S. Jain, J. Raisoni, Trans. Met. Chem. 33 (2008) 243–249.
[9] N. Singh, N. Kaur, J.F. Callan, Tetrahedron Lett. 51 (2010) 3385–3387.
[10] Y.C. Hsieh, J.L. Chir, H.-H. Wu, C.-Q. Guo, Tetrahedron Lett. 51 (2010) 109–111.
[11] S. Wakida, N. Sato, K. Saito, Sens. Actuators B 130 (2008) 187–192.
[12] S. Goswami, R. Chakrabarty, Tetrahedron Lett. 50 (2009) 5910–5913.
[13] G. Goretaki, P.V. Bonnesen, R. Dabestani, G.M. Brown, ACS Symp. Ser. 943 (2006)
12–33.
The reversibility of the chemosensor function was tested by
titration of the copper-sensor complex with EDTA, which is a
well-known chelator of Cu2+. Addition of EDTA into a solution of
the 1–Cu2+ complex induced the opposite trend in the absorption
spectra to that observed on titration with Cu2+. Upon addition of
1.0 equiv. of EDTA, the optical absorbance intensity returned to
the levels observed for the free compound 1 (Fig. 7). This shows
that the process of titrating sensor 1 with Cu2+ is reversible, and
that compound 1 could therefore be used as an off-on-off switch
chemosensor.
To further elucidate the binding mode of sensor 1 with Cu2+ 1H
,
NMR-titration spectra were measured, which illustrated the char-
acteristic structural changes occurring upon interaction with Cu2+
in DMSO-d6 solution. As shown in Fig. 8, before the addition of the
Cu2+, the 1H NMR chemical shifts of the phenol, thiol and HC N pro-
tons of sensor 1 were at ı 12.14, 11.25 and 8.84 ppm, respectively.
After the addition of 0.2 equiv. of Cu2+, significant downfield shifts
[14] A. Senthilvelan, I.T. Ho, K.-C. Chang, G.H. Lee, Y.-H. Liu, Chem. Eur. J. 15 (2009)
6152–6160.
[15] S.K. Mittal, A. Kumar, N. Gupta, S. Kaur, S. Kumar, Anal. Chim. Acta 585 (2007)
161–170.
[16] E.A. Ambundo, M.V. Deydier, L.A. Ochrymowycz, D.B. Rorabacher, Inorg. Chem.
39 (2000) 1171–1179.
were observed for the thiol proton. After adding 0.5 equiv. of Cu2+
three weak, broad signals appeared for the phenol, thiol and HC
,
N
[17] R. Martinez, A. Espinosa, A. Tarraga, P. Molina, Org. Lett. 7 (2005) 5869–5872.
[18] Z.-T. Jiang, R.-R. Deng, L. Tang, Sens. Actuators B 135 (2008) 128–132.
[19] Y.-Q. Weng, F. Yue, Y.-R. Zhong, B.-H. Ye, Inorg. Chem. 46 (2007) 7749–7755.
[20] I.S. Cho, H. Han, J.H. Shim, J.S. Lee, J.H. Shin, G.S. Cha, B.H. Kim, Tetrahedron Lett.
51 (2010) 2835–2839.
[21] S. Goswami, D. Sen, N.K. Das, Org. Lett. 12 (2010) 856–859.
[22] M.V. Selma, J.C. Espn, F.A. Tom, J. Agric. Food Chem. 57 (2009) 6485–6501.
[23] K.R. Krishnapriya, D. Saravanakumar, P. Arunkumar, M. Kandaswamy, Spec-
trochim. Acta A 69 (2008) 1077–1081.
[24] A. Helal, S.H. Lee, S.H. Kim, H.S. Kim, Tetrahedron Lett. 51 (2010) 3531–3535.
[25] L. Wang, W.W. Qin, X.L. Tang, W.S. Liu, J. Phys. Chem. A 115 (2011) 1609–1611.
[26] Y.-M. Zhang, Q. Lin, T.-B. Wei, D.-D. Wang, H. Yao, Y.-L. Wang, Sens. Actuators
B 137 (2009) 447–455.
Fig. 8. Cu2+ 1H NMR titration of sensor 1 (10.0 mM) in DMSO-d6: (a) 1 only, (b)
1 + 0.2 equiv. of Cu2+, (c) 1 + 0.5 equiv. of Cu2+ and (d) 1 + 1.0 equiv. of Cu2+
[27] Y.-M. Zhang, J.-D. Qin, Q. Lin, T.-B. Wei, J. Fluorine Chem. 127 (2006) 1222–1227.
.

1842
M.-X. Liu et al. / Spectrochimica Acta Part A 79 (2011) 1837–1842
[28] Y.-M. Zhang, Q. Lin, T.-B. Wei, X.-P. Qin, Y. Li, Chem. Commun. (2009)
6074–6076.
Ming-Xia Liu is a postgraduate at Northwest Normal University. Her major is inor-
ganic chemistry.
[29] S. Goswami, D. Sen, N.K. Das, G. Hazra, Tetrahedron Lett. 51 (2010) 5563–5566.
[30] J.S. Wu, I.C. Hwang, K.S. Kim, J.S. Kim, Org. Lett. 9 (2007) 907–910.
[31] J.R. Reid, N.D. Heindel, J. Heterocycl. Chem. 13 (1976) 925–926.
[32] Z.-T. Jiang, R.-R. Deng, L. Tang, P. Lu, Sens. Actuators B 135 (2008) 128–132.
[33] S.H. Kim, J.S. Kim, S.M. Park, S.-K. Chang, Org. Lett. 8 (2006) 371–374.
[34] D.Y. Lee, N. Singh, M.J. Kim, Tetrahedron Lett. 66 (2010) 7965–7969.
Qi Lin graduated from Northwest Normal University as a Master in 2005. He received
his PhD from Northwest Normal University in 2009. His main research fields are
chemical and biological sensors, molecular recognition and synthetic chemistry.
Tai-Bao Wei received his master’s degree from Lanzhou Institute of Chemical
Physics, Chinese Academy of Sciences in 1991. In the same year, he joined the Depart-
ment of Chemistry at Northwest Normal University. He became professor in 2000.
His research interests include synthetic chemistry and supramolecular chemistry.
You-Ming Zhang received his master’s degree from the Qinhai Institute of Salt Lakes,
Chinese Academy of Sciences in 1988. In the same year, he joined the Department
of Chemistry at Northwest Normal University. He became a professor in 1999. His
research interests include supramolecular chemistry and Coordination Chemistry.