A highly selective and colorimetric naked-eye chemosensor for Cu2+

Article abstract of DOI:10.1016/j.saa.2008.03.021

A sample and practical colorimetric naked-eye chemosensor 3-nitro-4-ethylenediamido-nitrobenzene (2) for metal cations was designed and synthesized. It displays high selectivity and sensitivity for Cu²⁺ by the UV absorption which appeared a new peak at 525 nm and color change from yellow to red by naked-eye in CH₃OH/H₂O pH 7.6.

Full text of DOI:10.1016/j.saa.2008.03.021

Spectrochimica Acta Part A 71 (2008) 1224–1227
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
A highly selective and colorimetric naked-eye chemosensor for Cu2+
Zhijun Wanga, Xiaojun Fanb, Donghong Lic, Liheng Fengc,∗
a Department of Chemistry, Changzhi University,
Changzhi 046011, PR China
b Key Laboratory of Chemical Biology and Molecular Engineering of
Ministry of Education, Institute of Biotechnology,
Shanxi University, Taiyuan 030006, PR China
c School of Chemistry and Chemical Engineering,
Shanxi University, Taiyuan 030006, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 11 January 2008
Accepted 19 March 2008
A sample and practical colorimetric naked-eye chemosensor 3-nitro-4-ethylenediamido-nitrobenzene (2)
for metal cations was designed and synthesized. It displays high selectivity and sensitivity for Cu2+ by the
UV absorption which appeared a new peak at 525 nm and color change from yellow to red by naked-eye
in CH3OH/H2O pH 7.6.
Keywords:
Chemosensor
© 2008 Elsevier B.V. All rights reserved.
Colorimetric naked-eye
Copper ion (Cu2+
Selectivity
)
To detect Cu2+, some receptors indicating remarkable colori-
metric [12], electrochemical [13] and fluorescent responses [14]
1. Introduction
have been generally investigated. Since Cu2+ is well known to be
quenched effectively by fluorescence [15], most of fluorescent sen-
sors for Cu2+ were designed by fluorescence quenching strategy
[16]. Only a few sensors in which the binding of Cu2+ caused an
increase in the fluorescence emission have been reported [17]. Sen-
sors with ratiometric fluorescence measurements have scarcely
been reported [18]. As a result, the design and synthesis of col-
orimetric chemosensors for Cu2+ has become a very active area
of research owing to the demand for more sensitive and selective
chemosensors for visible to the naked-eye.
It is well known that during the derivatives of aminobenzene
simple ethylenediamine receptors were chosen as the electron
donors and nitro moiety as the electron acceptor. Therefore,
we designed and synthesized four derivatives of aminobenzene
(Scheme 1), The recognition behavior of 1, 2, 3 and 4 with several
metal cations (Na+, K+, Al3+, Mg2+, Ca2+, Co2+, Ni2+, Fe2+, Fe3+, Ag+,
Cu2+, Zn2+, Cd2+, Hg2+, Pb2+) in CH3OH and H2O (v:v = 2:1) pH 7.6
(0.1 M HEPES), was investigated by UV–vis measurements, respec-
tively. 2 has high selectivity and sensitivity of this sensor for Cu2+
under physiological pH conditions. Here, the Cu2+ detection gives
rise to large changes in the absorption spectra (form yellow to red),
which are clearly visible to the naked-eye. However, for 1, 3 and
4, no transition-metal ion sensing was observed. It is can be inter-
preted that in the case of 2, the use of o-nitro functionality gave rise
to an extra chelation site, however, for 1, no the third chelation site
Design and synthesis of new chemosensors for transition and
heavy metal ions have been of interest to chemists for many years
because these ions play important roles in the areas of biological,
environmental and chemical systems [1,2]. Especially important in
this regard is sensors that monitor toxic heavy metal ions [3]. As
we know, copper (Cu2+) is the third in abundance (after Fe3+ and
Zn2+) among the essential heavy transition metals in the human
body and plays an important role in various physiologic processes
[4,5]. Moreover, Cu2+ can be toxic to biological systems when levels
of Cu2+ ions exceed cellular needs, and it is also able to displace
other metal ions which act as cofactor in enzyme-catalyzed reac-
tions [6,7]. Thus, copper, on one hand, is important for life, however,
on the other hand, is highly toxic to organisms. For these reasons,
a number of the design and synthesis of fluorescent sensors for the
detection of Cu2+ ions have been reported in the past few years
[8–10]. Among these, the UV–vis absorption and fluorescent emis-
sion chemosensors have been developed quickly for their simplicity
and high sensitivity. Recently, colorimetric sensing of metal ions has
been shown to be a less labor-intensive alternative to techniques
based on UV–vis absorption and fluorescent emission [11].
∗
Corresponding author. Tel.: +86 351 7018731; fax: +86 351 7018731.
E-mail address: zbchen@sxu.edu.cn (L. Feng).
1386-1425/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2008.03.021

Z. Wang et al. / Spectrochimica Acta Part A 71 (2008) 1224–1227
1225
Scheme 1. The synthesis route of 1–4.
was offered. Addition, owing to the space-configuration of chela-
tion of 3 and 4, it would block the effective combine of ligand and
metal ion.
calcd. (%) for C10
found: C, 52.97; H, 5.92; N, 18.86.
H
13N3O3 (223.23) C, 53.80; H, 5.87; N, 18.82;
4: 1H NMR (CDCl3, ı ppm): 8.98(s, 1H), 8.27–8.11(m, 2H), 7.12(d,
1H), 4.26(t, 1H), 3.38(m, 2H), 3.06(m, 2H), 2.38(s, 3H); elemental
analysis: calcd. (%) for C10H12N4O5 (268.23) C, 44.78; H, 4.51; N,
20.89; found: C, 44.71; H, 4.62; N, 20.34.
2. Experimental
2.1. Materials and instrument
3. Results and discussion
All the solvents were of analytic grade. 1H NMR was measured
on a Bruker ARX300 spectrometer with chemical shifts reported as
ppm (in CDCl3, TMS as an internal standard). Elemental analyses
were performed on a Vario EL elemental analysis instrument (Ele-
mentar Co.). Absorption spectra were recorded on a Varian Cary
300 absorption spectrophotometer. All the experiments were car-
ried out at room temperature. A Metrohm 632 pH-meter with a
Metrohm double junction glass electrode was used for pH adjust-
ment. Spectral titrations were carried out by injection of aliquots
of metal ion solutions into receptor solutions. The standard stock
solutions (1.0 × 10−3 M) inorganic salts were prepared in redistilled
water and CH3OH (v:v = 1:2); working solutions were made by dilu-
tion of the stock solutions. The stock solution (1.0 × 10−3 M) of 1, 2,
3 and 4 were prepared by dissolving corresponding mass of com-
pounds in 100 mL of CH3OH and H2O (v:v = 2:1). Working standard
solutions of lower concentrations were prepared by suitable dilu-
tion of the stock solution. All of the working solutions were buffered
at pH 7.6 0.1 using 0.1 mol/L HEPES.
3.1. The selectivity of 1–4 for metal ions
The UV–vis absorption spectra of 1–4 were investigated in Fig. 1.
It can be seen from Fig. 1, the maximum wavelength of 2 and 4
were almost same at around 348 nm, it indicated the acetyl group
was hardly effect to the electron conjugation process. However, the
maximum wavelength of 1 and 3 were at 380 and 425 nm, respec-
tively, it showed that o-nitro group was more intense drawing
electron action that o-nitro group.
Firstly, we investigated derivatives of aminobenzene 1–4
chemosensor selectivity for metal cations (K+, Ca2+, Al3+, Fe2+, Co2+
,
Ni2+, Ag+, Pb2+, Cu2+, Cd2+, Zn2+ and Hg2+, respectively). The results
showed that K+, Ca2+, Al3+, Fe2+, Co2+, Ni2+, Ag+, Cd2+ and Pb2+
nearly had no significant effect on absorption spectra of compounds
1–4, only slightly intensity reduction of absorption spectra. Sur-
prisingly, the absorption response of 1–4 had obviously different
change in the presence of Cu2+ (Figs. 2 and 3). Here, during the
derivatives of aminobenzene 1–4 selectivity, the absorption peaks
of 2 at 348 and 416 nm gradually reduced in intensity with the for-
mation of two new absorption bands at ca. 376 and 525 nm and with
2.2. Synthesis and characterization of compounds 1–4
Derivatives of aminobenzene 1 and 2 were synthesized by
ethylenediamine and the corresponding chloro-nitrobenzene in
THF. 3 and 4 both prepared by two steps: firstly, it was the likely
processes with 1 and 2, then the obtained middle compounds were
mixed with acetyl chloride in THF and refluxed for 2 h. The obtained
crude products were purified by ethanol recrystallization and fully
characterized by 1H NMR, elemental analysis.
1: 1H NMR (CDCl3, ı ppm): 8.12(d, 2H), 6.94(d, 2H), 4.32(t, 1H),
3.41(m, 2H), 3.04(m, 2H), 2.33(t, 2H); elemental analysis: calcd.
(%) for C8H11 N3O2 (108.19) C, 53.03; H, 6.12; N, 23.19; found: C,
52.97; H, 6.14; N, 23.03.
2: 1H NMR (CDCl3, ı ppm): 8.96(s, 1H), 8.33(d, 1H), 7.03(d, 1H),
4.28(t, 1H), 3.36(m, 2H), 3.08(m, 2H), 2.31(t, 2H); elemental anal-
ysis: calcd. (%) for C8H10N4O4 (226.19) C, 42.48; H, 4.46; N, 24.77;
found: C, 42.53; H, 4.48; N, 25.13.
3: 1H NMR (CDCl3, ı ppm): 8.08(t, 1H), 7.82–7.15(m, 4H), 4.21(t,
1H), 3.33(m, 2H), 3.02(m, 2H), 2.40(s, 3H); elemental analysis:
Fig. 1. The absorption spectra of 1, 2, 3, 4 in CH3OH/H2O (1:1, v:v) pH 7.6. Concen-
tration: 1, 5.28 × 10−5 M; 2, 5.53 × 10−5 M; 3, 5.67 × 10−5 M; 4, 5.39 × 10−5 M.

1226
Z. Wang et al. / Spectrochimica Acta Part A 71 (2008) 1224–1227
Fig. 4. Absorption of 2 (1.2 × 10−4 M) at 348 nm vs. pH in a mixed solution of
CH3OH/H2O (1:1, v:v). Absorption spectra were recorded on a Varian Cary 300
absorption spectrophotometer.
Fig. 2. The different intensity change profile of 2 (1.2 × 10−4 M) at 525 nm in
CH3OH/H2O (1:1, v:v) in the presence of Na+, K+, Ca2+, Mg2+, Al3+, Fe3+, Cr3+, Fe2+
,
Co2+, Ni2+, Cu2+, Zn2+, Ag+, Cd2+, Hg2+, and Pb2+ ions (6.0 × 10−5 M, for all).
clearly indicated that 2 can be used in physiological environment
where the pH > 6.
the formation of isosbestic points at 364 and 392 nm, respectively
(Fig. 3). The appearance of 525 nm absorption peak was due to the
d–d transition of Cu2+ and indicated the form of complex of Cu2+
and 2. More importantly, the Cu (II) sensing and the concomitant
absorption changes were clearly visible to the naked-eye that the
yellow solution of 2 became red upon titration with Cu (II). More-
over, these changes are also fully reversible as the addition of EDTA
reversed the color changes. The above results showed that 2 was
3.3. The stoichiometry and sensitivity of 2 with the metal ions
A titration experiment was conducted to determine the binding
ratio between Cu2+ and the 2 molecule (Fig. 5). The titration curve of
highly selective and colorimetric naked-eye chemosensor for Cu2+
.
3.2. The pH effect of 2 to recognize Cu2+
Photoionophores are usually disturbed by a proton in the detec-
tion of metal ions, so their low sensitivities to the operative pH
are extremely important [19,20]. The absorption spectra change of
2 in the different pH was investigated (Fig. 4). The results showed
that the absorption maxima (340 nm) gradually decreased in inten-
sity at pH < 5.5. These changes correspond to the protonation of the
amino moiety, reducing the binding character of the molecule. By
plotting the changes at 340 nm as a function of pH a sigmoidal curve
was observed where the major changes occurred at pH < 5.0. These
changes were fully reversible, as the addition of strong base to this
acidic solution reversed these effects. It was also obtained that only
minor changes occurred above ca. pH 5.5. From the facts, it can be
Fig. 5. The titration curve of Cu2+ to 2 in CH3OH/H2O (1:1, v:v) pH 7.6.
Fig. 3. The difference spectra of 2 (3.0 × 10−5 M) in CH3OH/H2O (1:1, v:v) pH 7.6
Fig. 6. The absorption ratio of 2 (1.2 × 10−4 M) to Cu2+ in CH3OH/H2O (1:1, v:v) pH
with the addition of Cu2+
.
7.6.

Z. Wang et al. / Spectrochimica Acta Part A 71 (2008) 1224–1227
1227
To explore further the practical utility of 2 as an ion-selective
chemosensor for Cu2+, the interference in the selective responses of
2 in the presence Cu2+, from the other metal cations tested, was also
studied by using cross-selectivity experiments (Figs. 7 and 8). No
significant variation in its spectrum and solution color was found by
comparison with that without the other metal ions besides Cu2+
.
Moreover, no obvious interference was observed in its spectrum
while performing the titrations with Cu2+ in the different mixtures
of metal ions. The above results indicated that its selectivity for Cu2+
was remarkable.
4. Conclusion
In summary, we have developed
a simple colorimetric
chemosensor 2 for recognition of metal cations, and it displays
high selectivity and sensitivity for Cu2+ by the UV–vis absorption
(appearing a new peak at 525 nm) and color change. The recog-
nition of Cu2+ gave rise to major color changes from yellow to
red that was clearly visible to the naked-eye. Such Cu2+ selec-
tive colorimetric chemosensors could be of great importance and
practicability in widely field, such as serum detection of med-
ical diagnostics. The practical application of chemosensor 2 to
recognition Cu2+ in some samples will be investigated in the
future.
Fig. 7. Absorption spectra of 2 (1.2 × 10−4 M) in a mixture (1:1, v:v) of CH3OH/H2O
(1:1, v:v) with increasing of Cu2+ in the presence of Na+, K+, Ca2+, Mg2+ and Al3+
(6.0 × 10−5 M, respectively).
Acknowledgements
This work was supported by the National Natural Science
Foundation of PR China (No. 30700534) and the Natural Science
Foundation of Shanxi Province (No. 20031017).
References
[1] Z.C. Xu, X.H. Qian, J.N. Cui, Org. Lett. 7 (2005) 3029.
[2] L.H. Feng, Z.B. Chen, Sens. Actuators B: Chem. 120 (2007) 665.
[3] R. Sundari, M. Ahmad, L.Y. Heng, Sens. Actuators B: Chem. 113 (2006) 201.
[4] T. Mayr, I. Klimant, O.S. Wolfbeis, T. Werner, Anal. Chim. Acta 462 (2002) 1.
[5] V.K. Gupta, A.K. Jain, G. Maheshwari, H. Langb, Z. Ishtaiwi, Sens. Actuators B:
Chem. 117 (2006) 99.
[6] N. Mahendra, P. Gangaiya, S. Subramaniam, R. Narayanaswamy, Sens. Actuators
B: Chem. 90 (2003) 118.
[7] Y. Xiang, A.J. Tong, P.Y. Jin, Y. Ju, Org. Lett. 8 (2006) 2863.
[8] K. Rurack, M. Kollmannsberger, U.R. Genger, J. Daub, J. Am. Chem. Soc. 122
(2000) 968.
[9] Q. Wu, E.V. Anslyn, J. Am. Chem. Soc. 126 (2004) 14682.
[10] J.S. Yang, C.S. Lin, C.Y. Hwang, Org. Lett. 3 (2001) 889.
[11] R. Martinez, F. Zapata, A. Caballero, A. Espinosa, A. Ta´rraga, P. Molina, Org. Lett.
8 (2006) 3235.
[12] T. Gunnlaugsson, J.P. Leonard, N.S. Murray, Org. Lett. 6 (2004) 1557.
[13] M.L. Jose, M.M. Ramon, P. Teresa, S. Juan, E.P.T. Miguel, Chem. Commun. (1998)
837.
[14] Y. Xiao, X. Qian, Tetrahedron Lett. 44 (2003) 2087.
[15] H. Yang, Z.Q. Liu, Z.G. Zhou, E.X. Shi, F.Y. Li, Y.K. Du, T. Yia, C.H. Huang, Tetrahe-
dron Lett. 47 (2006) 2911.
[16] Y. Zheng, J. Orbulescu, X. Ji, F.M. Andreopoulos, S.M. Pham, R.M. Leblanc, J. Am.
Chem. Soc. 125 (2003) 2680.
Fig. 8. Difference UV spectra of 2 (1.2 × 10−4 M) in a mixture (1:1, v:v) of CH3OH/H2O
(1:1, v:v) with increasing of Cu2+ in the presence of Fe3+, Cr3+, Fe2+, Co2+, Ni2+, Zn2+
,
Ag+, Cd2+, Hg2+, and Pb2+ (6.0 × 10−5 M, respectively).
Cu2+ to CH3OH/H2O 2 suggests a 2:1 binding mode. This 2:1 binding
stoichiometry was also accordant with hypothesis binding model
of 2 and Cu2+
.
The sensitive signal response of 2 toward Cu2+ was preserved in
CH3OH–H2O (v/v = 1/1, pH 7.6) by absorption spectra. The complex-
ation resulted in a strong change of 2 in its absorption intensity and
appeared a new length wave peak upon the addition of increasing
amounts of Cu2+, which might be caused by the interaction of Cu2+
with the lone electron pair of N, O atoms and formed stable com-
plex. Its new absorption increased linearly with the concentration
[17] S. Banthia, A. Samanta, J. Phys. Chem. B 106 (2002) 5572.
[18] Z. Xu, Y. Xiao, X. Qian, J. Cui, D. Cui, Org. Lett. 7 (2005) 889.
[19] H. Stephan, H. Spies, B. Johannsen, C. Kauffmann, F. Vogtle, Org. Lett. 2 (2000)
2343.
[20] D.A. Loy, B. Mather, A.R. Straumanis, C. Baugher, D.A. Schneider, A. Sanchez, K.J.
Shea, Chem. Mater. 16 (2004) 2041.
of Cu2+ ((0.01–0.6) × 10−4 M, R2 = 0.99854) up to a ratio (2/Cu2+
)
of 2:1, and there it remained (Fig. 6). Furthermore, Cu2+ could be
detected at least down to 1.0 × 10−6 M when 2 was employed at
1.00 × 10−5 M in CH3OH–H2O (v/v = 1/1, pH 7.6), and its absorbance
intensity also increased linearly with the concentration of Cu2+
.