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A highly selective colorimetric chemosensor for detecting the respective

amounts of iron(II) and iron(III) ions in water
Zuo-Qin Liang,a Cai-Xia Wang,a Jia-Xiang Yang,*abc Hong-Wen Gao,b
Yu-Peng Tian,a Xu-Tang Taoc and Min-Hua Jiangc
Received (in Montpellier, France) 25th January 2007, Accepted 13th March 2007
First published as an Advance Article on the web 29th March 2007
DOI: 10.1039/b701201m
Published on 29 March 2007. Downloaded by York University on 27/08/2013 12:10:24.

A novel colorimetric chemosensor containing terpyridine was synthesized. It showed high

selectivity and sensitivity for Fe(II) and Fe(III) ions in neutral aqueous solution in the presence of
other metal ions such as Cd2+, Cr3+, Zn2+, Co2+, Ni2+, Cu2+, Pb2+, Na+, Ca2+, Mg2+, K+
and Ag+. Upon the addition of Fe2+ or Fe3+, the sensor displayed a unique new peak around
567 nm in its absorption spectra, and the color of the solution changed from light yellow to light
magenta. In particular, the respective amounts of Fe(II) and Fe(III) ions in the solution can be
detected using the light-absorption ratio variation approach (LARVA).

Introduction spectra. Here, we report on the synthesis and the sensing

application of 3-{4-[2-(4-dibutylaminophenyl)vinyl]phenyl}-1-
The development of chemosensors for metal ions occurred (4-[2,20 :6 0 ,200 ]terpyridin-4 0 -yl-benzyl)-3H-imidazol-1-ium bromide
early,1 but the design of fluorescent and chromogenic chemo- (TBIB) (e275 nm = 3.80
104 M1 cm1, e318 nm = 1.50
104
sensors for the detection of low concentrations of metal ions is M1 cm1 and e366 nm = 1.46
104 M1 cm1) in aqueous
still an active area of research.2 This is because chemosensors solution. The terpyridine ligand showed high sensitivity and
not only possess simplicity and high sensitivity, but are cap- selectivity for Fe2+ and Fe3+ over other cations in aqueous
able of specific recognition of particular ions in the presence of solution. In its absorption spectra, a new band appeared at 567
related ones.3 Fe ion is the most abundant transition-metal ion nm only in the presence of Fe2+ or Fe3+, and the color of the
in humans and other mammals, and it plays important roles in solution changed from light yellow to light magenta (Fig. 1).
various biological systems.4 It has been studied with methods5 In addition, we can determine the respective amounts of Fe2+
such as atomic absorption spectrometry, spectrophotometry, and Fe3+ in the solution using the light-absorption ratio
and so on. These methods can only detect the total amount of variation approach (LARVA).12
Fe(II + III) or a certain valence iron. In recent years, Meier
et al. and Kimura et al. both described a terpyridine-based
chemosensor to recognize Fe(II).6 Nevertheless, their sensors Results and discussion
were not selective for a special metal ion. The properties of a
sensor in aqueous solution are very important for compounds The chromophore of the chemosensor was based on a do-
intended for application in living systems.7 Lately we have nor–p–acceptor system. This could display a strong color
developed a sensor for anionic surfactants in water, which has development as well as great absorbance. This feature could
been applied to the analysis of water samples with satisfactory make it possible for the chemosensor to be a colorimetric one.
results,8 but most of the studies have been concerned with non- The amino group conjugated to the phenyl ring was the
aqueous solutions of ions.9 In addition, colorimetric sensors electron donor and the two butyl groups introduced were to
are useful to develop simple-to-use, naked eye diagnostic enhance the electron-donating ability of the nitrogen atom.
tools.10 Therefore, our target is to design a highly selective The imidazolium salt was the electron acceptor, and made
colorimetric sensor in aqueous solution, which can discrimi- TBIB possess some solubility in aqueous solution. The syn-
nate between Fe(II) and Fe(III). thetic strategy and the structure of the resulting product are
Terpyridine ligands themselves have generally not been used depicted in Scheme 1. 4-(4-(1H-Imidazol-1-yl)styryl)-N,N-
for sensors, due to possessing an excellent ability to coordinate
with a large variety of transition metal ions with high binding
constants.11 But we found that iron terpyridine complexes
generally show a band in the visible region in absorption

a
Department of Chemistry, Anhui University, Hefei 230039, People’s
Republic of China. E-mail: jxyang@ahu.edu.cn
b
Key Laboratory of Yangtze Water Environment of Ministry of
Fig. 1 Color changes observed for TBIB in water upon addition of
Education, College of Environmental Science and Engineering,
Tongji University, Shanghai 200092, People’s Republic of China cations. From left to right: 1: none; 2: Co2+; 3: Ni2+; 4: Ag+; 5: Fe2+
c
State Key Laboratory of Crystal Materials, Shandong University, or Fe3+. Upon the respective addition of Na+, Ca2+, Mg2+, K+,
Jinan 250100, People’s Republic of China Cd2+, Cr3+, Cu2+, Pb2+, Zn2+, the color is similar to 3.

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Scheme 1 Synthesis of TBIB (7).

dibutylbenzenamine 5 was prepared from 4-imidazol-1-yl- The selective and sensitive signal response of TBIB toward
benzaldehyde 1 and phosphonium salt 4 by the Wittig reac- Fe2+ ion and Fe3+ ion was preserved in absorption. All
tion. 4 0 -(400 -Bromomethylphenyl)-2,2 0 :6 0 ,200 -terpyridine 6 was titration experiments were performed in aqueous solution
prepared according to the literature.8 Finally, 5 and 6 in 1,4- around pH 6.0. As shown in Figs. 3 and 4, the addition of
dioxane were stirred at 100 1C for three days to give the final low concentration of Fe2+ or Fe3+ ion to the solution of
product 7 (TBIB). TBIB led to a sharp new band at 567 nm (eFe(tpy)2+ 2
= 1.84

The influence of pH on the absorbance of TBIB was 104 M1 cm1; eFe(tpy)3+2
= 1.98
10 4
M 1
cm1
), which was
determined in aqueous solution as shown in Fig. 2. The caused by the metal-to-ligand-charge-transfer (MLCT).6a
absorbance of TBIB at 567 nm remained unaffected by varying With the increasing concentration of Fe2+ ion, the sharp
pH. The ratios of absorbance at 318 nm and 366 nm were new peak gradually rose until a mole ratio (TBIB/Fe2+) of
almost a constant minimal value in the pH range 6.28 to 4.46, 2 : 1 was reached. The relationship between TBIB concentra-
and then rapidly increased from pH 4.46 to pH 2.20. This tion and the formation of the Fe(tpy)22+ complex is shown in
change may be caused by the protonation of the pyridyl the inset in Fig. 3. From the inset we also found the absorption
nitrogen. at 567 nm showed a linear increase and a sharp endpoint at
TBIB/Fe2+ ratio of 2 : 1 as the concentration of TBIB
increased. The two experiments indicate that there is no
dissociation from Fe(tpy)22+ to Fe(tpy)2+ in the experimental
process. The binding mode of the terpyridine unit for Fe3+
was similar to that of Fe(tpy)22+ as shown in Fig. 4. Interest-
ingly, with the increasing concentration of Fe2+ from 0 to 50.0
mg L1 in the solution, the bands of the Fe(tpy)22+ at 318 nm
and 366 nm rose simultaneously, and the absorbance ratio
A318 nm/A366 nm didn’t change. However, the band of the
Fe(tpy)23+ rose at 318 nm, and descended at 366 nm. As a
result, the absorbance ratio A318 nm/A366 nm of the Fe(tpy)23+
solutions increased rapidly with the increase of Fe3+ concen-
tration. Based on these characteristics, the LARVA has been
applied to the determination of Fe3+, and its main equations
Fig. 2 Influence of pH on the absorbance of TBIB in aqueous are given as eqns (2) and (3).12 The symbol DAr is the
solution. difference of absorbance ratios between the MLn and L

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Fig. 5 Standard curves for the determination of Fe3+ (1) and the
total amount of Fe2+ and Fe3+ (2).

Fig. 3 Changes in absorption spectra of TBIB (1
105 M) on the

addition of Fe2+ in aqueous solution (pH = 6.0). The Fe2+ concen- where p is the sensitivity factor and the inverse reverse ratio of
tration is 0, 20.0, 30.0, 50.0 mg L1, respectively. The inset shows the CL0,12d and q is the linear regression intercept, which often
relationship between TBIB concentration and the absorbance of approaches 0. The less L is added, the higher the analytical
Fe(tpy)22+ solution at 567 nm. The concentration of Fe2+ is 3.5
sensitivity obtained. However, too low a value of L can cause a
106 M in the solution. The concentration of TBIB is 0, 2.0, 3.0, 4.0, considerable error of measurement because of the instrument
5.0, 6.0, 7.0, 8.0
106 M, respectively.
background noise. From the absorption spectra of the
TBIB–Fe(III) reaction as shown in Fig. 4, 318 and 366 nm
solutions. CM0 is the initial concentration of M. Both p 0 and q 0 were selected as the work wavelengths. Thus, DAr may be
are constants when the reaction and measurement conditions calculated by the relation:
are selected. The symbols Al1, Al2, ALl1 and ALl2
A318 nm A0318 nm
DAr ¼  ð4Þ
DA1
r ¼p 0 1
CM0 0
þq ð1Þ A366 nm A0366 nm

where where A318 nm and A366 nm are the absorbances of Fe(tpy)23+

solution measured at 318 nm and 366 nm against water.
Al2 ALl2 A0318 nm and A0366 nm are the absorbances of Fe(tpy)22+
DAr ¼ Ar  Ar0 ¼  ð2Þ
Al1 ALl1 solution or the TBIB solution measured at 318 nm and 366
nm against water. The linear regression curves from a series of
are the absorbances of MLn and L solutions, respectively
standard Fe(II, III) solutions are shown in Fig. 5, where curve 1
measured at wavelengths l1 and l2 against water. However,
is used for the determination of the amount of Fe3+ and curve
if CM0 is low enough, eqn (1) may be simplified into:
2 for the detection of the total amount of Fe2+ and Fe3+ by
DAr ¼ pCM0 þ q ð3Þ using the absorbances of Fe(tpy)22+ and Fe(tpy)23+ at 567 nm.
To further investigate the selectivity and sensitivity of the
described sensory system for metal ions, a series of coloring
experiments were performed in water. The addition of other
metal ions such as Cd2+, Cr3+, Ni2+, Zn2+, Cu2+, Pb2+,
Co2+, Na+, Ca2+, Mg2+ and K+ did not produce significant
changes in the UV/Vis spectra at 567 nm in aqueous solution.
Only upon addition of Ag+ did the system display a new band
(Fig. 6(b)) at 450 nm. Fortunately, in the competition experi-
ments Ag+ merely showed a little interference. The competi-
tion experiments were conducted in the presence of 5
105 g
L1 Fe2+ and 2
104 g L1 Fe3+ mixed with Cd2+, Cr3+,
Ni2+, Zn2+, Cu2+, Pb2+, Ag+, Co2+, Na+, Ca2+, Mg2+
and K+ in the TBIB solution. The experimental results are
listed in Table 1. The results indicate that the terpyridine
ligand has a high selectivity for Fe2+ and Fe3+ over other
metal ions. In the competition experiments, both Mg(II) and
Fig. 4 Changes in absorption spectra of TBIB (1
105 M) on the
Ca(II) appear in error over 10% only when their mole con-
addition of Fe3+ in aqueous solution (pH = 6.0). The Fe3+ concen-
centrations are more than 200 times that of Fe(II). Besides,
tration is 20.0, 30.0, 50.0, 70.0, 100.0, 150.0, 200.0, 250.0, 300.0 mg L1,
respectively. The inset shows the relationship between TBIB concen- Co(II), Ag(I) and Cu(II) caused over 10% of error, resulting
tration and the absorbance of Fe(tpy)23+ solution at 567 nm. The from their competition coordination with TBIB. However,
concentration of Fe3+ is 3.5
106 M in the solution. The concen- their amounts should be less than such addition amounts in
tration of TBIB is 0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0
106 M, physiological studies. We estimated that the errors caused by
respectively. Co(II), Ag(I) and Cu(II) would be less than 10% in

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Experimental
Syntheses
The resulting compounds were characterized by 1H and 13C
NMR spectrometry using a Bruker Avance 300 MHz or 400
MHz spectrometer. Electrospray mass spectra (ESI-MS) were
recorded on an ABI API 4000 mass spectrograph. Melting
points were measured with a Mettler Toledo FP62 instrument.
Elemental analyses were performed on an Elementar Vario
EL-III instrument. IR spectra were recorded on a Nicolet
FT-IR-170SX infrared spectrometer. All chemicals were pur-
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chased from Aldrich, Acros or Shanghai Reagent Institute and

the solvents were purified according to conventional methods
before use.
Fig. 6 UV/Vis absorption of TBIB in the presence of Ag+ and Zn2+
in water. [TBIB] = 1
105 M, [Ag+] = 5
106 M, [Zn2+] = 4-Imidazol-1-yl-benzaldehyde 1. 4-Fluorobenzaldehyde (25.0
3.67
106 M. g, 0.200 mol), imidazole (20.4 g, 0.300 mol) and anhydrous
K2CO3 (40.0 g) were mixed in DMF (300 mL), and then
several drops of catalytic reagent Aliquat 336 were added. The
Table 1 The effect of foreign ions in the solutions and error shown mixture was refluxed for 24 h at 100 1C. Half of the solvent
was removed under low pressure. After the mixture returned
Ion added Added, mg/10 mL Error1, %a Error2, %a to room temperature, it was poured into ice water and left
Fe(II) 0.50 8.62 3.68 overnight. After filtration, the light yellow product (31.6 g,
Fe(III) 2.00 yield 92.0%) was obtained. 1H NMR (CDCl3, 400 MHz) d:
Cd(II) 2.00 4.20 8.60 9.20 (1H, s), 8.03 (2H, d, J = 8.40 Hz), 8.00 (1 H, s), 7.59 (2H,
Cr(III) 4.00 5.04 4.41
Zn(II) 1.17 4.86 1.09 d, J = 8.40 Hz), 7.43 (1H, s), 7.26 (1H, s). IR (KBr, cm1):
Co(II) 2.00 16.18 7.59 3110, 2846, 2819, 2750, 1690, 1610, 1520, 1310, 1060, 835.
Ni(II) 4.00 6.1 8.95
Mg(II) 44.0 4.02 14.98 4-(N,N-Di-n-butylamino)benzaldehyde 2. This compound
Ca(II) 72.0 3.32 12.34 was prepared according to the literature.13
Cu(II) 0.700 8.58 11.6
Pb(II) 38.0 5.79 1.15 4-Dibutylaminobenzyl alcohol 3. Compound 2 (11.7 g, 50
Na(I) 41.4 6.68 4.20
K(I) 69.7 6.85 1.11
mmol) was dissolved in methanol (350 mL) in an ice-bath.
Ag(I) 1.93 9.15 10.82 NaBH4 (3.80 g, 100 mmol) was added before the temperature
a
Error1 stands for the metrical error of Fe3+. Error2 symbolizes the
was allowed to rise to room temperature. After refluxing for
metrical error of total iron. 2 h, the solvent was removed under vacuum. Water was added
to the residue, and the product was extracted with CH2Cl2.
The organic phase was washed with water and saturated NaCl
physiological studies. Although the sensor has a few deficien- solution two times, respectively. Then it was dried with
cies, it can determine the respective amounts of Fe2+ and anhydrous magnesium sulfate. The solvent was removed to
Fe3+ in the solution. give a yellow product, which did not need to be isolated.
Fe2+ and Fe3+ ions can be detected at least down to 1.97

107 M and 1.67
107 M, respectively, when TBIB is (4-Dibutylaminobenzyl)triphenylphosphonium iodide 4. The
employed at 1
105 M in water. The range makes this mixtures of CHCl3 (100 mL), H2O (3.50 mL), PPh3 (10.7 g,
system quite sensitive, so the detection of small quantities of 40.0 mmol), HAc (7.30 g, 0.120 mol), KI (6.70 g, 40.0 mmol),
Fe2+ ion and Fe3+ ion is feasible. and compound 3 (9.40 g, 40.0 mmol) were stirred and refluxed
for 10 h. After the solvent was removed, the toluene was added
to the residue. Stirring and refluxing were continued for an
Conclusions hour. It was subsequently cooled in a refrigerator overnight to
give a white solid. After filtration, the solid was washed with
We have made full use of the characteristics of the terpyridine
THF and dried to give compound 4 (18.7 g, yield 76.5%). 1H
to synthesize a novel sensor for Fe2+ and Fe3+ ions in
NMR (CDCl3, 300 MHz) d: 0.93 (6H, t, J = 7.20 Hz), 1.30
aqueous solution. Our sensor system displayed a unique new
(4H, m), 1.47 (4H, m), 3.18 (4H, t, J = 7.65 Hz), 4.95 (4H, d,
peak at around 567 nm in the absorption spectra upon the
J = 12.91 Hz), 6.37 (2H, d, J = 8.70 Hz), 6.82 (2H, d, J =
addition of Fe2+ or Fe3+, and the color of the solution
8.70 Hz), 7.68 (12H, m), 7.80 (3H, m).
changed. In particular, the sensor can measure the respective
amounts of Fe2+ and Fe3+ in aqueous solution. To sum up, it 4-(4-(1H-Imidazol-1-yl)styryl)-N,N-dibutylbenzenamine 5.
showed high selectivity and sensitivity for Fe2+ and Fe3+ in Compound 4 (7.30 g, 12.0 mmol), compound 1 (1.70 g, 10.0
aqueous solution in the presence of other metal ions. It is a mmol) and solid NaOH (4.00 g, 100 mmol) were crushed in a
potential Fe2+ and Fe3+ chemosensor through UV/Vis spec- mortar for 15 min. The powder was dissolved in CH2Cl2. The
trometry. organic phase was washed thoroughly with water and

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saturated NaCl solution, and then was dried with anhydrous CaCl2, Cu(NO3)2  3H2O, Pb(NO3)2, NaCl, KCl, AgNO3,
magnesium sulfate. After filtration, the CH2Cl2 was removed. respectively, dissolved in deionized water.
The crude product was purified by silica-gel column chroma-
tography with ethyl acetate as the eluent to give the yellow Acknowledgements
product (1.90 g, yield 51.0%). 1H NMR (CDCl3, 400 MHz) d:
0.95 (6H, m), 1.34 (4H, m), 1.50 (4H, m), 3.29 (4 H, m), 6.63 The work was supported by grants from the National Natural
(2H, d, J = 8.84 Hz), 6.87 (1H, d, J = 16.24 Hz), 7.04 (1H, d, Science Foundation of China (50532030, 50325311,
J = 16.24 Hz), 7.21 (1H, s), 7.28 (1H, s), 7.32 (2H, d), 7.38 50335050), the Doctoral Program Foundation of the Ministry
(2H, d, J = 8.84 Hz), 7.54 (2H, d, J = 6.70 Hz), 7.85 (1H, s). of Education of China, the Education Committee of Anhui
Province (2006KJ032A, 2006KJ135B), the National Natural
4 0 -(400 -Bromomethylphenyl)-2,2 0 :6 0 ,200 -terpyridine 6. This Science Foundation of Anhui Province (070414188), The
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compound was prepared according to the literature.8 Team for Scientific Innovation Foundation of Anhui Province
(2006KJ007TD), the Key Laboratory of Opto-Electronic In-
3-{4-[2-(4-Dibutylaminophenyl)vinyl]phenyl}-1-(4-[2,2 0 :6 0 ,200 ]
formation Acquisition and Manipulation (Anhui University),
terpyridin-4 0 -yl-benzyl)-3H-imidazol-1-ium bromide 7. A mix-
the Ministry of Education, the Person with Ability Founda-
ture of compound 6 (3.40 g, 8.50 mmol) and compound 5 (3.15
tion of Anhui University.
g, 8.50 mmol) in 1,4-dioxane (30.0 mL) was stirred at 100 1C
for three days, under refluxing. A brown viscous liquid was
obtained which was washed with ethyl ether. The crude References
compound was purified by silica-gel column chromatography 1 F. Goppelsröder, J. Prakt. Chem., 1867, 101, 408.
with CH3CN–H2O (4 : 1, v/v) as the eluent to give a pale 2 (a) L. Fabbrizzi and A. Poggi, Chem. Soc. Rev., 1995, 197; (b) A. P.
yellow powder (4.92 g, yield 74.6%). Mp: 273 1C. 1H NMR de Silva, H. Q. N. Gunaratne, T. Gunnlaugsson, A. J. M. Huxley,
C. P. McCoy, J. T. Rademacher and T. E. Rice, Chem. Rev., 1997,
(DMSO, 400 MHz) d: 0.92 (6H, t), 1.34 (4H, m), 1.51 (4H, m), 97, 1515; (c) L. Prodi, F. Bolletta, M. Montalti and N. Zaccheroni,
3.29 (6H, m), 5.63 (2H, s), 6.66 (2H, d, J = 8.73 Hz), 7.01 (1H, Coord. Chem. Rev., 2000, 205, 59.
d, J = 16.30 Hz), 7.28 (1H, d, J = 16.30 Hz), 7.43 (2H, d, J = 3 Chemosensors for Ion and Molecule Recognition, ed. J. P. Des-
8.73 Hz), 7.54 (2H, m), 7.77 (6H, m), 8.02–8.10 (5H, m), 8.39 vergne and A. W. Czarnik, Kluwer Academic, Dordrecht, The
Netherlands, 1997.
(1H, s), 8.68 (2H, d, J = 7.90 Hz), 8.73 (2H, s), 8.77 (2H, d, J 4 J. J. R. Fausto da Silva and R. J. P. Williams, The Biological
= 4.46), 10.06 (1H, s). 13C NMR (DMSO, 150.90 MHz): Chemistry of the Elements, Oxford University, New York, 1992.
13.87, 19.67, 29.06, 49.83, 52.06, 111.40, 118.05, 121.00, 5 S. Pehkonen, Analyst, 1995, 120, 2655.
6 (a) M. A. R. Meier and U. S. Schubert, Chem. Commun., 2005,
121.52, 121.98, 123.28, 124.61, 126.91, 127.63, 128.15, 4610; (b) M. Kimura, T. Horai, K. Hanabusa and H. Shirai, Adv.
129.59, 131.04, 132.48, 135.39, 135.65, 137.52, 138.06, Mater., 1998, 10, 459.
139.67, 147.91, 148.89, 149.36, 154.88, 155.79. ESI-MS: m/z 7 (a) A. W. Czarnik, Acc. Chem. Res., 1994, 27, 302; (b) J. B. Wang,
695.9, 348.8 and 233.0. Calcd. for C47H47N6Br: C, 72.76; H, X. H. Qian and J. N. Cui, J. Org. Chem., 2006, 71, 4308; (c) V.
Dujols, F. Ford and A. W. Czarnik, J. Am. Chem. Soc., 1997, 119,
6.11; N, 10.83. Found: C, 72.66; H, 6.14; N, 10.71%. IR (KBr, 7386; (d) K. G. Thomas, K. J. Thomas, S. Das and M. V. George,
cm1): 2952, 2926, 2874, 2357, 1590, 1522, 1380, 1180, 792. Chem. Commun., 1997, 597.
8 J. X. Yang, H. W. Gao, Z. J. Hu and M. H. Jiang, J. AOAC Int.,
General instrumentation and reagents for titration experiments 2005, 88, 866.
9 (a) T. Ghosh, B. G. Maiya and A. Samanta, Dalton Trans., 2006,
Absorption spectra were recorded with a Model S-4100 spec- 795; (b) S. P. Gromov, E. N. Ushakov, O. A. Fedorova, I. I.
trophotometer (Scinco Instruments, Korea). A Model BS110S Baskin, A. V. Buevich, E. N. Andryukhina, M. V. Alfimov, D.
electronic balance (Sartorius Instruments, Beijing) was used to Johnels, U. G. Edlund, J. K. Whitesell and M. A. Fox, J. Org.
Chem., 2003, 68, 6115; (c) E. Quinlan, S. E. Matthews and T.
accurately weigh the standard substances. A Model RO DI Gunnlaugsson, Tetrahedron Lett., 2006, 47, 9333.
Water Ultra Purification System (Hi-tech Instruments, Shang- 10 (a) D. A. Jose, D. K. Kumar, B. Ganguly and A. Das, Org. Lett.,
hai, China) was used to produce the deionized water. The 2004, 6, 3445; (b) S. Y. Moon, N. R. Cha, Y. H. Kim and S. K.
Chang, J. Org. Chem., 2004, 69, 181.
solution pH was measured with a Model pHS-25 acidity meter 11 (a) B. G. G. Lohmeijer and U. S. Schubert, Macromol. Chem.
(Shanghai Precise Sci. Instrum., China). Standard stock solu- Phys., 2003, 204, 1072; (b) R. Dobrawa, M. Lysetska, P. Ballester,
tion of Fe2+ was prepared every time by dissolving ammo- M. Grüne and F. Würthner, Macromolecules, 2005, 38, 1315.
nium iron(II) ((NH4)2Fe(SO4)2  6H2O, A. R., Shanghai 12 (a) H. W. Gao, J. F. Zhao, Q. Z. Yang, X. H. Liu, L. Chen and L.
T. Pan, Proteomics, 2006, 6, 5140; (b) H. W. Gao, S. Q. Xia, H. Y.
Chemical Reagents, China) in deionized water. Standard stock Wang and J. F. Zhao, Water Res., 2004, 38, 1642; (c) H. W. Gao,
solution of Fe3+ was prepared by dissolving FeCl3  6H2O H. Y. Wang, S. Y. Zhang and J. F. Zhao, New J. Chem., 2003, 27,
which was purchased from the Institute for Reference Materi- 1649; (d) H. W. Gao, X. Q. Lu and J. R. Ren, Anal. Sci., 2005, 21,
als of SEPA, Beijing, China. The solutions of other metal ions 1043.
13 Y. Ren, X. Q. Yu, D. J. Zhang, D. Wang, M. L. Zhang, G. B. Xu,
were prepared from Cd(NO3)2  4H2O, Cr(NO3)3  9H2O, X. Zhao, Y. P. Tian, Z. S. Shao and M. H. Jiang, J. Mater. Chem.,
Zn(NO3)2, Co(NO3)2  6H2O, Ni(NO3)2  6H2O, MgSO4, 2002, 12, 3431.

910 | New J. Chem., 2007, 31, 906–910 This journal is 

c the Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2007