Synthesis of novel colorimetric probe molecules and their application in anion recognition based on strong hydrogen bond

Article abstract of DOI:10.1016/j.jorganchem.2012.12.012

A novel pair of ferrocene-containing azobenzene-based probe molecules, which behave as a selective probe for sensing fluoride and dihydrogen phosphate in colorimetric systems (even by naked eye), were designed. The probe 2 (N,N'-bisamideazophenyl-ferrocene) showed a high selectivity toward F ^- and H₂PO₄^- with a color change from yellow to salmon pink without any interference from other ions. Meanwhile, the probe 1 (4-amideferrocenylazobenzene) showed only high selectivity for F^- with a color change from yellow to salmon pink without any interference from other ions.

Full text of DOI:10.1016/j.jorganchem.2012.12.012

Journal of Organometallic Chemistry 726 (2013) 32e36
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis of novel colorimetric probe molecules and their application
in anion recognition based on strong hydrogen bond
1
1
1
1
1
1
*
Chao Li , Li Wang , Haojie Yu , Liang Ma , Zhefu Chen , Qian Wu , Wael A. Amer
State Key Laboratory of Chemical Engineering, Department of Chemical and Biological Engineering, Zhejiang University, Hangzhou 310027, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel pair of ferrocene-containing azobenzene-based probe molecules, which behave as a selective probe
Received 12 July 2012
Received in revised form
4 December 2012
for sensing fluoride and dihydrogen phosphate in colorimetric systems (even by naked eye), were designed.
ꢀ
The probe 2 (N,N0-bisamideazophenyl-ferrocene) showed a high selectivity toward Fꢀ and H2PO4 with
a color change from yellow to salmon pink without any interference from other ions. Meanwhile, the probe
1 (4-amideferrocenylazobenzene) showed only high selectivity for Fꢀ with a color change from yellow to
salmon pink without any interference from other ions.
Accepted 11 December 2012
Keywords:
Ó 2012 Elsevier B.V. All rights reserved.
Ferrocene-containing
Azobenzene-based
Probes
Selective sensing
Fluoride
Dihydrogen phosphate
ꢀ
1. Introduction
developed for the recognition of Fꢀ and H2PO4 ions’, including Fꢀ
(or H2PO4ꢀ)-selective electrodes [4e10,17e21], probes utilizing
hydrogen-bonding interactions [22e29], receptors based on Lewis
acidebase interactions [30e36] and so forth. Most of these che-
mosensors focused on high sensitivity with the lack of a good
selectivity. Some of synthesized chemosensors had a low detection
limit of about 1 ꢁ 10ꢀ5 M and some others showed lower sensing
concentration. Miguel Vzquez and co-workers synthesized
thiourea-containing receptors for the selective sensing of Fꢀ up to
1 ꢁ10ꢀ3 M [17e21]. Suning Wang and co-workers designed a series
of sensors which had excellent selectivity and sensitivity (lower
than 1 ꢁ 10ꢀ5 M), but the disadvantage is that the sensing process
took place in non-polar solvents [17e21]. Jong Seung Kim and co-
workers investigated a series of Fꢀ receptors which possessed
high sensitivity in high-polar solvents, but the major handicap is the
interfered with other ions like acetate and H2PO4ꢀ. However, few
sensors can combined the selectivity and low detection limit in
polar solvents, even in water.
The keen interest in the recognition and sensing of anions lies in
their major concern with environmental chemistry and biological
science [1e3]. In particular, fluoride (Fꢀ) and dihydrogen phosphate
ðH2PO4ꢀÞ anions’ sensing have attracted a growing attention in the
past decades, due to their close relationship with the people’s health
and the environmental protection. For example, the dental fluorosis
and skeletal fluorosis [4e10], reported in different countries around
the world, have been believed to be associated with the presence of
high concentration of Fꢀ in drinking water. Recently, Fꢀ was accused
of being a main reason for osteosarcoma [11,12], and intelligence
growing problems by injuring the brain, especially for the children.
ꢀ
Moreover, H2PO4 is involved in the hydrolysis process of adeno-
sine triphosphate, which is essential for organisms [13,14]. World
Health Organization published Guidelines for Drinking-Water
Quality in 2004 [15,16], in which the value of Fꢀ in drinking water
should be 1e5 mg/L, and the optimal concentration is 1.5 mg/L;
ꢀ
meanwhile, the concentration of H2PO4 should not be more than
Herein, we report a novel pair of ferrocene-containing azo-
benzene-based colorimetric probe molecules (Scheme 1) for the
5 mg/L. During the past few decades, various chemosensors were
ꢀ
selective sensing of Fꢀ and H2PO4 ions in polar solvents. The most
interesting finding was that thisꢀpair of sensors allowed the naked-
eye detection of Fꢀ and H2PO4 ions around the guideline value
reported by the World Health Organization for Drinking-Water
Quality.
* Corresponding author. Tel.: þ86 571 87953200; fax: þ86 571 87951612.
E-mail address: opl_wl@dial.zju.edu.cn (L. Wang).
Tel.: þ86 571 87953200; fax: þ86 571 87951612.
1
0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2012.12.012

C. Li et al. / Journal of Organometallic Chemistry 726 (2013) 32e36
33
chemicals were used as received. 4-Aminoazobenzene (98%) was
supplied from TCI. Ferrocene carbonate acid was supplied by China
National Pharmaceutical Group Chemical Co. Ltd.
N
N
Fe
O
2.2. Synthesis process
O
C
C
NH
HN
Chlorocarbonyl-ferrocene and 1,10-dichloro-carbonylferrocene
were synthesized as reference [37].
Fe
HN
C
O
N
N
2.2.1. Synthesis of 4-amideazophenylferrocene (probe molecule 1)
As shown in Scheme 2, 0.789 g (4 mmol) 4-aminoazobenzenewas
dissolved in 20 mL CH2Cl2 in a flask and 0.4 mL triethylamine was
added as catalyst. Afterward, 30 mL refluxed CH2Cl2, containing
1.950 g (7.8 mmol) chlorocarbonyl-ferrocene was added dropwise
into the system. The reaction mixture was stirred at room temper-
ature for 10 h and then filtered the mixture solution to remove the
precipitated salt, meanwhile the filtrate was recrystallized to get the
pure product chemosensor 1 as a yellow powder. Yield: 0.98 g
(59.8%).
N
N
probe molecule 2
probe molecule 1
Scheme 1. Structures of probe molecule 1 and 2.
2. Experimental section
2.1. Materials
2.2.2. Synthesis of N,N0-bisamideazophenylferrocene (probe
molecule 2)
As shown in Scheme 2, 3.548 g (18 mmol) 4-aminoazobenzene
was dissolved in 30 mL CH2Cl2 in a flask and 0.8 mL triethylamine
Dichloromethane (CH2Cl2, AR) and triethylamine (Et3N, AR)
were distilled over calcium hydride, while dimethyl sulfoxide
(DMSO, AR) was dried under molecule sieves (4A), and all other
O
C
Fe
O
C
H
N
Cl
N
Fe
N
probe molecule 1
N
NH2
N
N
Et3N in CH2Cl2
room temperature
N
O
C
NH
NH
O
Fe
C
Cl
Cl
O
C
Fe
O
C
probe molecule 2
N
N
Scheme 2. Synthetic procedure of probe molecule 1 and 2.
Fig. 1. UVevis absorption spectral changes of probe molecule 1 (5 ꢁ 10ꢀ5 M in DMSO) (a) and probe molecule 2 (2.5 ꢁ 10ꢀ5 M in DMSO) (b) upon addition of Fꢀ.

34
C. Li et al. / Journal of Organometallic Chemistry 726 (2013) 32e36
Fig. 2. UVevis absorption spectral changes of probe molecule 1 (5 ꢁ 10ꢀ5 M in DMSO) (a) and probe molecule 2 (2.5 ꢁ 10ꢀ5 M in DMSO) (b) upon addition of H2PO4
.
ꢀ
Fig. 3. UVevis absorption spectra of probe molecule 1 (5 ꢁ 10ꢀ5 M in DMSO) (a) and probe molecule 2 (2.5 ꢁ 10ꢀ5 M in DMSO) (b) upon the addition of different anions (none, Fꢀ,
Clꢀ, Brꢀ, Iꢀ, H2PO4ꢀ, HSO4ꢀ, NO3 or mixture).
ꢀ
ꢀ
Fig. 4. (a) Colorimetric changes of probe molecule 1 upon different anions in DMSO(from left to right: 1 (2.63 ꢁ 10ꢀ4 M); 1 þ Fꢀ (1 equiv); 1 þ H2PO4 (10 equiv); 1 þ Clꢀ
(10 equiv); 1 þ Brꢀ (10 equiv); 1 þ Iꢀ (10 equiv); 1 þ HSO4 (10 equiv); 1 þ NO3 (10 equiv)), (b) colorimetric changes of probe molecule 2 upon different anions iꢀn DMSO (from left
ꢀ
ꢀ
to right: 1 (2.63 ꢁ 10ꢀ4 M); 1 þ Fꢀ (1 equiv); 1 þ H2PO4 (1 equiv); 1 þ Clꢀ (10 equiv); 1 þ Brꢀ (10 equiv); 1 þ Iꢀ (10 equiv); 1 þ HSO4 (10 equiv); 1 þ NO3 (10 equiv)).
ꢀ
ꢀ

C. Li et al. / Journal of Organometallic Chemistry 726 (2013) 32e36
35
The probe molecules 1 and 2 were titrated with Fꢀ in DMSO
under room temperature, and the UVevis absorption spectra were
recorded as shown in Fig. 1. In Fig. 1(a), a significant phenomenon
was detected that as the concentration of Fꢀ increased, the
absorption band of the probe molecule 1 around 465 nm increased
with a slight decrease in the absorption band around 360 nm. The
same spectral change was observed fro the probe molecule 2 in
Fig. 1(b). However, the absorption band around 360 nm decreased
obviously when adding more than 30ꢀequiv Fꢀ. The same titration
experiments were done using H2PO4 as a titrant for the probe
molecules 1 and 2, and the UVevis spectra were recorded as shown
in Fig. 2(a) and (b). The probe molecules 1 and 2 had different
phenomenons upon addition of H2PO4ꢀ. The UVevis spectrum of
ꢀ
the probe molecule 1 was not affected by the addition of H2PO4
,
while probe molecule 2’s changed obviously, as shown in Fig. 2.
Fig. 5. Colorimetric changes of probe molecule 1 with(II) or without(I) Fꢀ in DMSO
under different concentration of probe molecule 1: (a) 2.63 ꢁ 10ꢀ4 M; (b) 5.3 ꢁ 10ꢀ5 M.
Fig. 3 showed the UVevis absorption spectral changes of the
probe molecules 1 and 2 in DMSO upon the addition of 10 equiv
ꢀ
anions (Fꢀ, Clꢀ, Brꢀ, Iꢀ, H2PO4ꢀ, HSO4 or NO3ꢀ) and 10 equiv
anions’ mixture. As shown in Fig. 3(a), only Fꢀ increased the
was added as catalyst. Then 20 mL refluxed CH2Cl2, containing
1.870 g (6 mmol) 1,10-dichloro-carbonylferrocene was added drop-
wise into the system. The reaction mixture was stirred at room
temperature for 10 h, filtered and the precipitate was washed with
ethanol three times to get pure product chemosensor 2 as a yellow
powder. Yield: 2.56 g (67.4%).
absorption peak around 465 nm for the probe molecule 1. On the
ꢀ
other hand, H2PO4 lead to a slightly different absorption band
around 465 nm, but the other anions did not result in any difference
of absorption spectra. Meanwhile, as shown in Fig. 3(b) both Fꢀ and
ꢀ
H2PO4 led to absorption spectra changes around 465 nm for the
probe molecule 2, and little difference could be discriminated
between the ions mixture and the Fꢀ anion solution.
The probe molecules 1 and 2’s colorimetric recognition and
2.3. Characterization
ꢀ
their sensing of Fꢀ or H2PO4 ions were demonstrated as shown in
1H NMR spectra of the probe molecules 1, 2 and their Fꢀ ðH2PO4ꢀÞ
titration were recorded on a 400 MHz AVANCE DMX spectrometer
instrument using deuterated chloroform (CDCl3-d6) or dimethyl
sulfoxide (DMSO-d6) as solvents. UVevis absorption spectra of the
probe molecules 1, 2 and their anions titration were obtained on
a UNIC 3802 UVevis spectrophotometer.
Fig. 4, in which the concentration of probe molecules 1 and 2 were
2.63 ꢁ 10ꢀ5 M. In Fig. 4(a), the solution color changed from yellow
to salmon pink upon the addition of Fꢀ. In contrast, the addition of
the other anions did not induce any color change. From above, it can
be deduced that probe molecule 1 can serve as a selective Fꢀ sensor
without interferenceꢀfrom any other ions. From Fig. 4(b), 1 equiv Fꢀ
and 10 equiv H2PO4 lead the probe molecule 2’s solution color
change from yellow to salmon pink. Therefore, the probe molecule
ꢀ
2 can serve as a selective sensors for Fꢀ and H2PO4 without
3. Results and discussion
interference from any other ions. More importantly, the concen-
tration of Fꢀ added into the probe molecule 1’s solution is
2.63 ꢁ 10ꢀ4 M that equals to 5 mg/L which is the largest amount of
The 1H NMR spectra of the probe molecules 1 and 2 were shown
in the Supporting information (ESI).
F-
H
N
Fe
O
C
O
C
Fe
F-
H
N
N
N
N
N
1 F-
1
N
N
N
N
O
C
O
NH
C
N
N
H
H
-
F- or H2PO4
-
Fe
F- or H2PO4
Fe
O
C
HN
C
O
N
N
N
N
2 ions
2
Scheme 3. Schematic representation of sensing Fꢀ and H2PO4 processes.
ꢀ

36
C. Li et al. / Journal of Organometallic Chemistry 726 (2013) 32e36
Fꢀ concentration that can exist in drinking water. Furthermore, it
was found that the colorimetric change is highly dependent on the
concentrations of the probe molecule 1 and Fꢀ, as shown in Fig. 5.
Inspiringly, the concentration of probe molecule 1 and Fꢀ in
Fig. 5(b) is 5.3 ꢁ 10ꢀ5 mol/L, that equals to 1 mg/L, which is the
lowest concentration of Fꢀ in drinking water.
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From above, a possible mechanism was proposed to illustrate
the sensing Fꢀ and H2PO4ꢀ process by the probe molecules 1 and 2.
For probe molecule 1, one amide group would only bind with Fꢀ
tightly in DMSO, which can be demonstrated by Figure S5 and
Figure S7. Meanwhile, the probe molecule 2 could provide two
ꢀ
amide groups at the same side to bind with Fꢀ or H2PO4 via
hydrogen bonding. In Figure S5, we can see clearly that the peak
belonging to proton from amide group (red arrow) was shifted to
the upfield, after the addition of Fꢀ or H2PO4ꢀ. In Figure S6, the
situation was similar. In which the peak at 9.81 ppm (red arrow)
was shifted to the upfield around 4.40e4.50 ppm, after the addition
of Fꢀ or H2PO4ꢀ, and also the peak at 9.81 ppm, which belonged to
the diproton of amide group, disappeared. Therefore, we supposed
that the free rotation of the two cyclopentadienyl rings of the
ꢀ
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,
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direction. The proposed mechanisms were shown in Scheme 3.
4. Conclusions
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probe for sensing fluoride and dihydrogen phosphate ions in
colorimetric systems (even by the naked eye). The sensing prop-
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shown in Scheme 3.
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Acknowledgments
The authors gratefully acknowledge financial support by the
National Science Foundation of China (20672097, 20772108 and
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Appendix A. Supporting information
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Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2012.12.012.