Acenaphthenequinone based simple colorimetric anion sensor with only one binding site

Article abstract of DOI:10.1007/s10847-010-9865-6

Quinonehydrazone compound 1 was designed to be a simple chromogenic anion sensor with one anion binding site. The sensor 1 was easily obtained in 83% yield by the condensation of acenaphthenequinone with 4-nitrophenylhydrazine in ethanol solution. In DMSO

Full text of DOI:10.1007/s10847-010-9865-6

J Incl Phenom Macrocycl Chem (2011) 70:91–95
DOI 10.1007/s10847-010-9865-6
ORIGINAL ARTICLE
Acenaphthenequinone based simple colorimetric anion sensor
with only one binding site
Jie Shao
Received: 26 March 2010 / Accepted: 9 September 2010 / Published online: 24 September 2010
Ó Springer Science+Business Media B.V. 2010
Abstract Quinonehydrazone compound 1 was designed
to be a simple chromogenic anion sensor with one anion
binding site. The sensor 1 was easily obtained in 83% yield
by the condensation of acenaphthenequinone with 4-ni-
trophenylhydrazine in ethanol solution. In DMSO, sensor 1
could high selectively and visually detect anions with
strong basicity (e.g., AcO-, F- and H2PO4-) from chlo-
ride, bromide, and iodide ions with weak basicity.
signal processing, and membrane transport [5]. But over
use of agricultural fertilizers causes eutrophication of lakes
and inland waterways. As a result, the search for efficient
chemosensors that can recognize and detect these anionic
analytes would continue to be a major research area in
current times [6–9].
Generally, a sensor molecule is be composed of a
receptor component that is responsible for binding the
analyte and a signaling unit that is capable of translating
the analyte-binding induced changes into an output signal
[10, 11]. In the case of binding modes of the receptor with
anions, those are classified basically into electrostatic
interactions [12], hydrogen bond interactions [13], elec-
tron-deficient Lewis acid coordination via orbital overlap
[14] and interactions with metal centers [15] etc. The
hydrogen binding is widely used in anion recognition due
its directionality, a feature which allows the design of
receptors having ability to differentiate between anions
with different geometries and hydrogen-bonding require-
ments [16–18]. The output signals are commonly probed
either by spectroscopic techniques (e.g., fluorescence [19],
absorption [20] and NMR [21] spectroscopy), a color
change [22] or by evaluating the change in redox potential
values [23]. Among these, a colorimetric response has a
distinct advantage as they allow for ‘‘naked-eye’’ detection
of the targeted analyte through a change in color.
Accordingly, an increasing amount of research effort has
been devoted to the design and development of novel
colorimetric anion sensors. Such sensors require compli-
cated preparation process [24–26] and hence, there is an
urgent need for the development of simple colorimetric
anion sensors.
Keywords Anion sensor ꢀ ‘‘Naked-eye’’ ꢀ
Quinonehydrazone ꢀ Acenaphthenequinone ꢀ
Tautomerization
Introduction
It has been well documented that anions such as F–,
–
CH3COO–, and H2PO4 are important in many biological
processes and are known to be present in many commonly
used agricultural fertilizers as well as in food additives [1].
For example, fluoride is associated with dental health and
has a potential in treatment of osteoporosis [2, 3]. The
chronic poisoning can be induced owing to the fact that
fluoride is easily absorbed but is excreted slowly from the
body. Overexposure to fluoride can lead to acute gastric
and kidney problems [4]. Phosphates are biologically rel-
evant anions that commonly occur; phosphorylated species
play critical roles in a variety of fundamental processes
such as genetic information storage, energy transduction,
J. Shao (&)
Department of Chemistry and Materials Science,
Nanjing Forestry University, 210037 Nanjing,
People’s Republic of China
In this study, a simple novel colorimetric sensor is
designed and synthesized following the binding site-sig-
naling subunit approach. Sensor 1 could be easily prepared
e-mail: njshao@live.cn
123

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J Incl Phenom Macrocycl Chem (2011) 70:91–95
Synthesis of 5-(4’-Nitrophenylhydrazone)
by conjugating 4-nitrophenylhydrazine and acenaphthen-
equinone in a high yield. In the compound 1, the nitro and
acenaphthenequinone groups acted as signalling unit, and
the hydrazone moiety (–NH) was an anion binding site.
The sensor 1 exhibited a significant colorimetric response
to anions with strong basicity in dry DMSO.
acenaphthenequinone-2-one (1)
The sensor 1 was synthesized according to Scheme 1.
Acenaphthenequinone (0.18 g, 1.0 mmol) with a catalytic
amount of acetic acid in ethanol was added dropwise a
solution of 4-nitrophenylhydrazine (0.15 g, 1.0 mmol) in
ethanol. Then the mixture was heated to reflux under
magnetic stirring for 2 h. During the reaction a yellow
precipitate appeared which was collected by filtration,
Experimental section
1
washed with ethanol and dried in vacuo. Yield = 83%. H
Apparatus
NMR (400 MHz; DMSO-d6; Me4Si): dH 13.029 (s,–NH,
1H), 8.379 (d, J = 8.0 Hz, Ar–H, 1H), 8.282 (d,
J = 9.2 Hz, Ar–H, 2H), 8.108 (t, Ar–H, 2H), 7.952 (d,
J = 6.8 Hz, Ar–H, 1H), 7.906 (t, Ar–H, 1H), 7.831 (t, Ar–
H, 1H), 7.759 (d, J = 8.8 Hz, Ar–H, 2H); ESI-mass: m/z
calcd. for C18H11N3O3 [M] 317.08, found: 316.22 ([M–
H]-); Elemental analysis calcd for C18H11N3O3: C 68.14%,
H 3.49%, N 13.24%, found: C 68.21%, H 3.62%, N
13.56%.
1H NMR spectra were obtained on a Varian UNITY Plus-
400 MHz Spectrometer. ESI–MS was performed with a
MARINER apparatus. C, H, N elemental analyses were
made on an elementar vario EL. UV–vis spectra were
recorded on a Shimadzu UV2450 Spectrophotometer at
298.2 0.1 K.
Materials
All reagents for synthesis obtained commercially were
used without further purification. In the titration experi-
ments, all the anions were added in the form of tetra-
n-butylammonium (TBA) salts, which were purchased
from Sigma–Aldrich Chemical, stored in a vacuum desic-
cator containing self-indicating silica and dried fully before
using. DMSO was dried with CaH2 and then distilled in
reduced pressure.
Results and discussion
The quinonehydrazone derivatives were proven to be
excellent colorimetric sensors for anions in dry DMSO or
acetonitrile–water medium. In particular, such sensors
ordinarily exhibit anion-induced tautomeric equilibriums
between azophenol and quinone-hydrazone, being respon-
sible for ‘‘Naked-eye’’ detection of anions. For example,
we [27] and S. J. Shao’s group [28] prepared some anion
sensors by the reaction of isatin with the corresponding
hydrazine, respectively, which showed high selectivity for
acetate. C. Y. Duan and co-workers [29] reported a
chromo- and fluorogenic hybrid chemosensor based quin-
onehydrazone, which could detect fluoride ion in natural
aqueous environments without any spectroscopic instru-
mentation. However, they only investigated the spectral
responses of the chemosensor to fluoride with strong
basicity and did not show spectral changes resulting from
other anions (AcO- and H2PO4-) with similar basicity
with fluoride. Usually, detection and sensing of fluoride
General method
All titration experiments were carried out at 298.2 K,
unless otherwise mentioned. UV–vis spectra and fluores-
cent spectra were measured using a Shimadzu UV2450
Spectrophotometer and a Shimadzu RF-5301PC Spectro-
photometer, respectively. A 5.0 9 10-5 M solution of the
compound 1 in dried DMSO and solutions of 0.10 M tet-
rabutylammonium (TBA) salts of the respective anions
were prepared in dried DMSO and were stored under a dry
atmosphere. These solutions were used for all spectro-
scopic studies after appropriate dilution. Then, given
amount of the solution of 1 was added to the quartz cuvette
and the increased amount of anions tested (0.1 M in
DMSO-d6) was added to the solution above-mentioned,
whose absorbance spectra was tested immediately.
1HNMR titration experiments were carried out in the
DMSO-d6 solution (TMS as an internal standard). A
1.0 9 10-2 M solution of the compound 1 in DMSO-d6
was prepared. Then, the increased amount of acetate anion
(1.0 M in DMSO-d6) was added to the solution above-
mentioned and 1H NMR of the host–guest system was
tested.
NO2
O
O
NHNH2
ethanol
HN
+
O
N
refluxing, 83%
NO2
Scheme 1 The synthesis route of the receptor 1
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J Incl Phenom Macrocycl Chem (2011) 70:91–95
93
extremely suffers from interference from such anions. As
part of our ongoing research programe into the develop-
ment of quinonehydrazone based colorimetric anion sen-
sor, a new sensor based on 5-(4’-nitrophenylhydrazone)
acenaphthenequinone-2-one (1) was designed and synthe-
sized. In compound 1, the nitro group (an electron with-
drawing group) not only acts as a chromogenic unit but
also can increase the acidity of the anion binding site (the
hydrazone moiety: –NH) [30]. Importantly, the sensor 1 is
easily prepared through only one step from starting mate-
rials. Next, the interactions between 1 and anions with
different configuration (e.g., F-, AcO-, and H2PO4-) were
investigated using the spectral titrations Fig. 1.
NO2
NO2
HN
N
N
-
A-
O
N
O
+ HA
Scheme 2 Anion-induced tautomerism of the sensor 1 in solution
interaction with AcO-, the quinonehydrazone isomer of
the compound 1 dominates in solution, and thus the weak
absorption centered at 603 nm (e = 10500 M-1 cm-1) is
observed. Upon interaction with AcO-, the quinonehyd-
razone tautomer of 1 is promoted to the azophenol tauto-
mer, resulting in that the absorption at 603 nm
The changes in absorption spectra of the sensor 1
(2 9 10-5 M, DMSO) during the acetate titration are
shown in Fig. 2. Free sensor 1 exhibited three absorption
peaks centered at 384, 461, and 603 nm, respectively. On
addition of AcO- to the solution of 1, the absorption band
at 384 and 461 nm decreased, and the other bands at
603 nm increased prominently with isosbestic points at 319
and 488 nm. The possible explanation for the spectral
changes could be given as follow (see Scheme 2). Before
(e = 52500 M-1 cm-1
)
of the azophenol tautomer
increases, which is consistent with the reported results [29].
Synchronously, addition of AcO- to the solution of 1
induced a visual change in color from light green to blue,
possibly resulting from deprotonation of 1 (see Fig. 3).
In addition, the sensor 1 has similar spectral responses
-
towards H2PO4 and F- with similar basicity with AcO-
NO2
and is insensitive to addition of a large excess of chloride,
bromide and iodide ions (see Fig. 4). The results indicate
that the sensor 1 can high selectively recognize anions with
strong basicity (e.g., AcO-, F-, and H2PO4-) from chlo-
ride, bromide, and iodide ions with weak basicity.
The association constants of the compound 1 for anionic
species were determined by nonlinear fitting analyses of
the titration curves according to the eq. (1), 1:1 host–guest
complexation [31].
HN
Chromogenic unit
O
N
Anion binding site
Fig. 1 The structure of the sensor 1
1.2
1.0
0.8
0.6
0.4
0.2
0.0
300
400
500
600
700
800
Wavelength/nm
Fig. 3 Color changes of the receptor 1 (2 9 10-5 M) in absence and
presence of different anions (a the free 1; b 1 ? 5 equiv AcO-,
H2PO4- , or F-; c 1 ? excessive equiv Cl-, Br-, or I-) in DMSO
Fig. 2 Spectral changes of the sensor 1 (2 9 10-5 M) with increas-
ing concentrations of AcO- in DMSO
123

94
J Incl Phenom Macrocycl Chem (2011) 70:91–95
ꢀ
ꢁ
h
i
1=2
2
ðAlim ꢁ AÞ cH þ cG þ 1=kass ꢁ ðcH þ cG þ 1=kassÞ ꢁ4cHcG
2cH
A ¼ A0 þ
ð1Þ
Where, cG and cH are the concentration of guest and host,
respectively, and A is the intensity of absorbance at certain
concentration of host and guest. A0 is the intensity of
absorbance of host only and Alim is the maximum intensity
of absorbance of host when guest is added. Kass is the
equilibrium constant. The association constants displayed
in Table 1 were obtained by fitting the profiles of absor-
bances measured at the fixed wavelength (603 nm) versus
[Anion] to Eq. 1 for a 1:1 binding isotherm.
values of AcO-, F-, and H2PO4- in water are 9.24, 10.83,
and 11.88 [33], respectively). The selectivity of 1 for AcO-
agrees well with that reported by us [27] and S. J. Shao [28]
previously.
To further investigate the nature of host–guest interac-
1
tions, H NMR titration experiments were conducted in
DMSO-d6. Figure 5 depicts changes in chemical shifts of 1
in absence and presence of AcO-. Clearly, the peak at
13.04 ppm, which is assigned to –NH, disappeared when 2
equiv AcO- ions are added. The result implies the hydra-
zone moiety acts as an anion binding site and exhibits
deprotonation upon exposure to AcO-. Also, the color
response to AcO- of 1 is well supported by this finding. In
addition, the phenyl protons shifted upfield significantly,
indicating that the increase of the electron density on the
phenyl ring owing to the through-bond effects [34].
Therefore, the proposed anion binding mode is demon-
strated in Scheme 2.
Table 1 demonstrated binding abilities of the sensor 1
with different anions with disparate shapes and basicity.
Obviously, the selectivity trends of binding affinities of
anions for 1 were determined to be AcO- [ H2PO4 – F-
-
[ Cl- – Br- – I-. In general, such selectivity of sensors
with only a single binding site could be rationalized on the
basis of the guest basicity, which had been proven in the
literatures [32]. It seemed that the selectivity of 1 for AcO-
could be ascribed to the basicity of the anions (the pKb
1 + 5 equiv AcO-
Free 1
1 + 5 equiv H2PO-4
1 + 5 equiv F-
1 + excessive equiv Cl-
1 + excessive equiv Br-
1 + excessive equiv I-
Conclusion
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
In conclusion, a new and simple colorimetric anion sensor
based on a quinonehydrazone derivative was successfully
designed and prepared. The sensor 1 showed a tautomeric
equilibrium between azophenol form and quinonehydraz-
one form in solution. Upon interaction with anions with
300
400
500
600
700
800
Wavelength/nm
1 + 2 equiv AcO-
Fig. 4 The spectral changes of the sensor 1 (2 9 10-5 M) induced
by the different anions tested in MMSO
Table 1 Association constants (Kass 9 104 mol-1 L) of the sensor 1
with anions in DMSO at 298.2 0.1 K
1 only
11
-
Anion
AcO-
H2PO4
F-
Cl- Br- I-
14
13
12
10
9
8
7
Kass 9 104 6.30 0.35 2.00 0.22 1.76 0.24 ND ND ND
(M-1
R2
ppm
)
Fig. 5 1H NMR titration of
[Bu4N]AcO
1
(1 9 10-2 M, DMSO-d6)with
0.999
0.997
0.995
–
–
–
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J Incl Phenom Macrocycl Chem (2011) 70:91–95
95
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