A novel acetate selective chromogenic chemosensor based on phenanthroline

Article abstract of DOI:10.1016/j.saa.2011.03.013

A novel colorimetric anion-chemosensor based on 1,10-phenanthroline-2,9- dicarbonyl-p-nitro-phenylhydrazine has been synthesized. Among the different anions tested, it shows the best selectivity towards AcO^-. The addition of acetate causes the

Full text of DOI:10.1016/j.saa.2011.03.013

Spectrochimica Acta Part A 79 (2011) 471–475
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Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
A novel acetate selective chromogenic chemosensor based on phenanthroline
Weiwei Huanga, Yaping Lia, Zhongyue Yanga, Hai Linb, Huakuan Lina,∗
a Department of Chemistry, Nankai University, Tianjin 300071, People’s Republic of China
b Key Laboratory of Functional Polymer Materials of Ministry of Education, Nankai University, Tianjin 300071, People’s Republic of 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 anion-chemosensor based on 1,10-phenanthroline-2,9-dicarbonyl-p-nitro-
Received 19 October 2010
Received in revised form 14 February 2011
Accepted 9 March 2011
phenylhydrazine has been synthesized. Among the different anions tested, it shows the best selectivity
towards AcO−. The addition of acetate causes the color to change from yellow to red, which could be
detected with naked eyes. The binding ability of chemosensor 1 with anions has been investigated
through UV–vis spectral titrations. In addition, 1H NMR experiment was carried out to explore the nature
of interaction between chemosensor 1 and acetate.
Keywords:
Chromogenic chemosensor
Anion sensing
© 2011 Elsevier B.V. All rights reserved.
Acetate chemosensor
Naked-eye detection
1. Introduction
chemosensor utilizing 2,4-dinitrophenylhydrazine as binding site,
which could show naked-eye detection to F− ion in natural water
It is commonly believed that anions play essential roles in a wide
range of chemical, medical and biological processes. For example,
carboxylate anion [1–3] exhibits many biochemical functions in
the enzymes and antibodies and plays important roles in numer-
ous metabolic processes. Acetate, the unique trigonal carboxylate
anion, can form the strong hydrogen-bond when interacting with
hydrogen-bond donors. Fluoride primarily plays a significant role
in the prevention of dental caries [4]; however, over exposure
to fluoride can result in nephrotoxic change in both humans and
animals, and lead to urolithiasis [5]. Dihydrogen phosphate anion
[6–9] plays a key role in energy storage and signal transduction.
Thus, the recognition to anions is of vital importance in the filed
of supramolecular chemistry [10,11], and it is necessary to develop
selective chemosensors to optically detect anions without resorting
to any expensive spectroscopic instrumentation.
[21]. Lin has reported a turn-on fluoresecent anion chemosensor
based on 1,10-phenanthroline-2,9-diamide (chemosensor 2, see
Scheme 1), which could show high selectivity to F− ion [22]. Besides
that, they have also reported a new chemosensor 3 (see Scheme 1)
based on phenanthroline-bridged diamide, which could present
high recognition affinity to anions, in particular the fluoride ion
[23].
In this paper, we demonstrate a new sensitive AcO− anion
chemosensor in DMSO utilizing hydrazine NH group as binding site,
the recognition to anions can be obviously seen from the solution’s
color change with naked-eye.
2. Experimental
2.1. Apparatus
In recent years, a number of neutral chromogenic and fluores-
cent anion chemosensors have been reported. A common approach
to obtain such anion chemosensors is to link chromophoric group
to the functional group such as amine [1,12–14], urea/thiourea [15],
–OH [16] as well as pyrrole [17]. Nitro-substitute phenylhydrazine
has been reported as a chromophoric group and hydrogen bonding
donor to anions. Our research group has synthesized several colori-
metric anion chemosensors by coupling 4-nitrophenylhydrazine
with a different chromophore [18–20]. Duan and co-workers
have reported a highly selective chromo- and fluorogenic fluoride
1H NMR spectra were obtained on a Varian UNITY Plus-400 MHZ
Spectrometer. ESI-MS 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 UV-2450 Spectrophotometer
(Shimadzu 2.1 Apparatus Corp., Kyoto, Japan) with a quartz cuvette
(path length = 1 cm) at 298.2 0.1 K.
2.2. Chemicals
All reagents for synthesis were obtained commercially and used
without further purification. In the titration experiments, all the
anions were added in the form of tetrabutylammonium (TBA) salts,
which were purchased from Sigma–Aldrich Chemical, stored in a
∗
Corresponding author. Tel.: +86 22 23502624; fax: +86 22 23502458.
E-mail address: hklin@nankai.edu.cn (H. Lin).
1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2011.03.013

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W. Huang et al. / Spectrochimica Acta Part A 79 (2011) 471–475
N
H
N
H
O-
N
N
O
N
N
H
O
O-
O
O
O
O
O
O
N
N
NH
HN
N
H
O
N
N-
N-
O-
O
HN
NH
N
N
O-
H
H
NO2
NO2
NO2
NO2
NO2
NO2
N
N
N
N
O
O
O
O
F
H
H
NH
HN
N
N
F
chemosensor 2
N
N
N
N
H
F
O
O
O
O
H
NH
HN
N
N
F
NO2
NO2
NO2
NO2
chemosensor 3
Scheme 1. The possible binding model of chemosensor 1 with AcO−
.

W. Huang et al. / Spectrochimica Acta Part A 79 (2011) 471–475
473
N
N
O
O
H1
NH
HN
a) SOCl2
H2
HN
NH
b) N(Et)3
N
N
4-nitrophenylhydrazine
HOOC
COOH
NO2
NO2
Scheme 2. The synthesis of chemosensor 1.
vacuum desiccator containing self-indicating silica and dried fully
before use. DMSO was dried with CaH2 and then distilled in reduced
pressure.
phen-H), 8.50 (d, 2H, phen-H), 8.30 (s, 2H, phen-H), 8.10 (d, 4H,
phenyl-H), 6.93 (d, 4H, phenyl-H); Elemental analysis calcd for
C26H18N8O6·H2O: C, 56.04; H, 3.77; N, 16.92. Found C, 56.82; H,
3.77; N, 16.82.
2.3. General method
A 2.0 × 10−3 mol/L solution of chemosensor 1 in DMSO was pre-
pared and stored in the dry atmosphere. Solutions of 1.0 × 10−1 and
1.0 × 10−2 mol/L tetrabutylammonium salt of the respective anion
were prepared in dried and distilled DMSO and were stored under
a dry atmosphere.
3. Results and discussion
3.1. UV–vis spectral titrations
Firstly, in order to study binding selectivity of the chemosensor
1, UV–vis titrations have been carried out in DMSO at a concen-
tration of 2.0 × 10−5 mol/L by adding tetrabutylammonium salts of
1H NMR titration experiments were carried out in the DMSO-
d6 solution (TMS as an internal standard). Certain amount of
chemosensor 1 solution in the DMSO-d6 was prepared with a con-
centration of 0.01 mol/L. 1H NMR of the host–guest system was
recorded by adding increasing amount of acetate anion (1.0 mol/L
in DMSO-d6) into chemosensor 1 solution.
anions. Fig. 1 displays the notable changes in the UV–vis spectrum
of chemosensor 1 (2 × 10−5 mol/L) on the addition of AcO−, H2PO4
,
−
Cl−, Br− and I− ions. Obvious spectra changes were observed after
adding AcO− to the solution (see Fig. 1). Moreover, the color of
chemosensor 1 solution was changed from yellow to red. How-
ever, no detectable spectral responses and color responses were
observed even after adding large amount of F−, H2PO4−, Cl−, Br−
and I− ions. These results suggest that chemosensor 1 can distin-
guish acetate from many other anions.
2.4. Synthesis of
1,10-phenanthroline-2,9-dicarbonyl-p-nitrophenylhydrazine (1)
The synthesis route of chemosensor 1 is demonstrated in
Scheme 2. To 1,10-phenanthroline-2,9-dicarboxylic acid 0.268 g
(1 mmol) was added freshly distilled thionyl chloride (25 mL) and
the mixture solution was refluxed for 6 h. Then, the solution was
concentrated under reduced pressure. The slight yellow residue
was dissolved in 25 mL dry CH2Cl2 followed by the addition of a cat-
alytic amount of triethylamine. 4-Nitrophenylhydrazine (0.306 g,
2 mmol) was added slowly to the above-mentioned cold mix-
ture solution, stirred for 3 days at room temperature, poured
into water, filtered and washed to give 0.33 g pure yellow solid
Secondly, to explore more about the applicability of chemosen-
sor 1 for acetate, the UV–vis titrations were performed in DMSO
(see Fig. 2). The presence of acetate resulted in the intensity
of the absorbance band at 370 nm significantly decreases while
the absorbance band at 525 nm increases. The significant spec-
tral changes indicate the internal-molecular charge-transfer (ICT)
between anion bonding of the NH structures and the electron-
deficient NO2 moiety [24]. Additionally, as the intensity of the
polarization is increased by the –NO2 substituent, the electron den-
sity of the hydrazone is transferred to the nitro moiety resulting
in the possibility of realizing visual inspection. These results sug-
after recrystallization from DMF/CH3CN (v/v = 7:3). Yield = 60%. 1
NMR (DMSO-d6): ı11.37 (s, 2H, NH), 9.47 (s, 2H, NH), 8.82 (d, 2H,
H
Fig. 1. The left: Absorption spectra of chemosensor 1 (2 × 10−5 mol/L) on the addition of 2.5 equiv. of various anions such as AcO−, H2PO4−, F−, Cl−, Br−, and I− in DMSO. The
right: Color changes of chemosensor 1 in DMSO. [1] = 1.0 × 10−5 mol/L, [anion] = 2.5 equiv.: A = free chemosensor, B = AcO−, C = H2PO4−, D = F−, E = Cl−, F = Br− and G = I−
.

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W. Huang et al. / Spectrochimica Acta Part A 79 (2011) 471–475
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
2.0 equiv
1.6 equiv
1.2 equiv
0.8 equiv
2.5 equiv
0.4 equiv
0 equiv
Ha
H1
H2
0 equiv
12
11
10
9
8
7
6
ppm
300
400
500
600
700
800
Fig. 4. 1H NMR titration of chemosensor 1 in DMSO-d6 with AcO−
.
Wavelength/nm
Fig. 2. Evolution of the UV–vis spectra of chemosensor 1 (2.0 × 10−5 mol/L) during
the titration with AcO− in DMSO. Inset: titration plots (observed binding profiles and
corresponding non-linear fit plots monitored by the absorption increase at 525 nm).
listed in Table 1.
X = X0 + (Xlim − X0)
{CH + CG + (1/Kass) − [(CH + CG + (1/Kass))2 − 4CHCG]1/2
}
gest that chemosensor 1 can distinguish acetate from many other
anions.
(1)
2CH
Table
1 demonstrates the apparent affinity constants of
3.2. Determination of affinity constants
chemosensor 1 with different anions. As is obviously illustrated
in Table 1, the selectivity trends of binding affinities of anions for
1 are determined to be AcO− > F− > H2PO4− ꢀ Cl− ∼ Br− ∼ I−. The
main reason for preferring AcO− is that the triangular shape of AcO−
postures −the angle of O–C–O about 120◦ while the angle of O–P–O
of H2PO4 is about 108◦, the distance between two oxygen atoms
of AcO− might be more fit for the distance between two –NH of
1, that is to say the configuration of AcO− and 1 is better matched
[27]. Furthermore, the basicity of AcO− is stronger, which can form
the strongest multiple-hydrogen bonding when interacting with
NH groups, thiourea, and amidourea units in acceptor. The affinity
constants of Cl−, Br−, and I− are very small due partly to their weak
basicity.
Compared with previous literature [22,23], chemosensor 2 [22]
without the chromophore like –NO2 group has been only investi-
gated by the fluorescent spectroscopic titrations, not by the UV–vis
spectral titrations and the ‘naked-eye’ detection could not be acces-
sible. In another literature [23], the chemosensor 3 has two binding
sites, which shows selectivity for recognizing fluoride. In this
paper, we synthesized the new chemosensor 1 containing the chro-
mophore and four binding sites, these advantages contribute to the
acetate detection from other anions by ‘naked-eye’ experiments.
To determine the stoichiometry of the host–guest complex, Job’s
plots have been obtained according to the method reported by Con-
nors [25]. Job’s plots of chemosensor 1 and AcO− in DMSO (see
Fig. 3) show the maxima are all at a molar fraction of 0.5. This
result indicates that chemosensor 1 binds acetate anion guest with
a 1:1 ratio. Moreover, similar results can also be obtained for other
anions.
For a complex of 1:1 stoichiometry, the relation in Eq. (1) could
be derived easily, where X is the absorption intensity, and CH or CG
is the concentration of the host or the anion guest correspondingly
[26]. A is the intensity of absorbance at certain concentration of
the host and the guest. A0 is the intensity of absorbance of host
only and Alim is the maximum intensity of absorbance of host when
gust is added. K is the affinity constant. The affinity constants of
chemosensor 1 for the studied anionic species are calculated and
0.50
0.45
0.40
0.35
0.30
3.3. 1H NMR titrations
To further investigate the interaction mechanism between
chemosensor 1 with AcO− ion, the 1H NMR titration is conducted in
the DMSO-d6 solution of 1 (5 × 10−3 mol/L) to monitor the changes.
Two factors that affect the shift of hydrogen are considered. They
are the results from the formation of hydrogen bond between the
binding moieties of NH sites and the anion. The first factor is that the
increased electron density of the phenyl rings can result in proton
upfields in the 1H NMR spectrum, and the second factor is that space
effects which polarize C–H bond in proximity to hydrogen bond
and produce the partial positive charge in the proton can lead to the
deshielding effect and downfield shift [28]. Fig. 4 shows the 1H NMR
titration spectra of chemosensor 1 with acetate anion. The peaks at
11.371 ppm and 9.472 ppm, which could be attributed to the NH
moieties’ protons, exhibited an obvious downfield shift upon addi-
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
[Anion]/([Host]+[Anion])
Fig. 3. Job’s plot for
1
with AcO− determined by UV–vis in DMSO,
[1] + [anion] = 2.0 × 10−3 mol/L.

W. Huang et al. / Spectrochimica Acta Part A 79 (2011) 471–475
475
Table 1
Association constants of chemosensor 1 with anions in DMSO at 298.2 0.1 K.
−
Anionsa
AcO−
F−
H2PO4
Cl−
Br−
I−
Kass, 1
Kass, 2
Kass, 3
3.84 × 104
2.72 × 102
1.96 × 105
1.66 × 104
7.38 × 103
5.64 × 106
1.03 × 104
<10
ND
NDb
ND
ND
ND
ND
2.66 × 103
3.33 × 105
1.89 × 105
1.24 × 104
a
All the anions were added in the form of tetra-n-butylammonium (TBA) salts.
ND the spectra have too small change with adding anion so we cannot determine the affinity constants by the spectra.
b
tion of acetate ions. The peak at 11.371 ppm broadened with the
addition of 0.5 equiv. acetate anions and completely disappeared
with the acetate ions being added up to 1.0 equiv., indicating the
fully deprotonation of the N–H1 groups of the host molecule [29].
What is more, the peak at 9.472 ppm just broadens but still exists
with further added acetate anion to 2.0 equiv. In addition, the res-
onance signal of H1 continues to broaden and shift downfield with
further increase in concentration of AcO− ions, which displays the
formation of the hydrogen-bonded chemosensor–anion complexes
occurred in the solution. In particular, the aromatic proton espe-
cially for the Ha obviously shifts upfield suggesting the increase of
the electron density on the phenyl ring due to the through-bond
effects. Also, the evidence indicates a higher negative charge and
H-bond acceptor tendencies. Such relationship points to the elec-
trostatic nature of chemosensor–oxoanion interaction and rules
out any geometrical effect of the binding [29]. Therefore, we pro-
pose the anion recognition process as shown in Scheme 1.
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To sum up, we have presented a simple and colorimetric charge-
neutral chemosensor 1, based on phenanthroline, which could
recognize acetate among the anions investigated. The whole pro-
cesses can be observed with the ‘naked-eye’, for the color changes
from yellow to red, so it is expected to find application detection of
acetate in the field of analytical chemistry.
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Acknowledgement
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This project was supported by the National Natural Science
Foundation of China (20371028, 20671052).
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