A highly selective naked-eye colorimetric sensor for acetate ion based on 1,10-phenanthroline-2,9-dicarboxyaldehyde-di-(p-substitutedphenyl-hydrazone)

Article abstract of DOI:10.1016/j.saa.2008.10.007

A new and simple colorimetric sensor with high selectivity for acetate ion based on 1,10-phenanthroline-2,9-dicarboxyaldehyde-di-(p-substitutedphenylhydrazone) receptor 2 has been synthesized. The selectively binding ability of receptor 2 to acetate ion o

Full text of DOI:10.1016/j.saa.2008.10.007

Spectrochimica Acta Part A 72 (2009) 378–381
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Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
A highly selective naked-eye colorimetric sensor for acetate ion based on 1,10-
phenanthroline-2,9-dicarboxyaldehyde-di-(p-substitutedphenyl-hydrazone)
Yan-Hong Qiaoa, Hai Linb, Jie Shaoa, Hua-Kuan Lina,∗
a Department of Chemistry, Nankai University, Tianjin 300071, PR China
b State Key Laboratory of Functional Polymer Materials for Absorption and Separation, Nankai University, Tianjin 300071, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A new and simple colorimetric sensor with high selectivity for acetate ion based on 1,10-phenanthroline-
Received 3 October 2007
Received in revised form 26 August 2008
Accepted 9 October 2008
2,9-dicarboxyaldehyde-di-(p-substitutedphenylhydrazone) receptor
2 has been synthesized. The
selectively binding ability of receptor 2 to acetate ion over other anions tested was demonstrated by
UV–vis absorption spectroscopy in DMSO. Comparing with other anions studied, the UV–vis absorp-
tion spectrum in dimethyl sulfoxide shows significant response toward acetate ion with high selectivity,
and meanwhile dramatic color change is observed from yellow to green in the presence of acetate ion
(5 × 10−6 mol/L). Little UV–vis absorption spectrum change has occurred when receptor 2 was titrated
Keywords:
Colorimetric chemosensor
Hydrazone
Phenantroline
Anion recognition
−
with other different guest (F−, Cl−, Br−, I−, H2PO4 and OH−). In addition, the 1H NMR spectrum titration
shows deprotonation of the receptor in the presence of acetate ion.
© 2008 Elsevier B.V. All rights reserved.
1. Introduction
withdrawing substituents (e.g., –NO2, CF3) or positively charged
groups (e.g., alkylpyridinium). In addition, the binding ability with
The design of new receptors with electrochemical or optical
properties for the selective detection of anions has received consid-
erable attention over the past several years, as anions are ubiquitous
throughout biological systems and play crucial roles in the areas of
medicinal, catalysis, and environmental chemistry. Nowadays, the
development of colorimetric anion sensing is particularly attractive
since it does not require expensive equipment as color changes can
be easily detected by the naked-eye [1]. Visual detection can give
immediate qualitative information and is becoming increasingly
appreciated in terms of quantitative analysis [2–9]. The chro-
mogenic sensors for anions generally consist of two parts: anion
receptors and chromophores. Typically, a colorimetric sensor is
constituted by a chromogenic subunit covalently linked to a recep-
tor. In general, binding sites are the hydrogen-bond-donor groups,
in most cases the –NH fragment of carboxyamides, sulfonamides,
ureas, thioureas and pyrroles [7,9,10]. Compared with well-known
hydrogen-bonding sites such as amides, pyrroles, and ureas and sul-
fonamide, hydrazone-based receptors for anions are rare, but they
have strong binding ability with anions and are readily available.
In anion coordination chemistry, the N–H fragment of a receptor
can be further polarized, and its H-bond donor tendencies increase,
through the insertion onto the molecular framework of electron-
anions can be significantly improved at the same time. To the best
of our knowledge, a few colorimetric sensors for acetate ion have
been reported [11,12] though a lot of that for fluoride ion have been
designed [12–17] according to this principle.
In this paper, we present two new colorimetric receptors 1 and
2 (Scheme 1) based on two –NH fragments in which contains two
hydrazone groups as the binding sites. Receptor 2 with –NO2 units
being electron-withdrawing substituents shows a high selective
binding ability to the acetate ion over other studied ions. All of
the optical properties for the selective detection were carried out
in aprotic media (DMSO).
2. Experimental
2.1. Reagents
All anions, in the form of tetrabutylammonium salts, were pur-
chased from Sigma–Aldrich Chemical Co., stored in a desiccator
under vacumm containing self-indicating silica, used without any
further purification and dried with P2O5 in vacumm desiccator
at 353 K for 24 h prior to use. Dimethyl sulfoxide was dried with
calcium hydride and distilled at reduced pressure prior to use.
Unless stated otherwise, A R grade chemicals were purchased
and used without further purification. The 1,10-phenanthroline-
2,9-dicarboxaldehyde was prepared according to the well-known
method [18].
∗
Corresponding author. Tel.: +86 22 23502624; fax: +86 22 23502458.
E-mail address: hklin@nankai.edu.cn (H.-K. Lin).
1386-1425/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2008.10.007

Y.-H. Qiao et al. / Spectrochimica Acta Part A 72 (2009) 378–381
379
2.4. 1,10-Phenanthroline-2,9-dicarboxyaldehyde-di-
(p-nitrophenylhydrazone) (2)
The receptor 2 was prepared by a similar procedure to the
above. 1,10-Phenanthroline-2,9-dicarboxaldehyde (0.47 g, 2 mmol)
and 2 equiv. of p-nitrophenylhydrazine was added in ethanol
(50 ml) and refluxed for 4 h. The mixture was filtered while hot,
washed with ethanol to give a red solid which was recrystal-
lized from DMF to yield 0.68 g (yield 68%). 1H NMR (DMSO-d6):
ı 11.92 (s,2H,NH), 8.78 (d,2H,phen-H), 8.64 (m,2H, phen-H), 8.46
(d,2H,phen-H), 8.22 (d,4H, phenyl-H), 7.84 (s,2H,CH), 7.42 (d,4H
phenyl-H). Anal. Caled. for C26
H
18 N8O4·H2O: C, 59.54; H, 3.82;
N,21.37. Found: C, 59.79; H, 3.88; N, 21.86.
3. Results and discussion
3.1. UV–vis titration
Spectrophotometric
titrations
were
performed
on
5.0 × 10−6 mol/dm3 solutions of receptor 1 and 2 in dimethyl
sulfoxide (redistilled before use). Typically, increasing concentra-
tion (1–20 equiv.) of a fresh tetrabutylammonium salt standard
Scheme 1. Structure of sensors.
solution of the required anion F−, Cl−, Br−, I−, AcO−, H2PO4 and
−
OH− were added, respectively, and the UV–vis absorptions of the
samples were recorded.
On addition of 5 equiv. of AcO [NBu4], the color of a DMSO solu-
tion of 2 turned from yellow to green. The color changes were not
observed at all when the receptor 2 was treated with other anions
(see the photograph in Fig. 1). However, receptor 1 has no color
changes resulting from addition of all anions studied.
2.2. Instruments
Elemental analyses for C, H, and N were carried out on a
PerkinElmer 240C element analyzer at Institute of Elemento-
Oganic Chemistry, Nankai University. The 1H NMR spectra were
recorded using a Varian UNITY-plus 400 MHz spectrometer at the
State Key Laboratory of Functional Polymer Materials for Absorp-
tion and Separation, Nankai University. UV–vis absorption spectra
were performed on a UV-2450 spectrophotometer of SHIMADZU.
The spectrophotometer was standardized.
Fig. 2 shows the family of spectra recorded by titrating a DMSO
solution 5.0 × 10−6 mol/dm3 of 2 with a standard DMSO solution
of acetate ion. Among all of the anions tested, only acetate anion
can result in the changes in the UV–vis spectrum. When acetate
anion was introduced to the solution of 2, the intensity of the
band at 447 nm decreases while a new absorption peak at 613 nm
was observed and gradually increased, the color of the solution
turning from yellow to green as the acetate ion concentration
increased which indicated that there was a strong binding inter-
action between the acetate ion and the receptor 2 (see spectra
in Fig. 2 and color change in Fig. 1). The satisfying result of non-
linear curve fitting (absorbance at 613 nm against equivalent of
acetate ion) confirmed that there formed the stable complex hav-
ing a certain stoichiometric ratio between the receptor 2 and AcO−
anion, which would be further confirmed by the Job plot. Under the
same conditions, there were no significant changes in spectrum and
color even in the presence of high concentration of anions such
as fluoride, chloride, bromide, iodide, dihydrogen phosphate and
hydroxide ions. These results suggest that the receptor 2 can pro-
vide a high selectivity for the acetate ion among the studied anions.
2.3. Synthesis
2.3.1. 1,10-Phenanthroline-2,9-dicarboxyaldehyde-
diphenylhydrazone (1)
1,10-Phenanthroline-2,9-dicarboxaldehyde (0.47 g, 2 mmol) and
2 equiv. of phenylhydrazine was added in ethanol (50 ml) and
refluxed for 6 h. The mixture was filtered while hot, washed with
ethanol to give an orange solid which was recrystallized from DMF
to yield 0.55 g (yield 60.1%). 1H NMR (DMSO-d6):ı 10.62 (s,2H,NH),
8.78 (d,2H,phen-H), 8.64 (m,2H, phen-H), 8.46 (d,2H,phen-H), 7.84
(s,2H,CH), 7.44 (d,4H, phenyl-H), 7.32(m,6H phenyl-H). Anal. Caled.
for C26H20N6·H2O: C, 71.89; H, 5.07; N,19.35. Found: C, 71.45; H,
4.86; N, 14.96.
−
Fig. 1. Color changes observed on addition of different anions to a DMSO solution of receptor 2: (a) free receptor 2; (b) 2 + F−; (c) 2 + Cl−; (d) 2 + Br−; (e) 2 + I−; (f) 2 + H2PO4
(g) 2 + OH−; (h) 2 + AcO− (plus 5 equiv. of studied anions).
;

380
Y.-H. Qiao et al. / Spectrochimica Acta Part A 72 (2009) 378–381
Fig. 2. Family of spectra recorded on titrating a DMSO solution 5.0 × 10−6 mol/dm3 of 2 with a standard DMSO solution of acetate ion at 25 ◦C; insert: titration profiles of the
bands at 613 nm, which correspond to the hydrogen-bond complex [2 AcO]−
.
(1). The Kass of receptor 2 binding with acetate ion is 3.06 × 105:
Similar changes were not observed when the anions were added to
the solution of the receptor 1, which shows that 1 has no binding
ability for all studied anions. This indicates that the N–H fragment
of a receptor can be further polarized, and its H-bond donor ability
was improved, through the insertion onto the molecular framework
of electron-withdrawing substituents (e.g., –NO2, CF3).
1/2
2
(Xlim − X0){cH + cG + 1/Kass − [(cH + cG + 1/Kass
2cH
)
− 4cHcG
]
}
X = X0
+
(1)
Non-linear curve of molar absorbance at 613 nm versus equiv-
alent of acetate anion has been inserted in Fig. 2. The result of
association constant of receptors 1 and 2 for anions was shown
in Table 1. The receptor 2 can recognize acetate anions with high
selectivity than other anions studied.
Continuous variation method was used to determine the sto-
ichiometric ratio of the receptor 2 and acetate ion. Fig. 3 shows
Job plot of the difference between the observed absorbance and
the absorbance of the free receptor 1 (613 nm with the molar
fraction of host {[H]/([H] + [G])} for a series of solutions in which
the total concentration of host and acetate anion was constant
(1.0 × 10−5 mol/dm3), with the molar fraction of host continuously
varying [19]. The result illustrates that 2-acetate complex concen-
tration approaches a maximum when the molar fraction of host
{[H]/([H] + [G])} is about 0.50, meaning that the stoichiometry of
Particularly, the result shows that the receptor 1 has no ability
to bind anions and the receptor 2 with –NO2 groups has a high
selectivity for triangular anion (AcO−) among the anions tested
such as F− and H2PO4−. In general, Detection or recognition of
acetate ion can be interfered by the other strong basic anions such
as F− and H2PO4 [11,12,21]. In other words, the single receptors
−
with high recognition for acetate ion were rarely reported in the
literature. For example, Jang et al. [22] successfully showed a
colorimetric anion chemosensor based on 2-aminobenzimidazole
for acetate. Unluckily, their receptor had no ability of recognizing
acetate from F− only through naked-eye. The receptor 2 exhibited
color response only to AcO− and addition of the other anions such
the 2-acetate interaction was confirmed to be 1:1 from the Job plot.
For a complex of 1:1 stoichiometry, the relation in Eq. (1) could
be derived easily, as reported formerly, where X is the absorption
intensity, and cH or cG is the concentration of host or anion guest
correspondingly [20] The association constant was determined by
nonlinear fitting analyses of the titration curves according to Eq.
as F− and H2PO4 resulted in no color changes of solution of the
−
receptor 2 (see Fig. 1). To best of our knowledge, such sensors were
not found in the literature. Therefore, the compound 2 could act as
a high selective and colorimetric sensor for naked-eye detection
of AcO− in organic medium.
3.2. 1H NMR titration
The interaction of receptor 2 with acetate (used as tetrabuty-
lammonium salt) was investigated by 1H NMR spectroscopy in
DMSO-d6. In particular, a 1.0 × 10−3 M DMSO-d6 solution in 2 was
titrated with AcO−, which was added stepwise up to 2 equiv. Fig. 4
shows the different patterns of 1H NMR spectra obtained in the
course of the titration. In fact, the –NH proton (11.47 ppm) ini-
tially broadened and finally disappeared while C–Ha protons of
the phenyl rings shifted upfield (from 7.21 ppm to 7.05 ppm) in the
0–2 equiv. ranges. The CH proton shifted downfield from 5.74 ppm
to 5.74 ppm. This result indicates that the NH proton has suffered a
deprotonation processes and a potential hydrogen bond has been
formed between N CH proton and acetate anion.
The result shows that binding ability of receptor 2 maybe con-
tributed to its basicity and geometry configuration. Receptor 2 has a
Fig. 3. Job plot of receptor 2 with acetate at 613 nm; the total concentration of the
host and guest is 1.0 × 10−5 mol/dm3.

Y.-H. Qiao et al. / Spectrochimica Acta Part A 72 (2009) 378–381
381
Table 1
Kass for 1:1 complex of receptor 1 with halide anions in DMSO at 298 K.
−
Aniona
F−
Cl−
Br−
I−
–
AcO−
H2PO4
OH−
b
Kass of 1
Kass of 2
–
–
–
–
–
<100
–
–
–
–
–
3.06 × 105
a
The anions were added as their tetrabutylammonium salts.
The reliable Kass could not be obtained due to little changes of intensity.
b
that a strong binding interaction took place between the acetate
ion and the receptor 2. The receptor 2 also distributes a dramatic
color change from yellow to green with the 2-acetate interaction.
The receptor 1 has no abilities with all anions studied. That indi-
cates the N–H fragment of a receptor can be further polarized, and
its H-bond donor tendencies increased, through the insertion onto
the molecular framework of electron-withdrawing substituents
(e.g., –NO2, CF3). This investigation may represent a case study
for the interaction of hydrazones with anions. Phenylhydrazones
with an electron-withdrawing substituent is an appropriate recep-
tor for acetate ion. It has a high selective binding ability for
acetate while can distribute a dramatic color change with the
host–guest interaction. This study indicates that the receptor 2 has
latent application as a naked-eyes colorimetric sensor for acetate
ion.
Acknowledgement
Fig. 4. 1H NMR spectra taken in the course of the titration of a DMSO-d6 solution
1.0 × 10−3 m in receptor 2 (a) with a standard solition of acetate: (a) free receptor;
(b) 2 + 0.25 equiv. of acetate; (c) 2 + 0.5 equiv. of acetate; (d) 2 + 1 equiv. of acetate;
(e) 2 + 2 equiv. of acetate.
This project was supported by the National Natural Science
Foundition of China (NO. 20371028 and NO. 20671052).
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high selectivity for triangular anion (AcO−). The two oxygen atoms
of acetate have bind with two hydrogen atoms of –CH via hydrogen
bond since angle of two oxygen atoms is 120◦ and the distance of
two oxygen atoms maybe fit to the two oxygen atoms on the cavity
plane of receptor 2 in the triangular configuration. The angle of two
oxygens is 108◦ for H2PO4− (tetrahedral configuration), the distanc−e
of two oxygens of H2PO4− is less than AcO−, two oxygens of H2PO4
cannot be fit to two hydrogens which can form hydrogens bond with
AcO− in receptor 2. The OH– (linear molecule) only has one oxygen
which cannot be fit to two hydrogens of –NH in receptor 2. This is
the most possible reason why the binding ability of AcO− is much
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higher than H2PO4 and OH−. Also another evidence indicated
−
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