An efficient novel anion sensor for the recognition of acetate

Article abstract of DOI:10.1007/s10847-010-9814-4

A novel colorimetric compound anthraceno-9, 10-dicarbaldehyde bis-(phenyl-semithiocarbazone) as sensor 1 is synthesized and characterized. It showed significant color changed from light yellow to purple upon the presence of acetate. This outstanding prope

Full text of DOI:10.1007/s10847-010-9814-4

J Incl Phenom Macrocycl Chem (2011) 69:63–68
DOI 10.1007/s10847-010-9814-4
ORIGINAL ARTICLE
An efficient novel anion sensor for the recognition of acetate
•
•
•
Weiwei Huang Hai Lin Zunsheng Cai
Huakuan Lin
Received: 11 April 2010 / Accepted: 27 May 2010 / Published online: 11 June 2010
Ó Springer Science+Business Media B.V. 2010
Abstract A novel colorimetric compound anthraceno-9,
10-dicarbaldehyde bis-(phenyl-semithiocarbazone) as sen-
sor 1 is synthesized and characterized. It showed significant
color changed from light yellow to purple upon the pres-
ence of acetate. This outstanding property was also bol-
stered by UV–Vis and fluorescent titrations experiments in
DMSO or DMSO–H2O (95:5, v/v) solution. In addition,
1H NMR experiments were carried out to explore the
nature of interaction between sensor 1 and acetate.
biochemical behavior, and make them the critical compo-
nents for numerous metabolic processes [10]. In addition,
acetate is the anion with strong basicity, and has the tri-
gonal chemical structure, which can form hydrogen-bond
interaction with hydrogen-bond donors. Many examples
are available about the selective sensor molecules for
acetate anion in the literatures [11–13]. At the moment, a
lot of researchers have focused on the neutral chromogenic
and/or fluorescent anion sensors. Especially, colorimetric-
based sensing is very attractive, as it may allow naked-eye
detection of the analyte without resorting to any expensive
equipment [14].
Keywords Acetate ꢀ Anion recognition ꢀ Naked-eye ꢀ
Colorimetric
In our previous studies, we prepared a colorimetric
anion sensor based on an anthracene derivative, which
showed significant color changes upon the presence of
fluoride [15]. With this information, we have designed and
synthesized another novel sensor 1 by a simple reaction of
anthracene-9, 10-dicarbaldehyde and 4-phenylthiosemi-
carbazide (see Scheme 1). This sensor contains four rec-
ognition sites and has good selectivity for recognizing
acetate.
Introduction
Anions are ubiquitous in nature. Recently, recognition and
sensing of anions have attracted considerable attention for
their diversity of functions [1–8]. Among various important
anionic analytes, acetate is one of the most significant
species due to its specific biochemical functions in the
enzymes and antibodies [9]. In enzymes and antibodies the
functions of carboxylates ascribe to their specific
Generally speaking, the recognition studies of the past
were usually performed in aprotic media (e.g. DMSO,
acetonitrile, CHCl3, etc.), to avoid the competition from the
protic solvent (e.g., water or alcohols) working as another
hydrogen-bonding donor [16, 17]. Thus, it is urgent to
develop sensors that are able to bind anions within the
competitive media, and to be simultaneously accompanied
with the ‘naked-eyed’ detectable color changes. Sensor 1 is
selective and effective to recognize AcO- in dry DMSO.
More importantly, it also presents recognition ability in
aqueous medium: DMSO–H2O (95:5, v/v) solution. The
processes of sensing can literally be seen through the
‘naked-eye’ for the sharply color changes from light yellow
to purple.
W. Huang ꢀ H. Lin (&)
Department of Chemistry, Nankai University, Tianjin 300071,
People’s Republic of China
e-mail: hklin@nankai.edu.cn
H. Lin ꢀ Z. Cai
Key Laboratory of Functional Polymer Materials
of Ministry of Education, Nankai University, Tianjin 300071,
People’s Republic of China
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J Incl Phenom Macrocycl Chem (2011) 69:63–68
Scheme 1 General synthetic
routes to the target sensor 1
NH NH2
S
S
NH
N
N
N
H
CHO
CHO
NH
EtOH, Reflux, 2h
H
N
NH
S
Experimental
prepared, into which the increased amount of acetate anion
(1.0 M in DMSO-d6) was added and 1H NMR of the host–
guest system was recorded.
Materials
All reagents for synthesis obtained commercially were used
without further purification. In the titration experiments, all
anions were added in the form of tetrabutylammonium
(TBA) salts, which were purchased from Sigma-Aldrich
Chemical, stored in a vacuum desiccator containing self-
indicating silica and dried fully before using. DMSO was
dried with CaH2 and then distilled in reduced pressure.
Synthesis of anthraceno-9, 10-dicarbaldehyde
bis-(phenyl-semithiocarbazone)
The sensor 1 was synthesized in three steps (see Scheme 1)
starting from anthracene-9, 10-dicarbaldehyde [18, 19] and
4-phenylthiosemicarbazide [20] that were prepared
according to the literature. A mixture of 0.234 g (1 mmol)
anthracene-9, 10-dicarbaldehyde, 0.334 g phenyl-semit-
hiocarbazide (2 mmol) and three drops of acetic acid were
dissolved in 60 mL CH3CH2OH and then the resulting
solution was heated and refluxed for 2 h. The formed
precipitate was immediately filtered, and then 0.452 g red
solid was obtained after recrystallization from CH3CN.
This procedure yields 0.452 g (85%). 1H NMR (400 MHz,
DMSO-d6, Me4Si) dH 7.16 (pseudo-t, J1 = 7.2 Hz, 2 H,
Ph-H), dH 7.33 (pseudo-t, J1 = 7.4 Hz, 2 H, Anthracene-
H), 7.56 (d, J1 = 7.8 Hz, 4 H, Ph-H), 7.68 (dd,
J1 = 2.9 Hz, J2 = 6.8 Hz,4 H, Anthracene-H), 8.59 (dd,
J1 = 3.1 Hz, J2 = 6.8 Hz, 4H, Ph-H), 9.37 (s, 2 H, NC-H),
10.01 (s, 2 H, NNCS-H), 12.12 (s, 2 H, PhNCS-H). ESI–
MS (m/z): calcd. for C30H24N6S2 [M]?: 522.11, found:
522.15. Elemental analysis calcd for C30H24N6S2: C,
67.64; H, 4.54; N, 15.78. Found: C, 67.86; H, 4.51; N,
15.59.
Apparatus
1H NMR spectra were obtained on a Varian UNITY Plus-
400 MHz Spectrometer. ESI–MS were 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 and
the width of the slits used is 10 nm. Fluorescent spectra
were recorded on an FP-750 fluorescence spectrometer at
298.2 0.1 K and the width of the slits used is 10 nm.
General method
All experiments were carried out at 298.2 0.1 K, unless
otherwise mentioned.
A 2.0 9 10-3 M solution of the sensor 1 in DMSO was
Results and discussion
prepared and stored in the dry atmosphere.
A
2.0 9 10-5 M solution of the sensor 1 in DMSO–H2O
(95:5, v/v) was also prepared. Solutions of 1.0 9 10-2 and
1.0 9 10-1 M tetrabutylammonium salt of the respective
anion were prepared in dried and distilled DMSO and were
stored under a dry atmosphere.
1H NMR titration experiments were carried out in the
DMSO-d6 solution (TMS as an internal standard). 2.5 mL
of 0.01 M solution of the sensor 1 in the DMSO-d6 was
UV–Vis anion titration studies
First, to evaluate the binding ability of sensor 1 to anions,
the UV–Vis titration experiments of the sensor 1 were
carried out in dry DMSO solvent using standard solution of
tetrabutylammonium salts of AcO-, F-, H2PO4-, Cl-, Br-
and I- anions at 298.2 0.1 K. In the process, we
observed obviously spectra changes after adding AcO- and
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J Incl Phenom Macrocycl Chem (2011) 69:63–68
65
1+C1-, Br-, I-
0.5
It is well known that protic solvents such as water or
methanol will competitively form hydrogen-bonding with
the binding site of sensor for anions. In view of the
selectivity of sensor 1 in dry DMSO, we have also designed
the experiments carried out in DMSO–H2O (95:5, v/v)
solution to further investigate their performance. Fortu-
nately, a similar phenomenon was actually observed in
DMSO–H2O (95:5, v/v), so the sensor 1 still has the rec-
ognition capability for AcO- (see Fig. 3), but similar
phenomenon was not observed in DMSO–H2O (95:5, v/v)
for F-, H2PO4-. At the same time, the solution color
changed from light yellow to purple, which provide a
method to detect AcO- by naked-eye conveniently.
1+ H2PO4-
1+F-
0.4
0.3
0.2
0.1
0.0
1+AcO-
400
500
600
700
800
Wavelength/nm
Fluorescence anion titration studies
Fig. 1 UV–Vis spectrum of 1 (2 9 10-5 M) in the presence of 10
equiv of AcO-, F-, H2PO4-, Cl-, Br- and I- in DMSO
The anion binding behavior of the sensor 1 was also
investigated by fluorescence titrations in DMSO, which
was consistent well with the UV–Vis titrations. Obviously,
there was a strong emission band centered at 554 nm, when
excited at k = 476 nm. Upon addition of acetate, there was
a significant decrease in the emission intensity of 1 (see
Fig. 4). Such fluorescence quenching could be ascribed to
the increased photoinduced electron transfer (PET) process
between the anthracene moiety and the binding site [21]. It
was clear that in this system where anthracene moiety and
binding site were separated, anion binding to N–H hydro-
gens caused an in reduction potential of N–H bonds, make
the electron transfer more feasible (see Scheme 2). After
more acetate anions were added to system, it appeared that
the deprotonated species were more electron rich compared
with the hydrated acetate anion, and activated the PET
the color of the solution of 1 changed from light yellow to
purple. A similar spectral change was observed upon the
addition of F-, H2PO4-, but the change were not signifi-
cant like that of acetate. However, as the Cl-, Br- and I-
were titrated into 1, the spectra were hardly changed even
the anions were excessive (see Fig. 1).
Then UV–Vis titrations were carried out in DMSO at a
certain concentration of 1 (2.0 9 10-5 M) with the addi-
tion of the tetrabutylammonium salt of AcO- to study the
anion-binding properties (see Fig. 2). In the absence of the
anion, an absorption maximum was found at 439 nm. Upon
addition of AcO-, the peak at 439 nm decreased gradually
while the new formed peak at 548 nm increased, at the
same time, an isosbestic point at 476 nm was observed.
0.035
0.5
0.030
0.025
0.5
0.4
0.3
0.2
0.4
0.020
0.015
0.010
0.3
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
-
[host]/([host]+[AcO])
0.2
0.1
0.0
20 equiv
0 equiv
40 equiv
0 equiv
0.1
400
500
600
700
800
0.0
400
500
600
700
800
Wavelength/nm
Wavelength/nm
Fig. 2 Evolution of the UV–Vis spectrum of sensor
1
(2.0 9 10-5 M) during the titration with AcO- in DMSO. Inset:
Job’s plot for sensor 1 with AcO- determined by UV–Vis in DMSO,
Fig. 3 Evolution of the UV–Vis spectrum of sensor
1
(2.0 9 10-5 M) during the titration with AcO- in DMSO/H2O
(95:5, v/v)
[1] ? [anion] = 2.0 9 10-3
M
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J Incl Phenom Macrocycl Chem (2011) 69:63–68
350
300
250
200
150
100
50
fluorescence signal intensity F can be expressed in the
following Eq. 1 [25]:
4.6
4.4
4.2
4.0
3.8
3.6
3.4
0 equiv
n
ꢂB
½Gꢁ Fmax þ 10
F
min
20 equiv
F ¼
ð1Þ
n
Y=1.9675X+4.1374
10ꢂB þ ½Gꢁ
In the spectrofluorometry of this work, Fmin, Fmax and F are
the emission intensities of the solution at wavelength
554 nm in the absence of guest, presence of a large excess
of guest, and after addition of a given amount of guest to
certain concentration, respectively. [G] is the concentration
of guest, n is the number of G bound per sensor 1. The
sigmoid curve was obtained and the total binding constant
B was deduced. Practically, this equation can be linearised
in the form of Hill plot and the Hill coefficient (n) can also
be obtained from Eq. 2 [26–29] (see Fig. 4).
-0.4
-0.3
-0.2
-0.1
0.0
0.1
0.2
log[G]
0
-50
500
550
600
650
700
750
Wavelength/nm
Fig. 4 Fluorescence emission changes of sensor 1 upon the addition
of AcO- in DMSO. Inset: fluorescence intensity at 554 nm (F554) of 1
versus increasing concentration of log[G]. kex = 476 nm, the con-
F ꢂ Fmin
centration of 1 is 2.0 9 10-5
M
log
¼ n log½Gꢁ þ B
ð2Þ
Fmax ꢂ F
process more efficiently, resulting in even greater
quenching [22]. This might indicate that the sensor 1
exhibited a good interaction with acetate ions [23].
As shown in Fig. 4, the binding constant of sensor 1 to
AcO- (logb or B) is 4.1374, and the Hill coefficient (n) is
1.9675 indicating sensor 1 binds the acetate anion guest
with a ratio of 1:2 which is consistent with Job plots.
Therefore, the results drawn from the data of fluorescent
titrations are qualitatively matched with that from the
UV–Vis spectral titrations. The affinity constants of sensor 1
for anionic species have been calculated and listed in Table 1.
According to the results from UV–Vis titrations and
fluorescent titrations, the proposed mode for the host–guest
bonding in solution was depicted (see Scheme 2). In the
structure, two acetate anions are located at the each side of
sensor 1 via hydrogen bonding.
Determination of the binding constant
and stoichiometry
Obviously, only one well-defined isosbestic point appeared
at 476 nm in Fig. 2, which indicated that the forming stable
complex had a certain stoichiometric ratio between sensor
1 and AcO-. Further, from Job’s plot [24] of sensor 1 and
AcO- in DMSO we found the maximum at a mole fraction
of 0.3 (see Fig. 2, inset), which indicated that sensor 1
binded AcO- guest with an 1:2 ratio.
As clearly shown in Table 1, the order of binding
affinity of 1 with anions (in DMSO or DMSO-water) is
Meanwhile, we also treated the data from fluorescence
anion titration in another way as below. The total
AcO- ꢃ F- [ H2PO4 * Cl- * Br- * I-. Because
-
Scheme 2 The proposed
binding mode of 1 with AcO-
activating PET process
O
Ha
O
PET
H
S
H
hv1
N
NH
N
N
N
N
H
S
AcO-
S
H
N
N
N
N
N
NH
H
H
S
O
hv2
PET
Hb
O
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J Incl Phenom Macrocycl Chem (2011) 69:63–68
67
Table 1 Affinity constants of sensor 1 with anions in DMSO and
DMSO/H2O (95:5, v/v)
(e)
(d)
(c)
Anions AcO-
F-
H2PO4
Cl- Br- I-
-
lgKaass 4.02 0.15 3.31 0.03 3.01 0.11 ND ND ND
lgKbass 4.13 0.10 3.50 0.10 3.09 0.02 ND ND ND
lgKcass 3.10 0.13 ND
ND
ND ND ND
a
The affinity constants determined by UV–Vis in dry DMSO
The affinity constants determined by fluorescence in dry DMSO
The affinity constants determined by UV–Vis in DMSO–H2O (95:5,
b
c
(b)
(a)
v/v) solution
Hb
Ha
ND cannot determined
acetate is the anion with strongest basicity among the six
tested anions, and has the trigonal chemical structure,
which can form hydrogen-bond interaction with hydrogen-
bond donors. The angle of O–C–O in AcO- is about 120°
13
12
11
10
9
8
7
6
ppm
Fig. 5 1H NMR titration of a 1.0 9 10-2 M solution of 1 in DMSO-
d6 with [Bu4N] AcO-. a 0 equiv.; b 0.2 equiv.; c 0.4 equiv.; d 0.6
equiv.; e 1.2 equiv
-
while the angle of O–P–O in H2PO4 is about 108°, so
AcO- might be more fit to the distance between two –NH
on each side of sensor 1, and forming N–Hꢀꢀꢀ anion
hydrogen bonds. The affinity constants of Cl-, Br-, and I-
are very small due partly to their weak basicity.
1H NMR titrations
To shed a little light on the nature of the intermolecular
interactions between AcO- and sensor 1, 1H NMR spectral
changes upon addition of AcO- in DMSO-d6 solution of 1
(1.0 9 10-2 M) were investigated. Obviously, the proton
signals at 10.01 and 12.12 ppm which have been assigned
to Ha and Hb (marked in Scheme 2) can be observed in the
absence of the AcO- (see Fig. 5). Upon addition of 0.2
equiv of AcO-, the signals of Ha and Hb are broadened,
and anthryl rings exhibited an upfield shift slightly, which
indicates the formation of a host–guest complex [15]. As
increasing the addition of AcO-, the signals of Hb even-
tually disappear, which displays the complete deprotona-
tion of the sensor 1.
Fig. 6 Color changes of the sensor 1 (2.0 9 10-5 M) in DMSO (a)
and DMSO/H2O (95:5, v/v) (b) in absence and presence of five equiv
of anions (from the left to the right: 1 only, 1 ? AcO-, 1 ? F-,
1 ? H2PO4-, 1 ? Cl-, 1 ? Br- and 1 ? I-)
expected to help to extend the development fluorescent
sensors for biologically anions in aqueous medium.
Analytical application
Conclusions
The potential application of sensor 1 in analytical chem-
istry field was evaluated in DMSO and DMSO/H2O (95:5,
v/v). The results show that sensor 1 could be applied in
detection of biologically important anions such as acetate
ion in DMSO (Fig. 6). Upon addition of five equiv anions,
the color of solution of sensor 1 changed from light yellow
to purple by the introduction of AcO-. It is interesting that
the selective recognition ability of sensor 1 for AcO- in
DMSO/H2O (95:5, v/v) mixed solvent is better than dry
DMSO, for the naked-eye discrimination between the
acetate and other anions. Such methodology would be
In conclusion, we have successfully presented a new kind
of colorimetric sensor which can recognize acetate selec-
tively in DMSO or DMSO–H2O (95:5, v/v) solution.
UV–Vis and 1H NMR titration experiments were per-
formed to support this conclusion. It is expected to be
applied for detection of acetate in real life for its good
recognition ability toward acetate.
Acknowledgement This project was supported by the National
Natural Science Foundation of China (20371028, 20671052).
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