A simple ratiometric and colorimetric chemosensor for the selective detection of fluoride in DMSO buffered solution

Article abstract of DOI:10.1016/j.saa.2015.08.030

A derivative of squaramide (cyclobuta[b]quinoxaline-1, 2(3H, 8H)-dione) has been synthesized for the ratiometric and colorimetric sensing of F^- in aqueous solution in competitive fashion. With F^-, probe 1 showed a highly selective naked-eye detectable color change along with a characteristic UV-Vis absorbance over other tested ions, which probably originates from the deprotonation occurred between 1 and F^-, as proved by the ¹H NMR titration experiments and DFT calculations.

Full text of DOI:10.1016/j.saa.2015.08.030

A simple ratiometric and colorimetric chemosensor for the selective detection
of fluoride in DMSO buffered solution
Hu Niu, Qinghai Shu, Shaohua Jin, Bingjun Li, Jiaping Zhu, Lijie Li,
Shusen Chen
PII:
DOI:
Reference:
S1386-1425(15)30188-8
doi: 10.1016/j.saa.2015.08.030
SAA 14040
To appear in:
Received date:
Revised date:
Accepted date:
31 May 2015
31 July 2015
12 August 2015
Please cite this article as: Hu Niu, Qinghai Shu, Shaohua Jin, Bingjun Li, Jiaping Zhu,
Lijie Li, Shusen Chen, A simple ratiometric and colorimetric chemosensor for the selective
detection of fluoride in DMSO buffered solution, (2015), doi: 10.1016/j.saa.2015.08.030
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ACCEPTED MANUSCRIPT
A simple ratiometric and colorimetric chemosensor for the selective
detection of fluoride in DMSO buffered solution
a
a*
a
a
a
a
a
Hu Niu , Qinghai Shu , Shaohua Jin , Bingjun Li , Jiaping Zhu , Lijie Li , Shusen Chen
a
School of Materials Science & Engineering, Beijing Institute of Technology, Beijing, China. Tel: +86-10-68915072; Email: qhshu121@bit.edu.cn,
qinghai@chemie.uni-siegen.de.
Abstract
A derivative of squaramide (cyclobuta[b]quinoxaline-1, 2(3H, 8H)-dione) has been synthesized for the ratiometric and colorimetric
-
-
sensing of F in aqueous solution in competitive fashion. With F , probe 1 showed a highly selective naked-eye detectable color change
along with a characteristic UV-Vis absorbance over other tested ions, which probably originates from the deprotonation occurred
-
1
between 1 and F , as proved by the H NMR titration experiments and DFT calculations.
Key words: Chemosensor; Fluoride detection; Ratiometric; DFT calculation
The field of anion receptor chemistry initiated in the late 1960s
color change.
1
2
by Shriver and Biallas and by Park and Simmons has blossomed
to develop over the past two decades. To achieve the central
theme which is the rapid, sensitive and selective detection of
analytes, much effort has been made on the development of new
receptors that are able to quantitatively detect anions in
Table 1 A comparison of probe 1 with other reported presentative easy-
to-prepare fluoride sensors.
Representative
Detection
method
Detection
medium
Detection
limit
Easy-to-prepare
Fluoride sensors
3
competition fashion. Specifically, colorimetric or ratiometric
chemosensors have attracted a large number of focuses because
they not only can identify the target species but also provide
qualitative and quantitative analysis without the help of any
Naked-
eye/Test strip
Probe 1
DMSO/H
2
O
4.8 μM
1
9
4
,5
Sensor A (E.J. Cho)
Naked-eye
Naked-eye
DMSO/CH
3
CN
Not given
Not given
spectroscopic instrumentation. As reported, plenty of anions
which can influence environmental, medical career and physical
2
0
Sensor B (Y.P. Zhang)
DMSO/H
2
O
6
condition have provoked excessive attentions to researchers,
21
Sensor C (Y.P. Zhao)
Fluorescence
CDCl
3
Not given
especially in aqueous solutions for monitoring environmental
pollution, medicinal diagnostic and health quality standard.
Among the various anions, fluoride ions are omnipresent in daily
life which is widely used as additives in water and toothpastes to
enamel demineralization and prevent dental caries wearing
Experimental
Synthetic materials and instrumentation
7
orthodontic appliances. Thus, fluoride detection is of rapidly
All the chemicals used for the synthesis of probe 1 were of AR
grade unless otherwise stated. All the reagents and solvents were
purchased from commercial sources and used without further
treatment. The aqueous stock solutions of anions of concentration
increasing interest in virtue of its special significance in many
8
fields. So far, there are three main mechanisms between anions
9
-12
and sensors: Lewis acid-base interactions,
hydrogen-bond
1
3,14
interactions, and fluoride anion-induced chemical reactions,
including a large body of deprotonation reactions.
−1
1
5-18
1.5  10 mol/L were prepared from their n-tetrabutylammonium
TBA) salts. The stock solution of probe 1 was prepared by
dissolving an accurately weighed probe 1 in DMSO, and then
Though
(
considerable fluorescent sensors have been designed for detecting
fluoride ions depending on the above mechanisms, most of them
need a help of chemical tests or the synthesis of probe compound
was extremely complicated. In addition, ion-selective electrodes
and colorimetry acting as the most widespread methods for
recognizing fluoride ions are also special instrumentation
dependent and relatively high cost. Therefore, there is a demand
for developing a simple, cost-effective and reliable method to
detect fluoride ions in aqueous environments.
-
5
diluted to 5  10 mol/L with buffer solution (pH = 7.24, DMSO
/
buffer = 90 / 10, v / v, aq. buffer = 0.1 M Tris-ClO4).
The IR spectra were recorded on a Fourier Transform Infrared
Spectrometer with KBr as discs and the IR bands are expressed in
-
1
1
13
frequency (cm ). The H-NMR and C NMR were recorded on a
Varian mercury-plus 400 NMR spectrometer at room temperature
using d -DMSO as solvent and tetramethylsilane (TMS) as
6
1
9
internal standard. The F NMR was recorded on the same
Herein, a derivative of squaramide (cyclobuta[b]quinoxaline-1,
instrument using d -DMSO as solvent and trichlorofluoromethane
6
2
(3H, 8H)-dione) probe 1 was designed and simply synthesized
(
CFCl ) as standard. Elemental analyses were determined on a
3
for the desirable detection of fluoride ions in aqueous solution,
and its advanced performance have been listed in Table 1. Acting
as an absorption-based colorimetric chemosensor, probe 1 not
only can identify the fluoride ions selectively and sensitively but
also detect fluoride ions by naked-eye owing to its distinct visual
vario EL cube elemental analyzer. Absorption spectra were
performed on a TU-1810 ultraviolet spectrophotometer.
Synthesis of cyclobuta[b]quinoxaline-1, 2(3H, 8H)-
dione (Probe 1)
1

ACCEPTED MANUSCRIPT
The probe 1 was synthesized as shown in scheme 1. O-
The probe 1 showed three peaks at 264 nm, 312 nm and 347 nm
phenylenediamine (59 mg, 0.55 mmol), suquaric acid diethyl
in 0.1 M Tris-ClO buffer solution (pH = 7.24, DMSO: buffer =
4
ester (81 μL, 0.50 mmol), zinc trifluoro-methanesulfonate (40 mg,
90 / 10, v / v). The peak at 264 nm was observed due to the π→π*
electronic transition while the absorption at 312 nm and 347 nm
appeared due to the n→π* transition. Upon the addition of
equivalent anions into the buffered aqueous solution of probe 1,
the characteristic red shift (from 347 nm to 372 nm) of absorption
0
.11 mmol), and mixture (10 mL) of toluene and DMF (toluene:
DMF = 19:1) were added in a 100 mL three-necked, round-
bottomed flask equipped with a magnetic stirrer, reflux condenser,
and thermometer socket. The reaction temperature was kept at
-
1
00 ℃ for 12 h. After cooling to room temperature, a red-brown
wavelength could only be observed in the case of F , while
precipitate was observed and isolated by filtering. The obtained
solid was further washed with methanol (35 mL) to produce the
target compound probe 1 as yellow powder in 74% yield (69 mg).
addition of other anions did not cause any significant change in
the absorption profile except CN shown a tiny inessential hump
-
proved by following competition experiments. Therefore, it can
-
1
-
IR (cm ) [KBr]: 3121, 2950, 1656, 1656, 1611, 1548, 1479, 1356;
be concluded that probe 1 can recognize F selectively over other
1
H NMR (400 MHz, DMSO-d , δ ppm): 6.34-6.36 (2H, m, ArH),
.63 (2H, m, ArH), 10.00 (2H, S, NH); C NMR (100 MHz,
anions.
6
1
3
6
1.0
DMSO-d , δ ppm): 116.4, 124.9, 131.7, 174.4, 178.2. Anal, calcd
6
1
and other anions
for C H O N : C, 64.52; H, 3.23; N, 15.05. Found: C, 64.41; H,
1
0
6
2
2
0.8
3
.26: N, 14.87.
0.6
0.4
0.2
0.0
O
O
-
F
O
O
O
O
NH2
NH2
Zn(OTf)2 (20 mol%)
toluene / DMF, 100 o
+
HN
NH
C
-
CN
Scheme 1. The synthetic route for the preparation of probe 1
Computational study
300
350
400
450
Wavelength(nm)
The structural optimization and theoretical UV-Vis spectral of
probe 1, 1-2F and fully deprotonated form 1 were performed
using the computer program Gaussian 09W by applying the DFT
-
2-
-5
Fig. 2 UV-Vis spectral changes of probe 1 (5  10 mol/L) in 0.1 M Tris-
ClO
4
buffer solution (pH = 7.24, DMSO: buffer = 90 / 10, v / v) upon
addition of 10 equivalents of different anions in TBA salts.
(
density functional theory) and TD-DFT methods with a hybrid
functional B3LYP using the basis sets 6-31G (d,p).
In order to eliminate the interference of other anions,
selectivity of probe 1 for F over other anions were further
-
Results and discussion
examined by competitive experiments which were carried out by
reacting probe 1 with 10 equivalents F in the presence of 10
equivalents other anions. By comparing the absorption intensity
at 372 nm, no obvious interference was found from the histogram
-
-
Sensing of F by probe 1
The selective detection of fluoride ions can be seen from the
observed color change of probe 1 solution from pale-yellow to
orange-yellow (Fig. 1). In order to perform these naked-eye
(Fig. 3). These results revealed that 1 showed excellent selectivity
towards the fluoride ions even in the present of other competitive
anions and thus can be used for the efficient detection of fluoride
ions in the samples of different origins.
-
1
experiments, 10 equivalents of various ions (10 μL, 1.5  10
-
mol/L, in buffer) including F ions were added to the solution of
-
5
probe 1 (3 mL, 5  10 mol/L) in 0.1 M Tris-ClO buffer solution
4
-
1
+ F
(
pH = 7.24, DMSO: buffer = 90 / 10, v / v). As show in Fig. 1, no
0.5
-
-
-
1 + F + X
significant color change was observed with other ions except CN
-
-
and F , but the color change caused by CN can be ignored
0.4
0.3
-
completely compared with the color change caused by F , which
indicate the ability of probe 1 to recognize F ions selectively
-
from aqueous system.
0.2
0.1
0.0
1
2
3
4
5
6
7
8
-
5
Fig. 3 UV-Vis of probe 1 (5  10 mol/L) at 372 nm upon the addition of
-
-
-
2-
-
Fig. 1 Naked-eye detection of F ion by probe 1 in the presence of other
ions under visible.
4 3
10 equivalents F and 10 equivalents other anions (X = SO (1), NO
- - - - - -
2
(2), CN (3), NO (4), Cl (5), Br (6), I (7) , AcO (8).
The sensing properties of probe 1 combine with various anions
were investigated by UV-Vis absorption spectroscopy (Fig. 2).
In addition, the sensitive recognition and binding mode of
probe 1 with F was demonstrated by carrying out absorption
-
2

ACCEPTED MANUSCRIPT
titration experiment. With the progressive addition of fluoride
1
1
1
-
5


2
0
(1)

ions from 0-10 equivalents to the solution of probe 1 (5  10
mol/L) in 0.1 M Tris-ClO buffer (pH = 7.24, DMSO: buffer = 90
A A0 K(Amax  A )[F ]
Amax  A0
0
4
/
10, v / v), the absorption intensity at 266 nm and 372 nm was
A and A present the absorbance of 1 before and after addition
0
-
increased gradually along with the simultaneous intensity
decrease of two broad shoulder centered at 307 nm and 342 nm.
The resulting significant bathochromic shift (around 30 nm) of
absorption peak and the two forming absorption isosbestic points
at 284 nm and 356 nm were clearly seen. (Fig. 4) According to
the following analysis of experimental results, we can conclude
that these spectral changes are caused by the deprotonation of
of F , respectively, and Amax is the absorbance obtained with
-
-2
-
excess amount of F . K is the association constant (M ), and [F ]
0
-
is the concentration of F added (M).
Furthermore, to confirm the mechanism of action of probe 1
-
1
with F , H NMR titration experiments were carried out, in which
spectra were recorded by adding 0-6.0 equivalents fluoride ions
into the solution of probe 1 in DMSO-d . It is observed that the
6
-
amino by F . The occurrence of deprotonation would suggest that
peak corresponding to -NH proton at δ = 10.00 ppm was
weakened with the increase of fluoride ions and the peak
disappeared when 2.0 or more equivalents fluoride ions were
added into the solution of 1 (Fig. 6). The result clearly showed
2
-
HF and the negatively charged 1 were formed. This causes an
obvious increase in the charge density on the amino nitrogen
which is verified by our computational study.
-
that the –NH proton of probe 1 was captured by F which was
0.5
0.4
0.3
0.2
0.1
0.0
-
2
proved by the observing bifluoride anion (HF ) signal at around
0.8
0.6
0.4
0.2
0.0
24
19
δ = -141 ppm in F NMR spectroscopy (Fig. S5) and
2
-
25
1
r
= 0.992
characteristic absorption peak of HF2 around 16.5 ppm in H
NMR spectroscopy (Fig. S6). These results further confirmed our
conclusion that the color change was caused by the deprotonation
of amino.
0
2
4
6
8
-
10
Mole Equiv. of F
3
00
350
400
450
Wavelength(nm)
-
5
Fig. 4 UV-Vis titration experiments of 1 (5  10 mol/L) in 0.1 M Tris-
ClO buffer solution (pH = 7.24, DMSO / buffer = 90 / 10, v / v) with the
addition of 0-10 equivalents of n-Bu NF. Inset: The absorption intensity
I) of 1 at λ = 372 nm as a function of mole equivalents of F ions.
4
4
-
(
-
To determine the stoichiometry between probe 1 and F , Job’s
plot (Fig. 5) was employed and the 1:2 stoichiometry was found,
2
2
-
suggesting the deprotonation of amino by basic F was possibly
occurred. Moreover, the association constant K between 1 and
-
23
8
-2
two F is determined from eq (1) to be 4.00610 M (Fig. S4).
1
Fig. 6 H NMR spectrums of probe 1 in the presence of 0-6 equivalents of
0.08
0.06
0.04
0.02
0.00
TBA·F.
-
The limit of detection of the receptor 1 was calculated for F
2
6
ions by using absorption titration . Before calculated the relative
standard deviation, the absorption measurements of ten blank
samples were taken. The detection limit is then calculated with
the following equation: detection limit = 3δ /m (δ is the
standard deviation of blank measurements, and m is the slope
between intensity versus sample concentration). The calculated
bi
bi
-
LOD value of probe 1 for F ions is 4.8 μM.
Application of probe 1
0.0
0.2
0.4
1] / [1]+[F ]
0.6
0.8
1.0
-
[
-
In order to explore the application for the recognition of F , the
test strip with probe 1 was prepared. The test trip was prepared by
Fig. 5 Job plot for the interaction between 1 and TBA·F: the change in
absorption intensity (△A) at λ = 372 nm as a function of mole equivalents
of [1] / ([1] + [F ]).
soaking small strips of cellulose paper in the solution of probe 1
-
-2
(110 mol/L) in Tris-ClO
buffer solution and dried in air.
4
3

ACCEPTED MANUSCRIPT
-
-2
When the strip was dipped in aqueous solution of F (510
in the probe 1. These entire phenomena represented a total
agreement with the disappearance of -NH in the H-NMR
1
mol/L) the colorless (A) strip turned into dark yellow (B)
immediately. (Fig. 7)
titration experiments. Furthermore, the HOMO and LUMO
diagrams of probe 1, 1-2F and 1 indicate that the internal
-
2-
charge transfer occurred during the anion recognition process.
-
2-
Also, the HOMO-LUMO band gaps of 1-2F and 1 were
approximately equal suggested that occurrence of deprotonation
during the recognition. Besides, compared with probe 1, the
-
2-
HOMO-LUMO band gaps of 1-2F and 1 were decreased, which
supports the absorbance at longer wavelength (Fig. 9).
Finally, in order to readily confirm the occurrence of
deprotonation during the recognition between probe 1 and F , TD-
-
Fig. 7 Application of probe 1 for detection of F by test strip method
-
DFT calculation was employed to predict the theoretical UV-Vis
spectral changes of 1, 1-2F and deprotonated 1, from which we
Theoretical results
-
can also observe three peaks at 171 nm, 245 nm and 312 nm of
To understand the intermolecular charge transfer process that
occurred between probe 1 and F , DFT calculations were
performed using the B3LYP/6-31G (d,p) basis set. The optimized
structure of the receptor probe 1 and the stable structure after
adding fluoride ions and fully deprotonated form of the probe 1
probe 1 and a obvious shift of absorption from 312 nm to 363 nm
-
-
after adding F , which was in agreement with the experimental
results. In addition, the appearance of absorption peak at 388 nm
for the fully deprotonated form of the probe 1 further indicate that
the characteristic red shift of 1-2F was caused by deprotonation.
were shown in Fig. 8. The calculated interaction energy (E
=
int
-
Ecomplex − Ereceptor − E ) was -125.44 kcal/mol which indicated the
F
3
5000
0000
formation of stable structure. In the optimized structure, the
distance (1.47Ǻ) between N and H beyond the bond length scope
3
1
1
1
-
-2F
2-
(1.01Ǻ) of -NH and the distance (1.00Ǻ) between F and H is
25000
nearly equal to the bond length (0.92 Ǻ) of HF.
20000
15000
10000
5000
0
200
400
600
Excitation Energy (nm)
2-
Fig.10 TD-DFT computed UV spectral diagrams of the 1, 1-2F and 1 .
2-
Fig. 8 Optimized structure of the probe 1 (a), 1-2F(b) and 1 (c) in the gas
phase using DFT calculation at B3LYP/6-31G (d,p) level.
Conclusion
In summary, we have successfully developed a derivative of
squaramide probe 1 as desirable ratiometric and colorimetric
chemosensor for the recognition of fluoride ions in aqueous
media with high selectivity and sensitivity.
The recognition of fluoride ions was confirmed by obvious
color change from pale-yellow to orange-yellow due to the
appearance of a new charge transfer band. The remarkable
colorimetric sensing of probe 1 confirmed a 1:2 action model.
-
Furthermore, probe 1 can be used to detect F in the aqueous
media by naked-eye and induce a remarkable spectroscopic
response by giving a new intense peak in the absorption spectrum
at 372 nm. Considering the good selectivity and sensitivity of
-
chemosensor probe 1 for the detection of F from aqueous system,
its applications in chemical and daily life will become more
convenient.
Acknowledgements
Fig. 9 DFT computed LUMO and HOMO diagrams of the probe 1 (a), 1-
-
2-
2
F (b) and 1 (c) in the gas phase.
We acknowledge the financial support from the Excellent Young
Scholar Research Found of Beijing Institute of Technology of
China (No. 3090012331542).
Apparently, occurrence of deprotonation was attributed to the
strong electronegativity of fluoride which induced charge transfer
4

ACCEPTED MANUSCRIPT
Notes and references
a
School of Material Science and Engineering, Beijing Institute of
Technology, 100081 Beijing, China
5

ACCEPTED MANUSCRIPT
Graphical Abstract
A simple ratiometric and
colorimetric chemosensor for the
selective detection of fluoride in
DMSO buffered solution
a
a*
a
a
Hu Niu , Qinghai Shu , Shaohua Jin , Bingjun Li , Jiaping
a
a
a
Zhu , Lijie Li , Shusen Chen
a
School of Materials Science & Engineering, Beijing Institute of
Technology, Beijing, China. Tel: +86-10-68915072; Email:
qhshu121@bit.edu.cn, qinghai@chemie.uni-siegen.de.
6

ACCEPTED MANUSCRIPT
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