The synthesis and recognition properties of colorimetric fluoride receptors bearing sulfonamide

Article abstract of DOI:10.1016/j.jfluchem.2007.01.005

Two artificial receptors, 1,2-bis-p-substituted phenyl-sulfonamido-4,5-bis-nitrobenzene, have been designed and synthesized. The interactions of these receptors with halide anions are determined by UV-vis and ¹H NMR titration experiments. Resul

Full text of DOI:10.1016/j.jfluchem.2007.01.005

Journal of Fluorine Chemistry 128 (2007) 530–534
www.elsevier.com/locate/fluor
The synthesis and recognition properties of colorimetric
fluoride receptors bearing sulfonamide
Xue-Fang Shang a, Hai Lin b, Hua-Kuan Lin a,
*
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
Received 11 September 2006; received in revised form 26 December 2006; accepted 6 January 2007
Available online 20 January 2007
Abstract
Two artificial receptors, 1,2-bis-p-substituted phenyl-sulfonamido-4,5-bis-nitrobenzene, have been designed and synthesized. The interactions
of these receptors with halide anions are determined by UV–vis and 1H NMR titration experiments. Results indicate that two receptors have strong
sensitivity and selectivity for fluoride among halide anions. In addition, the visible color changes upon the addition of fluoride anion can make the
receptors as convenient detection tools for fluoride anion.
# 2007 Elsevier B.V. All rights reserved.
Keywords: Fluoride anion; Colorimetric detection; Sulfonamide
1. Introduction
also studied that the sulfonamide system had strong affinity to
chloride anion. However, the recognition properties of
sulfonamide receptor that can be detected by naked eyes when
they act with fluoride anion are few reported. It is limited for
sulfonamide receptors to use extensively and conveniently.
According to this information, we synthesized two
sulfonamide receptors (see Scheme 1) and studied anion
recognition properties to halide anions by UV–vis and 1H NMR
titration experiments. The sulfonamide receptors show the
noticeable color changes and the high selectivity and affinity
for fluoride ion among halide anions. The above advantages can
make the receptors as convenient detection tools for fluoride
anion.
The development of design and synthesis of new artificial
receptors for selective anion recognition has attracted
considerable attention in the field of host–guest chemistry
because of the important roles of anion in biomedicinal and
chemical processes [1]. Artificial anion receptor has repre-
sented the unique application prospects in anion sensors [2],
membrane transmit carrier [3] and mimic enzyme catalyst
synthesis, etc. [4,5]. Because the hydrogen bond has good
directionality and selectivity [6], urea, sulphur urea and amide,
etc., groups that can form strong hydrogen bond ability to
anions have been used extensively in the design and synthesis
of the neutral anion receptors [7]. It is the key point for the
molecular designs of the fluoride anion recognition that shows
how to achieve the specific recognition of fluoride anion and
how to convert the recognition event into a signal. In particular,
the sensing of fluoride anion has attracted growing attention and
several types of synthetic chemosensors have been developed to
date. Shin-ichi et al. [8] have reported that sulfonamide
receptors exhibit large affinity constants for acetate and
dihydrogen phosphate ions. Crabtree and co-workers [9,10]
2. Results and discussion
1 and 2 were synthesized according to the route shown in
Scheme 2.
Briefly, o-phenylenediamine was reacted with p-substituted
phenylsulfonylchloride under the conditions of pyridine and
373 K to produce 1,2-bis-p-substituted phenyl-sulfonamido-
benzene [11]. Direct nitration [12] of 1,2-bis-p-substituted
phenyl-sulfonamido-benzene with fuming HNO3 gave the
target compounds 1 or 2 in high yield and were characterized by
* Corresponding author. Tel.: +86 22 23502624; fax: +86 22 23502458.
1
E-mail address: hklin@nankai.edu.cn (H.-K. Lin).
IR, H NMR spectroscopy, elemental analysis and ESI-MS.
0022-1139/$ – see front matter # 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2007.01.005

X.-F. Shang et al. / Journal of Fluorine Chemistry 128 (2007) 530–534
531
Scheme 1. The structure of receptors.
UV–vis spectral titration method is applied extensively to
the system of coordination reaction that can induce absorption
spectrum change [13]. It is a convenient and swift method to
determine the affinity constant of supramolecular complex.
Recognition properties of 1 and 2 for halide anions [tetra-(n-
butyl)-ammonium salts] were examined by UV–vis spectral
titration method in DMSO.
As shown in Fig. 1, the spectra change clearly with the
increase of fluoride ion concentration. Receptor 1 has a certain
absorption band centered at 430 nm, and the intensity of
absorbance at 430 nm decreases upon the addition of fluoride
anion. At the same time, a new absorbance peak appears at
550 nm, and the intensity of this absorbance increases. The
color of the solution changes from yellow to red with the
increase of fluoride anion concentration (Fig. 2). When the
concentration of fluoride anion is 30-fold greater than that of
receptor 1, no further change of electronic spectrum or color
Fig. 2. Color changes observed with the addition of various anions to DMSO
solution of 1 and 2, 5 equiv. for each anion were used.
occurs. In addition, two clear isosbestic points appear at 400
and 475 nm. This shows that the stable complex forms with a
certain stoichiometric ratio between 1 and fluoride anion.
However, the additions of Clꢀ, Brꢀ and Iꢀ virtually lead to no
spectral changes. Also there exist similar spectrum changes
between 2 and Fꢀ, Clꢀ, Brꢀ and Iꢀ, compared with 1.
Scheme 2. Synthesis route for 1 and 2.
Fig. 1. UV–vis spectral changes of receptors 1 and 2 upon the addition of fluoride anion (added in the form of tetra-n-butylammonium salts) at 298 K,
[1] = [2] = 2 ꢁ 10ꢀ5 mol/l, [Fꢀ] = 0–160 ꢁ 10ꢀ5 mol/l. Arrows indicate the direction of increasing anion concentration.

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X.-F. Shang et al. / Journal of Fluorine Chemistry 128 (2007) 530–534
Fig. 3. Fitting curves of receptors 1 and 2 with fluoride anion using non-linear least square method.
Job’s plots of receptors 1, 2 and various anions in DMSO
than the radius of Clꢀ, Brꢀ and Iꢀ, and easily forms hydrogen
bonds between Fꢀ and –NH. Therefore, 1 and 2 have strong
recognition for fluoride anion. In addition, for Fꢀ, the affinity
constant of 2 is 1.8-fold than that of receptor 1. Comparison
with 2, the electron-giving effection of –CH3 in receptor 1
induces the increase of electron cloud density of –NH. Thus, the
binding ability of 1 for fluoride anion is weaker than that of 2.
The sulfonamide system of Crabtree and co-workers [9,10]
have strong affinity to chloride anion because the coordination
space of two –NH locating meta-site is fit for the size of
chloride anion. While, the two –NH of our sulfonamide system
is located ortho-site. We speculate the space of anionic
coordination in this system is fit for the size of fluoride anion
according to the affinity constants (see Table 1). Therefore,
sulfonamide receptor with –NH located ortho-site may have
strong affinity to fluoride anion, and Crabtree’s sulfonamido
with –NH located meta-site may have strong selectivity for
chloride anion.
show the maximum at a molar fraction of 0.5. The results
indicate that the receptors bind anion guest with a 1:1 ratio.
Affinity constants of receptor for anionic species are calculated
according to the relational expression (1) of 1:1 host–guest
complexation [14]:
ꢀ
1
X ¼ X0 þ 0:5 De cH þ cG þ
Ks
ꢁꢂ
ꢃ
ꢄ
ꢅ
1=2
1
ꢀ
cH þ cG þ
2 ꢀ 4cHcG
(1)
Ks
where cG and cH are the concentration of guest and host,
respectively, X the intensity of absorbance at certain concen-
trations of host and guest, X0 the intensity of absorbance of host
when the anion is not added, Ks the affinity constant of host–
guest complexation and De is the change in molar extinction
coefficient. Fig. 3 shows the fitting curves by non-linear least
square method. The higher correlation coefficients (r > 0.98)
of fitting curves also prove the receptors 1 and 2 bind fluoride
anion for 1:1 ratio. The affinity constants obtained by the
method of non-linear least square calculation are summarized
in Table 1.
Obviously, the recognition function of 1 and 2 for fluoride
anion are the most remarkable among halide anions. The
binding abilities between 1 or 2 and various anions lie in the
order: Fꢀ ꢂ Clꢀ ꢃ Brꢀ ꢃ Iꢀ. The affinity constant between 1
and Fꢀ is about 1200-fold greater than that for Clꢀ, Brꢀ and Iꢀ,
and the affinity constant between 2 and Fꢀ is about 1500-fold
greater than that for other anions observed. The reason may be
that spatial steric hindrance of oxygen atoms limits the
interactions of receptors with anions in space, and only matched
anion may have strong binding ability with receptors.
Furthermore, the radius of fluoride anion is much smaller
Table 1
Affinity constants of 1 and 2 with various anions
Anion
Fꢀ
Clꢀ
Brꢀ
Iꢀ
Ks (1) (Mꢀ1
Ks (2) (Mꢀ1
)
)
(1.4 ꢄ 0.4) ꢁ 104
(2.5 ꢄ 0.6) ꢁ 104
11
20
12
14
14
19
Fig. 4. Plots of 1H NMR spectra of receptor 2 in DMSO-d6 upon the addition of
various quantities of Bu4NF.

X.-F. Shang et al. / Journal of Fluorine Chemistry 128 (2007) 530–534
533
On the other hand, the synthesis route for 1 and 2 were short
and simple. The materials were cheap and easily obtained. It is
convenient and available for us to make 1 and 2 as good
chemosensors.
anions, in the form of tetrabutylammonium salts, were
purchased from Sigma–Aldrich Chemical Co., stored in a
desiccator under vacuum containing self-indicating silica, and
used without any further purification. Dimethyl sulfoxide
(DMSO) was distilled in vacua after dried with CaH2. Tetra-n-
butylammonium salts (such as (n-C4H9)4NF, (n-C4H9)4NCl, (n-
C4H9)4NBr and (n-C4H9)4NI) need to be dried 24 h in vacuum
with P2O5 at 333 K before use. C, H, N elemental analyses were
made on Vanio-EL. 1H NMR spectra were recorded on Varian
UNITY Plus-400 MHz Spectrometer. UV–vis spectroscopy
titrations were made on Shimadzu UV2550 Spectrophotometer
at 298 K. IR spectra were obtained of KBr pellets on a 560E.S.
PFT spectrophotometer spectrum. ESI-MS was performed with
a MARINER apparatus.
Very recently, a number of fluorogenic and/or chromogenic
anion sensors comprising recognition moieties with acidic
protons, such as urea, thiourea, or amide have been reported to
undergo an anion-induced deprotonation [15–17]. According to
these reports, one triplet resonance appears at 16.1 ppm, the
characteristic resonance of bifluoride (F–H–F) and the non-
interacted protons undergo upfield shift. To look into the anion
binding properties of receptors for halide anions, the 1H NMR
titration experiment in DMSO-d6 between receptor 2 and Fꢀ is
shown in Fig. 4. Upfield proton shift are observed in the phenyl
rings signals (d = 7.8–7.54 ppm) with the addition of 1 equiv.
Fꢀ. That suggests that the amides of receptor 2 occur
deprotonation according to reported literature [18]. In fact,
the negative charge of nitrogen atom, after the amides occur
deprotonation, causes a shielding effect and should promote an
upfield shift. In addition, the chemical shift of phenyl rings
signals are stopped after addition of 1 equiv. Fꢀ. This also
explains the binding between receptor 2 and fluoride anion is
1:1. As for receptor 1, the amides may occur deprotonation due
to the similar system with receptor 2 only the difference of
substituent group.
1,2-Bis-p-substituted phenyl-sulfonamido-benzene were
synthesized according to the reported process [11].
1,2-Bis-( p-methylphenylsulfonamido)-4,5-bis-nitroben-
zene (1) [12]. 1,2-Bis-phenyl-sulfonamido-benzene (50 g,
0.25 mol) was put in 500 ml three-neck flask and CH3COOH
(250 ml) was added. Then the mixture acid with 11 ml fuming
HNO3 and 13 ml CH3COOH was added dropwise at 333 K with
stirring. After the addition was completed, the mixture solution
was reacted again for 0.5 h at 333 K, then was cooled, filtrated
and obtained shallow yellow solid. The product was washed
with acetic acid, alcohol, recrystallized from ethyl acetate and
dried in vacuum. mp 248–250 8C; IR (KBr): n = 3264 (NH),
1357 and 1335 cmꢀ1 (NO2). 1H NMR (400 MHz DMSO-d6), d:
7.75 (s, 2H), 7.68 (d, 4H), 7.36 (d, 4H), 2.37 (s, 6H). Elemental
analysis calcd. for C20H18N4O8S2: C, 47.4; H, 3.6; N, 11.1;
found: C, 47.9; H, 3.5; N, 11.3. ESI-MS (m/z): 504.8 (M ꢀ H)ꢀ.
1,2-Bis-(phenylsulfonamido)-4,5-bis-nitrobenzene (2) was
synthesized according to the above procedure only the
replacement of 1,2-bis-( p-methylphenylsulfonamido)-benzene
with 1,2-bis-(phenylsulfonamido)-benzene. mp 246–248 8C;
3. Conclusions
In summary, we synthesized and studied the recognition
properties of 1,2-bis-( p-methylphenylsulfonamido)-4,5-bis-
nitrobenzene (1) and 1,2-bis-(phenyl-sulfonamido)-4,5-bis-
1
nitrobenzene (2) with halide anions by UV–vis and H NMR
titrationexperiments. ThestudiesofUV–visspectraclearlyshow
that theaffinity constants of1 and 2 to Fꢀ are about 1.4 ꢁ 104 and
2.5 ꢁ 104 Mꢀ1, respectively, almost 1200- and 1500-fold greater
than that forClꢀ, Brꢀ andIꢀ. Thus, these receptors (1 and2) have
strong sensitivity and selectivity for fluoride anion over other
anions examined. What’s more, the visible color changes of the
interactions between 1 or 2 and fluoride anion may make 1 and 2
as colorimetric sensors. Accordingly, it is possible to conceive
the use of 1 and 2 in various sensing applications as well as in
other situations, such as anion transport and purification, where
the availability of cheap and easy-to-makeanion receptors would
be advantageous. Therefore, 1 and 2 not only have the important
theory significance, but also have the significant economic and
social efficiency. The above conclusion may have inspiring
meaning for us to research new kinds of color receptors and may
provide experimental method for the monitoring of fluoride
anion in biological system. However, we only study the
interactions of receptors and spherical anions. As for other type
anions(linear, trigonal, tetrahedral anions), furtherstudiesonthis
line are in progress.
1
IR (KBr): n = 3261 (NH), 1358 and 1335 cmꢀ1 (NO2). H
NMR (400 MHz DMSO-d6), d: 7.78 (d, 2H), 7.66 (s, 2H), 7.62
(s, 2H), 7.55 (d, 4H). Elemental analysis calcd. for
C18H14N4O8S2: C, 45.2; H, 3.0; N, 11.7; found: C, 45.6; H,
2.9; N, 11.6. ESI-MS (m/z): 476.6 (M ꢀ H)ꢀ.
Acknowledgements
This work was supported 20371028 by project from the
National Natural Science Foundation of China and 023605811
project from the Natural Science Foundation of Tianjin.
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