Study on the selectivity of anion receptors by adjusting the distance of two urea fragments and their analytical application

Article abstract of DOI:10.1007/s10847-010-9819-z

Three anion receptors based on urea: 1 N, N′-bis-(p- nitrophenylaminocarbonyl)-Hydrazine, 2 N, N′-bis-(p-nitrophenylaminocar- bonyl)-ethylenediamine and 3 N, N′-bis-(p-nitrophenylaminocarbonyl)-1, 3-propane-diamine are designed and synthesized. Studies of

Full text of DOI:10.1007/s10847-010-9819-z

J Incl Phenom Macrocycl Chem (2011) 69:101–106
DOI 10.1007/s10847-010-9819-z
ORIGINAL ARTICLE
Study on the selectivity of anion receptors by adjusting
the distance of two urea fragments and their analytical application
•
•
•
Weiwei Huang Jianwei Li Hai Lin
Huakuan Lin
Received: 27 March 2010 / Accepted: 8 June 2010 / Published online: 25 June 2010
Ó Springer Science+Business Media B.V. 2010
Abstract Three anion receptors based on urea: 1 N,
N0-bis-(p-nitrophenylaminocarbonyl)-Hydrazine, 2 N, N0-bis-
(p-nitrophenylaminocar-bonyl)-ethylenediamine and 3 N,
N0-bis-(p-nitrophenylaminocarbonyl)-1, 3-propane-diamine
are designed and synthesized. Studies of UV–vis spectra
presented that 1 was an excellent sensor of F- and 2 was
sensitive to H2PO4-. Unfortunately, 3 can not distinguish
the anions investigated in this paper. The color changes of
the hosts upon the addition of a variety of structurally
different anions were also utilized as naked-eye detection
which is very convenient. It also revealed significantly that
the distance between two recognition sites of receptor had
an immediate effect on the selectivity of receptor for
anions, which had been confirmed by the 1H NMR titration
and IR.
by the principle of size and shape complementarity: given a
particular guest, a host must be designed whose steric
configuration is complementary to that of the guest [2]. So
the length of the binding sites defines the shape and the size
of the anion, which is selective towards the anion. Creating
selectivity that extends beyond the mere binding capacity
and also allows anion recognition is the ultimate goal.
However, this is also the true challenge in host design. As a
corollary, selectivity could serve as a yardstick to asses the
quality of a particular design attempt and document the
progress [3, 4].
Inorganic anions are ubiquitous throughout biological
system; it is believed that they carry genetic information
(DNA is a polyanion) and participate in 70% of all enzy-
matic reaction. Among a range of biologically important
anions, fluoride is of particular interest owing to its
important role in the human body [5, 6]. Further more,
phosphate esters exist commonly in nature in the form of
nucleoside phosphates as components of RNA (or DNA)
[7]. Thus, development of artificial fluoride receptors and
phosphates receptors would afford new methodologies for
detection, separation, or transport of biologically important
fluoride anion and phosphate anion. Many anion receptors
based on urea emerged after the original papers by Wilcox
[8] and Hamilton [9] on urea–anion interactions. Notice-
ably, a series of receptors based on urea exhibit prominent
selectivity [10]. A lot of examples have been reported of
anion receptor systems that urea and urea groups [1] to
complex anionic guests. In this paper, three receptors
bearing two urea groups as colorimetric group were
designed and synthesized. The steric configuration can be
adjusted to an anion’s bulk by changing the distance
between the two fragments and receptors 1 and 2 have
potential application in analytical inorganic anions by
naked-eye detection.
Keywords Anion recognition ꢀ Sensor ꢀ Selectivity
Introduction
For years, the recognition of inorganic and biotic anions
has been a key research area of supramolecular chemistry
[1]. Selectivity of anion recognition receptor is governed
W. Huang ꢀ J. Li ꢀ H. Lin (&)
Department of Chemistry, Nankai University, Tianjin 300071,
People’s Republic of China
e-mail: hklin@nankai.edu.cn
H. Lin
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) 69:101–106
Experimental
Materials
6.4–6.6 (2H, m, CONH), 7.6 (4H, d, Ph), 8.1 (4H, d, Ph), 9.3
(2H, s, PhNHCO); Elemental analysis: Calc. for
C17H18N6O6: C, 50.75; H, 4.51; N, 20.89; Found: C, 51.08;
H, 4.26; N, 21.05.
All reagents for synthesis obtained commercially were
used without further purification. In the titration experi-
ments, all the anions were added in the form of tetrabu-
tylammonium (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.
Results and discussion
UV–vis anion titration studies
In order to study the binding selectivity of receptor 1, 2 and
3, UV–vis titrations were carried out in DMSO at a con-
centration of 1.0 9 10-5 M by adding tetrabutylammo-
nium salts of anions at 298.2 0.1 K. Among the six
anions investigated in DMSO solution, namely, AcO-, F-,
H2PO4-, Cl-, Br- and I-, 1 exhibited selective recognition
General method
1H NMR spectra were recorded on a Varian UNITY Plus-
400 MHz Spectrometer at the Key Laboratory of Func-
tional Polymer Materials of Ministry of Education, Nankai
University. UV–vis Spectroscopy titrations were performed
on a Shimadzu UV2450 Spectrophotometer at 298 K.
Infrared spectra were measured on a Perkin Elmer Model
1600 FT-IR Spectrophotometer. Elemental analysis for C,
H, and N were carried out on a PerkinElmer 240C element
analyzer at the Institute of Elemento-Organic Chemistry,
Nankai University.
-
for F- and 2 for H2PO4 as shown in Fig. 1.
Figure 1 (a) shows the UV–vis spectral changes of 1
during the titration with fluoride ions and Fig. 1 (b) shows
the UV–vis spectral changes of 2 during the titration with
dihydrogen phosphate ions. It turns out that the UV–vis
absorption band of 1 and 2 in DMSO undergoes a red shift.
In the absence of anions, the absorption spectrum of 1 is
characterized by the presence of one absorption maximum
peak at 345 nm. Upon addition of F-, the absorption peak
345 nm decreases while a new peak forms at 354 nm. On
the other hand, the absorption peaks at 350 nm of 2 was
A series of DMSO solutions having same host concen-
tration and different anion concentrations were prepared,
respectively. The affinity constants Ks were obtained by the
determination of absorption of the series of solutions and
analysis of obtained absorption values with non-linear least
square calculation method for data fitting.
-
shifted to 367 nm upon H2PO4 titration. In addition, the
presence of well-defined isosbestic points at 350 nm for (a)
and 354 nm for (b) indicated that there form the stable
complex with a certain stoichiometric ratio between the
receptors and anions [12]. However, as the Cl-, Br- and I-
were titrated into 1, 2 and 3, the spectra displayed slightly
change even the anions were excessive. In comparison,
Synthesis of receptors
-
receptor 3 does not distinguish AcO-, F- and H2PO4
1, 2 and 3 were synthesized according to the route shown in
Scheme 1 and 1-isocyanato-4-nitrobenzene was acquired
by the reported process [11]. 1-isocyanato-4-nitrobenzene
(15 mmol, 2.46 g) was dissolved in acetonitrile (50 ml). To
a solution of 0.0075 mol of hydrazine, ethylenediamine and
1, 3-propylenediamine was added respectively. The mixture
was refluxed on a water bath for 3 h. The solid product,
obtained on cooling, was washed with distilled water and
obviously.
In Fig. 2, job’s plot [13] of receptor 1 and F- in DMSO
shows the maximum at a molar fraction of 0.5. This result
indicates that the receptor 1 binds fluoride anion guest with
a 1:1 ratio. Moreover, similar results can also be obtained
for other anions (AcO- and H2PO4-). The semblable job’s
plot can be acquired from receptor 2 and 3.
1
recrystallized from ethanol. For 1, yield 73%, H NMR
(400 MHz; DMSO-d6; Me4Si) 7.8 (4H, d, Ph), 8.2 (4H, d,
Ph), 8.4 (2H, s, CONHNH), 9.6 (2H, d, PhNHCO), Ele-
mental analysis: Calc. for C14H12N6O6: C, 46.67; H, 3.36;
N, 23.33; Found: C, 46.70; H, 3.61; N, 23.13. For 2, yield
68%,1H NMR (400 MHz DMSO-d6; Me4Si) 1.7–1.9 (4H,
m, NCH2), 6.5 (2H, s, CONH), 7.6 (4H, d, Ph), 8.1 (4H, d,
Ph), 9.4 (2H, s, PhNHCO); Elemental analysis: Calc. for
C16H16N6O6: C, 49.49; H, 4.15; N, 21.64; Found: C, 49.40;
O2N
NH2
NH
HaN
n
ethyl
acetate
bis(trichlo
romethyl)
carbonate
O
O
HN
NHb
NH2
H2N
n
O2N
NCO
NO2
(1):n=0;(2):n=2;(3):n=3
O2N
n=0, 2, 3
1
H, 4.41; N, 22.13. For 3, yield 67%, H NMR (400 MHz
DMSO-d6; Me4Si) 1.6–1.9 (2H, m, CH2), 1.9 (s, NCH2),
Scheme 1 The synthesis of receptors
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J Incl Phenom Macrocycl Chem (2011) 69:101–106
103
Fig. 1 a Family of spectra
taken in the course of the
0.36
0.33
0.30
1.54
1.53
1.52
1.51
1.50
1.49
1.48
1.47
1.46
(a)
(b)
0.4
0.3
0.2
0.1
0.0
titration of a 5.0 9 10-5
M
1.5
1.0
0.5
0.0
solution of 1 with a standard
solution of F- at
0.0000 0.0002 0.0004 0.0006 0.0008
298.2 0.1 K. b Family of
spectra taken in the course of
0.0000 0.0001 0.0002 0.0003 0.0004 0.0005
the titration of a 1.0 9 10-5
solution of 2 with a standard
M
-
solution of H2PO4
300
350
400
450
300
350
400
Wavelength (nm)
Wavelength (nm)
0.5
0.4
0.3
0.2
0.1
0.0
[FHF-]
5.0 equiv
2.0 equiv
(e)
(d)
(c)
1.0 equiv
0.5 equiv
(b)
Hb
Ha
0 equiv
8
(a)
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
[host]/([host]+[F-])
16
14
12
10
ppm
Fig. 2 Job’s plot for complexion of receptor 1 with F- determined by
UV–vis in DMSO at 298.2 0.1 K, [1] ? [F-] = 3.5 9 10-5
M
Fig. 3 1H NMR spectra of 1 in DMSO-d6 a the absence and the
presence of b 0.5, c 1.0, d 2.0, e 3.0, f 5.0 equiv of F-
radius of F- is suitable for receptor 1. Receptor 2 is sen-
sitive to H2PO4-, which is also due to the steric configu-
ration-matching. For receptor 3, C3 chain makes the two
urea fragments too far to have selectivity to the guest we
investigated.
Table 1 The affinity constants of receptor 1, 2 and 3 with anions at
298.2 0.1 K, respectively
Anions F-
H2PO4
AcO-
Cl- Br- I-
-
log KS,1 5.31 0.35 3.66 0.14 3.47 0.18 ND ND ND
log KS,2 3.21 0.18 4.35 0.23 3.50 0.22 ND ND ND
log KS,3 3.49 0.19 3.78 0.21 3.49 0.21 ND ND ND
1H NMR anion titration studies
ND indicated that the spectra showed little or no change with the
addition of the anion so that the affinity constant can not be deter-
mined using the spectra
To further look into the nature of host–guest interactions,
1H NMR titration experiments were conducted in DMSO-
d6.
1
Figure 3 presents the H NMR spectra changes of the –
Affinity constants of receptor 1, 2 and 3 for anionic
species are calculated and listed in the Table 1 below.
Compared with the previous research in previous
research [14], receptor 1 and receptor 2 has higher selec-
tivity than compound 2 and 4. The reason may be that the
steric configuration of receptor 1 is proper to F-. Spherical
anions can geometrically match the receptor better than
trigonal, linear, and tetrahedral anions. Further more, the
NH moiety assigned as Ha and Hb (marked in Scheme 1)
upon addition of F-. It is obvious that upon addition of 0.5
equiv F- ions, Ha broadened, upfield shifted, and Hb dis-
appeared, which implied interaction of the fluoride ion with
Ha via favourable hydrogen bonding and deprotonation of
1
Hb [14–17]. In this HNMR titration experiments, we can
see complete deprotonation is not achieved until an excess
of the anion is added, presumably due to receptor 1 being
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J Incl Phenom Macrocycl Chem (2011) 69:101–106
more acidic than previous studies [14], which made the Hb
more active, and deprotonation achieved when 0.5 equiv
F- ions is added. Other studies in our group have similar
experimental phenomena [16, 17].
(d)
(c)
3.0 equiv
1.0 equiv
At the same time a new signal at 15.8 ppm appears
clearly, which is ascribed to the FHF- dimer [18, 19]. The
new peak at 15.8 ppm indicates the deprotonation of Hb. In
the other hand, the signals (shown in Fig. 4) of H at phenyl
ring fragment have upfield shifted, which means that
electron density in the phenyl fragment was increased
because of deprotonation of Hb [16]. These spectra changes
can prove ulteriorly that the complex between receptor 1
and F- has formed. In addition, we show the stepwise
changes [20] for 1 and F- interaction.
0.5 equiv
(b)
(a)
Water peak
Hb
Ha
-
The interaction of receptor 2 and H2PO4 exhibits
another way of combination (Fig. 5). In all cases the
0 equiv
12
10
8
6
4
-
addition of H2PO4 produced downfield shift of the
ppm
respective urea protons [14]. This suggests the complex
-
between receptor 2 and H2PO4 being formed. Remark-
1
Fig. 5 The partial H NMR spectra of 2 in DMSO-d6 a the absence
and the presence of b 0.5, c 1.0, d 3.0 equiv of H2PO4
-
ably, the water peak also downfield perturbations and
grows bigger gradually as the increasing quantity of
H2PO4-, which owe to the proton transferring from
-
H2PO4 to H2O.
(b)
(a)
100
80
100
80
Infrared spectral analysis of anion addition
Infrared spectra of receptor 1 in DMSO and the receptor 1
with F- are presented in Fig. 6. The main characteristic
peak of recognition sites of 1 is N–H flexible vibration
signal occurred at 3471.03 cm-1. After 3 equiv of F-
addition, the flexible vibration peak of N–H was moved to
3463.35 cm-1. Further more, the peak grows broader.
These changes are caused by the N–HꢀꢀꢀF hydrogen
bonding formed between the receptor and F-.
60
60
40
40
4000
3500
4000
3500
Wavenumbers (cm-1)
Wavenumbers (cm-1)
Fig. 6 N–H infrared spectra of 1 in DMSO-d6, a the absence and the
presence of b 3.0 equiv of F-
(f)
5.0 equiv
(e)
3.0 equiv
2.0 equiv
1.0 equiv
(d)
(c)
(b)
(a)
(a)
(b)
0.5 equiv
0 equiv
8.2
8.0
7.8
7.6
A
B
C
D
E
F
G
ppm
Fig. 4 Phenyl ring fragment 1H NMR spectra of 1 in DMSO-d6 a the
absence and the presence of b 0.5, c 1.0, d 2.0, e 3.0, f 5.0 equiv of F-
Fig. 7 Color changes of receptors 1 (a) and 2 (b) in DMSO.
[1] = [2] = 1.0 9 10-5 M, [anion] = 3 equiv: A free receptor, B
AcO-, C F-, D H2PO4-, E Cl-, F Br- and G I-
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J Incl Phenom Macrocycl Chem (2011) 69:101–106
105
Fig. 8 a UV–vis changes of 1
operated in DMSO
0.4
0.3
0.2
0.1
0.0
(a)
(b)
2 + H2PO-
-
2, 2 + Cl,Br-,I-
-
4
(5.0 9 10-5 M) after the
1 + F
1.5
addition of 1 equiv of anions.
b UV–vis changes of 2 operated
1+ H2PO-, AcO
-
in DMSO (1.0 9 10-5 M) after
the addition of 3 equiv of anions
4
1.0
-
1, 1 + Cl-, Br, I-
2 + AcO-
420
0.5
-
2 + F
0.0
270
300
330
360
390
300
350
400
450
Wavelength (nm)
Wavelength (nm)
Analytical applications
exhibit different selectivity towards anions which have
different size and shape. Also, this could provide a con-
venience and shortcut method as an application of analyt-
ical chemistry.
According to the results summarized in Table 1 of analyses
performed by UV–vis titration using the method of non-
linear least square fitting, the anion affinity constants of
receptor 1 are in the order: F- [ H2PO4- [ AcO- [[
Cl-, Br- and I-, while that of receptor 2 are in the order:
H2PO4- [ AcO- [ F- [[ Cl-, Br- and I-, which
implied that receptor 1 and 2 could have potential appli-
cation in analytical chemistry. To prove the supposition,
color changes of receptor 1 and 2 were tested in DMSO
(1.0 9 10-5 M). Upon addition of 3 equiv anions, the
color of solution of receptor 1 changed from light yellow
to red by the introduction of F- while the color changed
Acknowledgment This work was supported by the projects
20371028, 20671052 from the National Natural Science Foundation
of China.
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