2-Hydroxy-naphth-1-aldehyde phenyl-thiosemicarbazone: Effective thiourea-based sensor for acetate anion

Article abstract of DOI:10.1007/s10847-011-9969-7

A novel urea-based sensor displaying selective recognition for AcO ^- had been designed and synthesized. Experiments showed that sensor 1 can selectively recognize acetate in DMSO. The evaluation of the sensor's interaction with a variety of structurally different anions was performed by UV-vis titration experiments in DMSO. In addition, the nature of interaction between sensor 1 and AcO^- was investigated by ¹H NMR titrations.

Full text of DOI:10.1007/s10847-011-9969-7

J Incl Phenom Macrocycl Chem (2012) 72:221–225
DOI 10.1007/s10847-011-9969-7
ORIGINAL ARTICLE
2-Hydroxy-naphth-1-aldehyde phenyl-thiosemicarbazone:
effective thiourea-based sensor for acetate anion
•
Hongyan Su Weiwei Huang Zhongyue Yang
•
•
•
Hai Lin Huakuan Lin
Received: 11 July 2010 / Accepted: 22 April 2011 / Published online: 23 August 2011
Ó Springer Science+Business Media B.V. 2011
Abstract A novel urea-based sensor displaying selective
recognition for AcO- had been designed and synthesized.
Experiments showed that sensor 1 can selectively recog-
nize acetate in DMSO. The evaluation of the sensor’s
interaction with a variety of structurally different anions
was performed by UV–vis titration experiments in DMSO.
In addition, the nature of interaction between sensor 1 and
pyrroles [5, 6] indoles [7, 8] calixpyrroles, urea and thio-
ureas [9] have been cited as anion recognition moieties. For
example, the construction of anion sensors consisted of
urea and thiourea motifs have been demonstrated to be
good hydrogen bond donors and excellent sensors for
‘‘Y-shaped’’ acetate ion. A selective sensor molecule is
mostly composed of a component specific for a selected
analyte and a signaling unit capable of translating the
analyte-binding induced changes into an output signal [10].
Furthermore, the information of the anion binding process
can be detected, as optical signals, by simple spectroscopic
methods, such as UV–vis and NMR titration experiments.
Spherical ions (e.g., halide ions), tetrahedral-shaped
phosphate, and planar carboxylate anions are easy to form
hydrogen bonds with urea/thiourea based sensor molecules
[11–13]. In this paper, we synthesized a naphthalene-based
thiourea molecule and performed a systematic study with a
number of anionic guest species such as halides, carbox-
1
AcO- was investigated by H NMR titrations.
Keywords Anion recognition ꢀ Hydrogen-bonding ꢀ
Deprotonation ꢀ Thiourea
Introduction
Anions, such as CH3COO-, F- and H2PO4-, play a fun-
damental role in a wide range of biological, chemical,
medical and environmental process as well as in agricul-
tural fertilizers and food additives [1–3]. Thus, consider-
able attention has been focused on the search for
chemosensors that recognize and detect these anionic
analytes. Full charged host molecules, such as protonaed
polyamines, guanadinium [4], transition metal, and aza-
macrocycles based complexes were first employed in the
anion recognition. More recently neutral sensors such as
1
ylate and phosphate anions. UV–vis and H NMR titration
experiments were carried out to investigate the binding
properties of the sensor 1 in the presence of various anions
in dry DMSO.
Experimental
Apparatus and measurements
H. Su ꢀ W. Huang ꢀ Z. Yang ꢀ H. Lin (&)
Department of Chemistry, Nankai University, Tianjin 300071,
People’s Republic of China
UV-vis spectra were recorded with a Shimadzu UV-
2450PC spectrophotometer at 298.2 0.1 K. The 1H
NMR spectra were performed on a Varian UNITY-plus
400 MHz spectrometer using tetramethylsilane (TMS) as
an internal standard. ESI-MS was carried out with a Mar-
iner apparatus. Elemental analysis (C, N and H) was made
on a Vario ELIII instrument.
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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Reagents
Results and discussion
The binding properties of the sensor 1 toward AcO-, F-,
H2PO4-, Cl-, Br-, and I- were explored with UV–vis
All reagents were of analytical grade and used without
further purification unless otherwise specified. All the
anions, which were purchased from Sigma-Aldrich
Chemical, were added in the form of tetra-n-butylammo-
nium (TBA) salts, and stored in a vacuum desiccator
containing self-indication silica. DMSO used in the titra-
tion experiments, was dried with CaH2 and then distilled in
reduced pressure.
1
titrations, the H NMR experiment. All the anions added
were in the form of tetrabutylammonium salts to
2.0 9 10-5 M solutions of the host molecule 1 in DMSO.
UV–vis experiments
UV–vis titrations were conducted to investigate the inter-
action of the sensor 1 with anions by adding a standard
solution of the tetrabutylammounium salt of anions to dry
DMSO solution of sensor (2 9 10-5 M) at 298.2 0.1 K.
Figure 1 shows the UV–vis spectral changes of the sensor 1
during the titration with acetate ion. With the addition of
various molar of acetate ions, the strong absorbance peak at
the kmax of 430 nm resulting from the p–p* transition of
the chromophore, disappeared gradually, while a new band
at 458 nm with two shoulder bands at 429 and 488 nm
formed and developed [15, 16], and the phenomenon may
be owing to the intramolecular charge transfer (ICT) from
the –OH and –NH units to the electron-deficient –C6H5
moeity. At the same time, the pale yellow of the solution
became deeper. Also, four well-defined isosbestic points
indicating the formation of stable complex presented at
303, 335, 345 and 398 nm, respectively, and the stoichi-
ometry of the sensor-acetate interaction was confirmed to
be 1:1 by Job plot (Fig. 1 inset).
Synthesis
Synthesis of 2-hydroxynaphthalene-1-carbaldehyde [14]
2-Naphthol (22.2 g, 130 mmol) and hexamethylenetetra-
mine (23.8 g, 170 mmol) were added slowly to acetic acid
(30 mL) in a 200 mL three-necked round flask equipped
with a magnetic stir bar. The mixture was reacted in 60 ° C
water bath for 20 min. And then the solution was heated to
90 °C, 98% H2SO4 (33 mL) was added dropwise to the
mixture with stirring. After the addition, the temperature of
the solution was elevated to 95–98 °C for next 3 h. The
reaction mixture was cooled to room temperature and then
poured into water (100 mL). At 30 °C, additional water
(200 mL) was added and the solution was stirred for
another 1 h, which was cooled to room temperature and left
to stand for 24 h. The solid was filtered off, washed with
water until the pH = 7, and then dried at 50 °C. The crude
product was filtered and 18.5 g pure product was obtained
after recrystallization from C2H5OH. (70%) mp: 79–80 °C
(lit. 78–79 °C).
Similar changes were also observed in UV–vis spectra
of the sensor 1 upon addition of H2PO4-, and F-, never-
theless the addition of Cl-, Br-, and I- did not result in
any spectra response even in abundance.
Synthesis of 2-hydroxy-naphth-1-aldehyde phenyl-
thiosemicarbazone (see Scheme 1)
0.050
0.9
0.045
0.040
0.8
To a vigorously stirred and refluxing solution of 4-phe-
nylthiosemicarbazide (0.835 g, 0.5 mmol) in C2H5OH
(20 mL) in the presence of catalytical amount of acetic
acid, 2-hydroxynaph-1-aldehyde (0.0865 g, 0.5 mmol) in
C2H5OH (10 mL) was added dropwise. After stirring and
refluxing for 2 h, yellow precipitate formed was filtered off
and washed twice with C2H5OH (5 mL). The crude product
was successively recrystallized from ethanol to give the
pure sensor 1. Yield: 67%. 1H NMR (DMSO-d6, 400 MHz,
Me4Si) d (ppm): 11.749 (s, 1H, CS-NH), 10.678 (s, 1H,
aromatic-OH), 10.062 (s,1H, Phen-NH), 9.158 (s, 1H, aro-
matic-CH), 8.499 (d, 1H, aromatic-H), 7.892 (s, 2H, aro-
matic-H), 7.570 (s, 3H, aromatic-H) 7.377 (s, 3H, Phen-H),
7.230 (s, 2H, Phen-H); Elemental analysis calcd (%). for
C18H15N3OS: C 67.27; N 13.07; H 4.70; Found: C 67.31; N
13.32; H 4.91; ESI-mass: m/z calcd. For C18H15N3OS
[(M ? H)-: 321.09, Found: 321.11.
0.035
0.030
0.7
0.025
0.6
0.020
0.015
0.5
0.010
-0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
[G]/[H]+[G]
0.4
0.3
0.2
0.1
0.0
11 equiv
0 equiv
0
250
300
350
400
450
500
550
Wavelength/nm
Fig. 1 UV-vis spectrum of the sensor 1 (2 9 10-5 M) in the
presence of AcO- ion in DMSO. Inset: The stoichiometry analysis
of complex 1-AcO- by Job plot analysis ([H] ? [G] = 4910-5 M)
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J Incl Phenom Macrocycl Chem (2012) 72:221–225
223
Obviously from Fig. 2, the order of the sensor’s selec-
tivity toward different anions was determined to be
Fig. 3 interpreted the spectral shifts of the aromatic protons
of the phenyl rings linked to the thiourea moiety when
adding acetate. It is well known that, two effects might be
responsible for the formation of hydrogen bonds between
the thiourea subunit and anion. Through-bond effects,
which increase the electron density of the benzene ring and
promote upfield shifts in 1H NMR spectrum, through-space
effects, which polarize C–H bond in proximity to hydrogen
bond, create the partial positive charge on the proton and
cause downfield shifts [19].
AcO- [H2PO4 ꢁ F- [Cl- * Br- * I-. Although the
-
principles that govern anion recognition have not been
completely understood, it is apparently that the selectivity
for specific anions can be rationalized on the basis of the
shape complementarity and the guest basicity [17]. Urea is
an appropriate sensor for oxoanions because of the easy
formation of N–H_O bonds with two neighboring oxygen
atoms of the anion [18]. The distance between two oxygen
atoms of AcO- might be more fits to two –NH of sensor 1
than those spherical and tetrahedral anions (see Scheme 1).
This shows that sensor 1 has a high selectivity for anions
that with a two- or three-dimensional structure of space,
rather than globular.
1
As shown in H NMR titration spectra of sensor 1 in
Fig. 3, upon addition of 0.2 molar equiv of acetate ions, the
downfield shift and broadness of the protons Ha and Hb
signals (the peaks at 11.749 and 10.062 ppm, respectively)
were observed, which indicated the formation of hydrogen
bonds between host and guest for two –NH at this stage.
And it might be ascribed to through-space effects, polar-
iztion C–H bond in proximity to hydrogen bond. With the
further addition of acetate ions, deprotonation of one –NH
fragment took place, and the majority of signals on the
phenyl rings especially for He (8.499 ppm) and Hf
(7.230 ppm) shifted upfield clearly, which indicated the
increase of the electron density on the aromatic rings owing
to the through-bond effects. As mentioned above, the
proposed anion recognition process was illustrated in
1H NMR titrations
1
We conducted H NMR titrations experiments in DMSO-
d6 to investigate the nature of the new peaks formed in
1
UV–vis spectra. The H NMR titrations course listed in
0.7
0.6
0.5
0.4
2eq
1eq
0.3
0.2
0.1
0.0
-
AcO
F-
0.5eq
0.2eq
HPO-
2
4
-
Cl-,Br,I-
f
a
d
c
e
b
0 eq
250
300
350
400
450
500
550
Wavelength/nm
14
13
12
11
10
9
8
7
6
Fig. 2 Changes in absorption spectra of the sensors
1
(2 9 10-5 mol/L) in DMSO upon addition of five equiv of various
anions
Fig. 3 1H NMR titration of a 1 9 10-2 M solution of the sensor 1 in
DMSO-d6 with tetrabutylammonium acetate
Scheme 1 The synthetic
procedure for an anion sensor 1
H
N
H
N
reflux,2h
H2N
+
c
OH
OH
EtOH
S
b
a
e
f
d
H
H
N
CHO
N
HC
N
S
f
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J Incl Phenom Macrocycl Chem (2012) 72:221–225
Table 1 The constants (Ka) and correlation coefficients (R) of sensor
1 with various anions in DMSO
O
H
O
H
Aniona
Ka (M-)b
R^d
AcO-
HC
HC
N
N
AcO-
7.83 9 104
7.89 9 103
2.72 9 103
NDc
0.97161
0.98661
0.96512
ND
N
S
H
N
-
HN
H2PO4
F-
H
O
N
S
H
C
Cl-
Br-
I-
O
ND
ND
ND
ND
Scheme 2 The proposed host–guest binding mode in solution
a
The anion were added as their tetrabutylammonium salts at
298.2 0.1 K
Scheme 2. It was noteworthy that excess acetate ion added
results the deprotonation of sensor 1, which agreed well
with the Fabbrizzi paradigm for anion-induced urea de-
protonation process [20].
b
Ka was determined in dry DMSO
c
ND indicated that the spectra showed little or no change with the
addition of anion so that the association constants cannot be deter-
mined using the spectra
d
Correlation coefficient (R^) determined by non-linear fitting
The calculation of Ka from UV–vis titration spectra
analyses
For a complex of 1:1 stoichiometry, the constants (Ka) can
be calculated by non-linear fitting analyses of the titration
curves according to the following Eq. 1 reported before
[21], where CG and CH represent the corresponding con-
centration of the guest and host, and A is the intensity of
absorbance at certain concentration of the host and guest.
A0 represents the intensity of absorbance of host only and
Alim is the maximum intensity of absorbance of host when
guest is added. Kass is the affinity constant of host–guest
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In conclusion, the thiourea-based sensor 1 which shows
good recognition for acetate ion has been successfully
synthesized. UV–vis spectral titration experiments showed
that the sensor formed 1:1 stoichiometric complexes with
anions in DMSO solution and it is an excellent sensor for
AcO-. Furtheremore, the proposed binding mode of sensor
1 with acetate was shown in Sheme 2 according to the
proton NMR titration experiments.
Acknowledgment This project was supported by the National
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