A versatile approach toward chemosensor for Hg2+ based on para-substituted phenylazocalix[4]arene containing mono ethyl ester unit

Article abstract of DOI:10.1016/j.dyepig.2014.04.005

In the present study, six new azocalix[4]arenes have been synthesized by reacting calix[4]arene with p-substituted aniline and ethyl bromoacetate. Characterization of these compounds has been used by elemental analyses, UV-Vis, FT-IR and ¹H NMR spectroscopic studies. Their phase transfer studies have been performed by using liquid-liquid extraction procedure. With respect to the chromogenic behavior of hosts upon metal ion complexation, mono ethyl ester azocalix[4]arene derivatives have shown a significant selectivity toward Hg²⁺ and Hg⁺ over many other cations. It has been deduced that these new compounds are selective ionophores toward metal cations (Na ⁺, K⁺, Sr²⁺, Ag⁺, Hg⁺, Hg²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn ²⁺, Cr³⁺, Al³⁺ and La³⁺).

Full text of DOI:10.1016/j.dyepig.2014.04.005

Dyes and Pigments 107 (2014) 166e173
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A versatile approach toward chemosensor for Hg2þ based on para-
substituted phenylazocalix[4]arene containing mono ethyl ester unit
*
Serkan Elçin , Hasalettin Deligöz
Department of Chemistry, Faculty of Science-Arts, Pamukkale University, 20017 Denizli, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
In the present study, six new azocalix[4]arenes have been synthesized by reacting calix[4]arene with p-
substituted aniline and ethyl bromoacetate. Characterization of these compounds has been used by
elemental analyses, UVeVis, FT-IR and 1H NMR spectroscopic studies. Their phase transfer studies have
been performed by using liquideliquid extraction procedure. With respect to the chromogenic behavior
of hosts upon metal ion complexation, mono ethyl ester azocalix[4]arene derivatives have shown a
significant selectivity toward Hg2þ and Hgþ over many other cations. It has been deduced that these new
Received 16 January 2014
Received in revised form
21 March 2014
Accepted 2 April 2014
Available online 12 April 2014
compounds are selective ionophores toward metal cations (Naþ, Kþ, Sr2þ, Agþ, Hgþ, Hg2þ, Co2þ, Ni2þ
,
Keywords:
Cu2þ, Zn2þ, Cr3þ, Al3þ and La3þ).
Calix[n]arene
Azocalix[4]arene
Mono ester
Ó 2014 Elsevier Ltd. All rights reserved.
Selective extraction
Optimized structure
Hg2þ
1. Introduction
that the metal selectivity is based on the calix[n]arene ring size
structure, for example, calix[4]aryl acetates and acetamides with a
cone conformation show remarkably high Naþ selectivity.
Calix[n]arene family is one of the most prominent molecular
building platforms in hosteguest chemistry. A new member of the
calix[n]arene family is based on the replacement of the traditional
methyl bridges with azo groups [18]. Up to now, azocalix[n]arenes
and their binding properties were only studied by Chawla [19], Kim
[20] and Lu [21].
Recently, Arnaud-Neu and co-workers [22] have studied the
transport of alkaline-earth metal cations with p-tert-butylcalix[n]
arene esters and amides. Reinhoult and co-workers prepared 1,3-
alternate calix[4]arene-crown-6 as a new class of cesium-selective
ionophore [23]. In addition, Ungaro and co-workers have re-
ported the synthesis, structure and complexing properties of
several 1,3-dialkoxy-p-tert-butylcalix[4]arene-crown-5, a new class
of potassium-selective ligands [24].
Until now, our group and co-workers have synthesized the
functionalized calix[n]arene derivatives and studied their se-
lective extraction of various transition metals [25e30]. In the
course of the synthesis of new chromogenic azocalix[4]arene
derivatives containing the phenolic neighboring groups at lower
rim [31], we have extended our research into transition metal
cations.
Heavy metal contamination of water is a serious concern due to
the toxic effect of heavy metal ions on the living organisms and
environment [1,2]. Therefore, effective removal of heavy metal ions
from water or various industrial effluents is crucially important. It
has attracted considerable research and practical interest. Many
methods such as chemical precipitation, ion exchange, reverse
osmosis and sorption have been used to remove metal ions from
various aqueous solutions [3,4]. Among the stated methods ab-
sorption has increasingly received more attention in recent years
due to its relative simplicity, cost efficiency and high effectivity in
removing heavy metal ions, especially at low to medium metal ion
concentrations from wastewater [5,6].
The calix[n]arenes are among the most fascinating families of
host compounds, and their chemistry have been significantly
developed in the last 30 years [7,8]. Hosteguest chemistry of the
calixarenes is of great interest due to their complexing abilities
toward various metal cations by means of functional group modi-
fication at the phenolic groups [9e12]. Later, it was found that calix
[n]arenes can be converted into neutral ligands by converting the
hydroxyl groups to esters or amides [13e17]. It has demonstrated
In the present work, we have mainly focused on the develop-
* Corresponding author. Tel.: þ90 258 296 3613; fax: þ90 258 296 3593.
E-mail address: serel20@mynet.com (S. Elçin).
ment of
a
new class of chromogenic azocalix[4]arene
http://dx.doi.org/10.1016/j.dyepig.2014.04.005
0143-7208/Ó 2014 Elsevier Ltd. All rights reserved.

S. Elçin, H. Deligöz / Dyes and Pigments 107 (2014) 166e173
167
chemosensors (4aef) as shown in Scheme 1. Then, six new com-
pounds containing more than one tetra azo (eN]Ne) groups and
mono ester were synthesized, and their ion binding properties
were studied.
where A and A0 are the absorbencies with and without ligand,
respectively.
2.3. Preparation of the esterification
2. Experimental
We have followed the procedure given in Refs. [11,36] to carry
out the experiment.
All of the chemical reagents and solvents used were of analytical
grade purity and used without further purification. All aqueous
solutions were prepared with deionized water purified by Human
Power Plus I þ UV water purification system.
2.3.1. Preparation of 25-(ethoxycarbonylmethoxy)-26,27,28-
trishydroxy-5,11,17,23-tetrakis[(4-methoxyphenyl)azo]calix[4]arene
(4a)
p-tert-Butylcalix[4]arene, calix[4]arene, 5,11,17,23-tetrakis[(4-
methoxyphenyl)azo] calix[4]arene (3a), 5,11,17,23-tetrakis[(4-meth
ylphenyl)azo]calix[4]arene (3b), 5,11,17,23-tetrakis[(4-ethylphenyl)
azo]calix[4]arene (3c), 5,11,17,23-tetrakis[(4-chlorophenyl)azo]
calix [4]arene (3d), 5,11,17,23-tetrakis[(4-bromophenyl)azo]calix[4]
arene (3e) and 5,11,17,23-tetrakis[(4-nitrophenyl)azo]calix[4]arene
(3f)] were synthesized as described previously [32e35].
Azocalix[4]arene 3a (1 g, 1.04 mmol) and K2CO3 (1.15 g,
8.32 mmol) in dry acetonitrile (100 mL) was mixed with ethyl
bromoacetate (0.36 mL, 2.19 mmol). The reaction mixture was
stirred at room temperature for 4 days and then allowed to cool
down to room temperature. After evaporation of the solvent with a
rotary evaporator, the mixture was taken into CHCl3 (100 mL). It
washed first with 0.5 N HCl (250 mL) and then with water (300 mL).
The organic layer was dried over MgSO4 and evaporated to half
volume. The addition of ethanol yielded the pale brown product
(yield, 0.92 g (84%), mp. 245e247 ꢀC). Found: C: 68.72; H: 5.26; N:
2.1. Instrumental
Melting points were measured using an Electrothermal IA9100
digital melting point apparatus with capillaries sealed under ni-
trogen and were uncorrected. Microwave assisted synthesis was
performed using a CEM Discover synthesis unit (monomode sys-
tem). 1H NMR spectra were referenced to tetramethylsilane (TMS)
at 0.00 ppm as internal standard solution and recorded on a Bruker
400 MHz spectrometer at room temperature (25 ꢀC). IR spectra
were recorded by a Mattson 1000 FTIR spectrometer as KBr pellets.
UVevis spectra were recorded by a Shimadzu 1601 UVeVisible
spectrophotometer. The elemental analyses were performed in the
TUBITAK (The Scientific and Technological Research Council of
Turkey) Laboratories.
10.73; C60H54N8O10 requires C: 68.82; H: 5.20; N: 10.70. IR (KBr) y:
3336 cmꢂ1 (eOH), 1740 cmꢂ1 (eC]O), 1449 cmꢂ1 (eN]N),
1245 cmꢂ1 (CeO). 1H NMR (CDCl3, 25 ꢀC) dH: 1.45 (t, J ¼ 7.14 Hz, 3H,
CH2eCH3), 3.72 (d, J ¼ 6.17 Hz, 2H, ArCH2Ar), 3.75 (d, J ¼ 6.09 Hz,
2H, ArCH2Ar), 3.80e3.85 (m, 12H, OeCH3), 4.40 (d, J ¼ 13.69 Hz, 2H,
ArCH2Ar), 4.48 (q,
J
¼
7.15 Hz, 2H, OeCH2eCH3), 4.57 (d,
J ¼ 13.61 Hz, 2H, ArCH2Ar), 4.95 (s, 2H, OeCH2eC]O), 6.90e6.97
(m, 8H, ArH), 7.70e7.83 (m, 16H, ArH), 9.33 (s, 2H, ArOH), 9.81 (s,
1H, ArOH).
2.3.2. Preparation of 25-(ethoxycarbonylmethoxy)-26,27,28-
trishydroxy-5,11,17,23-tetrakis[(4-methylphenyl)azo]calix[4]arene
(4b)
2.2. Solvent extraction
Azocalix[4]arene 4b is prepared as described above, using 3b,
ethyl bromoacetate with K2CO3 and obtained an orange crystal
product (yield, 0.89 g (81%), mp. 298e300 ꢀC). Found: C: 73.47; H:
5.63; N: 11.43; C60H54N8O6 requires C: 73.30; H: 5.54; N: 11.40. IR
A solution (10 mL) of ligand (1 ꢁ 10ꢂ3 M) in chloroform and an
aqueous solution (10 mL) containing 2 ꢁ 10ꢂ5 M picric acid and
1 ꢁ 10ꢂ2 M metal nitrate was stirred at 25 ꢀC for an hour. An
aliquot of the aqueous solution was withdrawn, and its UV spec-
trum was recorded. A similar extraction was performed in the
absence of picrate ion in the aqueous solution. The extractability
of the metal cations is expressed by means of the following
equation:
(KBr) y
: 3324 cmꢂ1 (eOH), 1742 cmꢂ1 (eC]O),1448 cmꢂ1 (eN]N),
1239 cmꢂ1 (CeO). 1H NMR (CDCl3, 25 ꢀC) dH: 1.45 (t, J ¼ 7.15 Hz, 3H,
CH2eCH3), 2.34e2.40 (m, 12H, AreCH3), 3.74 (d, J ¼ 6.36 Hz, 2H,
ArCH2Ar), 3.77 (d, J ¼ 6.26 Hz, 2H, ArCH2Ar), 4.41 (d, J ¼ 13.75 Hz,
2H, ArCH2Ar), 4.49 (q, J ¼ 7.15 Hz, 2H, OeCH2eCH3), 4.59 (d,
J ¼ 13.57 Hz, 2H, ArCH2Ar), 4.96 (s, 2H, OeCH2eC]O), 7.19e7.27
(m, 8H, ArH), 7.67e7.80 (m, 16H, ArH), 9.40 (s, 2H, ArOH), 10.09 (s,
1H, ArOH).
Extractabilityð%Þ ¼ ðA0 ꢂ AÞ=A0 ꢁ 100
2.3.3. Preparation of 25-(ethoxycarbonylmethoxy)-26,27,28-
trishydroxy-5,11,17,23-tetrakis[(4-ethylphenyl)azo]calix[4]arene
(4c)
Azocalix[4]arene 4c is prepared as described above, using 3c,
ethyl bromoacetate with K2CO3 and obtained a pale orange crystal
product (yield, 0.85 g (78%), mp. 268e270 ꢀC). Found: C: 73.83; H:
5.97; N: 10.83; C64H62N8O6 requires C: 73.97; H: 6.01; N: 10.78. IR
(KBr) y
: 3332 cmꢂ1 (eOH), 1740 cmꢂ1 (eC]O),1449 cmꢂ1 (eN]N),
1238 cmꢂ1 (CeO). 1H NMR (CDCl3, 25 ꢀC) dH: 1.24 (t, J ¼ 8.21 Hz,
12H, AreCH2eCH3), 1.46 (t, J ¼ 7.16 Hz, 3H, CH2eCH3), 2.68 (q,
J ¼ 7.68 Hz, 8H, AreCH2eCH3), 3.74 (d, J ¼ 6.49 Hz, 2H, ArCH2Ar),
3.77 (d, J ¼ 6.41 Hz, 2H, ArCH2Ar), 4.41 (d, J ¼ 13.90 Hz, 2H,
ArCH2Ar), 4.49 (q,
J
¼
7.16 Hz, 2H, OeCH2eCH3), 4.59 (d,
J ¼ 13.23 Hz, 2H, ArCH2Ar), 4.92 (s, 2H, OeCH2eC]O), 7.24e7.29
(m, 8H, ArH), 7.71e7.79 (m, 16H, ArH), 9.40 (s, 2H, ArOH), 10.26 (s,
1H, ArOH).
Scheme 1. Structure of azocalix[4]arene mono ester derivatives (4aef).

168
S. Elçin, H. Deligöz / Dyes and Pigments 107 (2014) 166e173
2.3.4. Preparation of 25-(ethoxycarbonylmethoxy)-26,27,28-
trishydroxy-5,11,17,23-tetrakis[(4-chlorophenyl)azo]calix[4]arene
(4d)
product (yield, 0.59 g (54%), mp. 292e294 ꢀC). Found: C: 60.88; H:
3.77; N: 15.11; C56H42N12O14 requires C: 60.76; H: 3.82; N: 15.18. IR
(KBr) y
: 3302 cmꢂ1 (eOH),1754 cmꢂ1 (eC]O),1466 cmꢂ1 (eN]N),
Azocalix[4]arene 4d is prepared as described above, using 3d,
ethyl bromoacetate with K2CO3 and obtained a dark orange crystal
product (yield, 0.73 g (67%), mp. 307e308 ꢀC). Found: C: 63.29; H:
4.02; N: 10.47; C56H42Cl4N8O6 requires C: 63.17; H: 3.98; N: 10.52.
1278 cmꢂ1 (CeO). 1H NMR (CDCl3, 25 ꢀC) dH: 1.43 (t, J ¼ 7.16 Hz, 3H,
CH2eCH3), 3.74 (d, J ¼ 5.41 Hz, 2H, ArCH2Ar), 3.78 (d, J ¼ 5.32 Hz,
2H, ArCH2Ar), 4.41 (d, J ¼ 13.98 Hz, 2H, ArCH2Ar), 4.50 (q,
J ¼ 7.15 Hz, 2H, OeCH2eCH3), 4.60 (d, J ¼ 13.29 Hz, 2H, ArCH2Ar),
4.99 (s, 2H, OeCH2eC]O), 7.62e7.96 (m, 24, ArH), 9.42 (s, 2H,
ArOH), 10.12 (s, 1H, ArOH).
IR (KBr) y
: 3303 cmꢂ1 (eOH), 1733 cmꢂ1 (eC]O), 1467 cmꢂ1 (eN]
N), 1273 cmꢂ1 (CeO). 1H NMR (CDCl3, 25 ꢀC) dH: 1.43 (t, J ¼ 7.16 Hz,
3H, CH2eCH3), 3.74 (d, J ¼ 5.37 Hz, 2H, ArCH2Ar), 3.78 (d,
J ¼ 5.29 Hz, 2H, ArCH2Ar), 4.41 (d, J ¼ 13.98 Hz, 2H, ArCH2Ar), 4.50
(q, J ¼ 7.14 Hz, 2H, OeCH2eCH3), 4.60 (d, J ¼ 13.28 Hz, 2H, ArCH2Ar),
4.98 (s, 2H, OeCH2eC]O), 7.39e7.45 (m, 8H, ArH), 7.72e7.80 (m,
16H, ArH), 9.50 (s, 2H, ArOH), 9.92 (s, 1H, ArOH).
3. Results and discussion
The binding ability of the azocalix[4]arenes depends on the
macrocyclic ring sizes, their conformations and the nature of the
functional groups [18]. All these six new compounds (4aef) took
partial cone conformation in solution. The presence of tetra azo (e
N]Ne) groups and mono ester in the azocalix[4]arenes were
observed to play an important role in cation complexation with
corresponding azocalix[4]arene derivatives.
The selectivity of azocalix[4]arene derivatives toward transition
metal cations has been reported in the literature [25]. Bingol et al.
reported the selectivity of a novel benzothiazole based azocalix[4]
arene toward selected metal cations, particularly Hg2þ [37].
In this work, it was aimed to synthesize azocalix[4]arenes
containing mono ester groups which are suitable for Hgþ metal
complexation. 5,11,17,23-tetrakis[(4-methoxy phenyl)azo]calix[4]
arene (3a) was obtained by the diazo-coupling reaction. The
esterification reaction of 5,11,17,23-tetrakis[(4-substituephenyl)
azo]calix[4]arene (3aef) were performed with the presence of
K2CO3 and ethyl bromoacetate in dry acetonitrile at room
temperature for 4 days. Other azocalix[4]arene derivatives (4ae
f) were also synthesized in a similar manner but their yields
were lower as compared to (3aef). The obtained azocalix[4]
arenes (4aef) were further purified by recrystallization, and
2.3.5. Preparation of 25-(ethoxycarbonylmethoxy)-26,27,28-
trishydroxy-5,11,17,23-tetrakis[(4-bromophenyl)azo]calix[4]arene
(4e)
Azocalix[4]arene 4e is prepared as described above, using 3e, ethyl
bromoacetate with K2CO3 and obtained an orange crystal product
(yield, 0.67 g (62%), mp. 283e285 ꢀC). Found: C: 54.24; H: 3.37; N:
9.09; C56H42Br4N8O6 requires C: 54.13; H: 3.41; N: 9.02. IR (KBr) y:
3309 cmꢂ1 (eOH), 1742 cmꢂ1 (eC]O), 1467 cmꢂ1 (eN]N),
1270 cmꢂ1 (CeO). 1H NMR (CDCl3, 25 ꢀC) dH: 1.45 (t, J ¼ 7.16 Hz, 3H,
CH2eCH3), 3.73 (d, J ¼ 5.28 Hz, 2H, ArCH2Ar), 3.77 (d, J ¼ 5.19 Hz, 2H,
ArCH2Ar), 4.41 (d, J ¼ 13.96 Hz, 2H, ArCH2Ar), 4.49 (q, J ¼ 7.15 Hz, 2H,
OeCH2eCH3), 4.59(d, J¼ 13.27 Hz,2H, ArCH2Ar), 4.97 (s, 2H, OeCH2e
C]O), 7.54e7.80 (m, 24, ArH), 9.40 (s, 2H, ArOH), 9.80 (s, 1H, ArOH).
2.3.6. Preparation of 25-(ethoxycarbonylmethoxy)-26,27,28-
trishydroxy-5,11,17,23-tetrakis[(4-nitrophenyl)azo]calix[4]arene
(4f)
Azocalix[4]arene 4f is prepared as described above, using 3f,
ethyl bromoacetate with K2CO3 and obtained an orange crystal
Scheme 2. Synthesized of azocalix[4]arene mono ester derivatives (4aef).

S. Elçin, H. Deligöz / Dyes and Pigments 107 (2014) 166e173
169
Fig. 1. 1H NMR spectra of azocalix[4]arene mono ester derivative (4a).
their purity was examined by thin-layer chromatography
(Scheme 2).
As shown in Table 1, when he compounds 4aef were dissolved
in methanol plus acid or base, significant changes at the peak values
were observed with the spectroscopic measurements (Fig. 4).
The stability constant value of the Hg2þ with the compounds
4aef demonstrates that they exhibit good Hg2þ recognition
properties, most probably due to having a more complementary
structure as compared to other heavy metal ions. Moreover, the
compounds 4aef have a higher association constant value for
Hg2þ than the other chemosensors reported in the literature
[37].
The IR and NMR spectra of the azocalix[4]arenes were recorded.
The IR spectra of the azocalix[4]arenes exhibited absorption be-
tween 1467 and 1448 cmꢂ1, which is characteristic for eN]Ne
vibration mode. Analysis of the IR spectra have revealed that these
compounds (4aef) were attached to each consecutive (eN]Ne)
groups in a regular array.
The 1H NMR spectra of compound 4a exhibited rather broad
signals for all protons, with each peak for the methyl (a) (t, 1.45), for
the methoxy (b) (m, 3.80e3.85), for the methylene (c) OCH2CO (d,
4.95) and for the aromatic (e) (m, 6.90e6.97 and 7.70e7.83) resi-
dues. The proton of the AB system, characteristic of the bridging
methylene protons in tetramers in the partial cone conformation,
partly obscured by four doublets at 3.72, 3.75, 4.40 and 4.57 ppm.
Among all of the proton chemical shifts in the azocalix[4]arene, the
two largest are those of the axial proton in methylene bridges of the
azocalix[4]arene in the partial cone conformation (0.10e0.30 ppm
upfield) and the aromatic protons (0.20 ppm downfield) (Fig. 1).
Probable three-dimensional structure of the (4b) molecule, was
drawn with GaussView 5.0 molecular imaging program [38] and
space settlements of atoms were determined. All theoretical cal-
culations were performed by Gaussian 09 W package program [39].
Showed in Fig. 2 the crystal structure of azocalix[4]arene ester
derivative (4b) exhibited as partial cone conformation.
The coloring ability of azocalix[4]arens 4aef in acetonitrile,
acetic acid, chloroform, DMF, DMSO and methanol solvents was
detected by either naked eye (visual) or UVeVis absorption (optical)
methods. The solution of the compounds 4aef showed dramatic
color changes from light orange to red in above solvents. The ab-
sorption spectrum of the compounds 4aef has a maximum ab-
sorption peak at 369 nm, corresponding to pep* transitions of the
eN]Ne bond. When 4aef (4 ꢁ 10ꢂ5 M) were treated with a series
of above solvents (2 ꢁ 10ꢂ4 M), bathochromic shifts were observed
only for DMF and DMSO. On the other hand, no significant change
was observed upon the addition of the other solvents. The results
can be attributed to the more suitable interaction between solvent
polarities and negative charge center in 4aef (Fig. 3) (Table 1).
Fig. 2. The optimized structure of (4b) molecule.

170
S. Elçin, H. Deligöz / Dyes and Pigments 107 (2014) 166e173
Fig. 3. Absorption spectra of azocalix[4]arene (4aef).
Solvent extraction experiments have been performed to ascer-
tain the effectiveness of the compounds 4aef in transferring the
metal cations, such as Naþ, Kþ, Sr2þ, Agþ, Hgþ, Hg2þ, Co2þ, Ni2þ
stronger affinity toward soft basic metal cations than toward hard
metal cations. In this case, the strong participation of the eN]Ne
groups in the hosteguest complexation was further confirmed by
the extraction results of azocalix[4]arenes (4aef). The extraction
values given in Table 2 clearly show that the eN]Ne groups
certainly play a decisive role in the extraction of Hg2þ due to its
,
Cu2þ, Zn2þ, Cr3þ, Al3þ and La3þ from the aqueous phase into the
organic phase. The results of the metal picrate extractions with
azocalix[4]arene derivatives 4aef are summarized in Table 2 and
are depicted in Fig. 5. It is obvious that the compounds 4aef are
more effective in transferring Hgþ/Hg2þ than the other cations.
However, this conclusion has been reported in the literature pre-
viously [8].
contribution to cationep interaction. This cationep interaction can
not be explained by the ionic radius of Hg2þ since the Co2þ having a
closely similar ionic radius with Hg2þ could not extracted as
effectively as Hg2þ. No simple explanation for this difference is
apparent at this time, but the cavity size, polarizability effects, the
number and type of the donor atoms, and conformational aspects
This phenomenon can be explained by the hard-soft acidebase
principle (HSAB). The eN]Ne groups are a soft base and show a

S. Elçin, H. Deligöz / Dyes and Pigments 107 (2014) 166e173
171
Table 1
Influence of solvent on lmax (nm) of azocalix[4]arenes (4aef).
Ligands
MeCN
347
AcOH
350
CHCl3
349
DMF
363
DMSO
364
MeOH
356
MeOH þ HCl
MeOH þ KOH
4a
352
499
338
472
341
479
341
348
358
361
353
357
4b
4c
336
338
335
336
339
338
367
371
359
358
339
338
4d
4e
4f
339
339
357
336
338
352
340
341
358
362
377
377
564
370
378
372
474
339
340
357
352
372
343
433
Fig. 4. Effect of acid and base absorption spectra of azocalix[4]arenes (4aef).

172
S. Elçin, H. Deligöz / Dyes and Pigments 107 (2014) 166e173
Table 2
Extraction of metal picrates with azocalix[4]arene derivatives 4aef.a
Ligands
Picrate salt extracted (%)
Naþ
Kþ
Sr2þ
Agþ
Hgþ
Hg2þ
Co2þ
Ni2þ
Cu2þ
Zn2þ
Cr3þ
Al3þ
La3þ
4a
4b
4c
4d
4e
4f
<3
<3
<3
<3
<3
<3
<3
<3
<3
<3
<3
<3
<3
<3
<3
<3
<3
<3
<3
3.6
<3
<3
<3
<3
20.9
17.6
8.6
9.6
9.6
21.7
21.4
21.7
16.0
22.3
21.4
<3
<3
<3
<3
<3
<3
<3
<3
<3
<3
<3
<3
<3
<3
<3
<3
<3
<3
<3
<3
<3
<3
<3
<3
4.2
4.2
<3
3.6
4.5
<3
<3
<3
<3
<3
<3
<3
<3
<3
<3
<3
<3
<3
13.3
a
H2O/CHCl3 ¼ 10/10 mL (v/v): [picric acid] ¼ 2 ꢁ 10ꢂ5 M, [ligand] ¼ 1 ꢁ 10ꢂ3 M, [metal nitrate] ¼ 1 ꢁ 10ꢂ2 M; 298 K, 1 h contact time.
a
ꢃ ꢄ2%.
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Since azocalix[4]arenes are easily available in larger quantities
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can be expected that even better extractants or ion carriers can be
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In conclusion, we have synthesized new azocalix[4]arene based
chemosensors that are particularly selective for Hg2þ. due to
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Acknowledgments
This work is supported in part by a grant from the Scientific and
Technical Research Council of Turkey (TUBITAK, 112T028). The au-
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