Syntheses of two diamine substituted 1,3-distal calix[4]arene-based magnetite nanoparticles for extraction of dichromate, arsenate and uranyl ions

Article abstract of DOI:10.1016/j.tet.2011.03.012

The synthesis of two new calixarene derivatives 4 and 5, functionalized at the lower rim with 4-amino-1-benzylpiperidine to give diamide and diamine derivatives of p-tert-butylcalix[4]arene, is described. They were obtained by the reaction of both the die

Full text of DOI:10.1016/j.tet.2011.03.012

Tetrahedron 67 (2011) 3743e3753
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Syntheses of two diamine substituted 1,3-distal calix[4]arene-based magnetite
nanoparticles for extraction of dichromate, arsenate and uranyl ions
,
b
Serkan Sayin a, Mustafa Yilmaz a , Mustafa Tavasli
*
a Department of Chemistry, Selcuk University, Konya 42075, Turkey
b Department of Chemistry, Uludag University, Bursa 16059, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis of two new calixarene derivatives 4 and 5, functionalized at the lower rim with 4-amino-1-
benzylpiperidine to give diamide and diamine derivatives of p-tert-butylcalix[4]arene, is described. They
were obtained by the reaction of both the diester derivative of p-tert-butylcalix[4]arene (2) and the
dialkyl bromide derivative of p-tert-butylcalix[4]arene (3) with 4-amino-1-benzylpiperidine. The 1H
NMR spectra of calixarene derivatives show that 4 and 5 exist in the cone conformation. Moreover, these
diamide and diamine derivatives of p-tert-butylcalix[4]arene (4 and 5) have been immobilized onto
[3-(2,3-epoxypropoxy)-propyl]-trimethoxysilane-modified Fe3O4 magnetite nanoparticles to obtain
calixarene-based magnetic nanoparticles M-DADBP-Calix (6) and M-DABP-Calix (7). The calix[4]arene
immobilized materials were characterized by a combination of Fourier Transform Infrared Spectroscopy
(FTIR), Transmission Electron Microscopy (TEM) and Thermogravimetric Analyses (TGA) and elemental
analysis. Additionally, the studies regarding the removal of As(V)/Cr(VI) ions as well as U(VI) ion from
aqueous solutions were also carried out by using these compounds in liquideliquid/solideliquid ex-
traction experiments.
Received 26 October 2010
Received in revised form 22 February 2011
Accepted 7 March 2011
Available online 12 April 2011
Keywords:
Calix[4]arene
Magnetite nanoparticles
Extraction
Arsenate/dichromate
Uranyl
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
blood and low molecular weight complexing agents, such as cit-
rates, bicarbonates and phosphates.16
Cr(VI)andinorganicarsenics, suchasAs(V)andAs(III)arecounted
among the top 20 most hazardous substances.1 It is well known that
these oxyanions have become the most serious environmental
pollutants.2e4 Among them, arsenic is a well-documented carcino-
genic causing various adverse health effects such as cancer and skin
diseases even at sub-ppm levels.4e7 About 150 million people are
threatened by this serious health hazard from over 70 countries.8,9
Typically in soils, arsenic occurs naturally at concentrations varying
between 0.2 and 40 mg/kg. Recently, the use of pesticides, herbicides
and wood preservatives containing arsenic has lead to an increase of
its concentration in soils.10,11
In nature, chromium exists in the Cr(VI) and Cr(III) forms, which
differ widely in their chemical properties and biological re-
activities.12,13 Many studies have indicated that Cr(VI), like As(V) is
highly toxic, carcinogenic and harmful to humans, while Cr(III) is
essential to mammals as it maintains effective glucose, lipid and
protein metabolisms.14
Uranyl ions are extremely mobile and once entered into living
bodies provoke inner irradiation which may cause cancers in the
long term.17 In this case, there has been increased special interest in
uranium (VI), in particular uranyl ion analysis in the nuclear in-
dustry, especially in fuel separation and processing steps, composed
of a few steps including leaching from ores, purification by ion
exchange and solvent extraction, precipitation, reduction, etc.18,19
In the last decade, increased investigations with several types of
iron oxide have been carried out in the field of nano-sized magnetic
particles (generally maghemite, g-Fe2O3, or magnetite, Fe3O4, sin-
gle domains of about 5e20 nm in diameter).20 Magnetite, Fe3O4, is
a common magnetic iron oxide. Due to this feature, the separation
process should be achieved quite easily and rapidly.
Recently, magnetic nanoparticles of iron oxide have shown great
potential in many fields like bioseparation,20,21 tumour hyper-
thermia,22 magnetic resonance imaging (MRI), diagnostic contrast
agents,23 magnetically guided site-specific drug delivery agents,24
biomolecules immobilization,25,26 as well as support materials for
some selective calixarene derivatives acting on arsenate or di-
chromate ions.2,4,27
Calixarenes, cyclic oligomers of phenolic units linked through
the ortho positions, are a fascinating class of macrocycle. Chemical
modification of the upper or lower rim has made this class of syn-
thetic ionophores effective extractants for transferring anionic28,29
Uranium is most commonly used as a nuclear fuel in fission
reactors for civilian purpose.15 In a nuclear accident, uranium is at
the origin of severe internal contaminations by ingestion or in-
halation.15 In mammalian systems, the uranyl ion interacts with
* Corresponding author. Tel.: þ90 332 2233873; fax: þ90 332 2410520; e-mail
address: myilmaz42@yahoo.com (M. Yilmaz).
0040-4020/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2011.03.012

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S. Sayin et al. / Tetrahedron 67 (2011) 3743e3753
and cationic ions30,31 or neutral molecules from aqueous solution
into an organic layer. These molecules are generally calix[4]arene
derivatives containing amine or amide functions, capable of inter-
acting with anions/cations by hydrogen bonds.2,4,32
arsenate/dichromate anions as well as uranyl cation by means of
liquid liquid/solideliquid extraction process.
2. Results and discussion
Until now, calixarene-based materials have seen increased use
as uranophiles with either a pseudoplanar pentaco-ordinate or
hexaco-ordinate structure.33,34 It is well known that the high se-
lectivity is attributed to the rigid skeleton of calix[5]arenes and
calix[6]arenes towards the uranyl ion since these derivatives can
provide the pre-organized hexa- or penta-coordination geometry
2.1. Synthesis of new host molecules
The main goal of this work was the design and synthesis of new
calixarene derivatives (4 and 5) and exploration of their binding
properties towards arsenate/dichromate anions and uranyl cations.
Scheme 1 shows the route to the first target calixarene derivatives 4
and 5. p-tert-Butylcalix[4]arene (1), diester derivative of p-tert-
butylcalix[4]arene (2) and dialkyl bromide derivative of p-tert-
butylcalix[4]arene (3) were synthesized by a modification of the
2þ
35
required for the binding of UO2
.
Herein, we have synthesized two new calixarene derivatives and
immobilized them onto the silica based iron oxide nanoparticles
surface and then investigated their extraction capability towards
OH
OH
i
ii
OH
HO
Br
Br
O
O
O
(1
)
O
O
OH
O
OH
OH
O
OH
O
(2)
(3)
iii
iv
N
N
N
N
NH
HN
NH
O
NH
O
O
OH
O
OH
OH
O
OH
O
(4)
(5)
Scheme 1. The synthetic route for synthesis of 4 and 5. Reaction conditions: (i) K2CO3, acetone, methyl bromo acetate; (ii) K2CO3, CH3CN, NaI, 1,3-dibromopropane; (iii) toluene/
methanol, 4-amino-1-benzylpiperidine; (iv) CH3CN, K2CO3, NaI, 4-amino-1-benzylpiperidine.

S. Sayin et al. / Tetrahedron 67 (2011) 3743e3753
3745
literature route.35e37 The substitution of diester derivative of p-tert-
butylcalix[4]arene (2) was conducted in the presence of toluene/
methanol with 4-amino-1-benzylpiperidine, which acts as
a monoamine releasing agent with 20- to 48-fold selectivity for
releasing dopamine versus serotonin,38 to afford the cone con-
former DADBP-Calix (4) in 54% yield. The formation of DADBP-
Calix was confirmed by the appearance of the characteristic amide
bands at about 1672 cmꢀ1 and by the disappearance of the ester
carbonyl band at 1750 cmꢀ1 in the IR spectra. Reaction of dialkyl
bromide derivative of p-tert-butylcalix[4]arene (3) with the
4-amino-1-benzylpiperidine in the presence of K2CO3 and NaI in
CH3CN gave the diamine derivative DABP-Calix (5) (42% yield). The
1H NMR spectra of 4 or 5 have a typical AX pattern for the meth-
ylene bridge proton (ArCH2Ar) of the calixarene moiety,
respectively, at 3.42 and 4.15 ppm (J¼13.2 Hz) or at 3.36 ppm
(J¼12.8 Hz) and 4.26 ppm (J¼12.4 Hz), which demonstrates that the
compound 4 and 5 exists in the cone conformation.39
It is well known that in extraction processes, separation is a time
consuming task. In our previous studies,4,29 we prepared silica based
magnetic nanoparticles (see Scheme 2) and immobilized various
calixarene derivatives onto its surface for easy separation of these
from solvents by using a magnet. In view of this, in this study we
immobilized two new calixarene derivatives 4 and 5 onto silica
based magnetic nanoparticles surface (EPPTMS-MN) to prepare two
new magnetic calixarene derivatives (6 and 7) as our second target
(see Scheme 3). Binding properties of these calixarenes towards
arsenate/dichromate anions and uranyl cations have been in-
vestigated. All new compounds have been characterized by 1H NMR
and IR spectroscopy, TGA, TEM and Elemental analyses techniques.
the electrostatic repulsion force and steric hindrance between the
calix[4]arenes on the surface of Fe3O4 nanoparticles.
The thermal properties of EPPTMS-MN and magnetic calixarene
derivatives (M-DADBP-Calix and M-DABP-Calix) were analyzed by
the thermogravimetric method. The indication of coating formation
onthemagnetite nanoparticles surface can be obtained fromtheTGA
measurement. Upon heating, the weight loss of EPPTMS-modified
magnetite nanoparticles (EPPTMS-MN) was shown to be about 5%
within a broad temperature range of 250 and 650 ꢂC. The de-
composition of both calix[4]arene units and 3-(2,3-epoxypropoxy)-
propyl groups of 6 was observed as 22% between 325 and 550 ꢂC. On
the other hand, the weight loss of 7 indicated thermal degradation
between325and832ꢂCtemperatureranges. Thesteparisesfromthe
decomposition of both calix[4]arene units and 3-(2,3-epoxy-
propoxy)-propyl groups (22% for 6, 34% for 7) (see Fig. 2).
FTIR spectroscopy was used to elaborate the structure of Fe3O4,
EPPTMS-modified Fe3O4 and CB-MNs. The IR peak at 568 cmꢀ1 be-
longs to the stretching vibration mode of FeeO bonds in Fe3O4.
Compared with the IR spectrum of EPPTMS-modified Fe3O4, the
calix[4]arene derivatives (6 and 7) possessed peaks at 1646 cmꢀ1
(for 6) and 1648 cmꢀ1 (for 7), both of which are stretching vibrations
of the amide carbonyl (NeC]O). The peaks at 1479, 1410 cmꢀ1 (for
6) and 1598, 1408 cmꢀ1 (for 7) are attributed to the bending vibra-
tion of the aromatic C]C bonds of the p-tert-butylcalix[4]arene
derivatives. Additional peaks centered at 1044, 945, 789 cmꢀ1 (for 6),
1046, 950, 781 cmꢀ1 (for 7) and 1116, 1090, 955 cmꢀ1 (for EPPTMS-
MN) were most probably due to the symmetric and asymmetric
stretching vibration of framework and terminal SieOe groups (see
Fig. 3a and b).
The elemental analysis results of 6 and 7, given in Table 1, con-
firmed that the immobilization of calix[4]arene derivatives was
accomplished. The amount of the loaded calix[4]arene derivatives 4
or 5 onto the polymeric support was evaluated from the results of
elemental analysis. According to the elemental analysis, the
resulting 6 and 7 contain 0.11% and 0.09% nitrogens corresponding
to 0.32 mmol of 6/g and 0.26 mmol of 7/g of supports, respectively.
O
O
O
O
O
O
O
O
O
Si
Si(OC2H5)4
1% NaF
Si
O
Fe3O4
Fe3O4
+
O
O
Si
O
Si
Si
O
O
O
2.2. Two-phase solvent extractions
O
O
O
O
2.2.1. Dichromate anion. The removal of the dichromate anion from
wastewater sources has gained high attention because of its highly
toxic effects. It is well known that at pH<6, the oxyanions structure
(EPPTMS-MN)
ꢀ40
2ꢀ
Scheme 2. Preparation of the EPPTMS-MN.
changes from the monomeric CrO4 to the dimeric HCr2O7
.
These oxides are potential sites for hydrogen bonding to the host
molecule. For this purpose, we were interested in synthesizing two
calix[4]arene derivatives at the lower rim, functionalized with 4-
amino-1-benzylpiperidine as a host having proton-switchable
binding lobes for extraction studies. A preliminary evaluation of the
binding efficiencies of the hosts was carried out by liquideliquid
extraction of Na2Cr2O7 from an aqueous solution at the range of pH
1.5e4.5. The binding efficiency of the diamine derivative DABP-
Calix (5) was not evaluated due to its solubility in water at this pH
range. The binding efficiencies of the other host (DADBP-Calix)
The magnetic (Fe3O4) nanoparticles and EPPTMS-modified
Fe3O4 nanoparticles (EPPTMS-MN) were prepared according to the
published procedures4 (see Scheme 2). The immobilization of 4 or 5
onto EPPTMS-MN was carried out in the presence of NaH in THF/
DMF to obtain magnetic calix[4]arene derivatives 6 or 7 (M-
DADBP-Calix or M-DABP-Calix). The formation of M-DADBP-Calix
or M-DABP-Calix (6 or 7) was confirmed by a combination of FTIR,
TEM, TGA and elemental analysis.
In order to receive more direct information on the particle size
and morphology, transmission electron microscopy (TEM) micro-
graphs of pure Fe3O4 nanoparticles and magnetic calixarene de-
rivatives (M-DADBP-Calix and M-DABP-Calix) were investigated
(Fig. 1aec). Observing the TEM micrographs (Fig. 1), nanoparticles
formed dense aggregates due to the lack of any repulsive force
between the magnetic nanoparticles, which is mainly due to the
nano-size of the EPPTMS-modified Fe3O4, which is about 10ꢁ2 nm.
This may be considered as indirect evidence that the magnetic core
of the EPPTMS-modified magnetic particles consist of a single
magnetic crystallite with a typical diameter of 8ꢁ3 nm, and that
difference corresponds to the EPPTMS coating. After p-tert-butyl-
calix[4]arene immobilization, the dispersion of particles was im-
proved greatly (Fig. 1b/c, for 6/7), which can easily be explained by
were carried out by liquideliquid extraction system of HCr2O7
ꢀ
from aqueous solution at different pH.
The extraction results (see Fig. 4) depicted that the diamide
derivative DADBP-Calix (4) is an effective extractant at low pH
between 1.5 and 4.5. The percentage of dichromate ions extracted
was 23% when the pH of the aqueous solution was 1.5 and attained
minimum 8% when pH of the aqueous solution increased to 4.5. The
extractant 4 provides suitable binding sites for dichromate anions
at the low pH due to the presence of protonable amine moieties.
Both to prevent solubility of 5 and to obtain a more rigid
structure of 4 and 5, the binding efficiencies of the magnetic cal-
ixarene derivatives (M-DABP-Calix and M-DADBP-Calix) were
ꢀ
carried out by the solideliquid extraction of HCr2O7 from an

3746
S. Sayin et al. / Tetrahedron 67 (2011) 3743e3753
N
N
HN
O
HN
O
O
Fe3O4
O
O
O
HO
O
O
i
O
O
O
O
O
Si
Si
4
Fe3O4
(6)
Si
Si
O
O
ii
O
O
4
O
O
Fe3O4
(EPPTMS-MN)
O
OH
O
NH
N
HN
N
(7)
Scheme 3. The synthetic routes for preparation of 6 and 7. Reaction conditions: (i) 4, NaH, THF/DMF; (ii) 5, NaH, THF/DMF.
aqueous solution at different pH. The extraction results of M-
DADBP-Calix (6) and M-DABP-Calix (7) are summarized in Fig. 5.
These receptors (6 and 7) have increased the anion extraction
ability of these compounds to a remarkable extent. It is clear that
this pronounced increase is due to the more rigid structural fea-
tures and protonation of the amine groups of 6 and 7, which helps
anion transfer. From the results, it is clear that these receptors (6
and 7) are more effective hosts for the removal of dichromate an-
ions. Namely, the extraction data given in Fig. 5 indicates that the
magnetic calix[4]arene derivatives (6 and 7) have notably increased
the anion extraction ability. This increase can be explained by the
fact that the magnetic calix[4]arene derivatives (6 and 7) are pro-
tonable in acidic conditions due to the presence of the amine
groups and can easily form complexes with dichromate anions by
electrostatic interactions and hydrogen bonding.
To understand the foreign anion effect on the dichromate anion,
we examined the dichromate anion retentions of 4 by using dif-
ferent inorganic sodium salts (Clꢀ, SO42ꢀ and NO3ꢀ) as additives. The
results given in Table 2 showed the retentions of dichromate anion
with 4 in the presence of the other anions. The extraction of
Na2Cr2O7 with 4 was not affected greatly by the presence of the
other sodium salts. Hence these new calixarene derivatives 4 could
be used selectively in the presence of foreign anions.
2.2.2. Arsenate anion. For a molecule to be effective as a host, it is
necessary that its structural features should be compatible with
those of the guest anions. The arsenate species occur mainly in the
form of H2AsO4ꢀ in the pH range between 3 and 6, while a divalent
anion HAsO42ꢀ dominates at higher pH values (such as between pH 8
and 11). This is evident in the extraction of arsenate by calixarenes. In
higher acidic conditions (pH 1e3) the arsenate ions will be pro-
tonated to generate the H3AsO4 form. Besides this, the monoanion
(H2AsO4ꢀ)willhaveasmallerfreeenergyofhydrationascomparedto
ꢀ
its dianionic form HAsO42ꢀ. In brief, the arsenate ions (H2AsO4
/
HAsO42ꢀ)arethedianionsthathaveoxidemoietiesattheperipheryof
the anions. These oxides are potential sites for hydrogen bonding to
the host molecule.
A preliminary evaluation of the extraction efficiencies of DADBP-
Calix (4) has been carried out by the liquideliquid extraction of ar-
senate ions from an aqueous solution into dichloromethane at the
range of pH 3.5e7.0. The extraction result depicts that arsenate anion
is efficiently extracted by 4 at pH 3.5e4.5. This is not a surprising
result because extractant 4 contains the appropriate proton switch-
able amine binding sites for arsenate anions at different pH.
From the extraction results, the maximum extraction values (90%
for 4) occurs at pH 3.5 (see Fig. 6), which indicate that the best in-
teraction between this ligand and arsenate ions occurs at this pH.

S. Sayin et al. / Tetrahedron 67 (2011) 3743e3753
3747
more acidic condition due to containing ether moieties, bearing
magnetic property support extracts arsenate ion with 18% in the pH
range of 3.5e4.5. The mainly maximum extraction value (91% for 6
and 73.8% for 7) occurs at pH 3.5. This is reflected in these receptors
(6 and 7), which have increased the arsenate ion extraction. The
proposed interaction of 6 with these anions is given in Scheme 4.
2.2.3. Uranyl cation. The mobility of U(VI) is enhanced in oxidizing
environments by the formation of uranyl (UO22þ), which hydrolyzes
to form a number of aqueous hydroxyl species.41 The hydrolysis
2þ
reactions of UO2 are listed in Table 3 according to the literature.42
It is well known that through a hydrolysis process, uranium may
2þ
form a series of aqua-complexes, such as UO2(OH)þ, (UO2)2(OH)2
þ
43,44
and (UO2)3(OH)5
.
The ratio of these species depends on the
concentration of uranyl ions, concentration and on the pH of the
solution. Over the 1.3e4.0 pH interval the predominant species are
2þ
þ
45
UO22þ, (UO2)2(OH)2 and (UO2)3(OH)5
.
Increasing pH over 4.0,
uranium adsorption decreases because in this range, the soluble
complexes of uranyl ions are the predominant species.46 At pH<4,
2þ
only a low amount of non-hydrolyzed UO2 ions are adsorbed. At
pH<6, the uranyl contaminant solution results in the formation of
uranium(VI)ehydroxo or uranium(VI)eaquo-complexes. At pH 5.3
2þ
the cationic uranium(VI) species, UO2 and UO2OHþ, are pre-
dominant in solution and the competition of protons, regarding
cation exchange, is relatively low.47,48
Although several studies have been published regarding the
host molecules, which act as complex for cations and anions, there
is no example of a magnetic calixarene nanoparticles receptor that
act as a host for the uranyl cation. Herein, we have designed the two
new calixarene receptors (DADBP-Calix and DABP-Calix) and have
also prepared their magnetic derivatives (M-DADBP-Calix and M-
DABP-Calix) to convert into more rigid structural feature and pri-
marily investigated their extraction capability towards U(VI). A
preliminary evaluation of the extraction efficiencies of DADBP-
Calix (4) and DABP-Calix (5) has been performed by liquideliquid
extraction of UO2(OAc)2$2H2O from water into dichloromethane at
different pH values. The extraction data (Fig. 8) showed that the
maximum percentage of U(VI) extracted was almost the same (74%)
both for 4 and 5 when the pH of the aqueous solution was 5.5 (for 4)
or 7.0 (for 5).
The conversions of 4 and 5 into the magnetic derivatives M-
DADBP-Calix and M-DABP-Calix have increased the uranyl ex-
traction ability. This increase can be explained by the fact that the
calixarene derivatives in the polymeric matrix may have gained
a more rigid and appropriate structure, which assists the transfer of
U(VI) when compared with monomers. The role of the silica based
magnetic nanoparticles backbone was used to convert rigid struc-
tures of 4 and 5. This implies a better preorganization of the
immobilized calixarenes (6 and 7), which occurs with a cooperative
effect of the amine groups and a number of donor atoms. This co-
operative effect may improve extraction ability.
The solideliquid extraction results show that 6 and 7 are the
effective ligands for the removal of U(VI) in aqueous solution at pH
5.5e8.5 (see Fig. 9). The maximum sorption values of the magnetic
calixarene derivatives occur at pH 8.0 (62% for 6) and at pH 8.5 (61%
for 7).
The foreign cation effect on the U(VI) retention of 4 and 5 in
the presence of different metal cations (Fe3þ, Ca2þ, Kþ and Naþ)
was also examined. The results showed that the selective re-
tention of U(VI) with 4 and 5 was affected by the presence of
other cations (see Table 4). The extraction of U(VI) with 4 and 5
was affected by the presence of Fe3þ and Ca2þ cations. On the
other hand, the extraction percentages of U(VI) was not affected
by the presence of Naþ and Kþ cations. In conclusion, all calixar-
ene derivatives could be used selectively in the presence of cat-
ions like Naþ and Kþ ions.
Fig. 1. TEM micrographs of (a) pure Fe3O4 nanoparticles, (b) 6, (c) 7.
These interactions include electrostatic interaction and hydrogen
bonding between protonable amine and the oxygens of arsenate
anions.2,27
The extraction binding efficiencies of M-DADBP-Calix (6), M-
DABP-Calix (7) and EPPTMS-MN were carried out by solideliquid
extraction studies. The extraction results of M-DADBP-Calix (6), M-
DABP-Calix (7) and EPPTMS-MN are summarized in Fig. 7. Magnetic
ligands 6 and 7 contain amine groups, which are protonable in acidic
conditions and easily form complexes with arsenate anions by
electrostatic interactions and hydrogen bonding. Although, the
magnetic support material EPPTMS-MN is hardly protonated under

3748
S. Sayin et al. / Tetrahedron 67 (2011) 3743e3753
Fig. 2. TG and their first derivatives (dTG) of 6 and 7.
3. Conclusion
4. Experimental
In summary, two new calixarene derivatives (4 and 5) were
synthesized and then immobilized onto the silica based magnetic
nanoparticles surface (EPPTMS-MN) to impact both more rigid
structural features and to prevent solubility of the compounds. This
immobilization provides an efficient way to improve the separation
capability of the calixarene compositae silica carriers due to their
magnetic properties. Additionally, extraction capability of these
new calixarene derivatives were investigated towards As(V), Cr(VI)
and U(VI) ions. The complexation studies by these ions showed that
these calixarene derivatives were effective extractants for the re-
moval of As(V), Cr(VI) and U(VI) from the aqueous solution. The
extraction results reflect that the complexation of arsenate/di-
chromate anions and the uranyl cation depends on the structural
properties of the receptors, such as stability or rigidity, proton-
switchable ability and hydrogen binding ability.
4.1. Apparatus
Melting points were determined on a Gallenkamp apparatus
in a sealed capillary glass tube and are uncorrected. 1H NMR
spectra were recorded on a Varian 400 MHz spectrometer. IR
spectra were obtained on a PerkineElmer 1605 FTIR spectrome-
ter using KBr pellets. UVevis spectra were obtained on a Shi-
madzu 160A UVevis spectrophotometer. Elemental analyses
were performed using a Leco CHNS-932 analyzer. Thermogravi-
metric analyses (TGA) was carried out with Seteram thermog-
ravimetric analyzer. The sample weight was 15e17 mg. Analysis
was performed from room temperature to 900 ꢂC at a heating
rate of 10 ꢂC/min under argon atmosphere with a gas flow rate of
20 mL/min. An Orion 410Aþ pH metre was used for the pH
measurements.

S. Sayin et al. / Tetrahedron 67 (2011) 3743e3753
3749
Fig. 3. (a) The IR spectrum of 4 and 6. (b) The IR spectrum of 5 and 7.
Table 1
Results of elemental analysis for EPPTMS-MN, 6 and 7
C (%)
H (%)
N (%)
Bounded amounta (mmol/g)
6
7
15.09
12.69
13.20
3.12
2.77
2.61
0.11
0.09
d
w0.32
w0.26
d
EPPTMS-MN
a
Calculated according to the N content.
4.2. Materials
TLC analyses were carried out on DC Alufolien Kieselgel 60 F254
(Merck). Generally, solvents were dried by storing them over molecular
ꢀ
sieves (Aldrich; 4 A, 8e12 mesh). All reactions, unless otherwise noted,
were conducted under a nitrogen atmosphere. All starting materials
and reagents used were of standard analytical grade from Merck or
Aldrich and used without further purification. Dry THF was distilled
from the ketyl prepared from sodium and benzophenone. CH2Cl2 was
distilled from CaCl2, while MeOH was distilled over Mg and stored over
molecular sieves. All commercial grade solvents were distilled, and
then stored over molecular sieves. The drying agent employed was
anhydrous magnesium sulfate. All aqueous solutions were prepared
Fig. 4. Extraction percentages of dichromate anion with 4 at pH 1.5e4.5. (H2O/CH2Cl2:
10/10 (v/v); sodium dichromate 1ꢃ10ꢀ4 M; ligand: 1ꢃ10ꢀ3 M, 1 h. 25 ꢂC).

3750
S. Sayin et al. / Tetrahedron 67 (2011) 3743e3753
Fig. 7. Extraction percentages of arsenate anion with 6 and 7 at pH 3.5e7.0. (Solid
phase, sorbent¼25 mg (6,7), aqueous phase, Na2HAsO4¼1.0ꢃ10ꢀ5 M (10 mL) at 25 ꢂC
for 1 h).
Fig. 5. Extraction percentages of dichromate anion with 6 and 7 at pH 2.5e4.5. (Solid
phase, sorbent¼25 mg (6,7), aqueous phase, Na2Cr2O7¼1.0ꢃ10ꢀ4 M (10 mL) at 25 ꢂC
for 1 h).
arsenazo III solution (0.01%) was prepared by dissolving reagent.
Adjusting the pH values of the working solutions was carried out using
5 M of sodium acetate buffer to determination of UO22þ in aqueous
solution.
Table 2
2ꢀ
Dichromate retention results of 4 pH 1.5, in the presence of foreign anions (Clꢀ, SO4
and NO3ꢀ) and their mixtures
4.3. Synthesis
Different anions
ꢀ
The compounds 1e3 were synthesized by procedures published
in the literature.35e37 Silica based magnetic nanoparticles
(EPPTMS-MN) was synthesized in our previously study.4 Com-
pounds 4 and 5 and magnetic derivatives of calix[4]arene (6 and 7)
are herein reported for the first time.
None
23
Clꢀ
SO42ꢀ
NO3
Mixture
18.21
4
22.77
22.69
20.32
[Sodium dichromate]¼1.0ꢃ10ꢀ4 M; ligand 4¼1.0ꢃ10ꢀ3 M at 25 ꢂC, pH 1.5.
The concentration of different anions¼1.0ꢃ10ꢀ2 M.
4.3.1. Synthesis of p-tert-butylcalix[4]arene diamide DADBP-Calix
(4). The diester derivative of p-tert-butylcalix[4]arene 2 (2.0 g,
2.52 mmol) was dissolved in toluene/methanol [2/1] (33 mL). 4-
Amino-1-benzylpiperidine (4.8 g, 25.22 mmol) was added into this
solution and the reaction mixture was stirred and heated at reflux.
The reaction was monitored by using combinations of TLC and IR.
After 10 days, most of the solvent was evaporated under reduced
pressure and the resulting solid was dissolved in dichloromethane
and washed three times with distilled water. The crude product was
purified by column chromatography (SiO2, EtOAc/n-hexane; 2:1).
Yellow powder 54% yield mp: 195e197 ꢂC. The IR spectral data is as
(KBr disk) cmꢀ1: 1672 (amide carbonyl band, NeC]O). 1H NMR
(400 MHz CDCl3):
d
1.06 (s, 18H, tBu), 1.28 (s, 18H, tBu), 1.64 (q, 8H,
J¼10.6 Hz, eCH2e), 2.15 (t, 8H, J¼11.2 Hz, eCH2e), 3.42 (d, 4H,
J¼13.2 Hz, AreCH2eAr), 3.44 (s, 4H, eCH2e), 3.89 (m, 2H, eCHe),
4.15 (d, 4H, J¼13.2 Hz, AreCH2eAr), 4.55 (s, 4H, eCH2e), 6.94 (s, 4H,
ArH), 7.08 (s, 4H, ArH), 7.27 (m, 10H, ArH), 7.83 (s, 2H, eOH), 8.97 (d,
2H, J¼7.6 Hz, eNHe). Anal. Calcd for C72H92N4O6: C, 77.94; H, 8.36; N,
5.05. Found (%); C, 78.02; H, 8.28; N, 5.10.
Fig. 6. Extraction percentages of arsenate anion with 4 pH 3.5e7.0. (H2O/CH2Cl2: 10/10
(v/v); Na2HAsO4¼1ꢃ10ꢀ5 M; ligand: 1.10ꢀ3 M, 1 h. 25 ꢂC).
4.3.2. Synthesis of p-tert-butylcalix[4]arene diamine DABP-Calix
(5). To a solution of dialkyl bromide of p-tert-butylcalix[4]arene (3)
(1.0 g, 1.12 mmol) in CH3CN (30 mL) were added K2CO3 (1.6 g,
11.58 mmol), NaI (0.7 g, 4.67 mmol) and 4-amino-1-benzylpiper-
idine (4.8 mL, 25.48 mmol) and the reaction mixture was stirred and
heated at reflux. The reaction was monitored by using a TLC. After
97 h, the reaction mixture was filtered and the solvent was removed
under reduced pressure. The residue was dissolved in CH2Cl2
(150 mL) and the organic layer extracted three times with water. The
combined organic phases were dried (anhydrous MgSO4), the sol-
vent was removed under reduced pressure; and the crude product
was purified by column chromatography (SiO2, CHCl3/MeOH; 10:1).
with deionized water that was passed through a Millipore milli-Q Plus
water purification system. Anions were used as their sodium salts.
Ammonium molybdate solution (3.15ꢃ10ꢀ2 M), methyl violet solution
(4.5ꢃ10ꢀ5 M)andhydrochloricacidsolution(6.85M)werepreparedby
dissolving the reagents in doubly distilled water. Arsenazo III, uranyl
acetate dihydrate were purchased from Fluka. Standard stock solution
of 0.9787
mg/mL uranium (VI) was prepared by dissolving the appro-
priate amounts of uranyl acetate dihydrate in deionized water. A stock

S. Sayin et al. / Tetrahedron 67 (2011) 3743e3753
3751
4
4
Fe3O4
Fe3O4
O
OH
O
O
O
O
OH
O
O
HO
H
O
N
NH
HN
NH
HN
N+
A
H
N
N
-
A = H2AsO4-/HCr2O7
Scheme 4. The suggested complexation phenomena of arsenate and dichromate ion with 6.
Table 3
Equilibrium constants
Reaction
Log K
Aqueous speciation
2þ
UO2 þH2O¼UO2(OH)þþHþ
ꢀ5.20a
ꢀ5.62a
ꢀ15.55a
ꢀ21.0a
2UO22þþ2H2O¼(UO2)2(OH)2 þ2Hþ
2þ
þ
3UO22þþ5H2O¼(UO2)3(OH)5 þ5Hþ
ꢀ
UO22þþ3H2O¼UO2(OH)3 þ3Hþ
Ion exchange reactions
2þ
,
c
UO2 þ2Xꢀ¼UO2X2
30.9b
UO2(OH)þþXꢀ¼UO2(OH)X
8.6c
þ
(UO2)3(OH)5 þXꢀ¼(UO2)3(OH)5X
ꢀ1.75c
a
Literature.42
b
Fixed relative to Naþ constant.
c
Literature.41
Fig. 9. Extraction percentages of uranyl cation with 6 and 7 at pH 5.5e8.5 (10 mL,
1.15ꢃ10ꢀ5 M) UO2(AcO)2$2H2O, magnetic calix[4]arene nanoparticles (25 mg of 6 or 7),
175 rpm, 25 ꢂC for 1 h.
Table 4
Uranyl retention results of 4 (pH 5.5) and 5 (pH 7.0), in the presence of foreign
cations (Fe3þ, Ca2þ, Naþ and Kþ)
Different cations
None
Fe3þ
Ca2þ
Naþ
Kþ
4
5
73.7
74.5
0
0
14.6
14.8
73.0
73.8
73.4
74.1
Uranyl acetate dihydrate¼1.15ꢃ10ꢀ5 M; 4 or 5¼1.0ꢃ10ꢀ3 M at 25 ꢂC.
The concentration of different cations¼1.15ꢃ10ꢀ3 M.
Fig. 8. The extraction percentages of uranyl cation with 4 and 5 at pH 5.5e8.5. (10 mL,
1.15ꢃ10ꢀ5 M) UO2(AcO)2$2H2O, calix[4]arene derivatives (10 mL of 1ꢃ10ꢀ3 M solution
of 4 or 5 in CH2Cl2), 175 rpm, 25 ꢂC for 1 h.
C
74H100N4O4: C, 80.10; H, 9.08; N, 5.05. Found (%); C, 79.94; H, 9.11;
N, 5.07.
4.3.3. General procedure for the preparation of magnetic p-tert-bu-
tylcalix[4]arene derivatives M-DADBP-Calix (6) and M-DABP-Calix
(7). A mixture of functionalized p-tert-butylcalix[4]arene de-
rivative (4 or 5) (0.3 g) and NaH (0.05 g) in a solution of THF/DMF
(20 mL, 3/1) was stirred for 30 min then EPPTMS-MN (0.9 g) was
added, and the solution heated under reflux for 5 days. After
magnetic separation, the resulting compound was washed with
dichloromethane three times to remove excess of functionalized
Yellow powder 42% yield mp: 161e162 ꢂC. 1H NMR (400 MHz
t
t
CDCl3):
d 1.19 (s, 18H, Bu), 1.22 (s, 18H, Bu), 1.66 (m, 8H, eCH2e),
2.05 (t, 8H, J¼11.2 Hz, eCH2e), 2.26 (m, 4H, eCH2e), 2.36 (m, 4H,
eCH2e), 3.36 (d, 4H, J¼12.8 Hz, AreCH2eAr), 3.45 (m, 2H, eCHe),
3.52 (s, 4H, eCH2e), 3.56 (t, 2H, J¼6.4 Hz, eNH), 4.01 (t, 4H, J¼4.8 Hz,
eCH2e), 4.26 (d, 4H, J¼12.8 Hz, AreCH2eAr), 7.00 (s, 4H, ArH), 7.08
(s, 4H, ArH), 7.26 (s, 2H, eOH), 7.32 (m, 10H, ArH). Anal. Calcd for

3752
S. Sayin et al. / Tetrahedron 67 (2011) 3743e3753
p-tert-butylcalix[4]arene derivative, then washed with water and
dried under vacuum.
For this propose, cations were used as corresponded with one
hundred-fold of uranyl cation concentration.
For 6: the IR spectral data is as (KBr disk) cmꢀ1: 3251,1646 (amide
C]O), 1479, 1410 (aromatic C]C), 1191, 1044, 945, 789 (SieO) and
572 (FeeO).
Acknowledgements
For 7: the IR spectral data is as (KBrdisk) cmꢀ1: 3424,1648 (amine
band), 1598, 1408 (aromatic C]C), 1150, 1046, 950, 781 (SieO) and
574 (FeeO).
We would like to thank The Scientific and Technological Re-
search Council of Turkey (TUBITAK Grant No. 107T873) and The
Research Foundation of Selcuk University (BAP) for financial sup-
port of this work.
4.4. Extraction studies
References and notes
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they could be present more than uranyl cation in aqueous solutions.

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