Synthesis and properties of novel magnetic nanoparticles grafted with nitropyridine-substituted calix[4]arene derivative as CR6+ extractant

Article abstract of DOI:10.3906/kim-1405-69

A new calix[4]arene derivative, 3, which functionalized at the lower rim with 2-(2-aminoethyl amino)-5-nitropyridine, was synthesized and characterized by a combination of FTIR, ¹ H NMR, ¹³ C NMR, and elemental analysis. Then the calix[4]arene 3 was grafted onto [3-(2,3-epoxypropoxy)propyl]trimethoxysilane-modified Fe ₃ O ₄- nanoparticles (EPPTMS-MN) to produce new calixarene-adorned magnetic nanoparticles (MN-DiNoPy-Calix (4)). The structure of the calixarene-adorned magnetic nanoparticles 4 was determined by a combination of FTIR, TEM, and elemental analysis. Moreover, a study regarding the removal of toxic HC_{r 2} O^-₇ anion from aqueous solution was also carried out with the calixarene-adorned magnetic nanoparticles in solid-liquid extraction studies.

Full text of DOI:10.3906/kim-1405-69

Turk J Chem
Turkish Journal of Chemistry
(2015) 39: 130 – 138
¨
http://journals.tubitak.gov.tr/chem/
˙
c
⃝ TUBITAK
doi:10.3906/kim-1405-69
Research Article
Synthesis and properties of novel magnetic nanoparticles grafted with
nitropyridine-substituted calix[4]arene derivative as Cr6+ extractant
∗
˘
Serkan SAYIN , Vildan DOGAN
Department of Chemistry, Sel¸cuk University, Konya, Turkey
Received: 25.05.2014
•
Accepted: 12.09.2014
•
Published Online: 23.01.2015
•
Printed: 20.02.2015
Abstract: A new calix[4]arene derivative, 3, which functionalized at the lower rim with 2-(2-aminoethyl amino)-5-
nitropyridine, was synthesized and characterized by a combination of FTIR, 1 H NMR, 13 C NMR, and elemental analysis.
Then the calix[4]arene 3 was grafted onto [3-(2,3-epoxypropoxy)propyl]trimethoxysilane-modified Fe3 O4 – nanoparticles
(EPPTMS-MN) to produce new calixarene-adorned magnetic nanoparticles (MN-DiNoPy-Calix (4)). The structure
of the calixarene-adorned magnetic nanoparticles 4 was determined by a combination of FTIR, TEM, and elemental
analysis. Moreover, a study regarding the removal of toxic HCr2 O−7 anion from aqueous solution was also carried out
with the calixarene-adorned magnetic nanoparticles in solid–liquid extraction studies.
Key words: Calixarene, proton-switchable, magnetic nanoparticles, dichromate anion, solid–liquid extraction
1. Introduction
Although it has a wide variety of industrial uses, chromium is highly toxic and hazardous to humans. Trans-
mitted to the environment via effluents produced in processes such as textile dyeing, mining, photography, and
steel fabrication,1−4 chromium in the aqueous phase can occur in several oxidation forms. However, only the
Cr(III) and Cr(VI) states are environmentally significant.5 Chromium(III) provides essential micronutrients to
various organisms, while chromium(VI) has extremely toxic and carcinogenic influences on biological systems
due to the strongly oxidizing biological anions Cr2 O27− and HCr2 O7−
.
6−8
Therefore, developing a method that
uses low-cost materials to remove oxidized forms of Cr(VI) from contaminated wastewater is essential.
One recent challenge has been to develop receptors that selectively respond to the removal of toxic as well
as carcinogenic ions, like Cr(VI), from contaminated water resources.9−12 Among these receptors, calixarenes,4,8
which are produced by a condensation reaction of phenol and formaldehyde, have been successfully employed
as receptors for the extraction of dichromate anions from aqueous solutions.13−17 Because of their unique
structure, which provides host–guest complexability and unlimited functionalization properties, calixarenes13,16
have been found to be magnificent supramolecular compounds.18−20
Although calixarene derivatives have been used as receptors for the removal of toxic ions such as dichro-
mate anions, they have led to a separation concern arising from the final step of the extraction. Moreover, some
calixarene derivatives might be soluble in the aqueous phase, which is when the wastewater is contaminated.
To address these disadvantages, calixarene-grafted magnetic nanoparticles4,16 have recently been developed so
that calixarene derivatives may acquire magnetic properties that prevent their solubility in water.21,22
∗Correspondence: saynserkan@gmail.com
130

˘
SAYIN and DOGAN/Turk J Chem
In our previous study, a disubstituted calixarene derivative containing pyridinium units was synthesized
and grafted onto Fe3 O4 nanoparticles to use as receptor for the extraction of dichromate anions (see Figure 1).
The magnetic nanoparticles-grafted calix[4]arenes were found to be effective ligands with maximum extraction
capabilities of 69% (for MN-Py-1) and 53% (for MN-Py-2) at pH 3.5 with respect to their convenient
complexability with dichromate anions.23
N
N
N
N
NH
NH
HN
HN
OH
OH
O
O
O
O
O
HO
O
HO
O
O
O
O
O
O
Fe3O4
Fe3O4
MN-Py-2
MN-Py-1
Figure 1. Structures of the magnetic nanoparticles-grafted calix[4]arenes (MN-Py-1 and MN-Py-2).
In the present study, we aimed to prepare new calixarene-grafted magnetic nanoparticles that would
be used as potential receptors for the removal of toxic dichromate anions from aqueous solutions. For this
purpose, the bis(nitropyridine)-substituted calix[4]arene 3 was synthesized and then immobilized onto silica-
coated magnetic nanoparticles to easily form complexes with dichromate anions by means of electrostatic
interactions and hydrogen bonding.
2. Results and discussion
2.1. Synthesis and characterizations of new receptors
The objective of this study was to synthesize bis(nitropyridine)-substituted calix[4]arene 3 and its magnetic
nanoparticles (MN-DiNoPy-Calix). Moreover, their extraction attractions towards dichromate ions were
evaluated for the first time. To achieve this goal, p-tert-butylcalix[4]arene 1 and its diester derivative 2 were syn-
thesized according to procedures outlined previously.24,25 The substitution of the diester derivative 2 at the lower
rim was conducted with 2-(2-aminoethylamino)-5-nitropyridine to afford 5,11,17,23-tetra-tert-butyl-25,27-bis(2-
nitropyridin-2-ylamino)ethylaminocarbonyl-methoxy)-26,28-dihydroxy calix[4]arene 3 (Scheme). The synthe-
sized new compound 3 was fully characterized by a combination of FTIR, 1 H NMR, 13 C NMR, and elemental
analysis techniques.
The FTIR spectra of the bis(nitropyridine)-substituted calix[4]arene 3 confirm its structure by its char-
acteristic peaks at 1670 cm−1 belonging to the vibration stretch of C=O bonds, as well as at 1481 and 1291
cm−1 , which are stretching vibrations of the NO2 group.
131

˘
SAYIN and DOGAN/Turk J Chem
O
O
iv
Fe3O4
Fe3O4
EPPTMS-MN
v
NO2
NO2
N
N
OH
OH
HN
NH
O
O
O
O
O
O
HN
HN
NH
HN
NH
NH
N
O
N
O
Fe3O4
NO2
OHOH O
O
O2N
iii
MN-DiNoPy-Calix (4)
(3)
O
O
O
O
OH
OHOHHO
OH
OHOH O
O
ii
i
(1)
(2)
Scheme. Synthesis of MN-DiNoPy-Calix. Reaction conditions: i) HCHO, NaOH; ii) methylbromoacetate, K2 CO3 ,
CH3 CN; iii) 2-(2-aminoethylamino)-5-nitropyridine, CH2 Cl2 /CH3 OH; iv) 3-(2,3-epoxypropoxy)propyl]trimethoxysilane,
tetraethyl orthosilicate, NaF, H2 O; v) NaH, THF/DMF.
As seen in the 1 H NMR spectrum of the bis(nitropyridine)-substituted calix[4]arene 3, there are 2 doublets
at 3.28 and 3.91 ppm (J = 13.2 Hz), which indicate compound 3 exists in the cone conformation (Figure 2).
In addition, the protons of the amide group, and the aromatic protons of the pyridine appeared at 8.94 ppm
(–NH), and 8.11 (ArH), 8.25 (ArH), and 8.79 ppm (ArH) in the 1 H NMR spectra (Figure 2). The 13 C NMR
spectra present useful information about the structure of the bis(nitropyridine)-substituted calix[4]arene 3 by
the peak at 169.72 ppm, which belongs to the C=O groups (Figure 3).
The iron oxide magnetic nanoparticles and epoxysilica-coated Fe3 O4 nanoparticles (EPPTMS-MN)
were prepared according to the literature.4,26 MN-DiNoPy-Calix (4) was prepared by the immobilization of
calix[4]arene 3 onto [3-(2,3-epoxypropoxy)-propyl]-trimethoxysilane-coated Fe3 O4 nanoparticles (EPPTMS-
MN) in the presence of NaH in THF/DMF (Scheme). The structure of the novel calix[4]arene-grafted magnetic
nanoparticles MN-DiNoPy-Calix (4) was determined by a combination of FTIR, TEM, and elemental analysis
techniques.
132

˘
SAYIN and DOGAN/Turk J Chem
Figure 2. 1 H NMR spectrum of the bis(nitropyridine)-substituted calix[4]arene 3.
Figure 3. 13 C NMR spectrum of the bis(nitropyridine)-substituted calix[4]arene 3.
133

˘
SAYIN and DOGAN/Turk J Chem
In order to elaborate the structure of MN-DiNoPy-Calix (4), FTIR spectroscopy was used. Its
characteristic peaks appeared at 1456 and 1411 cm−1 , which are stretching vibrations of the aromatic C=C
bonds, and a peak at 1634 cm−1 belonging to C=O groups. The characteristic vibration bend of N–O and
Fe–O groups centered at 1479 cm−1 (N–O stretch) and 560 (Fe–O stretch) can also be found. Additional peaks
of MN-DiNoPy-Calix (4) that appeared at 1107, 958, and 799 cm−1 may result from the symmetric and
asymmetric vibration bends of framework and terminal Si–O groups (Figure 4).
Figure 4. FTIR spectra of MN-DiNoPy-Calix (4).
Transmission electron microscopy (TEM) analysis of pure Fe3 O4 nanoparticles (Figure 5a) and MN-
DiNoPy-Calix (Figure 5b) was used, respectively, to obtain more direct information about particle size and
morphology (Figure 5). As seen in the micrographs, MN-DiNoPy-Calix has a distinctly different morphology
Figure 5. TEM micrographs of (a) pure Fe3 O4 nanoparticles, (b) MN-DiNoPy-Calix (4).
134

˘
SAYIN and DOGAN/Turk J Chem
than Fe3 O4 nanoparticles; the latter have a single magnetic crystallite with a typical size range of 8 ꢀ 3 nm.
After immobilization of the bis(nitropyridine)-substituted calix[4]arene 3, an increase in the particle dispersion
was observed (Figure 5b). This increase might have been due to the electrostatic repulsion force and steric
hindrance between the bis(nitropyridine)-substituted calix[4]arene units on the surface of Fe3 O4 nanoparticles.
The elemental analysis results of MN-DiNoPy-Calix confirmed that the bis(nitropyridine)-substituted
calix[4]arene 3 was successfully grafted onto EPPTMS-MN (Table). The results showed that MN-DiNoPy-
Calix contains 0.42% nitrogen corresponding to 2.40 mmol of MN-DiNoPy-Calix/g of support.
Table. Elemental analysis results of EPPTMS-MN and MN-DiNoPy-Calix.
C (%) H (%) N (%) Bound amount (mmol/g)a
EPPTMS-MN
MN-DiNoPy-Calix 14.53
aCalculated according to the N content.
13.20
2.61
2.90
-
0.42
-
2.40
2.2. Dichromate anion extraction studies
It is well known that dichromate anions (Cr2 O72− /HCr2 O−7 ) provide good potential interactions with host
molecules, which have proton-switchable binding lobes and/or can form hydrogen-bonding sites.16,27 An initial
study of the extraction was carried out by liquid–liquid extraction of Na2 Cr2 O7 from an aqueous solution
at a range of pH 1.5–4.5 in the presence of receptor 3. However, the binding affinity of receptor 3 was not
investigated because of the solubility of receptor 3 in water in the range of pH 1.5–4.5. In order to prevent
water solubility of receptor 3 and to acquire magnetic properties that enable easy separation of the receptor,
the bis(nitropyridine)-substituted calix[4]arene 3 was grafted onto epoxy-silica–coated magnetic nanoparticles.
The resulting MN-DiNoPy-Calix was tested as receptor 4 for the extraction of the dichromate anion from
an aqueous solution by means of solid–liquid extraction at a range of pH 1.5–4.5.
The extraction results of receptor 4 (MN-DiNoPy-Calix) are summarized in Figure 6. It was found
that receptor 4 was an effective host for the removal of dichromate anions. Because of the more rigid structural
features and the proton-switchable capability of the pyridine units of MN-DiNoPy-Calix, dichromate anion
extraction from an aqueous solution was achieved (Figure 6). Indeed, the highest extraction capacity by receptor
4 was observed in acidic nature, which confirmed that receptor 4 was protonated. These protonated units played
an important role in forming complexes with HCr2 O7− by electrostatic interactions and hydrogen bonding.
60
MN-DiNoPy-Calix
50
40
30
20
10
0
1.5
2.5
3.5
4.5
p H
Figure 6. Extraction percentages of dichromate anion with MN-DiNoPy-Calix at pH 1.5–4.5 (solid phase, sorbent
= 25 mg (MN-DiNoPy-Calix), aqueous phase, Na2 Cr2 O7 = 1.0 × 10−4 M (10 mL) at 25 ◦ C for 1 h).
135

˘
SAYIN and DOGAN/Turk J Chem
In order to see the interfering effect of other anions on dichromate anion retention of the receptor (MN-
DiNoPy-Calix), different inorganic sodium salts (SO24− , Cl− , and NO3−) were additionally mixed with the
solution at pH 1.5. The results given in Figure 7 clearly indicate that the receptor (MN-DiNoPy-Calix) is
a selective extractant for the extraction of Na2 Cr2 O7 owing to the small difference obtained in the extraction
value of Na2 Cr2 O7 with MN-DiNoPy-Calix by the presence of other anions.
60
50
40
30
20
10
0
None
Cl-
2-
SO4
-
NO3
Mixture
None
Cl-
SO42-
NO3-
Mixture
Foreign Anion s
Figure 7. Dichromate retention results of the receptor (MN-DiNoPy-Calix) in the presence of interfering anions
(Cl− , SO42− , and NO−3 ) at pH 1.5. Averages and standard deviations calculated for data received from 3 independent
extraction experiments. Sodium dichromate, 1 × 10−4 M; ligand, 1 × 10−3 M; NaCl, 1 × 10−2 M; Na2 SO4 , 1 ×
10−2 M; NaNO3 , 1 × 10−2 M; 1 h, 25 ◦ C.
3. Experimental
3.1. General remarks
An Ez-Melt apparatus in a sealed capillary was used to determine all melting points of the synthesized
compounds. NMR spectra were recorded on a Varian 400 MHz spectrometer, indicating chemical shifts as ppm
relative to an internal standard tetramethylsilane (δ= 0.0). FT-IR spectra were recorded with a PerkinElmer
100 spectrometer. A Shimadzu 160A UV-vis apparatus was used to analyze absorbance of Cr6+ in aqueous
solutions. For the pH measurements, an Orion 410A+ pH meter was used. Elemental analyses were performed
on a Leco CHNS-932 analyzer.
3.2. Synthesis
Compounds 1 and 224,25 and Fe3 O4 and EPPTMS-MN4,26 were prepared according to the literature
methods. The synthesis of compound 3 and the immobilization of compound 3 onto EPPTMS-MN in order
to produce MN-DiNoPy-Calix (4) are herein reported for the first time.
3.2.1. Synthesis of 5,11,17,23-tetra-tert-butyl-25,27-bis(2-nitropyridin-2-ylamino)ethylaminocar-
bonyl-methoxy)-26,28-dihydroxycalix[4]arene 3
To a solution of diester derivative 2 (1 g, 1.261 mmol) in 18 mL of a mixture of CH2 Cl2 /CH3 OH (2/1, v/v) was
added 2-(2-aminoethylamino)-5-nitropyridine, followed by stirring at room temperature for 34 h. The reaction
mixture was monitored by TLC (CH2 Cl2), and the volatile components were removed under reduced pressure.
The crude product was washed with water to adjust pH to 7.0 and then dried in an oven. The crude product
was purified by column chromatography (SiO2 , CH2 Cl2 /CH3 OH, 10/1). Yield: 52%, mp 274–275 ◦ C. FTIR
(ATR) cm−1 : 3450 (–OH), 3380 (–NH), 1670 (C=O), 1481 (N–O asymmetric stretch), 1291 (N–O symmetric
136

˘
SAYIN and DOGAN/Turk J Chem
stretch). 1 H NMR (400 MHz, DMSO): δ1.06 (s, 18H, But), 1.14 (s, 18H, But), 3.28 (d,4H, J = 13.2 Hz,
ArCH2 Ar), 3.35–3.58 (m, HOD shielded, 10H, –CH2 – and Ar–NH), 3.91 (d,4H, J = 13.2 Hz, ArCH2 Ar), 4.47
(s, 4H, OCH2), 6.99 (s, 4H, ArH), 7.08 (s, 4H, ArH), 7.46 (brs, 2H, OH), 8.11 (brs, 2H, ArH), 8.25 (s, 2H,
ArH), 8.79 (brs, 2H, ArH), 8.94 (brs, 2H, NH) (see Figure 2). 13 C NMR (100 MHz, DMSO): δ 31.26 (–C H3 ,
But), 31.80 (–C H3 , But), 34.04 (Ar–C H2 –Ar), 34.47 (–C , But), 34.49 (–C , But), 38.05 (–N–C H2), 72.40
(ArN–C H2), 74.83 (O–C H2), 125.74 (ArC), 125.90 (ArC), 126.29 (ArC), 127.17 (ArC), 127.53 (ArC),
133.16 (ArC), 133.29 (ArC), 134.59 (ArC), 141.99 (ArC), 146.96 (ArC), 147.91 (O–C Ar), 150.04 (O–C Ar),
168.49 (N–C Ar, Pyr), 169.72 (C =O) (see Figure 3). Anal. Calcd. for C62 H76 N8 O10 : C, 68.11; H, 7.01; N,
10.25. Found (%): C, 68.26; H, 6.97; N, 10.32.
3.2.2. Immobilization of 5,11,17,23-tetra-tert-butyl-25,27-bis(2-nitropyridin-2-ylamino)ethylami-
nocarbonyl-methoxy)-26,28-dihydroxycalix[4]arene onto silica-coated Fe3 O4 -nanoparticles
MN-DiNoPy-Calix
A mixture of the bis(nitropyridine)-substituted calix[4]arene 3 (0.35 g, 0.32 mmol) and NaH (0.06 g, 2.5 mmol)
in a solution of THF/DMF (20 mL, 3/1, v/v) was stirred at room temperature for 30 min. EPPTMS-MN (0.35
g) was added to the reaction mixture, followed by refluxing for 5 days. The mixture was separated via magnetic
separation and washed with DMF 3 times to remove the excess dipyridine amide-substituted calix[4]arene 3,
and then washed with 1 M HCl solution and water to neutralize it. The nanoparticles obtained were dried
under vacuum. Yield: 0.52 g. FTIR (KBr disk) cm−1 : 3411, 1634 (C=O), 1479 (N–O asymmetric stretch),
1456 and 1411 (C=C stretch), 1107, 958, and 799 (Si–O stretch), 560 (Fe–O stretch) (Figure 4).
3.3. Extraction experiments
Extraction studies were carried out using an aqueous solution of Na2 Cr2 O7 (1.0 × 10−4 M) and the calixarene
derivative (1.0 × 10−3 M solution of 3 in CH2 Cl2 for liquid–liquid extraction, 25 mg of MN-DiNoPy-Calix
(4) for solid–liquid extraction). A mixture of Na2 Cr2 O7 (10 mL, 1.0 × 10−4 M) and the calixarene derivative
(10 mL, 1.0 × 10−3 M solution in CH2 Cl2 for liquid–liquid extraction, 25 mg of MN-DiNoPy-Calix (4) for
solid–liquid extraction) was shaken in a stoppered flask at 175 rpm at 25 ◦ C for 1 h. For the determination
of the residual dichromate concentration, a UV-Visible spectrophotometer was used, and absorbance readings
were measured at 346 nm as described previously.4,13,27 The pHs of the dichromate solutions were adjusted by
using diluted HCl and KOH solution at 25 ◦ C, and the percent extraction (E%) was calculated27 according to
Eq. (1).
A0 − A
(E%) =
× 100
(1)
A0
where A0 and A are the initial and final concentrations of the dichromate anion before and after the extraction,
respectively.
4. Conclusion
A new bis(nitropyridine)-substituted calix[4]arene 3 was synthesized and grafted onto the surface of epoxy-
silica–coated magnetic nanoparticles to create more rigid structural features and to prevent water solubility
137

˘
SAYIN and DOGAN/Turk J Chem
of the bis(nitropyridine)-substituted calix[4]arene 3. In addition, the extraction capability of new calixarene-
adorned magnetic nanoparticles, MN-DiNoPy-Calix (4), was investigated with regard to dichromate anions.
In our previous studies we observed that the magnetic nanoparticles-grafted calix[4]arenes were selectively
functionalized with amino pyridine units (see Figure 1), and extracted dichromate anion in maximum extraction
capabilities at 69% (for MN-Py-1) and 53% (for MN-Py-2) at pH 3.5.23 However, when using MN-DiNoPy-
Calix (4) as an extractant, the maximum percentage of dichromate removal reached 54% at pH 1.5. These
findings clearly illustrate that the calixarene-adorned magnetic nanoparticles, which bear amino pyridine units,
have an affinity towards dichromate anions. The binding abilities of MN-DiNoPy-Calix with dichromate
clearly depend on the rigid structural properties, proton-switchability, and hydrogen-binding ability. In addition,
allowing calixarene compounds to acquire magnetic properties would bring new insight into the removal of toxic
and hazardous materials from water because they can be easily separated by using an external magnet.
References
1. Smith, W. A.; Apel, W. A.; Petersen, J. N.; Peyton, B. M. Bioremediation J. 2002, 6, 205–215.
2. Kumar, M. A.; Thirumalai, K.; Sathishkumar, P.; Palvannana, T. Chem. Eng. J. 2012, 185–186, 178–186.
3. Srivastava, V.; Sharma, Y. C. Water Air Soil Pollut. 2014, 225, 1776.
4. Sayin, S.; Ozcan, F.; Yilmaz, M. J. Hazard. Mater. 2010, 178, 312–319.
5. Goyal, N.; Jain, S. C.; Banerjee, U. C. Adv. Environ. Res. 2003, 7, 311–319.
6. Chen, S.; Yue, Q.; Gao, B.; Li, Q.; Xu, X.; Fu, K. Bioresour. Technol. 2012, 113, 114–120.
7. Racho, P.; Phalathip, P. J. Clean Energy Technol. 2014, 2, 18–22.
8. Sayin, S.; Eymur, S.; Yilmaz, M. Ind. Eng. Chem. Res. 2014, 53, 2396–2402.
9. Ayuso, E.; Sanchez, A.; Querol, G. X. J. Hazard. Mater. 2007, 142, 191–198.
10. Chen, L.; Lu, L.; Shao, W.; Luo, F. J. Chem. Eng. Data 2011, 56, 1059–1068.
11. Elwakeel, K. Z. Desalination 2010, 250, 105–112.
12. Miretzkya, P.; Fernandez, C. A. J. Hazard. Mater. 2010, 180, 1–19.
13. Bayrakcı, M.; Ertul, S¸.; Yilmaz, M. Tetrahedron 2009, 65, 7963–7968.
14. Bhatti, A. A.; Memon, S.; Memon, N. Sep. Sci. Technol. 2014, 49, 664–672.
15. Akkus, G. U.; Memon, S.; Sezgin, M.; Yilmaz, M. Clean-Soil, Air, Water 2009, 37, 109–114.
16. Sayin, S.; Yilmaz, M.; Tavasli, M. Tetrahedron 2011, 67, 3743–3753.
17. Tabakci, M.; Erdemir, S.; Yilmaz, M. J. Hazard. Mater. 2007, 148, 428–435.
18. Stastny, V.; Lhot´ak, P.; Michlova´, V.; Stibor, I.; Sykora, J. Tetrahedron 2002, 58, 7207–7211.
19. Sayin, S.; Yilmaz, M. RSC Adv. 2014, 4, 2219–2225.
20. Casnati, A. Chem. Commun. 2013, 49, 6827–6830.
21. Sayin, S.; Ozcan, F.; Yilmaz, M. Mater. Sci. Eng. C 2013, 33, 2433–2439.
22. Sayin, S.; Yilmaz, M. J. Chem. Eng. Data 2011, 56, 2020–2029.
23. Sayin, S.; Ozcan, F.; Yilmaz, M. J. Macromol. Sci., Pure Appl. Chem. 2011, 48, 365–372.
24. Gutsche, C. D.; Nam, K. C. J. Am. Chem. Soc. 1988, 110, 6153–6162.
25. Collins, E. M.; McKervey, M. A.; Madigan, E.; Moran, M. B.; Owens, M.; Ferguson, G.; Harris, S. J. J. Chem.
Soc., Perkin Trans. 1 1991, 3137–3142.
26. Yong, Y.; Bai, Y.; Li, Y.; Lin, L.; Cui, Y.; Xia, C. J. Magn. Magn. Mater. 2008, 320, 2350–2355.
27. Memon, S.; Roundhill, D. M.; Yilmaz, M. Collect. Czech. Chem. Commun. 2004, 69, 1231–1250.
138

Copyright of Turkish Journal of Chemistry is the property of Scientific and Technical
Research Council of Turkey and its content may not be copied or emailed to multiple sites or
posted to a listserv without the copyright holder's express written permission. However, users
may print, download, or email articles for individual use.