Novel Water-Soluble Calix[4,6]Arene Appended Magnetic Nanoparticles For The Removal Of The Carcinogenic Aromatic Amines

Aromatic Amines

Tuba Aksoy&Serkan Erdemir&H. Bekir Yildiz& Mustafa Yilmaz

Received: 28 January 2012 / Accepted: 11 April 2012 / Published online: 1 May 2012 # Springer Science+Business Media B.V. 2012

Abstract This article describes the synthesis of p-sul-fonated calix[4,6]arene derivatives and firstly their im-mobilization onto magnetic nanoparticles for removal of some carcinogenic aromatic amines. The prepared new water-soluble calix[4,6]arene appended magnetic nano-particles (p-C[4]-MN and p-C[6]-MN) were character-ized by a combination of Fourier transform infrared spectroscopy, scanning electron microscopy, and ther-mogravimetric analyses. The separation and quantifica-tion of aromatic amines were performed by high performance liquid chromatography. In batch sorption experiments, the compounds 7 and 8 were found to be effective sorbent for aromatic amines. It was observed that the percentage of aromatic amine removal was 44– 97 % for compound 7 and 63–97 % for 8 when the pH of the aromatic amine solution was in the range of 3.0–8.5. The sorption of aromatic amines by p-sulfonated cal-ix[n]arenes-based magnetic nanoparticles shows that sulfonic acid groups play a major role for the formation of hydrogen bonds and electrostatic interactions.

Keywords Calixarene . Nanoparticle . Aromatic amines . Sorption . HPLC

1 Introduction

In recent decades with the rapid development of hu-man society as well as science and technology, no doubt the world is reaching to new sky scraping hori-zon; but at the same time the cost in which the world is paying or will pay in the near future in the form of extensive global contamination is certainly very high (Gupta2009). Azo dyes pollution is one of the biggest problems in the world that troubles physically and economically (Vimonses et al. 2009; Olukanni et al.

2006). Azo dyes are synthetic organic colorants monly prepared by coupling of a diazonium com-pound with a phenol or an aromatic amine. They are widely used as colorants in a variety of consumer goods such as, leather, textiles, and foodstuff. Some of these dyes can be reduced in vivo through cleavage of the azo groups (N0N), forming mutagenic and carcinogenic aromatic amines (Golka et al. 2004; Chung 2000). With the increased awareness of the potential risk for consumers, the European Parliament recently accepted the 19th amendment of the Council Directive 76/769/EEC and issued the European Direc-tive 2002/61/EC (European Commission 2002). This directive particularly restricts the marketing and use of

T. Aksoy

:

:

e-mail: myilmaz@selcuk.edu.tr H. B. Yildiz

Department of Chemistry,

Karamanoglu Mehmetbey University, 70100 Karaman, Turkey

azo dyes, which may form any of the 22 listed harmful aromatic amines in textile and leather articles after reductive cleavage, and may come into direct and prolonged contact with human skin or oral cavity. Legally permissible limits of the banned amined on textiles is 30 mg/lg or 30 ppm.

Convectional wastewater treatment relying on aerobic biodegradation has low removal efficiency for anionic soluble dyes. Due to the low biodeg-radation of dyes, a conventional biological treat-ment process is not very effective in treating dyes in wastewater. Such wastewater is usually treated with either physical or chemical processes. How-ever, these processes are very expensive and can-not effectively be used to treat the wide range of dyes in wastewater (Garg et al. 2003). The adsorp-tion process is one of the effective methods for dye removal from effluents. The process of ad-sorption has an advantage over other methods due to its sludge free clean operation and complete removal of dyes, even from dilute solutions.

The increasing number of recent publications on adsorption of toxic compounds shows that there is widespread interest in the synthesis of adsorbent resins able to totally eliminate organic pollutants. Various chemical and physical processes are cur-rently in use. Solid phase extraction (SPE) using sorbents is one of the most efficient and well-established procedures in the field of separation science, which finds application in various fields like environmental, food, clinical, pharmaceutical, and industrial chemistry. SPE is usually performed using a small column or cartridge containing an appropriate sorbent. The sorbents may be of mineral or organic origin. Among these, modified silicas (C8 and C18), ion exchangers (Organ et al. 2002), graphitized carbon black (Vial et al. 2001), various polymeric sorbents polystyrene-divinyl benzene (Jung et al.2001), immunosorbents (Delaunay-Bertoncini et al.2001), molecularly imprinted polymers (Andersson and Nicholls2004), conductive polymers (Bagheri and Saraji2003), porous polymers (Gawdzik and Matynia

1996), polysaccharides such as chitin (Synowiecki and Al-Khateeb2003), starch (Yuryev et al.2002) and chi-tosan (Babel and Kurniawan2003), etc. are reported. In this respect, the supramolecular chemistry has provided a much beter solution to search for molec-ular structures that can serve as building blocks for

the production of sophisticated molecules by anchor-ing functional groups oriented in such a way that they provide a suitable binding site. This was achieved with the development of macrocyclic mol-ecules such as synthetic crown ethers, cryptands, spherands (Feber, 1978), natural cyclodextrins (Chern and Huang 1998), and calixarenes (Memon et al. 2005; Memon et al.2006; Tabakci et al.2003; Yilmaz et al. 2006).

Calixarenes have generated considerable interest as useful building blocks for the synthesis of hosts for cations, anions, and neutral molecules. During the last two decades, they have attracted much attention as receptors in supramolecular chemistry. The increasing interest in these compounds is stimulated by the simple large-scale synthesis of calixarenes, and the different ways in which they can be selectively functionalized at the narrow (phenolic groups) or at the wide rim (aromatic nuclei; Vicens and Bohmer 1991; Roundhill 1995; Gutsche 1998). Their rigid conformation enables calixarenes to act as host molecules because of their preformed hy-drophobic cavities. Due to this ability to form host– guest type complexes with a variety of organic or inorganic compounds, the calixarenes have received increasing attention (Feber 1978; Gutsche 1998; Delval et al. 2002; Janus et al. 1999).

In recent years, superparamagnetic nanoparticles of iron oxides have shown great potential applications in many biological fields. The application for biomole-cules immobilization is mainly based on the solid-phase magnetic feature that is able to achieve a rapidly easy separation and recovery from the reaction medi-um in an external magnetic field. Previously, we have synthesized various derivatives of calix[4]arene and immobilized upon magnetic nanoparticles and inves-tigated to their extraction abilities towards Cr(VI) ion (Ozcan et al. 2009; Sayin et al.2010a,b). Also, the different derivatives of calix[n]arene (n04,6 and 8) was prepared and their sorption efficiencies were in-vestigated for selected azo dye and aromatic amines by our group (Erdemir et al.2009; Ozmen et al.2007; Akceylan et al.2009). In the present study, we realized the synthesis of p-sulfonated calix[4,6]arenes and their immobilization onto 3-(glycidoxy)propyl functional-ized magnetic nanoparticles (EP-MN; see Schemes 1

and2). The new water souble calix[4,6]aren appended magnetic nanoparticles were used as sorbent in

removing of selected carcinogenic aromatic amines from aqueous solutions.

2 Experimental

2.1 Material and Method

Analytical TLC was performed on precoated silica gel plates (SiO2, Merck PF254), while silica gel

60 (Merck, particle size 0.040–0.063 mm, 230–240 mesh) was used for preparative column chroma-tography. Generally, solvents were dried by storage over molecular sieves (Aldrich; 4 Å, 8–12 mesh). All chemicals were purchased from Merck and Fluka and used without further purification. All aqueous solutions were prepared with deionized water that had been passed through a Millipore Milli-Q Plus water purification system. Melting points were determined on a Gallenkamp apparatus in a sealed capillary and are uncorrected. 1H NMR spectra were recorded with a Varian 400 MHz spectrometer in CDCl3. FT-IR spectra were recorded on a Perkin Elmer

Spectrum 100. UV–vis spectra were obtained with a Shimadzu 160A UV–vis recording spectrophotometer. High-performance liquid chromatography (HPLC) Agilent 1200 Series were carried out using a 1200 model quaternary pump, a G1315B model Diode Array and Multiple Wavelength UV–vis detector, a 1200 model Standard and preparative autosampler, a G1316A model thermostated column compartment, a 1200 model vacuum degasser, and an Agilent Chem-station B.02.01-SR2 Tatch data processor. The amines were separated on a Ace 5 C18 column (25 cm, 4.6 mm). The mobile-phase consisted of acetonitrile (eluent A) and water (eluent B), flow rate: 1 mL/min, at 25°C, injection volume 20 μL, gradient elution: 0 min 20 % A and 80 % B; 25 min 80 % A and

20 % B. Detection was performed at 280 nm. Thermal gravimetric analysis (TGA) was carried out with Seteram thermogravimetric analyzer. The sample weight was 15–17 mg. Analysis was per-formed from room temperature to 900°C at heating rate of 10°C/ min in argon atmosphere with a gas flow rate of 20 mL/min.

2.2 Synthesis

The synthesis of p-tert-butylcalix[4]arene (1), calix[4] arene (2), p-tert-butylcalix[6]arene (4), and calix[6] arene (5) was conducted using the procedures de-scribed by Gutsche (Gutsche and Iqbal 1990a, b; Gutsche and Lin 1986). Then, p-sulfonated ca-lix[4,6]arene derivatives 3, 6 were synthesized using H2SO4 referring to the literature (Shinkai et al. 1986). The structures of these compounds were characterized by FT-IR and 1H NMR analyses. 2.2.1 The Preparation of 3-(Glycidoxy) Propyl Functionalized Magnetic Nanoparticles (EP-MN) A microemulsion was prepared by dissolving 1.75 g of sodium dodecylbenzenesulfonate in 15 mL of xylene by sonication. Metal salts were dissolved in deionized (DI) water to enhance the hydrolysis reaction of TEOS (tetraethoxysilane). The salt solution was composed of FeCl2·4H2O, Fe(NO3)3·9H2O, and DI water. This salt

solution was added to the microemulsion under vigor-ous stirring, and the solution was kept at room tem-perature for about 12 h to allow for its stabilization. Then, the reverse-micelle solution was slowly heated to 90°C under continuously flowing nitrogen gas for an hour and 1 mL of hydrazine (34 wt% aqueous solution) was injected into the solution. These particles were aged at 90°C for 3 h, and then cooled down to 40°C within an hour. The

temperature was maintained at 40°C to prevent the complete evaporation of the water in the hydro-philic phase containing the magnetite nanoparticles. After the temperature of the magnetite solution reached 40°C and became stabilized, 2 mL of TEOS and 2 mL of 3-(glycidoxy)-propyltrimethoxysilane was injected into the mixture of the as-synthesized magnetite and xylene

under vigorous stirring. The silica coated magnetite nanoparticles were segregated from the xylene phase and dispersed well in water. After magnetic separation, the attained 3-(glycidoxy)-propyl func-tionalized magnetic nanoparticles (EP-MN) were washed three times with ethanol and deionized water turn in and dried at 80°C under vacuum.

2.2.2 Immobilization of p-Sulfonated Calix[4,6]arene on EP-MN

Compound 3 or 6 (0.3 g) and NaOH (0.11 g) were stirred in deionezied water (3 mL) for 30 min at room temper-ature. Then, 0.9 g of 3-(glycidoxy) propyl functionalized magnetic nanoparticles (EP-MN) and 12 mL of DMSO was added to the this solution. The mixture was stirred for about 48 h at 50°C. After magnetic separation, the resulting compounds (7 and 8) were washed three times with ethanol and water in turn and dried at 80°C under vacuum. The compounds 7 and 8 were named as the p-C[4]-MN and p-C[6]MN, respectively.

2.3 Batch Sorption Studies of Aromatic Amines An aqueous solution (10 mL) containing aromatic amine (see Fig.1for the structure formula) was pipet-ted into a vial at a concentration of 1×10−3M, and a

few drops of 0.01 M KOH/HCl solution in order to obtain the desired pH at equilibrium and maintain the ionic strength and 25 mg of the sorbent were added. The mixture was stirred at 25°C on a horizontal shaker at 170 rpm until equilibrium for 1 h. After the sorbent was removed by centrifugation the residual concentra-tion of the organic moiety was determined by means of HPLC. The sorption capacity was then calculated and expressed in percentage uptake.

3 Results and Discussion

3.1 Synthesis and Characterization of p-C[4]-MN and p-C[6]-MN Sorbents

In order to evaluate the aromatic amines removal effi-ciency of p-C[4]-MN and p-C[6]-MN sorbents, firstly, p-sulfonated calix[n]arenes (n04,6) were synthesized

Fig. 1 The chemical structures of aromatic amines used in experiments

Fig. 3 TGA curves of EP-MN, p-C[4]-MN, and p-C[6]-MN magnetic nanoparticles

according to known procedure (Shinkai et al.1986). On the other hand, magnetic Fe3O4nanoparticles were

pre-pared by the chemical co-precipitation of Fe(III) and Fe (II) ions and the nanoparticles were modified directly by 3-(glycidoxy)-propyltrimethoxy silane (GPTMS) to in-troduce reactive glycidoxy groups onto the particles’

surface (Scheme 1). Then, the synthesized water-soluble p-sulfonated calix[n]arenes (n04,6) were immo-bilized onto 3-(glycidoxy)-propyltrimethoxy functional-ized magnetic nanoparticles (EP-MN) in DMSO/H2O to

give p-C[4]-MN and p-C[6]-MN sorbents (Scheme2). It is well-known that in extraction processes, separation

Fig. 5 SEM micrographs of EP-MN (a), p-C[4]-MN (b), and p-C[6]-MN (c) magnetic nanoparticles

Fig. 6 Representative HPLC chromatograms of standard aro-matic amines solution (a) and aroaro-matic amines which were treated with the p-C[6]-MN (b), in double distilled water sam-ples. 1 benzidine, 2 p-chloroaniline, 3 α-napthylamine.

Conditions—mobile phase, acetonitrile (A) and water (B); flow rate, 1 mL/min, at 25°C, injection volume 20 μL; gradient elution—0 min, 20 % (A) and 80 % (B); 25 min, 80 % (A) and 20 % (B). Detection at 280 nm, pH 8.5

is a time consuming task. In view of this, we prepared the p-sulfonated calix[n]arene (n04,6) derivatives immobilized magnetic nanoparticles for

easy separation of these from solvents by using a mag-net (Fig. 2). The synthesized p-C[4]-MN and p-C[6]-MN sorbents have been characterized by FT-IR

Table 1 Percent sorption of aromatic amines by sorbents (%)a

Compound p-Chloroaniline Benzidine α-Naphthalamine

pH 3.0 pH 5.0 pH 7.0 pH 8.5 pH 3.0 pH 5.0 pH 7.0 pH 8.5 pH 3.0 pH 5.0 pH 7.0 pH 8.5 1b <1.0 – 2.2 4.3 <1.0 – 2.0 4.0 <1.0 – 1.5 4.7 2b <1.0 – 3.2 4.8 1.9 – 2.5 4.7 <1.0 – 3.1 4.8 4c – 3.0 3.0 4.3 – 2.0 12 7.5 – 3.0 9.0 5.5 p-C[4]-MN 53 44 52 47 78 61 72 71 77 70 69 73 p-C[6]-MN 86 79 63 78 94 67 76 73 97 97 95 97 a

Solid phase, adsorbent: 25 mg of p-C[n]-MN; aqueous phase, aromatic amines (benzidine, p-chloroaniline,α-naphthalamine) 1.0× 10−4 M, pH 3.0–8.5, 1 h

b

Akceylan et al. (2009)

c_{Erdemir et al. (2009)}

Fig. 7 pH effect on the sorption of aromatic amines by p-C[4]-MN (a) and p-C[6]MN (b)

nanoparticles’ surface can be obtained from TGA mea-surement. Figure3shows TGA curves of GPTMS-MN, p-C[4]-MN, and p-C[6]-MN magnetic nanoparticles. The total losses temperature range of 40–900°C are 9.5 %, 30.1 %, and 34.2 % for GPTMS-MN, p-C[4]-MN, and p-C[6]-p-C[4]-MN, respectively. Thermogravimetric results showed a direct relationship of the loss of mass to the amount of the calixarene molecules anchored on the nanoparticle surfaces. Also, from the Fourier transform infrared spectroscopy (FTIR) results, it was observed that compound 3 and 6 were immobilized onto EP-MN. Exemplary, the FT-IR spectra of compound 3 and p-C[4]-MN was depicted in Fig. 4 The peaks at 1459, 1,409 cm−1 for p-C[4]-MN (1457, 1,410 cm−1for p-C[6]-MN) are attributed to the bending vibration of the aromatic C0C bonds of the calixarene derivatives. Ad-ditional peaks centered at 1085, 913 cm−1for p-C[4]-MN (1082, 916 cm−1for p-C[6]-MN) were most prob-ably due to the symmetric and asymmetric stretching vibration of framework and terminal Si–O groups.

SEM is a kind of widely used surface analysis technique. It can examine the surface morphology of the solids rapidly without damages to the surface. To confirm the immobilization of the calixarenes on the magnetic nanoparticles surface, we chose the SEM technique to characterize the magnetic nanoparticles surface and displayed it in Fig.5. A SEM image of the GPTM-MN (Fig. 5a) was compared with images obtained for the p-C[4]-MN and p-C[6]-MN (Fig.5b,

c). The photographs were taken at 5,000 magnifica-tion. The SEM micrograph of EP-MN (Fig.5a) shows a very loose morphology, while after the immobiliza-tion of p-sulfonated calix[n]arenes onto the EP-MN (Fig.5b,c); it shows a regular morphology covered by foreign materials, i.e., p-sulfonated calixarenes. These changes occurred onto the surface of EP-MN confirms the immobilization.

3.2 Sorption Studies of Selected Aromatic Amines Azo dyes are readily decolorized by splitting the azo bond(s) in an anaerobic environment. Azo dye

MN magnetic nanoparticles, solid–liquid sorption experiments were carried out at different pHs (3.0, 5.0, 7.0, and 8.5). The aromatic amines removal was ana-lyzed by means of HPLC using acetonitrile-water as mobile phase at 280 nm (Fig. 6). The results of the sorption studies are summarized in Table 1 and also depicted in Fig.7. We reported that the parent calixar-enes (1, 2, 4) showed less sorption capacities for all three aromatic amines in our previous studies (Erdemir et al. 2009; Akceylan et al. 2009). After the parent calixarenes were converted to p-sulfonated calix[4,6] arene derivatives and immobilized onto magnetic nano-particles, the obtained p-C[4]-MN and p-C[6]-MN mag-netic nanoparticles showed high sorption ability towards all aromatic amines. The results obtained at pH 5.0, 7.0, and 8.5 are close to each other but different from those obtained at pH 3.0, which show significantly stronger interactions. Furthermore, it was observed that

Fig. 8 Proposed interaction model between p-C[6]-MN and α-naphthalamine

the percentage of benzidine removal was 61–72 % for p-C[4]-MN and 67–76 % for p-C[6]-p-C[4]-MN when the pH of the benzi-dine solution was 5.0–8.5. However, benzibenzi-dine removal attained a maximum to 78 % for C[4]-MN and 94 % for p-C[6]-MN when the amine solution pH decreased to 3.0. On the other hand, the HPLC results indicated that p-C[6]-MN is a more effective sorbent towardsα-naphthalamine.

The higher level of aromatic amine removal by p-C[4]-MN and p-C[6]-p-C[4]-MN magnetic nanoparticles suggests that a Coulomb interaction and intermolecular hydrogen bonds exist between the sulfonate groups of calixarene and the amino groups of aromatic amine (Fig.8). It is seen from Table1that p-C[6]-MN forms a stable complex than p-C[4]-MN with a guest molecule by entrapping it into the cavity. Previously, we have reported (Gungor et al.2008) the synthesis and inclusion abilities of calix[4] and ca-lix[8]arene derivatives for selected azo dyes. The results showed that calix[4]arene and its derivatives have no influence on the extraction of azo dyes. Comparing to calix[8]arene derivatives, the molecular size of calix[4] arene derivatives is smaller and has higher steric hin-drance. For this reason, it will be very difficult for azo dye molecules to enter into the cavity of calix[4]arene, resulting in no complex formation. Hence, the cyclic structure, the cavity size, and the functional groups of the calix[n]arene derivatives were found to be the decisive factors for the sorption of aromatic amines.

4 Conclusion

In summary, the preparation of two new water-soluble p-sulfonated calix[n]arenes (n04,6) immobilized magnetic nanoparticles was successfully achieved. They were uti-lized to extract selected toxic and carcinogenic aromatic amines from aqueous solution. It was observed that the sorption capacities of the prepared magnetic nanopar-ticles containing calixarene (p-C[4]-MN) and (p-C[6]-MN) were higher than that of parent calix[n]arenes. Also, it was observed that the highest sorption level for the selected aromatic amines was obtained at pH 3.0. It was concluded that the sorption of aromatic amines by p-C[4]-MN and p-C[6]-MN sorbents indicate that amino and sulfonic acid groups are responsible for the forma-tion of hydrogen bonds and electrostatic interacforma-tions.

Acknowledgments We thank the Scientific Research Projects Foundation of Selcuk University (SUBAP Grant Number 2010– 10201075) for the financial support of this work.

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