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International Journal of Biological Macromolecules journal homepage: www.elsevier.com/locate/ijbiomac

The novel synthesis of magnetically chitosan/carbon nanotube composites and their catalytic applications

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Zohre Zarnegar, Javad Safari ∗ Laboratory of Organic Compound Research, Department of Organic Chemistry, College of Chemistry, University of Kashan, P.O. Box: 87317-51167, Kashan, Islamic Republic of Iran

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Article history: Received 18 October 2014 Received in revised form 5 December 2014 Accepted 8 January 2015 Available online xxx

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Keywords: Chitosan Fe3 O4 nanoparticles 1,4-Dihydropyridines Hantzsch reaction Carbon nanotubes

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1. Introduction

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Chitosan-modified magnetic carbon nanotubes (CS-MCNTs) were synthesized and were investigated by FT-IR, EDX, FE-SEM, elemental analysis, XRD, VSM and TGA. In order to synthesize the CS-MCNTs composites, Fe3 O4 decorated carbon nanotubes (CNTs-Fe3 O4 ) were modified with a silica layer by the ammonia-catalysed hydrolysis of tetraethyl orthosilicate (CNTs-Fe3 O4 @SiO2 ). Then, CS-MCNTs were successfully grafted on the surface of CNTs-Fe3 O4 @SiO2 via a suspension cross-linking method. The CS-MCNT was found to be an excellent heterogeneous catalyst for the synthesis of 1,4-dihydropyridines (DHPs). The attractive advantages of the present process include short reaction times, milder and cleaner conditions, higher purity and yields, easy isolation of products, easier work-up procedure and lower generation of waste or pollutions. This catalyst was easily separated by an external magnet and the recovered catalyst was reused several times without any significant loss of activity. A combination of the advantages of CNTs, chitosan and magnetic nanoparticles provides an important methodology for carrying out catalytic transformations. Therefore, this method provides a green and much improved protocol over the existing methods. © 2015 Published by Elsevier B.V.

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It is widely acknowledge that there is a growing need for more environmentally acceptable processes in the chemical reactions used in manufacturing. This trend towards what has become known as Green Chemistry, or environmentally benign chemistry, necessitates a paradigm shift from traditional concepts of process efficiency that focus largely on chemical yield to one that assigns economic value to eliminating waste at source and avoids the use of toxic and hazardous materials, as well as the design of ecocompatible chemicals [1]. One of the methods for implementing the principles of Green Chemistry is to use catalysis. Catalysis is one of the key underpinning technologies on which new approaches to sustainable chemistry are based. Recently, the development of eco-friendly, non-toxic, low cost, recyclable green catalysts, which give high productivity under mild reaction conditions, has received much attention in modern chemical synthesis [1b]. In particular, it is necessary to design catalysts and catalysis processes with environmental considerations for the preparation of compounds with pharmacological properties.

∗ Corresponding author. Tel.: +98 361 5912320; fax: +98 361 5912397. E-mail address: [email protected] (J. Safari).

On the other hand, 1,4-dihydropyridines (DHPs) is one of the most important classes of heterocyclic compounds in the field of pharmaceutical and medicinal chemistry [2–6]. Due to the high medicinal and biological importance of DHPs derivatives, several methods have been developed for the synthesis of these heterocyclic compounds. Hantzsch DHPs synthesis is one of the most broadly used methods for the synthesis of structurally diverse DHPs. This classical method involves one-pot condensation of aldehydes with ethyl acetoacetate and ammonia in acetic acid or by refluxing in alcohol [7]. Up till now, numerous literature citations exist relating to various attempts to improve the Hantzsch reaction using alternative catalysts and greener protocols [8]. However, some drawbacks still exist, such as the use of expensive or toxic catalysts, high reaction temperatures, long reaction times, use of large quantities of volatile organic solvents, low yields and harsh reaction conditions [9]. Therefore, more general, efficient and viable routes employing recyclable catalysts in Hantzsch synthesis are very much desirable, in view of their broad array of biological activity and would be of great relevance to both synthetic and medicinal chemists. The most recent efforts in the development of cleaner sustainable chemistry are being driven by a shift from petrochemicalbased feed stocks toward biological compounds. Thus, there is a drive to produce raw materials from biofeed stocks, which in turn

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is stimulating considerable effort in new areas of chemistry and catalytic processes. Given these developments, it seems clear that the development of biopolymers as heterogeneous green catalytic systems will play a key role in this field [10]. Recently, biopolymers such as starch [11], cellulose [12], chitosan (CS) [13], or wool [14], have been used as catalysts in the organic reactions. In this context, chitosan can play a major role as a natural, biocompatible, biodegradable and bioactive polymer [15–17]. Chitosan, as a polyaminosaccharide, can be explored as a mild bi-functional heterogeneous catalyst in the organic reactions. In this regard, chitosan contains the primary amino groups at the C-2 position, the primary hydroxyl groups at the C-6 position and secondary hydroxyl groups at the C-5 in higher concentrations. Therefore, chitosan can activate the electrophilic and nucleophilic components of the reactions by hydrogen bonding and lone pairs, respectively [13a]. With the development of nanoscience and nanotechnology, chitosan nanostructures have received a great deal of attention because of their nano-size, large surface area and good biocompatibility. Moreover, unlike most other natural polymers, chitosan is a polymer with a positive charge in aqueous solution [18]. These characteristics favour the employment of nano-sized chitosan particles in a wide range of various applications, including drug delivery systems [19], gene delivery systems [20], sensors [16], protein carriers [18], tissue engineering [21] and catalysts [13]. Many recent attempts have been made to create chitosan nanoparticles through emulsion cross-linking [22], reverse micellar extraction [23], solvent evaporation [24], spray drying [25], coacervation [26] or thermal cross-linking [27]. These methods have intrinsic advantages, along with some limitations [18]. It should be noted that in spite of these favourable properties for chitosan, the poor mechanical strength and the loss of structural integrity especially under wet conditions, limits chitosan’s application in various fields [28]. Recently, carbon nanotubes (CNTs)/chitosan nanocomposites have been researched to unite the interesting properties of CNTs and chitosan [16a,18,28,29]. CNTs possess high tensile strengths and are ultra-light weight with excellent thermal and chemical stability. CNTs have large length-to-diameter aspect ratios, which provide high surface-to-volume ratios, therefore, making them promising materials for catalytic applications [29]. On the other hand, CNTs are ideal reinforcing agents, which improve the mechanical properties of polymers. Incorporation of super strong lightweight CNT nanostructures into a chitosan matrix offers a novel approach to the design of high performance nanocomposite materials with superior mechanical properties [28]. Generally, the numerous hydroxyl and amino groups in the polymer chains of polyaminosaccharide resulted in an obvious enhancement in the absorption of pollutants on CNTs/chitosan nanocomposites in various fields, especially in catalytic processes. However, the difficulty in collecting these CNTs-chitosan nanocomposites from treated effluents can cause inconveniences in their practical application. Therefore, it is necessary and significant to explore novel modified CNTs/chitosan nanocomposites that can be easily separated from the treated solution, in addition to the excellent dispersion in solution and absorption properties [29]. Magnetic nanoparticles are another reinforcing nanostructure material used in chitosan; nanocomposites made with this material combine the excellent functional properties of nanoparticles in separation techniques. Magnetically supported chitosan can be recovered with an external magnetic field due to the paramagnetic character of the support, without the need for a filtration step [29]. Recently, magnetic chitosan and magnetic CNTs-chitosan nanocomposites for separation techniques have been obtained and studied, as the magnetic separation technique has some advantages, such as high efficiency and cost-effectiveness [30].

Based on the above considerations, CS-MCNTs were synthesized via a suspension cross-linking method in this study and CS-MCNTs were used as an efficient catalyst for the effective synthesis of DHPs through the solvent-free Hantzsch reaction. This new approach has several superiorities versus previous reports for the synthesis of DHPs and introduces the important field of the use of magnetically recoverable and environmentally benign heterogeneous nanocatalysts in the synthesis of pharmaceutically important heterocyclic compounds (Scheme 1). 2. Experimental All chemicals were purchased from the Merck, Aldrich and Sigma Chemical Companies. Multi wall carbon nanotubes (MWNTs) with surface area of 136 m2 /g and 10–20 nm in diameter, used as a support, were supplied from Neutrino Company, Iran. Melting points (◦ C) were determined on an Electrothermal MK3 apparatus using an open-glass capillary and are uncorrected. 1 H NMR and 13 C NMR spectra were recorded with a Bruker DRX-400 spectrometer at 400 and 100 MHz respectively. FT-IR spectra were obtained with KBr pellets in the range 400–4000 cm−1 with a Perkin-Elmer 550 spectrometer. The magnetic measurement of samples were carried out in a vibrating sample magnetometer (VSM) (4 in., NDKF, Kashan, Iran) at room temperature. Nanostructures were characterized using a Holland Philips Xpert X-ray diffraction (XRD) diffractometer (CuK, radiation,  = 0.154056 nm), at a scanning speed of 2◦ /min from 10◦ to 100◦ (2). The surface morphology of nanocomposites was analyzed by field emission scanning electron microscopy (FESEM) (MAIA). Thermogravimetric analysis (TGA) was performed on a Linseis-TGA at a heating rate of 15 ◦ C/min under N2 flow (40 cm3 /min). 2.1. Preparation of Fe3 O4 @SiO2 -CS Fe3 O4 nanoparticles were synthesized by a chemical coprecipitation process and the Fe3 O4 @SiO2 core–shell nanoparticles were prepared according to the modified by the Stöber method [32]. Fe3 O4 @SiO2 -CS nanocomposites were prepared using the crosslinking method described in Ref. [33]. The details were as follows: 0.30 g of chitosan was firstly dissolved in 10.0 mL of acetic acid solution (2 wt.%), then 0.15 g of Fe3 O4 @SiO2 nanoparticles were dispersed in the chitosan solution under ultrasound irradiation for 20 min, followed by the addition of 135 ␮L of glutaraldehyde solution (25 wt.%) and the black gels were formed after 4 h. Then, the gels were dried in a vacuum oven at 60 ◦ C for 12 h, and washed with acetic acid solution (2 wt.%), hot water, and cool water several times to remove unreacted chitosan. The purified Fe3 O4 @SiO2 -CS was dried again in the vacuum oven at 50 ◦ C for 12 h. 2.2. Synthesis of CNTs-Fe3 O4 @SiO2 nanocomposite 0.5 g CNTs were added to 30 mL the mixture of 98% sulphuric acid and 70% nitric acid (volumetric ratio 3:1) at 50 ◦ C under sonication for 6 h. Then, carboxylic acid-functionalized CNTs (CNTsCOOH) were centrifuged and washed with distilled water and oven dried at 100 ◦ C for 24 h. CNTs-Fe3 O4 @SiO2 nanocomposites were prepared by growing silica layers onto the surface of the CNTsFe3 O4 as described by Zhang et al. [34]. FeCl2 ·4H2 O and FeCl3 .6H2 O precursors (2:1, molar ratio) were dissolved in 100 mL of water and heated to 90 ◦ C. Then, 10 mL of ammonium hydroxide (25%) and 0.4 g of CNTs-COOH were dispersed in 50 mL of water, which was added rapidly under continuous Ar atmosphere bubbling. The mixture was stirred at 90 ◦ C for 30 min. The black precipitate was then centrifuged, washed with distilled water and dried at 50 ◦ C for 24 h. The obtained black precipitate was Fe3 O4 -CNTs nanocomposites. Finally, 25 mL of ethanol, 1.0 mL of double-distilled water,

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Scheme 1. Solvent free synthesis of DHPs catalyzed by CS-MCNTs composites.

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1.0 mL of ammonium hydroxide and 150 ␮L of tetraethyl orthosilicate (TEOS) were added in a 250 mL three neck flask, which was set in a 40 ◦ C water bath. Then, 0.5 g of Fe3 O4 -CNTs nanocomposite was added and the mixture was processed for 12 h under mechanical stirring. The mixture was extracted by an external magnet and washed with double-distilled water and dried at 50 ◦ C in vacuum oven to obtain the CNTs-Fe3 O4 @SiO2 composite [35]. 2.3. Preparation of CS-MCNTs

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In order to prepare CS-MCNTs, 0.30 g of chitosan was firstly dissolved in 10.0 mL of acetic acid solution (2 wt.%), then 0.15 g of CNTs-Fe3 O4 @SiO2 nanocomposites were fully dispersed in the chitosan solution under sonic conditions for 20 min, followed by the addition of 135 ␮L of glutaraldehyde solution (25 wt.%), and the black gels were formed after four hours. Then the gels were dried in an oven at 60 ◦ C for 12 h, and washed successively with acetic acid solution (2 wt.%), hot water, and cool water several times to remove unreacted chitosan. The purified CS-MCNTs were dried again in the vacuum oven at 50 ◦ C for 24 h.

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2.4. General procedure for the preparation of DHPs

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A mixture of the aldehyde (1 mmol), ␤-dicarbonyl (2 mmol) and ammonium acetate (1.5 mmol) in the presence of 0.06 g CS-MCNTs was heated at 80 ◦ C, with stirring. The progress of the reaction was monitored by TLC (petroleum ether–ethyl acetate 3:2). After completion of the reaction, the mixture was dissolved in hot EtOH (5 mL) and the catalyst was separated by magnetic decantation. The crude product was either recrystallized from EtOH to give the pure products. 3,5-diethoxycarbonyl-4-(5-methyl-2-furiyl)-2,6-dimethyl-1,4dihydropyridines (4p) Yellow powder; M.Prep. (◦ C): 143–145; M.F: C18 H23 NO5 ; Rf (in petroleum ether:ethylacetate; 3:2 (v/v)): 0.61; M.W (amu): 334; U.V (EtOH) max (nm): 368, IR (KBr)  (cm−1 ): 3306 (NH), 1698 (C O),1648 (C C), 1495 (NH), 1210 (C–O); 1 H NMR (CDCl3 , 400 MHz) ı (ppm): 1.27 (t, 3 J = 7.2 Hz, 6H, 2CH3 ), 2.19 (s, 3H, CH3 ), 2.33 (s, 6H, 2CH3 ), 4.17 (q, 3 J = 7.2 Hz, 4H, 2CH2 ), 5.13 (s, 1H, CH), 5,78 (s, 1H, NH), 7.21 (m, 3H, Ar–H); 13 C NMR (CDCl3 , 100 MHz) ı (ppm): 13.69, 14.34, 19.34, 33.34, 59.73, 100.74, 105.00, 105.85, 145.13, 150.21, 157.06, 167.73.

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3. Results and discussion

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Catalysis is a key component of “green chemistry” and one of the key challenges facing chemists now is the design and use of environmentally benign catalysts for chemical reactions. Hybrid organic–inorganic materials based on CNTs and magnetite nanoparticles, as special immobilizing carriers of the catalysts’ active sites, have shown significant contributions to the current researches. This is due to their inherent properties, such as

biocompatibility, thermal stability against degradation, easy renewability and recovery by magnetic separation, large surface area and higher loading of active sites. Moreover, this kind of nanomaterial can be linked to a polymeric matrix resulting in multifunctional nanohybrids with enhanced properties. According to the catalytic properties of chitosan in organic reactions due to the presence of the reactive amino and hydroxyl functional groups, the magnetically CS-MCNTs nanocomposite was used as a new catalyst for the synthesis of Hantzsch 1,4-dihydropyridine compounds under mild reaction conditions for the first time. Furthermore, from the green perspective, the search for the possibility of performing Hantzsch reaction under solvent-free conditions with recoverable catalysts for the synthesis of these compounds is an active and ongoing research area and there is scope for further improvement toward milder reaction conditions and higher yields. This method is very flexible and makes preparation of a large number of DHPs possible. 3.1. Characterization of catalysts The oxidative functionalization of CNTs is an important procedure for enhancing chemical activity in a variety of applications [36]. Surface oxidation of CNTs was approached using nitric and sulphuric acids (1:3 v/v) under ultrasonic conditions. The synthesis process of CS-MCNTs hybrid material was schematically illustrated in Scheme 2. In this process, CNTs-COOH is functionalized with negative carboxylic groups, which have an affinity with positive ferrous and ferric ions. After the addition of ammonium hydroxide solution, Fe3 O4 nanoparticles were formed on the surface of CNTs. CNTs-Fe3 O4 was modified with a SiO2 layer by the ammonia-catalysed hydrolysis of tetraethyl orthosilicate (TEOS). Then, CS-MCNTs were synthesized via a suspension cross-linking method. Polymeric nanocomposites have been widely studied because of their unusual combinations of properties that are difficult to obtain from the individual components. The CS-MCNTs, as a three-component nanocomposite, is expected to have diverse properties, as each component would contribute different chemical and physical properties. On the other hand, an efficient improvement is the combination of chitosan with magnetic nanoparticles for the easy magnetic separation technique and CNTs for better physical and mechanical properties. Composition, morphology and magnetic properties of as-prepared CS-MCNTs were characterized by FTIR, XRD, FE-SEM, EDS, TGA and VSM. 3.1.1. FT-IR characterization Fig. 1 shows the FT-IR spectra of (a) CNTs-COOH (b) CNTs-Fe3 O4 , (c) CNTs-Fe3 O4 @SiO2 , (d) CS-MCNTs and (e) chitosan. In Fig. 1(a), the absorbance band at 1733 cm−1 is related to the –COOH groups of oxidized CNT and two absorbance bands at 1577 and 1164 cm−1 are related to C O and C–O stretching, respectively. The two weak peaks at 2919 and 2851 cm−1 correspond to the –CH stretching mode and a broad band peak at 3436 cm−1 is attributed to the

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Scheme 2. The procedure for preparation of CS-MCNTs nanocomposites.

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–COOH groups on the external surface of CNTs. These results agreed with the reported results in Refs. [35,37]. In addition, in Fig. 1(b), the peak at 588 cm−1 is the stretching vibration due to the interactions of Fe–O–Fe in Fe3 O4 . Compared with the two spectra (b and c), the existence of the characteristic Si–O–Si peak at 1093 cm−1 in Fig. 1(c) is direct evidence to verify the formation of the silica shell on the surface of CNTs-Fe3 O4 [35]. The FT-IR spectrum of chitosan (Fig. 1(e)) shows a broad band at 3433 cm−1 which corresponds to the stretching vibrations of O–H and N–H groups and broadens due to the inter-hydrogen bonds of polysaccharides. Peaks appearing at 2923 and 2855 cm−1 are characteristic of C–H stretching vibrations. The band at 1634 cm−1 is assigned to N–H bending vibration and that of 1423 cm−1 to C–O stretching of the primary alcoholic groups in unmodified chitosan. The band at 1084 cm−1 displays the stretching vibrations of the C–O–C bond. The Fe–O stretching vibration near 576 cm−1 , O–H stretching vibration near 3429 cm−1 , and O–H deformed vibration near 1620 cm−1 were observed for Fe3 O4 MNPs in Fig. 1(b). For Fe3 O4 @CS nanoparticles, chitosan absorptions appear in addition to a peak at 580 cm−1 , which corresponds to the stretching vibration of Fe–O groups; indicating that the magnetic Fe3 O4 MNPs are coated by chitosan (Fig. 1(c)). It can be seen in Fig. 3(d) that obvious peaks at 3440, 2922, 1631, 1408 and 1087 cm−1 are observed for the CS-MCNTs nanocomposite, attributed to the chitosan component [38]. In addition, a peak at 570 cm−1 , which corresponds to the stretching vibration of Fe–O groups, indicates that the magnetic CNTs-Fe3 O4 @SiO2 is coated by chitosan. 3.1.2. Field emission scanning electron microscopy (FE-SEM) and energy-dispersive spectra (EDS) The surface morphologies of CNT-COOH, CNTs-Fe3 O4 , CNTsFe3 O4 @SiO2 and CS-MCNTs were examined using FE-SEM (Fig. 2a–d, respectively). Fig. 2(a) and (b) showed FE-SEM micrographs of CNT-COOH and CNTs-Fe3 O4 , respectively. Fig. 2(a) showed that the surface morphology of the native CNTs indicated that the native nanotubes are snake-like with a smooth surface. The magnetite nanoparticles become adhered to the CNTs walls because the oxidation of CNTs with nitric and sulphuric acid results, under sonic conditions, in the formation of functional groups such as carbonyl, carboxyl and hydroxyl on the surface of the CNTs where magnetite Fe3 O4 nanoparticles bind [29]. As seen in Fig. 2(c), a lot of core–shell Fe3 O4 @SiO2 nanoparticles have been absorbed on the surface of the CNTs. Fig. 2(d) showed the surface morphology of the CS-MCNTs, while a considerable change is observed on the surface after the deposition of cross-linked chitosan, the size of CNTs

increased and the surfaces are fully covered with chitosan protuberances after the surface deposition. Furthermore, the SEM in Fig. 2(e) shows unmodified chitosan as an amorphous polymer and that its morphology is different from other nanocomposites. In order to further confirm the composition on the surface of nanocomposites, the energy-dispersive spectra (EDS) from different sample spots were performed. The EDS spectrum in Fig. 3(a) shows the presence of Fe and O elements in the sample and the calculated atomic ratio of Fe to O is close to 3:4, which further confirms that the Fe3 O4 nanoparticles attached to the CNTs surface are Fe3 O4 . The EDX shown in Fig. 3(b) confirms the presence of iron and silicon in the CNTs-Fe3 O4 @SiO2 nanocomposite. The EDS spectrum in Fig. 3(c) shows the presence of C, N, O, Si and Fe in CS-MCNTs. The C and N signals are originated from the chitosan, while the Fe signal came from the Fe3 O4 nanoparticles, which confirms the existence of Fe3 O4 . 3.1.3. X-ray diffraction (XRD) Diffraction patterns of CNT-COOH, Fe3 O4 , CNTs-Fe3 O4 , CNTsFe3 O4 @SiO2 , CS-MCNTs and unmodified chitosan are shown in Fig. 4(a–f, respectively). The characteristic sharp peak of CNT-COOH at 2 = 26◦ representing C (0 0 2) was attributed to the ordered arrangement of concentric cylinders of graphitic carbon in the CNTs [39]. This crystalline peak disappeared in the CNTs-Fe3 O4 , CNTs-Fe3 O4 @SiO2 , CS-MCNTs nanocomposite samples. XRD patterns for the CNTs-Fe3 O4 displayed characteristic peaks (2 = 26.3◦ , 30.5◦ , 35.9◦ , 43.6◦ , 54.0◦ , 57.5◦ and 63.1◦ ), which were consistent with those found in the JCPDS database (PDF No. 88-0315). The (3 1 1) peak at 2 = 35.9◦ indicates the presence of pure Fe3 O4 nanoparticles in the CNTs-Fe3 O4 , CNTs-Fe3 O4 @SiO2 , CS-MCNTs nanocomposites [40]. For unmodified chitosan, one broad peak was observed at 2 = 20.2◦ (maximum intensity), which corresponded to the characteristic peak of chitosan chains aligned through intermolecular interactions [41]. This peak disappeared in the CSMCNTs nanocomposite. The weaker diffraction lines of CS-MCNTs indicate that the CNTs-Fe3 O4 @SiO2 composites were successfully coated by amorphous chitosan on the surface of modified CNTs. 3.1.4. Thermogravimetric analysis Thermal stability analysis results (Fig. 5) indicated that the native CNTs-COOH is relatively stable in the temperature range investigated (25–600 ◦ C); while obvious weight loss (4%) is observed for the CNTs-Fe3 O4 , which can be due to the evaporation of physically absorbed water and surface hydroxyl groups. The TGA curve of the CNTs-Fe3 O4 @SiO2 shows a weight loss of about

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Fig. 1. The comparative FT-IR spectra for (a) CNT-COOH, (b) CNTs-Fe3 O4 , (c) CNTs-Fe3 O4 @SiO2 (d) CS-MCNTs, and (e) chitosan.

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2% from 200 to 450 ◦ C, resulting from the decomposition of silica layers grafting to the Fe3 O4 surface (Fig. 5(c)). The weight loss of CSMCNTs is about 40% at 250–400 ◦ C, corresponding to the pyrolysis of the deposited chitosan [38].

exhibit enough magnetic response to meet the need of magnetic separation. In the next step, we studied the efficacy of the nanocatalyst on the synthesis of DHPs through the Hantzsch reaction.

3.1.5. Vibrating-sample magnetometer (VSM) The magnetic hysteresis loops of magnetically formed CNTs nanocomposites are shown in Fig. 6. The saturation magnetization is found to be 32.0, 12.3 and 5.0 emu g−1 for CNTs-Fe3 O4 , CNTsFe3 O4 @SiO2 and CS-MCNTs, respectively. The decrease in magnetic saturation for CNTs-Fe3 O4 @SiO2 and CS-MCNTs is attributed to the silica layer covering and chitosan polymeric matrix on the surface of magnetic Fe3 O4 MNPs. Although the saturation magnetization values of CNTs-Fe3 O4 @SiO2 and CS-MCNTs are lower than CNTsFe3 O4 , it could be rapidly separated from their liquid dispersions under a magnetic field within several seconds, which is displayed in the nether inset of Fig. 6. These results indicate that CS-MCNTs

3.2. Evaluation of the catalytic activity of CS-MCNTs through the synthesis of DHPs A green chemical process always involves considerations, such as atom economy, using green catalysts, employing nontoxic solvents or the use of a solvent-free system and procedural simplicity. Conducting reactions in the absence of a solvent (i.e., neat conditions) is an important research field in green chemistry. Therefore, to overcome the problems associated with the synthesis of DHPs, it is highly desirable to develop a powerful method to meet the requirement of green chemistry in both academia and industry. For initial optimization of the reaction conditions, we initially studied

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Fig. 2. FE-SEM micrographs of (a) CNT-COOH, (b) CNTs-Fe3 O4 , (c) CNTs-Fe3 O4 @SiO2 and (d) CS-MCNTs nanocomposites. (e) SEM micrograph of unmodified chitosan.

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the effect of various solvents and catalytic efficiency of CS-MCNTs using the model reaction of ethyl acetoacetate (1), benzaldehyde (2) and ammonium acetate (3). As shown in Table 1, among the tested solvents, such as tetrahydrofuran, ethanol, methanol, acetonitrile, water and a solvent-free system, the best results were obtained after 25 min under solvent-free conditions in excellent yields (entry 6, 94%) at 80 ◦ C in the presence of 0.06 g of CSMCNTs. On the other hand, currently, organic synthesis under solvent-free conditions is of great relevance because of emerging environmental issues. This is due to the fact that the solvent-free technique usually needs a shorter reaction time, simpler reactors and simple and efficient workup procedures. Moreover, in the synthesis of DHPs, most of the immobilized catalysts are separated by

filtration or centrifugation; but this magnetite-supported catalyst can be separated from the reaction system by an external permanent magnet. This will circumvent time-consuming and laborious separation steps. Therefore, it makes the practical application for continuous catalysis possible. As can be seen from this table, temperature plays an important role in reaction time and product yield. Encouraged by this result, benzaldehyde, ethyl acetoacetate and ammonium acetate (1:2:1.5) were selected as representative reactants for further optimization of the reaction conditions. In view of these results, we selected the optimized reaction conditions to determine the scope of this CS-MCNTs-catalysed reaction. A wide range of aromatic and heteroaromatic aldehydes were subjected to react with ␤-keto compounds in the presence

Table 1 CS-MCNTs -catalyzed Hantzsch synthesis of DHP 4a under different conditions. Entry 1 2 3 4 5 6 7 8 9 10 11 12 13

Catalyst (g)

Solvent

Temperature (◦ C)

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Neat Neat Neat Neat Neat Neat Neat Neat Neat THF CH3 CN H2 O EtOH

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Time (min) 720 50 40 30 30 25 25 30 25 50 45 65 35

Yield (%) 32 55 70 80 90 94 90 90 92 55 75 40 85

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Fig. 3. EDX for (a) CNTs-Fe3 O4 , (b) CNTs-Fe3 O4 @SiO2 and (c) CS-MCNTs nanocomposites.

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of ammonium acetate and 0.06 g of CS-MCNTs, at 80 ◦ C under solvent-free conditions to generate the corresponding Hantzsch DHPs. The results are presented in Table 2. The results summarized in this table indicate that both aromatic and heterocyclic aldehydes underwent smooth reactions with ethyl acetoacetate

(or acetylacetone) and ammonium acetate to give well to high yields of the corresponding products. The catalytic system worked well. Clearly, the effect of the nature of the substituent on the aromatic ring showed no obvious effect on this conversion, because they were obtained in high yields of the corresponding products in

Table 2 Synthesis of DHPs in presence of CS-MCNTs as catalyst. Entry

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

R

Ph p-MeC6 H4 p-ClC6 H4 m-ClC6 H4 p-OMeC6 H4 p-(CH3 )2 NC6 H4 p-NO2 C6 H4 m-NO2 C6 H4 o-NO2 C6 H4 p-OHC6 H4 m-OHC6 H4 m,p-(CH3 O)2 C6 H3 C6 H5 –CH CH 2-Thienyl 2-Furyl 5-CH3 -2-furyl 3-Pyridyl m-OMeC6 H4 m-ClC6 H4 2-Thienyl 2-Furyl 3-Pyridyl

R

OC2 H5 OC2 H5 OC2 H5 OC2 H5 OC2 H5 OC2 H5 OC2 H5 OC2 H5 OC2 H5 OC2 H5 OC2 H5 OC2 H5 OC2 H5 OC2 H5 OC2 H5 OC2 H5 OC2 H5 CH3 CH3 CH3 CH3 CH3

Product

4a 4b 4c 4d 4e 4f 4g 4h 4i 4j 4k 4l 4m 4n 4o 4p 4q 4r 4s 4t 4u 4v

Time (min)

25 40 20 20 45 50 15 20 40 45 20 40 15 25 25 25 30 20 20 30 30 35

Yield (%)

94 90 97 96 90 88 98 97 95 93 95 90 98 98 95 97 95 97 95 97 94 90

Mp (◦ C) Found

Lit [Ref.]

155–157 143–144 144–146 141–142 155–156 202–203 128–130 165–167 170–171 227–228 173–175 163–164 143–145 172–174 160–161 144–145 189–190 203–205 221 171–172 168–170 262–264

155 [42] 142–145 [43] 145–146 [43] 141 [42] 156 [42] 201 [42] 128 [42] 165–167 [43] 171 [42] 227 [42] 172–175 [43] 161 [42] 146–148 [44] 171–173 [44] 159–162 [44] – 188–190 [43] 203–205 [43] 222–224 [43] 171–172 [43] 169–170 [43] 262–263 [43]

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Fig. 4. XRD patterns of (a) CNT-COOH, (b) Fe3 O4 , (c) CNTs-Fe3 O4 , (d) CS-MCNTs and (e) unmodified chitosan.

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Fig. 7. Reuse of chitosan derivatives in the synthesis of DPH 4a.

Fig. 5. The TGA results for (a) CNT-COOH, (b) CNTs-Fe3 O4 , (c) CNTs-Fe3 O4 @SiO2 , and (d) CS-MCNTs hybrids.

Fig. 6. Magnetization curves for the CNTs-Fe3 O4 , CNTs-Fe3 O4 @SiO2 , CS-MCNTs nanocomposites at room temperature.

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relatively short reaction times. Furthermore, the catalytic activity of CS-MCNTs catalysts for the synthesis of unsymmetrical Hantzsch reaction was evaluated (entry 23). This new catalyst was found to be a highly active catalyst for the synthesis of symmetrical and unsymmetrical Hantzsch heterocycles. The products were characterized by IR, 1 H NMR and 13 C NMR spectroscopy, and also by comparison with authentic samples. The proposed mechanism for the formation of DHPs is shown in Scheme 3. In this Hantzsch reaction, chitosan supported on the magnetic CNTs is supposed to facilitate the condensation between ethyl acetoacetate (or acetylacetone) 1 and aldehyde 2 for the formation of the corresponding Knovenagel product 5a, and the Michael addition between this intermediate and enamines 6a obtained from the reaction of ␤-keto compound 1a and ammonium acetate 3, for the formation of an open chain intermediates

7a, which undergo cyclohydration to furnish the desired DHPs 4 products [45]. The free hydroxyl and amino groups distributed on the surface of chitosan supported CNTs in high concentrations activate the carbonyl group of the aldehyde and ethyl acetoacetate (or acetylacetone). In order to show the capabilities of CS-MCNTs, with respect to chitosan derivatives, some comparative results are summarized in Table 3. As shown, the yields and time of reactions in the presence of CS-MCNTs are better than chitosan and Fe3 O4 @SiO2 -CS. The active surface area of the catalyst increases when the size of the catalyst decreases to the nano-scale. Since the reactions take place on the surface of the catalyst, the Fe3 O4 @SiO2 -CS exhibits better catalytic activity than commercial chitosan, which could be attributed to the effect of increased surface area. Interestingly, the CS-MCNTs are the best catalysts in the synthesis of DHPs compared with chitosan derivatives. It should be noted that CNTs are used as doping materials for three dimensional chitosan scaffolds to develop porous composite materials. Therefore, the CS-MCNTs nanomaterials in the chitosan film can form a porous structure to provide an enhanced effective surface area and active sites in practical applications [34]. According to this CS-MCNT is the most effective catalytic system in the Hantzsch reaction. In the interest of green chemistry and developing an environmentally benign process, the reusability of the magnetic catalyst was explored using the model reaction system under the optimized conditions. After completion of the reaction, the mixture was triturated with hot EtOH. Within a few seconds after stirring was stopped, the reaction mixture turned clear and the catalyst was deposited on the magnetic bar, which was easily removed using an external magnet. After being washed with acetone, ethyl acetate, ethanol and dried in air, the catalyst can be directly reused without any deactivation even after seven rounds of synthesis of product 4a (Fig. 7.). The SEM analysis of the recovered CS-MCNTs revealed that the morphology nanocomposites remain unchanged. In addition, as shown in Fig. 7, the recyclability of the catalyst was tested for both chitosan and Fe3 O4 @SiO2 -CS. The recyclability of the catalyst was more effective than the other two catalysts in terms of yield and number of turns. Due to its poor mechanical and electrical properties, it is the use of chitosan in a wider range of applications is restricted. An effective approach for improving the physical and mechanical properties of chitosan is to form organic–inorganic composites through incorporation of fillers, such as metal nanopar-

Table 3 Comparative synthesis of some DHPs in the presence of chitosan derivatives. Entry

Catalyst

Product: 4a Time (min)

1 2 3

Chitosan Fe3 O4 @SiO2 -CS CS-MCNTs

120 60 25

Product: 4g

Product: 4v

Yield (%)

Time (min)

Yield (%)

Time (min)

Yield (%)

90 94 94

60 40 15

95 97 98

70 50 35

93 91 90

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Scheme 3. Proposed mechanism for CS-MCNTs catalyzed Hantzsch synthesis.

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503

504 505 506 507 508 509 510 511 512 513 514

515 Q3

516

ticles and CNTs [42]. The CNTs can provide improved mechanical strength and better structural integrity. The green procedure combined with easy recovery and reuse of this catalyst makes this protocol economic, benign and a waste-free chemical process for the synthesis of 1,4-dihydropyridine derivatives.

4. Conclusions In summary, we have reported that chitosan derivatives, especially magnetically chitosan/CNTs composites, are highly efficient green catalysts for the one pot synthesis of a variety of DHPs by means of a three-component condensation of aldehyde, ethyl acetoacetate (acetyl acetone) and ammonium acetate. This green approach addresses the current drive toward green chemistry and will be attractive to chemists due to good yields, high atomeconomy, and the reusability of the magnetic catalyst. We believe that this present methodology is a convenient, economic and user-friendly process for the synthesis of DHPs of biological and medicinal importance.

Uncited reference [31].

Acknowledgments This study is part of Zohre Zarnegar PhD thesis entitled: “The preparation of magnetic iron oxide nanostructuers and their application in host–guest systems and some of the organic reactions” which has been conducted in the University of Kashan. We gratefully acknowledge the financial support from the Research Council Q4 of the University of Kashan for supporting this work by Grant No. 363022/2. References [1] (a) P. Gupta, S. Paul, Catal. Today 236 (2014) 153–170; (b) Z. Chen, R. Fu, W. Chai, H. Zheng, L. Sun, Q. Lu, R. Yuan, Tetrahedron 70 (2014) 2237–2245. [2] J.T. David, Biochem. Pharmacol. 74 (2007) 1–9. [3] (a) V.M. Briukhanov, Exp. Clin. Pharmacol. 57 (1994) 47–49; (b) S. Bahekar, D. Shinde, Acta Pharm. (Zagreb) A 52 (2002) 281–287. [4] R. Boer, V. Gekeler, Drugs Future 20 (1995) 499–509. [5] S. Gullapalli, P. Ramarao, Neuropharmacology 42 (2002) 467–475. [6] (a) F. Bossert, H. Mayer, E. Wehinger, Angew. Chem. Int. Ed. Engl. 20 (1981) 762–769; (b) P.K. Gilpin, L.A. Pachla, Anal. Chem. 71 (1999) 217–233; (c) S. Ghosh, F. Saikh, J. Das, A.K. Pramanik, Tetrahedron Lett. 54 (2013) 58–62. [7] F.K. Behbahani, M. Homafar, Synth. React. Inorg. Met. Org. Chem. 42 (2012) 291–295. [8] (a) W.H. Correa, J.L. Scott, Green Chem. 3 (2001) 296–301; (b) S.B. Sapkal, K.F. Shelke, B.B. Shingate, M.S. Shingare, Tetrahedron Lett. 50 (2009) 1754–1756;

Please cite this article in press as: Z. Zarnegar, J. Safari, Int. J. Biol. Macromol. (2015), http://dx.doi.org/10.1016/j.ijbiomac.2015.01.013

517

518 519 520 521 522 523 524

525

526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542

G Model BIOMAC 4820 1–11

ARTICLE IN PRESS Z. Zarnegar, J. Safari / International Journal of Biological Macromolecules xxx (2015) xxx–xxx

543 544 Q5 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566

[9] [10] [11] [12] [13]

567 568 569 570 571 572

[14] [15] [16]

573 574

[17]

575 576

[18]

577 578 579

[19] [20] [21]

(c) K.L. Bridgwood, G.E. Veitch, S.V. Ley, Org. Lett. 10 (2008) 3627–3629; (d) A. Kumar, R.A. Maurya, Synlett (2008) 883–885; (e) M.F. Gordeev, D.V. Patel, E.M. Gordon, J. Org. Chem. 61 (1996) 924–928; (f) G. Sabitha, G.S. Reddy, C.S. Reddy, J.S. Yadav, Tetrahedron Lett. 44 (2003) 4129–4131; (g) J.G. Breitenbucher, G. Figliozzi, Tetrahedron Lett. 41 (2000) 4311–4315; (h) A. Dondoni, A. Massi, E. Minghini, V. Bertolasi, Tetrahedron 60 (2004) 2311–2326; (i) L. Liu, R. Sarkisian, Y. Deng, H. Wang, J. Org. Chem. 78 (2013) 5751–5755; (j) J.P. Wan, R. Zhou, Y. Liu, M. Cai, RSC Adv. 3 (2013) 2477–2482; (k) S. Wang, H. Chen, H. Zhao, H. Cao, Y. Li, Q. Liu, Eur. J. Org. Chem. (2013) 7300–7304; (l) J. Safari, Z. Zarnegar, RSC Adv. 3 (2013) 26094–26101; (m) W. Gati, M.M. Rammah, M.B. Rammah, G. Evano, Beilstein J. Org. Chem. 8 (2012) 2212–2214; (n) J.P. Wan, S.F. Gan, G.L. Sun, Y.J. Pan, J. Org. Chem. 74 (2009) 2862–2865; (o) C.G. Evans, J.E. Gestwicki, Org. Lett. 11 (2009) 2957–2959; (p) J. Sun, Y. Sun, H. Gao, C.G. Yan, Eur. J. Org. Chem. (2011) 6952–6956; (q) T. Chen, X.P. Xu, H.F. Liu, S.J. Ji, Tetrahedron 67 (2011) 5469–5476. A. Kumar, R.A. Maurya, Tetrahedron 63 (2007) 1946–1952. D.J. Macquarrie, J.J.E. Hardy, Ind. Eng. Chem. Res. 44 (2005) 8499–8520. G. Chen, B. Fang, Bioresour. Technol. 102 (2011) 2635–2640. J. Safari, S.H. Banitaba, S.D. Khalili, J. Mol. Catal. A: Chem. 335 (2011) 46–50. (a) M.G. Dekamin, M. Azimoshan, L. Ramezani, Green Chem. 158 (2013) 811–820; (b) J. Zhu, P.C. Wang, M. Lu, New J. Chem. 36 (2012) 2587–2592; (c) A. Maleki, N. Ghamari, M. Kamalzare, RSC Adv. 49 (2014) 416–9423. S. Wu, H. Ma, X. Jia, Y. Zhong, Z. Lei, Tetrahedron 67 (2011) 250–256. G.A. Dee, O. Rhode, R. Wachter, Cosmet. Toilet. 116 (2001) 39–44. F. Kuralay, T. Vural, C. Bayram, E.B. Denkbas, S. Abaci, Colloids Surf. B 87 (2011) 18–22. K.R. Reddy, K. Rajgopal, C.U. Maheswari, M.L. Kantam, New J. Chem. 30 (2006) 1549–1552. C. Li, K. Yang, Y. Zhang, H. Tang, F. Yan, L. Tan, Q. Xie, S. Yao, Acta Biomater. 7 (2011) 3070–3077. A.M.D. Campos, A. Sanchez, M.J. Alonso, Int. J. Pharm. 224 (2001) 159–168. M.D.L. Fuente, B. Seijo, M.J. Alonso, Genetherapy 15 (2008) 668–676. S. Jana, S.J. Florczyk, M. Leung, M. Zhang, J. Mater. Chem. 22 (2012) 6291–6299.

11

[22] S.R. Jameela, A. Jayakrishnan, Biomaterials 16 (1995) 769–775. [23] S. Mitra, U. Gaur, P.C. Ghosh, A.N. Maitra, J. Control Release 74 (2001) 317–323. [24] S.T. Lim, G.P. Martin, D.J. Berry, M.B. Brown, J. Control Release 66 (2000) 281–292. [25] P. He, S.S. Davis, L. Illum, Int. J. Pharm. 187 (1999) 53–65. [26] A. Berthold, K. Cremer, J. Kreuter, J. Control Release 39 (1996) 17–25. [27] I. Orienti, K. Aiedeh, E. Gianasi, V. Bertasi, V. Zecchi, J. Microencapsul. 13 (1996) 463–472. [28] L. Carson, C. Kelly-Brown, M. Stewart, A. Oki, G. Regisford, Z. Luo, V.I. Bakhmutov, Mater. Lett. 63 (2009) 617–620. [29] K.Y. CastrejLn-Parga, H. Camacho-Montes, C.A. Rodrízguez-Gonzàlez, C. Velasco-Santos, A.L. Martínez-Hernàndez, D. Bueno-Jaquez, J.L. Rivera-Armenta, C.R. Ambrosio, C.C. Conzalez, M.E. Mendoza-Duarte, P.E. García-Casillas, J. Alloys Compd. (2014) http://dx.doi.org/10.1016/ j.jallcom.2013.12.269 [30] Z. Zarnegar, J. Safari, RSC Adv. 4 (2014) 20932–20939. [31] H.Y. Zhu, Y.Q. Fu, R. Jiang, J. Yao, L. Liu, Y.W. Chen, L. Xiao, G.M. Zeng, Appl. Surf. Sci. 285 (2013) 865–873. [32] J. Safari, Z. Zarnegar, J. Mol. Catal. A: Chem. 379 (2013) 269–276. [33] Y. Ren, H.A. Abbood, F. He, H. Peng, K. Huang, Chem. Eng. J. 226 (2013) 300–311. [34] Y. Hu, J. Li, Z. Zhang, H. Zhang, L. Luo, S. Yao, Anal. Chim. Acta 698 (2011) 61–68. [35] M. Arvand, M. Hassannezhad, Mater. Sci. Eng. C 36 (2014) 160–167. [36] J. Safari, Z. Mansouri Kafroudi, Z. Zarnegar, C. R. Chim. 17 (2014) 958–963. [37] M. Adeli, A. Bahari, H. Hekmatara, Nano 3 (2008) 1–8. [38] X. Chen, W. Wang, Z. Song, J. Wang, Anal. Methods 3 (2011) 1769–1773. [39] W. Li, C. Liang, W. Zhou, J. Quip, Z. Zhou, G. Sun, Q. Xin, J. Phys. Chem. B 107 (2003) 6292–6299. [40] J.B. Marroquin, K.Y. Rhee, S.J. Park, Carbohydr. Polym. 92 (2013) 1783–1791. [41] I. Yamaguchi, K. Tokuchi, H. Fukuzaki, Y. Koyama, K. Takakuda, H. Monma, J. Tanaka, J. Biomed. Mater. Res. 55 (2001) 20–27. [42] B. Datta, M.A. Pasha, Chin. J. Catal. 32 (2011) 1180–1184. [43] B. Palakshi Reddy, K. Rajesh, V. Vijayakumar, Arab. J. Chem. (2011), http://dx.doi.org/10.1016/j.arabjc.2011.01.027. [44] M. Tajbakhsh, E. Alaee, H. Alinezhad, M. Khanian, F. Jahani, S. Khaksar, P. Rezaee, M. Tajbakhsh, Chin. J. Catal. 33 (2012) 1517–1522. [45] N. Koukabi, E. Kolvari, A. Khazaei, M.A. Zolfigol, B. Shirmardi-Shaghasemic, H.R. Khavasid, Chem. Commun. 47 (2011) 9230–9232.

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carbon nanotube composites and their catalytic applications.

Chitosan-modified magnetic carbon nanotubes (CS-MCNTs) were synthesized and were investigated by FT-IR, EDX, FE-SEM, elemental analysis, XRD, VSM and ...
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