Accepted Manuscript Green synthesis of copper nanoparticles using Ginkgo biloba L. leaf extract and their catalytic activity for the Huisgen [3 + 2] cycloaddition of azides and alkynes at room temperature Mahmoud Nasrollahzadeh, S. Mohammad Sajadi PII: DOI: Reference:
S0021-9797(15)30023-0 http://dx.doi.org/10.1016/j.jcis.2015.07.004 YJCIS 20558
To appear in:
Journal of Colloid and Interface Science
Received Date: Accepted Date:
16 June 2015 1 July 2015
Please cite this article as: M. Nasrollahzadeh, S. Mohammad Sajadi, Green synthesis of copper nanoparticles using Ginkgo biloba L. leaf extract and their catalytic activity for the Huisgen [3 + 2] cycloaddition of azides and alkynes at room temperature, Journal of Colloid and Interface Science (2015), doi: http://dx.doi.org/10.1016/j.jcis. 2015.07.004
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Green synthesis of copper nanoparticles using Ginkgo biloba L. leaf extract and their catalytic activity for the Huisgen [3 + 2] cycloaddition of azides and alkynes at room temperature Mahmoud Nasrollahzadeh a,* and S. Mohammad Sajadib a
b
Department of Chemistry, Faculty of science, University of Qom, P. O. Box 37185-359, Qom, Iran.
Department of Petroleum Geoscience, Faculty of Science, Soran University, PO Box 624, Soran, Kurdistan Regional Government, Iraq
*Corresponding author. Tel: +98 25 32850953; Fax: +98 25 32103595. E-mail address: [email protected]
ABSTRACT During this study, we report the green synthesis of copper nanoparticles (Cu NPs) using Ginkgo biloba L. leaf extract as a reducing and stabilizing agent under surfactant-free conditions. The formation of Cu NPs is monitored by recording the UV-vis absorption spectra. The green synthesized Cu NPs are characterized by TEM, EDS, FT-IR and UV-visible techniques. According to UV-vis results, the synthesized Cu NPs by this method are quite stable even after one month indicating the stability of Cu NPs. In terms of environmental impact and economy, metallic Cu NPs offer several advantages over homogeneous and traditional heterogeneous catalysts. In addition, due to the increased metal surface area, Cu NPs shows very high catalytic activity for the Huisgen [3 + 2] cycloaddition of azides and alkynes at room temperature. Furthermore, the catalyst can be simply recovered and reused several times with almost no loss in activity.
Keywords: Metals; Organic compounds; Catalytic properties
1. Introduction Click chemistry is a highly efficient cycloaddition process that became very popular as a new synthesis route since its introduction in the dawn of the 21st century by Sharpless et al. [1]. Click chemistry is one of the most powerful tools for the construction of various triazoles, which are often considered in pharmaceuticals, drug discovery, polymers and material science [2,3].
1
The Huisgen cycloaddition process, involving copper (I)-catalyzed [3 + 2] cycloaddition of terminal alkynes and organic azides at room temperature is considered as the best click reaction to date [4]. However, there are several disadvantages in the literature methods such as the use of homogeneous catalysts and toxic organic solvents, low yields, long reaction times, harsh reaction conditions, environmental pollution due to the side products formed and tedious work-up [5]. Also, the early Huisgen cycloaddition process required a strong electron-withdrawing substituent either on azide or on alkyne and usually led to the isolation of a mixture of 1,4-disubstituted and l,5-disubstituted-l,2,3-triazoles regioisomers [5]. Therefore, it is desirable to develop a new, convenient and regio-controlled synthetic protocol for the synthesis of triazoles. Due to the importance of triazoles, several modifications to overcome the above drawbacks, improve the yield, efficiency or to reduce the cost have been reported using copper homogeneous catalysts such as Cu(I) salts [6] and Cu(I) complexes [4,7]. The problem with homogeneous catalysis is the difficulty to separate the catalyst from the reaction mixture and the impossibility to reuse it in consecutive reactions. Thus, we decided to concentrate on developing an efficient copper heterogeneous catalyst that is highly active. The transition metal nanoparticles play an important role in organic reactions because of their high surface to volume ratio that can dramatically enhance the interaction between reactants and catalysts and larger number of active sites per unit area compared to the parent metal [8]. In addition, nanocatalysis can make the products easily removable from the reaction mixtures and make the catalysts recyclable. There are several methods for the synthesis of copper nanoparticles (Cu NPs) using toxic and expensive chemicals, harsh reducing agents in organic solvents [9,10]. The presence of these toxic and dangerous materials on the surface of Cu NPs increases the toxicity issue while the use and disposal of toxic solvents triggers environmental issues. However, green synthesis of nanoparticles by various plants or gums is an ecologically friendly, cost effective method without use of tough chemicals. In addition, the other advantages of this environmentally benign and safe protocol include a simple reaction setup, very mild reaction conditions, use of nontoxic solvents such as water, elimination of harmful chemicals and cost effectiveness as well as compatibility for biomedical and pharmaceutical applications [11,12]. Also, in this method there is no need to use high pressure, energy, temperature and toxic chemicals.
2
The Ginkgo biloba Linn is from the family of Ginkgoaceae is world’s oldest tree mostly known as living fossils and only surviving member of seed plant groups. It is found growing naturally in very limited localities in the central Himalayan Mountain (Figure 1) [13-16]. The Leaves of this species is extensively used as a source of herbal medicine for presence of medicinal phytochemicals.
Figure 1. Image of Ginkgo biloba Linn leaves. Due to our ongoing interest on the green synthesis of metal NPs and heterogeneous catalysts [17-22], we wish to report a simple and eco-friendly protocol for synthesis of Cu NPs using aqueous extract of Ginkgo biloba Linn leaf. Also, the catalytic potential of Cu NPs was evaluated in the Huisgen [3 + 2] cycloaddition of azides and alkynes at room temperature (Scheme 1).
2. Experimental High-purity chemical reagents were purchased from the Merck and Aldrich chemical companies. All materials were of commercial reagent grade. Melting points were deter-mined in open capillaries using a BUCHI 510 melting point apparatus and are uncorrected. 1H NMR and 13C NMR spectra were recorded on a Bruker Avance DRX-400 spectrometer at 400 and 100 MHz, respectively. FT-IR spectra were recorded on a Nicolet 370 FT/IR spectrometer (Thermo Nicolet, USA) using pressed KBr pellets. The shape and size
3
of palladium nanoparticles crystals were identified by transmission electron microscope (TEM) using a Philips EM208 microscope operating at an accelerating voltage of 90 kV. UV-visible spectral analysis was recorded on a double‐beam spectrophotometer (Hitachi, U‐2900) to ensure the formation of nanoparticles. 2.1. Preparation of extract of leaves of Ginkgo biloba Linn 100 g of dried leaves powdered of Ginkgo biloba Linn was added to 500 mL double distillated water in 1000 mL flask and well mixed. The preparation of extract was done by using magnetic heating stirrer at 70 °C for 30 min. The obtained extract was centrifuged in 6500 rpm and filtered then filtrate was kept at refrigerator to use further. 2.2. Green synthesis of copper nanoparticles using Ginkgo biloba Linn leaves extract The copper nanoparticles were synthesized by the following process. In a 250 mL conical flask, 10 mL solution of CuCl2⋅2H2O 5 mM was mixed with 100 mL of the aqueous plant extract (100 g dried leaves of the plant extracted using 500 mL of deionized water while heating at 80 °C and pH 9 for 30 min then filtered) along with vigorous shaking until gradually changing the color of the mixture during 15 min to dark indicating the formation of Cu NPs (as monitored by UV-vis and FT-IR spectra of the solution). The well shaked mixture then filtered and centrifuged at 6500 rpm for 30 min and obtained precipitation washed with n-Hexane and absolute ethanol, respectively. 2.3. Preparation of 1-Benzyl-4-phenyl-1,2,3-triazole To a mixture of benzyl azide (1.0 mmol) and phenyl acetylene (1.1 mmol), 10 mol % of the Cu NPs in absolute ethanol was added (Table 1). The reaction mixture was then stirred at room temperature and the progress of the reaction was monitored using TLC. After completion of the reaction, the reaction mixture was centrifuged to pellet out the catalyst. The nanoparticles were washed three times with absolute ethanol, then three times with water with no further purification before reuse. The filtrate was further treated with EtOAc to ensure complete transfer. The solvent was removed under vacuum to give the desired pure products and characterized by 1 HNMR. All the products are known compounds and the spectral data and melting points were identical to those reported in the literature [23-29]. 1-Benzyl-4-phenyl-1,2,3-triazole (Table 2, entry 2): M.p. 130-131 °C (lit.23 132-133.1 °C); 1H NMR (DMSO-d6, 400 MHz) δH = 8.63 (s, 1H), 7.86-7.83 (m, 2H), 7.45-7.35 (m, 8H), 5.67 (s, 2H).
4
3. Results and discussion In the present work, we develop an ecofriendly, clean, non-toxic, facile chemically preparative method, for the generation of Cu NPs using the extract of the leaves of Ginkgo biloba Linn, acting as reducing as well as stabilizing agent. To date, there is no report on the green synthesis of Cu NPs by utilizing the leaves extract of Ginkgo biloba Linn. 3.1. Characterization of extract of leaves of Ginkgo biloba Linn The UV spectrum of extract (Figure 2) shows bonds at λmax 269 nm (bond Ι) due to the transition localized within the ring of cinnamoyl system; whereas the π → π* transition is shown by double bonds. The extract of Ginkgo biloba Linn leaf was obtained in aqueous media which this media is able to extract the highly polar phytoconstituents of the plant like polyphenolics with conjugated double bonds (in A, B and C ring of the flavone nuclei) and aromatic rings in their structure as major Ginkgo biloba Linn constituents. Then according the literatures about the plant and UV-vis fingerprint spectrum of its aqueous extract our result supports this idea. Therefore, the one centered at 235 nm (bond ΙΙ) is for absorbance of ring related to the benzoyl system and π → π* transitions on which these absorbent bonds demonstrate the presence of polyphenolics.
Figure 2. UV-vis spectrum of the aqueous extract of the leaves of the Ginkgo biloba Linn. The FT-IR analysis was carried out to identify the possible biomolecules responsible for the reduction of Cu nanoparticles and capping of the bioreduced nanoparticles. The FT-IR spectrum of the crude extract, (Figure 3) depicted some peaks at 3500 to 3100, 1643, 1575, 1395 and 1100 cm-1 which represent free OH in molecule and OH group forming hydrogen bonds, carbonyl group (C=O), stretching C=C aromatic ring
5
and C-OH and C-H stretching vibrations, respectively. These peaks suggested the presence of flavonoid and other phenolics in the plant leaves extract. The presence of flavonoid and other phenolics in the extract could be responsible for the reduction of metal ions and formation of the corresponding metal nanoparticles.
Figure 3. FT-IR spectrum of the aqueous extract of the leaves of the Ginkgo biloba Linn. 3.2. Reduction of metal ions In our research there is a focus on the synthesis of NPs in aqueous media using reducing properties of antioxidant phytochemicals inside the plant especially polyphenolics as a major reducing and highly polar agents in Ginkgo biloba Linn leaf extract [10,11] according the below mechanism (Scheme 2).
6
Scheme
2.
Production
of Cu NPs using the
quercetin 3-O-α-L-(β-D-glucopyranosyl)-(1,2)-
rhamnopyranoside as one of the potent antioxidants of Ginkgo biloba Linn. Of course, the effect of other phytochemicals inside the plant is maybe possible but not as reducing and highly polar agents involving the reaction while production of nanoparticles, also after precipitating the nano products, they were washed using n-Hexane (or chloroform) and ethanol respectively to remove impurities. 3.3. HPLC analysis According the Haiyan Xie et. al report on the Ginkgo biloba Linn and HPLC analysis of antioxidant content of the plant appeared in Figure 4, the presence of potent antioxidants such as quercetin 3-O-β-Drutinoside (1), quercetin 3-O-α-L-(β-D-glucopyranosyl)-(1,2)-rhamnopyranoside (2), kaempferol 3-O-β-Drutinoside (3), isorhamnetin 3-O-β-D-rutinoside (4), kaempferol 3-O-α-L-(β-D-glucopyranosyl)-(1,2)rhamnopyranoside (5), quercetin 3-O-α-(6′′′-p-coumaroyl glucopyranosyl-β-1,2-rhamnopyranoside) (6), and kaempferol 3-O-α-(6′′′-p-coumaroyl glucopyranosyl-β-1,2-rhamnopyranoside) (7) were demonstrated [10,11]. These phyto-constituents confirmed the application of Ginkgo biloba Linn leaves extract as a suitable source for synthesis of nanoparticles using the reducing ability of its antioxidant contents.
7
Figure 4. HPLC fingerprint of the extract of leaves of Ginkgo biloba Linn. 3.4. Characterization of Cu NPs Cu NPs was characterized using the UV-vis, FT-IR, EDS and TEM. The progression of the reaction, formation and stability of Cu NPs were controlled by UV-vis spectroscopy. The UV-vis spectrum of green synthesized Cu NPs using Ginkgo biloba Linn leaves extract (Figure 5) showed the significant changes in the absorbance maxima due to surface Plasmon resonance demonstrating the formation of Cu NPs. The color of the solution changed into dark with λ max ranging 560 to 580 nm indicating formation of Cu NPs as characterized by UV-vis spectrum. The synthesized Cu NPs by this method are quite stable and no obvious variance in the shape, position and symmetry of the absorption peak is observed even after one month indicating the stability of Cu NPs.
Figure 5. UV-vis spectrum of green synthesized Cu NPs using the aqueous extract of the leaves of the Ginkgo biloba Linn in 15 min (A) and 20 min (B).
8
Furthermore, the FT-IR of extract after adding CuCl2⋅2H2O while formation of Cu NPs shows demonstrative differences in the shape and location of signals indicating the interaction between CuCl2⋅2H2O and involved sites of phytochemicals for production of nanoparticles (Figure 6). Changing the location of peaks at 3500 to 3200, 1720, 1452, 1300 and 1000 cm -1 represent the OH functional groups, carbonyl group (C=O), stretching C=C aromatic ring and C-OH stretching vibrations, respectively. Polyphenolics could be adsorbed on the surface of metal nanoparticles, possibly by interaction through π– electrons interaction in the absence of other strong ligating agents. In fact the π–electrons of carbonyl group (C=O) from C ring of flavonoids in a Red/Ox system can transfer to the free orbital of metal ion and convert that to the free metal.
Figure 6. FT-IR spectrum of Cu NPs synthesized using aqueous extract of the leaves of Ginkgo biloba Linn. The size and shape of the products were examined by transmission electron microscopy (TEM). The TEM image of Cu NPs is shown in Figure 7. The products are of spherical morphology and have very narrow diameter distributions. The TEM observations showed the diameter of the Cu NPs was in the range of 15-20 nm.
9
Figure 7. TEM images of Cu nanoparticles. Energy dispersion X-ray spectroscopy (EDS) is shown in Figure 8. In the EDS spectrum of catalyst, peaks related to Cu and O is observed. The excess oxygen is due to physical absorption of oxygen from environment during sample preparation.
Figure 8. EDS spectrum of Cu NPs. 3.5. Evaluation of the catalytic activity of Cu NPs in the Huisgen [3 + 2] cycloaddition of azides and alkynes
10
In this step, we tested the catalytic activity of the Cu NPs for the Huisgen [3 + 2] cycloaddition of azides and alkynes in different solvents under ligand-free conditions. In our initial study, we chose benzyl azide and phenyl acetylene to optimize the reaction conditions. Various solvents and different amounts of catalyst were screened in order to establish ideal conditions. The results indicated that solvent had a remark effect on the yield of product and time of completion of the reaction. Among the various solvents tested in the presence of Cu NPs, EtOH led to significant conversion (Table 1, entry 4). In addition, in order to optimize the yields, different amounts of Cu NPs were used and best result was obtained with 10.0 mol% of Cu NPs in EtOH at room temperature, which gave the product in an excellent yield (Table 1, entry 4). No additive or ligand was required. Table 1. Optimization of reaction conditions in Huisgen [3 + 2] cycloaddition reaction of benzyl azide with phenyl acetylene.a
a
Entry
Cu NPs (mol%)
Solvent
Time (h)
Yield (%)b
1
10.0
Water
12
65
2
10.0
THF
48
Incomplete
3
10.0
t-Butanol
7
90
4
10.0
Ethanol
5
98
5
10.0
Ethanol : water
8
98
6
5.0
Ethanol
20
93
7
20
Ethanol
5
98
Reaction condition: 1.0 equiv of benzyl azide, 1.1 equiv of phenyl acetylene and 5.0 mL of solvent, room
temperature. b
Yields are after work-up.
11
The scope of the present catalytic system was extended by the reaction of azides with various alkynes (Table 2). Reactions were carried out in EtOH at room temperature and different times. As indicated in Table 3, in all cases the reaction gave the corresponding products in good to excellent yields. Table 2. Huisgen [3 + 2] cycloaddition reaction of azides with different alkynes. a
Time (h)
Yield b (%)
1
5
95
2
5
98
3
5
93
4
5
96
5
5
94
6
5
97
7
5
96
8
5
96
9
5
93
10
5
93
Entry
Azide
Alkyne
a
Reaction condition: 1.0 equiv of azide, 1.1 equiv of alkyne and 5.0 mL of solvent, room temperature.
b
Isolated yield.
The present method offers several notable features, compared with the other literature works [23-29] on the Huisgen [3 + 2] cycloaddition reaction of azides with different alkynes, i.e., (1) elimination of toxic additives and homogeneous catalysts, (2) the use of ethanol as a green solvent, (3) The use of Ginkgo biloba Linn leaf extract as an economic and effective alternative represents an interesting, fast and clean synthetic route for the large scale synthesis of Cu NPs, (4) wide substrate scope and generality, (5) higher
12
yields, (6) the catalyst can be recycled and reused several times without significant loss of their catalytic activity. 3.6. Catalyst recyclability One of the advantages of Cu NPs is their easy separation from the reaction mixture. The reusability of the catalyst was investigated for the Huisgen [3 + 2] cycloaddition of azides and alkynes under the present reaction conditions. After completion of the reaction, the catalyst could be easily separated and recovered conveniently by centrifugation from the reaction mixture and washed with ethanol, dried in an oven, then, new substrates were added to set up a new reaction. As shown in Table 3, the Cu NPs could be reused as a heterogeneous catalyst for the Huisgen [3 + 2] cycloaddition of benzyl azide with phenyl acetylene at least four times. This reusability demonstrates the high stability and turnover of catalyst under operating conditions. Table 3 Recycle of Cu NPs for Huisgen [3 + 2] cycloaddition reaction of benzyl azide with phenyl acetylene.
a
Entry
Cycle
Yielda (%)
1
Fresh
98
2
1st recycle
98
3
2nd recycle
97
4
3rd recycle
97
5
4th recycle
95
Yields are after work-up.
4. Conclusions In conclusion, we show a simple and green procedure to prepare stable copper nanoparticles using Ginkgo biloba Linn leaf extract as a reducing and stabilizing agent. The TEM analysis showed that the sizes of the synthesized Cu NPs ranged from 15 to 20 nm. This green procedure has many advantages such as, high yields and ease with which the process can be scaled up and economic viability. No toxic reagents or surfactant template was required in this protocol, which consequently enables the bioprocess with the advantage of being environmental friendly. Also, the catalytic activity of biologically synthesized Cu NPs was evaluated for the Huisgen [3 + 2] cycloaddition of azides and alkynes at room temperature, showing effective catalytic activity. The present method has the advantages of readily available starting materials,
13
straightforward and simple work-up procedures, high yields, tolerance for a wide variety of functionality, and excellent reusability of the catalyst.
Acknowledgements We gratefully acknowledge from the Iranian Nano Council and University of Qom for the support of this work.
References [1] H. C. Kolb, M. G. Finn and K. B. Sharpless, Angew. Chem., Int. Ed. 40 (2001) 2004. [2] P. Wu and V. V. Fokin, Aldrichimica Acta 40 (2007) 7. [3] H. C. Kolb and K. B. Sharpless, Drug Discovery Today 8 (2003) 1128. [4] M. Meldal, C.W. Tornøe, Chem. Rev. 108 (2008) 2952. [5] K. V. Gothelf and K. A. Jorgensen, Chem. Rev. 98 (1998) 863. [6] C.W. Tornøe, C. Christensen, M. Meldal, J. Org. Chem. 67 (2002) 3057. [7] B.W.T. Gruijters, M.A.C. Broeren, F.L. van Delft, R.P. Sijbesma, P.H.H. Hermkens, F.P.J.T. Rutjes, Org. Lett. 8 (2006) 3163. [8] S. Wei, Z. Dong, Z. Ma, J. Sun, J. Ma, Catal. Commun. 30 (2013) 40. [9] H. Wang, J. Xu, J. Zhu and H. Chen, J. Cryst. Growth 244 (2002) 88. [10] Haiyan Xie, Jing-Rong Wang, Lee-Fong Yau, Yong Liu, Liang Liu, Quan-Bin Han, Zhongzhen Zhao and Zhi-Hong Jiang, molecules. 19 (2014) 4466. [11] E.S. Abdel-Halim, M.H. El-Rafie, S.S. Al-Deyab, Carbohydr. Polym. 85 (2011) 692. [12] M. Nasrollahzadeh, S. M. Sajadi, M. Khalaj, RSC Adv. 4 (2014) 47313. [13] H.J. Gertz, M. Kiefer, Curr. Pharm. Des. 10 (2004), 261. [14] B.P. Jacobs, W.S. Browner, Am. J. Med. Sci. 108 (2000), 341. [15] C. Nasr, A. Lobstein-Guth, R.A. Haag-Berrurier, Phytochem. 26 (1987) 2869. [16] J.M. Cott, A. Raman, Clinical Efficacy and Pharmacodynamics. In American herbal Pharmacopoeia and Therapeutic Compendium: Ginkgo Leaf, Ginkgo Leaf Dry Extract, Ginkgo biloba L., R.U. Herabalist, A. Graff, Eds., American Herbal pharmacopoeia: Scotts Valley, CA, USA, (2003) pp. 26-27.
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[17] M. Nasrollahzadeh, S.M. Sajadi, A. Rostami-Vartooni, M. Khalaj, RSC Adv. 4 (2014) 43477. [18] M. Nasrollahzadeh, M. Maham, M. M. Tohidi, J. Mol. Catal. A, Chem. 391 (2014) 83. [19] M. Nasrollahzadeh, M. Enayati, M. Khalaj, RSC Adv. 4 (2014) 26264. [20] M. Nasrollahzadeh, S. M. Sajadi, A. Rostami-Vartooni, M. Khalaj, J. Mol. Catal. A, Chem. 396 (2015) 31. [21] P. Fakhri, M. Nasrollahzadeh, B. Jaleh, RSC Adv. 4 (2014) 48691. [22] M. Nasrollahzadeh, RSC Adv. 4 (2014) 29089. [23] F. Alonso, Y. Moglie, G. Radivoy, M. Yus, Eur. J. Org. Chem. (2010) 1875. [24] F. Alonso, Y. Moglie, G. Radivoy, M. Yus, Org. Biomol. Chem. 9 (2011) 6385. [25] K. Wang, X. Bi, S. Xing, P. Liao, Z. Fang, X. Meng, Q. Zhang, Q. Liu, Y. Ji, Green Chem. 13 (2011) 562. [26] J.-A. Shin, Y.-G. Lim, K.-H. Lee, J. Org. Chem. 77 (2012) 4117. [27] X. Meng, X. Xu, T. Gao, B. Chen, Eur. J. Org. Chem. (2010) 5409. [28] C. Shao, X. Wang, J. Xu, J. Zhao, Q. Zhang, Y. Hu, J. Org. Chem. 75 (2010) 7002. [29] A. Pathigoolla, R. P. Pola, K. M. Sureshan, Appl. Catal. A: Gen. 453 (2013) 151.
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Graphical Abstract Green synthesis of copper nanoparticles using Ginkgo biloba Linn leaf extract and their catalytic activity for the Huisgen [3 + 2] cycloaddition of azides and alkynes at room temperature Mahmoud Nasrollahzadeh * and S. Mohammad Sajadi
16
Research highlights:
Green synthesis of Cu NPs using Ginkgo biloba Linn leaf extract without application of toxic reagents or surfactant template.
The Cu NPs can efficiently catalyze the Huisgen [3 + 2] cycloaddition of azides and alkynes at room temperature in ethanol.
The advantages of Cu NPs are high efficiently, reusability and operational simplicity.
17
S0021-9797(15)30023-0 http://dx.doi.org/10.1016/j.jcis.2015.07.004 YJCIS 20558
To appear in:
Journal of Colloid and Interface Science
Received Date: Accepted Date:
16 June 2015 1 July 2015
Please cite this article as: M. Nasrollahzadeh, S. Mohammad Sajadi, Green synthesis of copper nanoparticles using Ginkgo biloba L. leaf extract and their catalytic activity for the Huisgen [3 + 2] cycloaddition of azides and alkynes at room temperature, Journal of Colloid and Interface Science (2015), doi: http://dx.doi.org/10.1016/j.jcis. 2015.07.004
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Green synthesis of copper nanoparticles using Ginkgo biloba L. leaf extract and their catalytic activity for the Huisgen [3 + 2] cycloaddition of azides and alkynes at room temperature Mahmoud Nasrollahzadeh a,* and S. Mohammad Sajadib a
b
Department of Chemistry, Faculty of science, University of Qom, P. O. Box 37185-359, Qom, Iran.
Department of Petroleum Geoscience, Faculty of Science, Soran University, PO Box 624, Soran, Kurdistan Regional Government, Iraq
*Corresponding author. Tel: +98 25 32850953; Fax: +98 25 32103595. E-mail address: [email protected]
ABSTRACT During this study, we report the green synthesis of copper nanoparticles (Cu NPs) using Ginkgo biloba L. leaf extract as a reducing and stabilizing agent under surfactant-free conditions. The formation of Cu NPs is monitored by recording the UV-vis absorption spectra. The green synthesized Cu NPs are characterized by TEM, EDS, FT-IR and UV-visible techniques. According to UV-vis results, the synthesized Cu NPs by this method are quite stable even after one month indicating the stability of Cu NPs. In terms of environmental impact and economy, metallic Cu NPs offer several advantages over homogeneous and traditional heterogeneous catalysts. In addition, due to the increased metal surface area, Cu NPs shows very high catalytic activity for the Huisgen [3 + 2] cycloaddition of azides and alkynes at room temperature. Furthermore, the catalyst can be simply recovered and reused several times with almost no loss in activity.
Keywords: Metals; Organic compounds; Catalytic properties
1. Introduction Click chemistry is a highly efficient cycloaddition process that became very popular as a new synthesis route since its introduction in the dawn of the 21st century by Sharpless et al. [1]. Click chemistry is one of the most powerful tools for the construction of various triazoles, which are often considered in pharmaceuticals, drug discovery, polymers and material science [2,3].
1
The Huisgen cycloaddition process, involving copper (I)-catalyzed [3 + 2] cycloaddition of terminal alkynes and organic azides at room temperature is considered as the best click reaction to date [4]. However, there are several disadvantages in the literature methods such as the use of homogeneous catalysts and toxic organic solvents, low yields, long reaction times, harsh reaction conditions, environmental pollution due to the side products formed and tedious work-up [5]. Also, the early Huisgen cycloaddition process required a strong electron-withdrawing substituent either on azide or on alkyne and usually led to the isolation of a mixture of 1,4-disubstituted and l,5-disubstituted-l,2,3-triazoles regioisomers [5]. Therefore, it is desirable to develop a new, convenient and regio-controlled synthetic protocol for the synthesis of triazoles. Due to the importance of triazoles, several modifications to overcome the above drawbacks, improve the yield, efficiency or to reduce the cost have been reported using copper homogeneous catalysts such as Cu(I) salts [6] and Cu(I) complexes [4,7]. The problem with homogeneous catalysis is the difficulty to separate the catalyst from the reaction mixture and the impossibility to reuse it in consecutive reactions. Thus, we decided to concentrate on developing an efficient copper heterogeneous catalyst that is highly active. The transition metal nanoparticles play an important role in organic reactions because of their high surface to volume ratio that can dramatically enhance the interaction between reactants and catalysts and larger number of active sites per unit area compared to the parent metal [8]. In addition, nanocatalysis can make the products easily removable from the reaction mixtures and make the catalysts recyclable. There are several methods for the synthesis of copper nanoparticles (Cu NPs) using toxic and expensive chemicals, harsh reducing agents in organic solvents [9,10]. The presence of these toxic and dangerous materials on the surface of Cu NPs increases the toxicity issue while the use and disposal of toxic solvents triggers environmental issues. However, green synthesis of nanoparticles by various plants or gums is an ecologically friendly, cost effective method without use of tough chemicals. In addition, the other advantages of this environmentally benign and safe protocol include a simple reaction setup, very mild reaction conditions, use of nontoxic solvents such as water, elimination of harmful chemicals and cost effectiveness as well as compatibility for biomedical and pharmaceutical applications [11,12]. Also, in this method there is no need to use high pressure, energy, temperature and toxic chemicals.
2
The Ginkgo biloba Linn is from the family of Ginkgoaceae is world’s oldest tree mostly known as living fossils and only surviving member of seed plant groups. It is found growing naturally in very limited localities in the central Himalayan Mountain (Figure 1) [13-16]. The Leaves of this species is extensively used as a source of herbal medicine for presence of medicinal phytochemicals.
Figure 1. Image of Ginkgo biloba Linn leaves. Due to our ongoing interest on the green synthesis of metal NPs and heterogeneous catalysts [17-22], we wish to report a simple and eco-friendly protocol for synthesis of Cu NPs using aqueous extract of Ginkgo biloba Linn leaf. Also, the catalytic potential of Cu NPs was evaluated in the Huisgen [3 + 2] cycloaddition of azides and alkynes at room temperature (Scheme 1).
2. Experimental High-purity chemical reagents were purchased from the Merck and Aldrich chemical companies. All materials were of commercial reagent grade. Melting points were deter-mined in open capillaries using a BUCHI 510 melting point apparatus and are uncorrected. 1H NMR and 13C NMR spectra were recorded on a Bruker Avance DRX-400 spectrometer at 400 and 100 MHz, respectively. FT-IR spectra were recorded on a Nicolet 370 FT/IR spectrometer (Thermo Nicolet, USA) using pressed KBr pellets. The shape and size
3
of palladium nanoparticles crystals were identified by transmission electron microscope (TEM) using a Philips EM208 microscope operating at an accelerating voltage of 90 kV. UV-visible spectral analysis was recorded on a double‐beam spectrophotometer (Hitachi, U‐2900) to ensure the formation of nanoparticles. 2.1. Preparation of extract of leaves of Ginkgo biloba Linn 100 g of dried leaves powdered of Ginkgo biloba Linn was added to 500 mL double distillated water in 1000 mL flask and well mixed. The preparation of extract was done by using magnetic heating stirrer at 70 °C for 30 min. The obtained extract was centrifuged in 6500 rpm and filtered then filtrate was kept at refrigerator to use further. 2.2. Green synthesis of copper nanoparticles using Ginkgo biloba Linn leaves extract The copper nanoparticles were synthesized by the following process. In a 250 mL conical flask, 10 mL solution of CuCl2⋅2H2O 5 mM was mixed with 100 mL of the aqueous plant extract (100 g dried leaves of the plant extracted using 500 mL of deionized water while heating at 80 °C and pH 9 for 30 min then filtered) along with vigorous shaking until gradually changing the color of the mixture during 15 min to dark indicating the formation of Cu NPs (as monitored by UV-vis and FT-IR spectra of the solution). The well shaked mixture then filtered and centrifuged at 6500 rpm for 30 min and obtained precipitation washed with n-Hexane and absolute ethanol, respectively. 2.3. Preparation of 1-Benzyl-4-phenyl-1,2,3-triazole To a mixture of benzyl azide (1.0 mmol) and phenyl acetylene (1.1 mmol), 10 mol % of the Cu NPs in absolute ethanol was added (Table 1). The reaction mixture was then stirred at room temperature and the progress of the reaction was monitored using TLC. After completion of the reaction, the reaction mixture was centrifuged to pellet out the catalyst. The nanoparticles were washed three times with absolute ethanol, then three times with water with no further purification before reuse. The filtrate was further treated with EtOAc to ensure complete transfer. The solvent was removed under vacuum to give the desired pure products and characterized by 1 HNMR. All the products are known compounds and the spectral data and melting points were identical to those reported in the literature [23-29]. 1-Benzyl-4-phenyl-1,2,3-triazole (Table 2, entry 2): M.p. 130-131 °C (lit.23 132-133.1 °C); 1H NMR (DMSO-d6, 400 MHz) δH = 8.63 (s, 1H), 7.86-7.83 (m, 2H), 7.45-7.35 (m, 8H), 5.67 (s, 2H).
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3. Results and discussion In the present work, we develop an ecofriendly, clean, non-toxic, facile chemically preparative method, for the generation of Cu NPs using the extract of the leaves of Ginkgo biloba Linn, acting as reducing as well as stabilizing agent. To date, there is no report on the green synthesis of Cu NPs by utilizing the leaves extract of Ginkgo biloba Linn. 3.1. Characterization of extract of leaves of Ginkgo biloba Linn The UV spectrum of extract (Figure 2) shows bonds at λmax 269 nm (bond Ι) due to the transition localized within the ring of cinnamoyl system; whereas the π → π* transition is shown by double bonds. The extract of Ginkgo biloba Linn leaf was obtained in aqueous media which this media is able to extract the highly polar phytoconstituents of the plant like polyphenolics with conjugated double bonds (in A, B and C ring of the flavone nuclei) and aromatic rings in their structure as major Ginkgo biloba Linn constituents. Then according the literatures about the plant and UV-vis fingerprint spectrum of its aqueous extract our result supports this idea. Therefore, the one centered at 235 nm (bond ΙΙ) is for absorbance of ring related to the benzoyl system and π → π* transitions on which these absorbent bonds demonstrate the presence of polyphenolics.
Figure 2. UV-vis spectrum of the aqueous extract of the leaves of the Ginkgo biloba Linn. The FT-IR analysis was carried out to identify the possible biomolecules responsible for the reduction of Cu nanoparticles and capping of the bioreduced nanoparticles. The FT-IR spectrum of the crude extract, (Figure 3) depicted some peaks at 3500 to 3100, 1643, 1575, 1395 and 1100 cm-1 which represent free OH in molecule and OH group forming hydrogen bonds, carbonyl group (C=O), stretching C=C aromatic ring
5
and C-OH and C-H stretching vibrations, respectively. These peaks suggested the presence of flavonoid and other phenolics in the plant leaves extract. The presence of flavonoid and other phenolics in the extract could be responsible for the reduction of metal ions and formation of the corresponding metal nanoparticles.
Figure 3. FT-IR spectrum of the aqueous extract of the leaves of the Ginkgo biloba Linn. 3.2. Reduction of metal ions In our research there is a focus on the synthesis of NPs in aqueous media using reducing properties of antioxidant phytochemicals inside the plant especially polyphenolics as a major reducing and highly polar agents in Ginkgo biloba Linn leaf extract [10,11] according the below mechanism (Scheme 2).
6
Scheme
2.
Production
of Cu NPs using the
quercetin 3-O-α-L-(β-D-glucopyranosyl)-(1,2)-
rhamnopyranoside as one of the potent antioxidants of Ginkgo biloba Linn. Of course, the effect of other phytochemicals inside the plant is maybe possible but not as reducing and highly polar agents involving the reaction while production of nanoparticles, also after precipitating the nano products, they were washed using n-Hexane (or chloroform) and ethanol respectively to remove impurities. 3.3. HPLC analysis According the Haiyan Xie et. al report on the Ginkgo biloba Linn and HPLC analysis of antioxidant content of the plant appeared in Figure 4, the presence of potent antioxidants such as quercetin 3-O-β-Drutinoside (1), quercetin 3-O-α-L-(β-D-glucopyranosyl)-(1,2)-rhamnopyranoside (2), kaempferol 3-O-β-Drutinoside (3), isorhamnetin 3-O-β-D-rutinoside (4), kaempferol 3-O-α-L-(β-D-glucopyranosyl)-(1,2)rhamnopyranoside (5), quercetin 3-O-α-(6′′′-p-coumaroyl glucopyranosyl-β-1,2-rhamnopyranoside) (6), and kaempferol 3-O-α-(6′′′-p-coumaroyl glucopyranosyl-β-1,2-rhamnopyranoside) (7) were demonstrated [10,11]. These phyto-constituents confirmed the application of Ginkgo biloba Linn leaves extract as a suitable source for synthesis of nanoparticles using the reducing ability of its antioxidant contents.
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Figure 4. HPLC fingerprint of the extract of leaves of Ginkgo biloba Linn. 3.4. Characterization of Cu NPs Cu NPs was characterized using the UV-vis, FT-IR, EDS and TEM. The progression of the reaction, formation and stability of Cu NPs were controlled by UV-vis spectroscopy. The UV-vis spectrum of green synthesized Cu NPs using Ginkgo biloba Linn leaves extract (Figure 5) showed the significant changes in the absorbance maxima due to surface Plasmon resonance demonstrating the formation of Cu NPs. The color of the solution changed into dark with λ max ranging 560 to 580 nm indicating formation of Cu NPs as characterized by UV-vis spectrum. The synthesized Cu NPs by this method are quite stable and no obvious variance in the shape, position and symmetry of the absorption peak is observed even after one month indicating the stability of Cu NPs.
Figure 5. UV-vis spectrum of green synthesized Cu NPs using the aqueous extract of the leaves of the Ginkgo biloba Linn in 15 min (A) and 20 min (B).
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Furthermore, the FT-IR of extract after adding CuCl2⋅2H2O while formation of Cu NPs shows demonstrative differences in the shape and location of signals indicating the interaction between CuCl2⋅2H2O and involved sites of phytochemicals for production of nanoparticles (Figure 6). Changing the location of peaks at 3500 to 3200, 1720, 1452, 1300 and 1000 cm -1 represent the OH functional groups, carbonyl group (C=O), stretching C=C aromatic ring and C-OH stretching vibrations, respectively. Polyphenolics could be adsorbed on the surface of metal nanoparticles, possibly by interaction through π– electrons interaction in the absence of other strong ligating agents. In fact the π–electrons of carbonyl group (C=O) from C ring of flavonoids in a Red/Ox system can transfer to the free orbital of metal ion and convert that to the free metal.
Figure 6. FT-IR spectrum of Cu NPs synthesized using aqueous extract of the leaves of Ginkgo biloba Linn. The size and shape of the products were examined by transmission electron microscopy (TEM). The TEM image of Cu NPs is shown in Figure 7. The products are of spherical morphology and have very narrow diameter distributions. The TEM observations showed the diameter of the Cu NPs was in the range of 15-20 nm.
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Figure 7. TEM images of Cu nanoparticles. Energy dispersion X-ray spectroscopy (EDS) is shown in Figure 8. In the EDS spectrum of catalyst, peaks related to Cu and O is observed. The excess oxygen is due to physical absorption of oxygen from environment during sample preparation.
Figure 8. EDS spectrum of Cu NPs. 3.5. Evaluation of the catalytic activity of Cu NPs in the Huisgen [3 + 2] cycloaddition of azides and alkynes
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In this step, we tested the catalytic activity of the Cu NPs for the Huisgen [3 + 2] cycloaddition of azides and alkynes in different solvents under ligand-free conditions. In our initial study, we chose benzyl azide and phenyl acetylene to optimize the reaction conditions. Various solvents and different amounts of catalyst were screened in order to establish ideal conditions. The results indicated that solvent had a remark effect on the yield of product and time of completion of the reaction. Among the various solvents tested in the presence of Cu NPs, EtOH led to significant conversion (Table 1, entry 4). In addition, in order to optimize the yields, different amounts of Cu NPs were used and best result was obtained with 10.0 mol% of Cu NPs in EtOH at room temperature, which gave the product in an excellent yield (Table 1, entry 4). No additive or ligand was required. Table 1. Optimization of reaction conditions in Huisgen [3 + 2] cycloaddition reaction of benzyl azide with phenyl acetylene.a
a
Entry
Cu NPs (mol%)
Solvent
Time (h)
Yield (%)b
1
10.0
Water
12
65
2
10.0
THF
48
Incomplete
3
10.0
t-Butanol
7
90
4
10.0
Ethanol
5
98
5
10.0
Ethanol : water
8
98
6
5.0
Ethanol
20
93
7
20
Ethanol
5
98
Reaction condition: 1.0 equiv of benzyl azide, 1.1 equiv of phenyl acetylene and 5.0 mL of solvent, room
temperature. b
Yields are after work-up.
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The scope of the present catalytic system was extended by the reaction of azides with various alkynes (Table 2). Reactions were carried out in EtOH at room temperature and different times. As indicated in Table 3, in all cases the reaction gave the corresponding products in good to excellent yields. Table 2. Huisgen [3 + 2] cycloaddition reaction of azides with different alkynes. a
Time (h)
Yield b (%)
1
5
95
2
5
98
3
5
93
4
5
96
5
5
94
6
5
97
7
5
96
8
5
96
9
5
93
10
5
93
Entry
Azide
Alkyne
a
Reaction condition: 1.0 equiv of azide, 1.1 equiv of alkyne and 5.0 mL of solvent, room temperature.
b
Isolated yield.
The present method offers several notable features, compared with the other literature works [23-29] on the Huisgen [3 + 2] cycloaddition reaction of azides with different alkynes, i.e., (1) elimination of toxic additives and homogeneous catalysts, (2) the use of ethanol as a green solvent, (3) The use of Ginkgo biloba Linn leaf extract as an economic and effective alternative represents an interesting, fast and clean synthetic route for the large scale synthesis of Cu NPs, (4) wide substrate scope and generality, (5) higher
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yields, (6) the catalyst can be recycled and reused several times without significant loss of their catalytic activity. 3.6. Catalyst recyclability One of the advantages of Cu NPs is their easy separation from the reaction mixture. The reusability of the catalyst was investigated for the Huisgen [3 + 2] cycloaddition of azides and alkynes under the present reaction conditions. After completion of the reaction, the catalyst could be easily separated and recovered conveniently by centrifugation from the reaction mixture and washed with ethanol, dried in an oven, then, new substrates were added to set up a new reaction. As shown in Table 3, the Cu NPs could be reused as a heterogeneous catalyst for the Huisgen [3 + 2] cycloaddition of benzyl azide with phenyl acetylene at least four times. This reusability demonstrates the high stability and turnover of catalyst under operating conditions. Table 3 Recycle of Cu NPs for Huisgen [3 + 2] cycloaddition reaction of benzyl azide with phenyl acetylene.
a
Entry
Cycle
Yielda (%)
1
Fresh
98
2
1st recycle
98
3
2nd recycle
97
4
3rd recycle
97
5
4th recycle
95
Yields are after work-up.
4. Conclusions In conclusion, we show a simple and green procedure to prepare stable copper nanoparticles using Ginkgo biloba Linn leaf extract as a reducing and stabilizing agent. The TEM analysis showed that the sizes of the synthesized Cu NPs ranged from 15 to 20 nm. This green procedure has many advantages such as, high yields and ease with which the process can be scaled up and economic viability. No toxic reagents or surfactant template was required in this protocol, which consequently enables the bioprocess with the advantage of being environmental friendly. Also, the catalytic activity of biologically synthesized Cu NPs was evaluated for the Huisgen [3 + 2] cycloaddition of azides and alkynes at room temperature, showing effective catalytic activity. The present method has the advantages of readily available starting materials,
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straightforward and simple work-up procedures, high yields, tolerance for a wide variety of functionality, and excellent reusability of the catalyst.
Acknowledgements We gratefully acknowledge from the Iranian Nano Council and University of Qom for the support of this work.
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Graphical Abstract Green synthesis of copper nanoparticles using Ginkgo biloba Linn leaf extract and their catalytic activity for the Huisgen [3 + 2] cycloaddition of azides and alkynes at room temperature Mahmoud Nasrollahzadeh * and S. Mohammad Sajadi
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Research highlights:
Green synthesis of Cu NPs using Ginkgo biloba Linn leaf extract without application of toxic reagents or surfactant template.
The Cu NPs can efficiently catalyze the Huisgen [3 + 2] cycloaddition of azides and alkynes at room temperature in ethanol.
The advantages of Cu NPs are high efficiently, reusability and operational simplicity.
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