Green synthesis of copper nanoparticles using Ginkgo biloba L. leaf ...

Journal of Colloid and Interface Science 457 (2015) 141–147

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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,⇑, S. Mohammad Sajadi b 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

h i g h l i g h t s

g r a p h i c a l a b s t r a c t

Green synthesis of Cu NPs using

Ginkgo biloba Linn leaf extract. Catalyst showed good activity in the

Huisgen [3 + 2] cycloaddition of azides and alkynes. The advantages of Cu NPs are high efficiently, reusability and operational simplicity.

a r t i c l e

i n f o

Article history: Received 16 June 2015 Accepted 1 July 2015 Available online 3 July 2015 Keywords: Copper nanoparticles Huisgen [3 + 2] cycloaddition Catalytic activity

a b s t r a c t 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. Ó 2015 Elsevier Inc. All rights reserved.

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]. ⇑ Corresponding author. Tel.: +98 25 32103595; fax: +98 25 32850953. E-mail address: [email protected] (M. Nasrollahzadeh). http://dx.doi.org/10.1016/j.jcis.2015.07.004 0021-9797/Ó 2015 Elsevier Inc. All rights reserved.

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

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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. 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 (Fig. 1) [13–16]. The Leaves of this species is extensively used as a source of herbal medicine for presence of medicinal phytochemicals. 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 G. biloba Linn leaves. Also, the catalytic potential of Cu NPs was evaluated in the Huisgen [3 + 2] cycloaddition of azides and alkynes at room temperature (Scheme 1).

Scheme 1. Huisgen [3 + 2] cycloaddition of azides and alkynes.

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. 1 H 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 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 G. biloba Linn 100 g of dried leaves powdered of G. 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 G. biloba Linn leaf extract The copper nanoparticles were synthesized by the following process. In a 250 mL conical flask, 10 mL solution of CuCl22H2O 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

Fig. 1. Image of Ginkgo biloba Linn leaves.

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 1HNMR. All the products are known compounds and the spectral data and melting points were identical to those reported in the literature [23–29].

M. Nasrollahzadeh, S. Mohammad Sajadi / Journal of Colloid and Interface Science 457 (2015) 141–147 Table 1 Optimization of reaction conditions in the Huisgen [3 + 2] cycloaddition reaction of benzyl azide with phenyl acetylene.a N

N

N Ph

Catalyst Conditions

+

N3

Ph

Entry

Cu NPs (mol%)

Solvent

Time (h)

Yield (%)b

1 2 3 4 5 6 7

10.0 10.0 10.0 10.0 10.0 5.0 20.0

Water THF t-Butanol Ethanol Ethanol: water Ethanol Ethanol

12 48 7 5 8 20 5

65 Incomplete 90 98 98 93 98

a Reaction conditions: 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.

Table 2 Huisgen [3 + 2] cycloaddition reaction of azides with different alkynes.a

Cu NPs (10 mol%) EtOH, r.t.

RN3 + R1

N R

N

N R1

Entry

Azide

Alkyne

1

b

(%)

N3

N3

5

98

5

93

5

96

3.2. Reduction of metal ions

5

94

5

97

5

96

5

96

5

93

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 G. biloba Linn leaf extract [10,11] according the below mechanism (Scheme 2). 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.

5

93

N3

6 N3

7 N3

HO

8 N3

N

9

The UV spectrum of extract (Fig. 2) shows bonds at kmax 269 nm (bond I) due to the transition localized within the ring of cinnamoyl system; whereas the p ? p⁄ transition is shown by double bonds. The extract of G. biloba Linn leaves 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 G. 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 II) is for absorbance of ring related to the benzoyl system and p ? p⁄ transitions on which these absorbent bonds demonstrate the presence of polyphenolics. 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, (Fig. 3) depicted some peaks at 3500 to 3100, 1643, 1575, 1395 and 1100 cm1 which represent free OH in molecule and OH group forming hydrogen bonds, carbonyl group (C@O), stretching C@C aromatic ring and CAOH and CAH stretching vibrations, respectively. These peaks suggested the presence of flavonoid and other phenolics in the plant leaf 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.

95

N

5

3.1. Characterization of extract of leaves of G. biloba Linn

5

HO

4

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 leaves of G. 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 leaf extract of G. biloba Linn.

Yield

N3

3

3. Results and discussion

Time (h)

N3

2

N3 Me

10

143

N3 Cl a

Reaction conditions: 1.0 equiv of azide, 1.1 equiv of alkyne and 5.0 mL of ethanol, room temperature. b Isolated yield.

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) dH = 8.63 (s, 1H), 7.86–7.83 (m, 2H), 7.45–7.35 (m, 8H), 5.67 (s, 2H).

Fig. 2. UV–vis spectrum of aqueous extract of leaves of Ginkgo biloba Linn.

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Fig. 3. FT-IR spectrum of aqueous extract of leaves of Ginkgo biloba Linn.

Scheme 2. Production of Cu NPs using the quercetin 3-O-a-L-(b-D-glucopyranosyl)-(1,2)-rhamnopyranoside as one of the potent antioxidants of Ginkgo biloba Linn.

3.3. HPLC analysis According the Haiyan Xie et al. report on the G. biloba Linn and HPLC analysis of antioxidant content of the plant appeared in Fig. 4, the presence of potent antioxidants such as quercetin 3-O-b-D-rutinoside (1), quercetin 3-O-a-L-(b-D-glucopyranosyl)-(1, 2)-rhamnopyranoside (2), kaempferol 3-O-b-D-rutinoside (3), isorhamnetin 3-O-b-D-rutinoside (4), kaempferol 3-O-a-L(b-D-glucopyranosyl)-(1,2)-rhamnopyranoside (5), quercetin 3-Oa-(6000 -p-coumaroyl glucopyranosyl-b-1,2-rhamnopyranoside) (6), and kaempferol 3-O-a-(600 0 -p-coumaroyl glucopyranosyl-b-1,2-

rhamnopyranoside) (7) were demonstrated [10,11]. These phyto-constituents confirmed the application of G. biloba Linn leaf extract as a suitable source for synthesis of nanoparticles using the reducing ability of its antioxidant contents. 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 G. biloba Linn leaf extract (Fig. 5)


145

Fig. 4. HPLC fingerprint of extract of leaves of Ginkgo biloba Linn.

Fig. 5. UV–vis spectrum of green synthesized Cu NPs using aqueous extract of leaves of Ginkgo biloba Linn in 15 min (A) and 20 min (B).

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 kmax ranging 560–580 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. Furthermore, the FT-IR of extract after adding CuCl22H2O while formation of Cu NPs shows demonstrative differences in the shape and location of signals indicating the interaction between CuCl22H2O and involved sites of phytochemicals for production of nanoparticles (Fig. 6). Changing the location of peaks at 3500 to 3200, 1720, 1452, 1300 and 1000 cm1 represent the OH functional groups, carbonyl group (C@O), stretching C@C aromatic ring and CAOH stretching vibrations, respectively. Polyphenolics could be adsorbed on the surface of metal nanoparticles, possibly by interaction through p–electrons interaction in the absence of other strong ligating agents. In fact the p–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. The size and shape of the products were examined by transmission electron microscopy (TEM). The TEM image of Cu NPs is shown in Fig. 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. Energy dispersion X-ray spectroscopy (EDS) is shown in Fig. 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.

Fig. 6. FT-IR spectrum of Cu NPs synthesized using aqueous extract of leaves of Ginkgo biloba Linn.

146

M. Nasrollahzadeh, S. Mohammad Sajadi / Journal of Colloid and Interface Science 457 (2015) 141–147 Table 3 Recycle of Cu NPs for the Huisgen [3 + 2] cycloaddition reaction of benzyl azide with phenyl acetylene.

a

Fig. 7. TEM images of Cu nanoparticles.

3.5. Evaluation of the catalytic activity of Cu NPs in the Huisgen [3 + 2] cycloaddition of azides and alkynes 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

Entry

Cycle

Yielda (%)

1 2 3 4 5

Fresh 1st recycle 2nd recycle 3rd recycle 4th recycle

98 98 97 97 95

Yields are after work-up.

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. 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. 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 G. 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 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

Fig. 8. EDS spectrum of Cu NPs.


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. 4. Conclusions In conclusion, we show a simple and green procedure to prepare stable copper nanoparticles using G. 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, straightforward and simple work-up procedures, high yields, tolerance for a wide variety of functionality, and excellent reusability of the catalyst. Acknowledgment We gratefully acknowledge from the Iranian Nano Council and University of Qom for the support of this work.

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