Steroidal saponin based extracellular biosynthesis of AgNPs

Journal of Molecular Liquids 199 (2014) 489–494

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Journal of Molecular Liquids journal homepage: www.elsevier.com/locate/molliq

Steroidal saponin based extracellular biosynthesis of AgNPs Shokit Hussain a, Ommer Bashir a, Zaheer Khan a,⁎, Shaeel Ahmed AL-Thabaiti b a b

Nano-Science Research Lab, Department of Chemistry, Jamia Millia Islamia (Central University), New Delhi 110025, India Department of Chemistry, Faculty of Science, King Abdulaziz University, P.O. Box 80203, Jeddah 21589, Saudi Arabia

a r t i c l e

i n f o

Article history: Received 19 August 2014 Received in revised form 23 September 2014 Accepted 25 September 2014 Available online 1 October 2014 Keywords: D. deltoidea extract CTAB Diosgenin AgNPs Morphology

a b s t r a c t Plant based synthesis of metallic nanoparticles is an increasing commercial demand due to its wide application in various areas such as electronics, catalysis, chemistry, energy, cosmetics and medicine. Silver nanoparticles were synthesized by adding an extract of Dioscorea deltoidea in AgNO3 solution and characterized by using UV–visible spectroscopy and, transmission electron microscopy (TEM). The main constituent of extract, i.e., Diosgenin, interacts with AgNO3 which showed gradual change in the color of the reaction mixture from colorless to yellowish brown with intensity increasing during the period of incubation. Hence, the extract acts as a reducing and capping agent. The cetyltrimethylammonium bromide (CTAB) markedly enhanced the reaction path and changed the morphology (size, shape and distribution). The diameter of the AgNPs ranged from 11.2 nm to 103.4 nm. © 2014 Elsevier B.V. All rights reserved.

1. Introduction Nanobiotechnology relates with the synthesis of nanoparticles using living organisms. Among the various living organisms for nanoparticle synthesis, plants have found application particularly in metal nanoparticle synthesis. The use of plant extract for synthesis of nanoparticles could be advantageous over other environmentally benign biological processes. Extracellular biosynthetic processes for nanoparticles would be more useful if nanoparticles were produced using plants or their extracts and in a controlled manner according to their size, disparity and shape. Plant product is used for large-scale synthesis of nanoparticles but only a few clues are available, like phenolics, proteins and reducing agents [1]. Nanoparticles can be synthesized by using a lot of methods through chemical and physical approaches. But these methods are very vigorous and more economical, and they employ toxic chemicals and nonpolar solvents in the synthesis procedure. Therefore it needs the development of a clean, reliable, biocompatible, benign, and ecofriendly process to synthesize nanoparticles. This leads to turning researchers toward “green” chemistry and bioprocesses [2]. The use of plant system has been considered a green route and a reliable method for the biosynthesis of nanoparticles owing to its environmental friendly nature [3,4]. Plants system has been used for rapid and extracellular biosynthesis of Nobel metal nanoparticles [5–7]. Extract of various leaves, plants, algae, fungi and yeast acted as reducing, capping and shape-directing agents for green synthesis of silver and gold nanoparticles [8–11]. Shankar et al. also synthesized gold and silver nanoparticles using plant extracts [12,13]. Bakshi et al. used zein protein as a reducing ⁎ Corresponding author. E-mail address: [email protected] (Z. Khan).

http://dx.doi.org/10.1016/j.molliq.2014.09.047 0167-7322/© 2014 Elsevier B.V. All rights reserved.

and capping agent towards the synthesis of bio-conjugated gold nanoparticles and explained the unfolding, fusogenic and hemolytic behaviors of protein with respect to temperature and time on the morphology of resulting nanoparticles. A layer of zein protein coating on the surface of nanoparticles significantly reduced the toxic and hemolytic properties of nanoparticles [14]. Recently, we synthesize silver nanoparticles by using Allium sativum, Camellia sinensis, and Citrus limon aqueous extract in the presence of shape-directing CTAB [15–17]. Dioscorea, belonging to the family Dioscoreaceae, comprises more than 600 species of the genus Dioscorea. Among them various species of this genus has been found in the Himalaya, great mountain system of Asia particularly in the great Pir Panjal Range. Dioscorea deltoidea is also found very easily in various forests of this area. D. deltoidea L. known as shingli mingli is a common herb, vine and climber. It is a perennial, twining vine of Dioscoreaceae. Underground, it has a deep, persistent, root-like tuber up to 4 or 5 cm long. An extensive climber with stems twining to the left. The leaves are stalked cordate, acute, and often triangular. Fruit triangular, trigonous membranous resembling the nose ornament (nath) worn by the ladies in the hills. Rhizomes are horizontal, borne close and are often deep in the soil (depending upon the site) mostly black in color with rigid scattered root like hair on them. A tuber of good quality is reported to contain 4.8–8% of diosgenin content, which is used in the partial synthesis of modern drugs like cortisone and other steroids. Diosgenin, the saponin, was first discovered in 1936 by Fujii and Matsukawa [18]. Its roots contain diosgenin, which is a compound often used in the manufacturing of progesterone and other steroid drugs. The main intermediate isolated from diosgenin is 16-DPA (16 dihydropregenolone acetate) which can further be synthesized to any desired steroid hormone used in various formulations including oral contraceptive pills [19]. The tuber is one of the

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richest sources for this valuable steroid sapogenin. Cortisone has been proven to be of great value in the treatment of a large number of diseases, such as rheumatic, ophthalmic disorder, and allergic states in idiopathic thrombocytopenic purpura. Being rich in saponin, locally the crushed rhizomes are given with kneaded flour to oxen for general complaints. The plant contents are utilized in the preparation of various injection and tablets used for birth control pills. The tuber has been eaten for the treatment of poor appetite, chronic diarrhea, asthma, arthritis, dry coughs, frequent or uncontrollable urination, diabetes, and emotional instability. Edible root tuber is also used for washing shawls and woolens cloth. Tuber used to kill lice. Phytochemical analysis showed that D. deltoidea tuber extract contains various constituents; among them some main constituents are flavonoid, phenolics, sugars, starch, diosgenin, ascorbic acid, and citric acid. The process of synthesis was completed within 5 h. The choice of D. deltoidea as reducing and capping agent is based on its rich content of steroid sapogenin known as Diosgenin. Disogenin, a typical steroid sapogenin, compound is the major existing species present in the D. deltoidea tuber aqueous extract [20]. Ghosh et al. used another Dioscorea species known as Dioscorea bulbifera tuber extract for the synthesis of silver, and gold nanoparticles [21]. However, to date, there are no reports on the synthesis of AgNPs using D. deltoidea tuber extract. This paper contributes first experimental evidence to the shape-directing role of [Ag+] and [CTAB] in the synthesis of AgNPs using D. deltoidea tuber extract at room temperature. We have focussed on the evaluation of optical properties of

A

the AgNPs during its formation. The effects of different parameters such as [CTAB], reaction time nucleation and growth of silver nanoparticles have been studied.

2. Experimental 2.1. Materials and methods 2.1.1. Materials and preparation of extract In the month of April, D. deltoidea tubers were collected from the Himalayan inner Pir Panjal Range (Jammu and Kashmir, India) and dried in dark places for six months. After peeling, plant tuber solution was prepared by taking 10 g of thoroughly washed tuber into 500 ml Erlenmeyer flask with 250 ml of sterile distilled water and then heated for 30 min. The resultant mixture was cooled, decanted, and filtered through Whatman no. 1 filter paper, and the filtrate was stored in amber colored air tight bottle at 10 °C and used within a week for the preparation of AgNPs. Double distilled (first time in alkaline KMnO4) water was used as the solvent to the preparation of all required solutions. Silver nitrate (oxidant, AgNO3, Merck India, 99.99%) and CTAB (stabilizer, 99%, Fluka) were used as received without further purification. All glassware apparatus were washed with aqua regia (3:1 HCl and HNO3) and rinsed with deionized water, followed by subsequent drying.

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Wavelength (nm) Fig. 1. UV–visible spectra of AgNPs in the absence (A) and presence of CTAB (=4.0 × 10−4 mol dm−3; B). Reaction conditions: [extract] = 3.3% v/v, [Ag+] = 3.3 (■), 10.0 (●), 16.6 (▲), 33.3 (♦), 50.0 × 10−4 mol dm−3 (○) (A), [Ag+] = 10.0 (■), 16.6 (●), 33.3 × 10−4 mol dm−3 (▲) (B), temperature = 30 °C.

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Wavelength (nm) Fig. 2. UV–visible spectra of AgNPs in the absence (A) and presence of CTAB (=4.0 × 10−4 mol dm−3; B). Reaction conditions: [Ag+ ] = 16.6 × 10 − 4 mol dm− 3 , [extract] = 3.3 (■), 10.0 (●), 16.6 (▲), 23.3 (♦), 33.3% v/v (○) (A), [extract] = 3.3 (■), 10.0 (●), 16.6% v/v (▲) (B), temperature = 30 °C.

S. Hussain et al. / Journal of Molecular Liquids 199 (2014) 489–494

2.1.2. Preparation and characterization of silver nanoparticles In this typical experiment D. deltoidea extract, 3.3% v/v was added in a reaction mixture containing (AgNO3, 5 cm3 of 0.01 mol dm−3 + distilled H2 O for dilution) in the absence and presence of CTAB (4.0 cm3 × 10−4 mol dm−3 of 0.01 mol dm−3). Interestingly, the colorless reaction mixture became yellowish brown indicating the reduction of Ag+ ions into Ag0, which leads to the formation of colloidal silver nanoparticles. Transmission Electron Microscope (Hitachi, and H7 100) was used to establish the morphology of AgNPs. For the sample preparation, yellowish color silver sols were deposited to the copper grid at room temperature. After drying at room temperature, the sample was analyzed at 80 kV. The optical property of AgNPs was analyzed via UV–visible (UV–Vis, Perkin Elmer, Lambda 35) absorption double beam spectrophotometer with a deuterium and tungsten iodine lamp in the range from 300–600 nm at room temperature.

2.1.3. Kinetic measurements Kinetic measurements were carried out in a three necked reaction vessel fitted with a double surface condenser to check the evaporation by adding the required concentrations of AgNO3 , CTAB whenever necessary and water. The progress of the reaction was followed spectrophotometrically by adding the required concentrations of D. deltoidea extract. The absorbance of the appearance of yellowish-brown color was measured at 400 nm at definite time intervals (vide infra).

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3. Results and discussion To the synthesis of stable prefect transparent AgNPs in aqueous solution through chemical reduction method, it is important to choose appropriate stabilizer and reducing agent. The choice of D. deltoidea dry tuber extract as reducing agent is based on its rich content of Diosgenin, a steroidal saponin. UV–vis absorption spectra are very sensitive for silver nanoparticles due to the particle size and their aggregation state, since the silver nanoparticles strongly absorb in the visible region due to surface plasmon resonance (SPR) [22–25]. The formation of AgNPs indicated by the change in color due to the reduction of silver ion during contact to the D. deltoidea tuber extracts. UV–visible spectroscopy is one of the commonly used techniques for characterization of AgNPs. SPR bands are influenced by the size, shape, morphology, composition and dielectric environment of the prepared nanoparticles [26]. The shape of the spectra and the position of the wavelength maximal give initial information about the size and the size distribution of the prepared AgNPs [27]. Therefore, a series of experiments were performed under different experimental conditions and the observed results (spectra and reaction–time plots) are depicted graphically in Figs. 1–4. Fig. 1 shows the UV–visible spectra of the nanoparticles obtained in the absence (A) and presence of [CTAB] = 4.0 × 10−4 mol dm−3 (B) at constant [extract] = 3.3% v/v and temperature = 30 °C with varying [Ag+] = 3.3 (■), 10.0 (●), 16.6 (▲), 33.3 (♦), 50.0 × 10−4 mol dm−3 (○) and 10.0 (■), 16.6 (●), and 33.3 × 10−4 mol dm−3 (▲) for (A) and (B), respectively. These observations indicate that the anisotropic growth of AgNPs was confirmed by the appearance of characteristic SPR band at ca. 400 nm in

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Time (min) Fig. 3. Reaction time plots for AgNPs at different [Ag+] in the absence (A) and presence of CTAB (=4.0 × 10−4 mol dm−3; B). Reaction conditions: [extract] = 3.3% v/v, [Ag+] = 3.3 (■), 10.0 (●), 16.6 (▲), 33.3 (○), 50.0 × 10−4 mol dm−3 (♦) (A), [Ag+] = 10.0 (■), 16.6 (●), 33.3 × 10−4 mol dm−3 (▲) (B), temperature = 30 °C.

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Time (min) Fig. 4. Reaction time plots for AgNP formation at different [extract] in the absence (A) and presence of CTAB (=4.0 × 10−4 mol dm−3; B). Reaction conditions: [Ag+] = 16.6 × 10−4 mol dm−3, [extract] = 3.3 (■), 10.0 (●), 16.6 (▲), 23.3 (○), 33.3% v/v (♦) (A), [extract] = 3.3 (■), 10.0 (●), 16.6% v/v (▲) (B), temperature = 30 °C.

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region which might be due to the anisotropic growth of AgNPs. The increases in absorbance is attributed to the increase in nanoparticle size with reaction time and [Ag+]. With increasing the reaction time, the width of the band has also increased, which may be due to the excitation of different multiple modes present in faceted and anisotropic growth of particles. Figs. 3 and 4 show the effects of [Ag+] and [extract] on the nucleation and growth (kinetic curves) of AgNPs in the absence (Figs. 3A and 4A) and presence of CTAB (Figs. 3B and 4B). We did not observe the appearance of any color at a short reaction time, i.e., 1 h but the reaction rate increased sharply after 90 min and the reaction was completed within ca. 5.0 h without CTAB (Fig. 3A). On the other hand, the reaction was completed within 3 h in the presence of CTAB (Fig. 3B). The reaction–time curve also indicates that absorbance remains constant after 5 h with and 3 h without stabilizer, suggesting the shapedirecting role of CTAB and growth process completed within this period. Fig. 4(A and B) shows that absorbance of AgNPs increases with [extract]. Thus we may safely conclude that morphology of AgNPs strongly depend on the [extract] as well as [CTAB]. The digital images of AgNPs prepared in the absence (A) and presence of CTAB (B) are shown in Fig. 5, respectively, indicating that the typical color of AgNPs strongly depends on the nature and/or types of the stabilizers. The yellowish color intensifies with time showing that the size of the nanoparticles increases (Fig. 5A). After the addition of CTAB intense yellow color appears within a short period of time (Fig. 5B) but the same color does not appear in absence of CTAB (Fig. 5A). From this observation it is clear that CTAB may be playing the role of a catalyst as well as a stabilizer and/or capping agent that increases the reaction rate which completes within 3 h but the same reaction without CTAB completed after 5 h. The perfect transparent yellowish-brown color remains stable with and without stabilizer for months with no visible sign of precipitation, aggregation, or oxidation. AgNPs formed with D. deltoidea dry tuber extract were found to be very stable, possibly because of the starch, diosgenin, ascorbic acid, citric acid and various other constituents present in the extract which not only stabilize it but also capped it for long times and also prevented it from agglomeration, even after 30 days. The photochemical studies and various other analyses indicate that this species is cultivated mainly

Fig. 5. Optical images of AgNP formation in the absence (A) and presence of CTAB (= 4.0 × 10 − 4 mol dm − 3 ; B) at different time intervals. Reaction conditions: [extract] = 3.3% v/v, [Ag+] = 16.6 × 10−4 mol dm−3, temperature = 30 °C.

the UV–Vis region. On increasing the reaction-time, a sharp peak begins to develop. In the presence of stabilizer, i.e., CTAB, the reaction completed within 3 h and the spectra show a SPR band at 400 nm with [Ag+] = 16.6 × 10−4 mol dm−3. Fig. 2 shows the effects of extract concentrations on the UV–visible spectra of the nanoparticles obtained at constant [Ag+] = 16.6 × 10−4 mol dm−3 in absence (Fig. 2A) and presence of [CTAB] = 4.0 × 10−4 mol dm−3 (B). The [extract] were varied from 3.3 to 33.3% v/v and 3.3 to 16.6 for Fig. 2(A) and (B), respectively. Interestingly, the absorbance increases with increasing [extract], indicating that the extract concentrations has significant effect on the morphology of the AgNPs. Inspections of Figs. 1 and 2 suggest that the resulting spectra show one SRP broad band and a weak shoulder in the whole UV–vis.

CH3

O CH3 CH3

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Scheme 1. Mechanism to the reduction of Ag+ ions into metallic silver by Diosgenin.

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for diosgenin. From Diosgenin the main intermediate isolated is 16-DPA (16 dihydropregenolone acetate). This 16-DPA (16 dihydropregenolone acetate) is the basic material for the synthesis of any desired steroidal drugs and various other formulations [19]. This diosgenin is mainly responsible for reducing the Ag+ to Ag0, but the shape is possibly believed to be controlled by chemical factors like ascorbic acid, citric acid, and starch. Mechanism to the reduction of Ag+ ions into metallic Ag0 by main constituent of D. deltoidea dry tuber extract is summarized in Scheme 1. In Scheme 1, hydroxy groups of reducing steroidal saponin diosgenin reduce Ag+ into Ag0. The neutral atom Ag0 reacts with Ag+ to form the + 2+ relatively stabilized Ag+ 2 clusters. Ag2 clusters dimerize to yield Ag4 (yellow-color silver sol; stable species for a long time in the presence of a diosgenin even under air and growth stops at the stage of this species).

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corresponding selected area electron diffraction of AgNPs was conducted (Fig. 7C), which also corroborate the small size and crystalline nature of the silver nanoparticles. The six-fold symmetry of the diffraction spots indicates that the surface of particles was bounded by {111} faces. The other sets of spots could be identified as {211}, {222}, {411} and {422} planes according to the pure face-centered cubic (fcc) silver structure. These results are in best agreement with the results of Bakshi et al. [14,22], due to the capping ability of zein protein, lipids and/or normal surfactants originates from electrostatic interactions between the polar head groups and charged nanoparticle surface; surface passivation exits in the form of a lipid bilayer which provides good steric and charge stabilization (due to Derjaguin–Landau–Verwey–Overbeek

3.1. TEM images Morphology of the AgNPs (reaction conditions: [Ag + ] = 16.6 × 10−4 mol dm−3, [extract] = 10.0% v/v, temperature = 30 °C, and [CTAB] = 4.0 × 10−4 mol dm−3, were determined by using TEM measurements. The results of these two experiments are given in Figs. 6 and 7. TEM image result shows the mix kind of AgNPs morphology and diameter ranging from 3.0 nm to 70 nm. The AgNPs look like a spherical, truncated triangular nanoplates or nanodisks with some irregular like structure and highly poly-dispersed (Fig. 6A, and B). In order to establish the effect of CTAB on the morphology of AgNPs, TEM samples were taken at the same time under the similar experimental conditions in the presence of CTAB (Fig. 7). Interestingly, TEM images show that the AgNPs aggregated in unsymmetrical manner lead to the formation of cloud-like structure of silver in the presence of CTAB (morphology has been changed entirely from truncated triangular nano-plates to cloud-like). Diffraction rings can be seen when

Fig. 6. TEM images of AgNPs. Reaction conditions: [Ag+] = 16.6 × 10−4 mol dm−3, [extract] = 10.0% v/v, temperature = 30 °C.

Fig. 7. TEM images (A, B) and selected electron diffraction ring patterns (C) of AgNPs. Reaction conditions: [Ag + ] = 16.6 × 10 − 4 mol dm − 3 , [extract] = 10.0% v/v, [CTAB] = 4.0 × 10−4 mol dm−3, temperature = 30 °C.

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theory) to colloidal nanoparticles. Morphology of silver nanoparticles can be controlled not only by the [CTAB] but also by the reaction–time alteration and [Ag+]. Result of TEM images indicates that the nanospheres dominated the population of the synthesized AgNPs as evident from TEM images, in some cases anisotropy was observed similar to other reports [28]. This anisotropy among the AgNPs could be due to the recent report by Huang et al. mentioning that nascent silver crystals formed using leaf powder of Cinnamomum camphora were gradually enclosed by protective molecules, which as a result eliminated rapid sintering of smaller nanoparticles, resulting in the formation of nanotriangles [29]. 4. Concluding remarks In summary, we have reported an easy, simple one-pot green chemical route to the preparation of stable Ag-nanostructures using D. deltoidea extract in the absence and presence of CTAB. The presence of several SPR bands in the UV–vis. spectra is due to the highly anisotropic growth of AgNPs. Out of various constituents present in D. deltoidea extract, diosgenin is mainly responsible for the reduction of Ag+ ions into the metallic Ag0. TEM results indicate that the mixed morphology of AgNPs looks like a spherical, truncated triangular nanoplates or nanodisks with some irregular like structure and highly poly-dispersed. Capping on AgNPs might be due to the combined effects of citric acid, ascorbic acid and starch on the nucleation and growth processes. Acknowledgment This project was funded by the Deanship of Scientific Research (DSR), King Abdulaziz Univeristy, Jeddah, under grant no. (MS/15/ 301/1434). The authors, therefore, acknowledge with thanks the DSR for the technical and financial support.

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