Study on synthesizing silver nanoparticles by using Muntingia calabura leaf extract Insights from experimental and theoretical studies Cite this paper Vietnam J Chem , 2021, 59(5), 606 611 Research Ar[.]
Cite this paper: Vietnam J Chem., 2021, 59(5), 606-611 Research Article DOI: 10.1002/vjch.202100012 Study on synthesizing silver nanoparticles by using Muntingia calabura leaf extract: Insights from experimental and theoretical studies Truong Tan Trung1*, Ngo Van Cuong2, Le Thi Thu Hong2, Nguyen Thi Nhu Quynh2, Cao Van Du2* Institute of Research and Applied Technological Science, Dong Nai Technology University Nguyen Khuyen, Trang Dai, Bien Hoa, Dong Nai 76000, Viet Nam Faculty of Pharmacy, Lac Hong University 10 Huynh Van Nghe, Buu Long, Bien Hoa, Dong Nai 76000, Viet Nam Submitted February 16, 2021; Revised May10, 2021; Accepted May 13, 2021 Abstract In this paper, a novel approach for green chemistry was employed for the synthesis of silver nanoparticles (AgNPs) using aqueous leaf extracts of Muntingia calabura (M calabura) Characterization of AgNPs such as the shape, size, morphology, and stability was made using Ultraviolet-Visible (UV-Vis) spectroscopy, and transmission electron microscopy (TEM) The results showed a surface plasmon band around 427 nm when analyzed via UV-Vis spectroscopy, indicated the silver particles of nano dimensions The TEM study revealed that spherical shapes sizing from to 16 nm with the average size was 11±5 nm were observed for the obtained sample The density functional theory (DFT) studies reveal that the quercetin (one of the flavonoids presented in M calabura) is responsible for behaving as a reducing agent for the reduction of Ag+ ion into Ag0 under different physicochemical conditions Keywords Muntingia calabura, silver nanoparticle, quercetin, Density Functional Theory (DFT) INTRODUCTION Nanoparticles (NPs) are particles having the size from to 100 nm.[1] In that range of size, they present special properties differing from bulk materials In particular, silver nanoparticles (AgNPs) exhibited antibacterial activity, therefore they are widely applied in medical products The suggested mechanisms for the antibacterial activity of AgNPs are: (1) the adhesion of AgNPs to the surface of the cell wall and cell membrane disturbs metabolic processes (2) penetration of AgNPs into the cell destroys intracellular structures (mitochondria, vacuoles, ribosomes) and structures of biological molecules (proteins, DNA), (3) AgNPs cause cytotoxicity by producing oxidative free radicals.[2] In the context of bacterial resistance to conventional antibiotics, AgNPs are considered a new hope for mankind To synthesize NPs, two common methods are used: (1) the bottom-up (ions are reduced into atoms, then those atoms joined together to form NPs) and (2) the top-down (the bulk materials are broken down into the NPs).[1] In the bottom-up method, reducing agents can be electromagnetic waves, chemical reducing agents (citric acid, ascorbic acid), or herbal extracts (green synthesis method).[1] Muntingia calabura leaf have activities such as antibacterial, anti-oxidant and their main components are polyphenols (tannins, flavonoids)[3-5] Polyphenols can be reducing agents in AgNPs synthesis Besides, their structure is also capable of being a stabilizer.[6] Recently, two new biosynthetic sources, Muntingia calabura leaf were employed and reported to obtained AgNPs.[7,8] Quercetin (molecular formula C15H10O7) is a polyphenolic flavonoid found in many fruits, vegetables, leaves, and grains[9], its also found in Muntingia calabura.[4] It can be the reduction of Ag ions via reductionoxidation reaction.[9] However, the effectiveness of the use of these leaf extracts as reducing and stabilizing agents has not been studied by quantum chemistry Thus, in this present study, AgNPs are synthesized from AgNO3 solution and Muntingia calabura leaf extract under different physicochemical conditions The Density Functional Theory (DFT) provides a basis for understanding the exact mechanism of how biomolecule present in Muntingia calabura (quercetin one of the main components in Muntingia calabura leaf extract) interact with silver ions and the process of their transformation into silver nanoparticles 606 Wiley Online Library © 2021 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH Vietnam Journal of Chemistry MATERIALS AND METHODS 2.1 Synthesis of silver nanoparticles 2.1.1 Preparation of leaf extract Based on the references, using extraction method with boiled water.[8,10] Leaves of Muntingia calabura are collected in Dong Nai province, Vietnam in January, 2020 They are washed with distilled water and then dried at 70 °C in a drying oven (Memmert, Germany) until their humidity lower than 13% Dried materials are ground, sifted Materials under sieve of mm in diameter and above sieve of 0.5 mm in diameter are used for extracting The aqueous leaf extract of Muntingia calabura was prepared as follows: 20 g of dry material was transferred into a 1000-mL Erlenmeyer flask containing 800 mL of distilled water This mixture was boiled for hours on infrared stove at 80 °C The water extract is filtered through a filter paper with a filter pore size of 22 μm and then heated on a water bath (Memmert, Germany) at 80 oC The soft extract with the moisture of 31.87 %, pH 5.06-5.29 was then stored at °C in a refrigerator The soft extract is dissolved in water (solution A) at the different rates: 0.5 g/100 mL (0.5 %), g/100 mL (1 %), 1.5 g/100 mL (1.5 %), g/100 mL (2 %) and 2.5 g/100 mL (2.5 %) to evaluate the most suitable concentration for synthesizing AgNPs 2.1.2 Preparation of 0.03 M Silver nitrate solution A solution of 0.003 M AgNO3 was prepared by dissolving 0.51 g AgNO3 (origin of China, purity 99.8%) with sufficient water in a 100-mL volumetric flask 2.1.3 Preparation of PVP % solution The PVP % solution was prepared by dissolving g of polyvinylpyrrolidone (PVP) in 100 mL of deionized water at room temperature Truong Tan Trung et al measuring the UV-Visible spectrum on a Thermo EVO300 PC UV machine at the Department of Analytical Chemistry, Lac Hong University using scanning method with wavelength from 300 to 600 nm The measuring mixture can be diluted suitably if its absorbance peak is too high 2.1.6 TEM analysis of silver nanoparticles Transmission Electron Microscopy (TEM) analysis was carried out using a JEM-1400 microscope at Ho Chi Minh University of Technology, Vietnam National University – HCMC to determine the synthesized nanoparticles 2.2 DFT calculations The quantum chemical calculations were performed using density functional theory (DFT) with Becke’s[11] three-parameter hybrid model, Lee, Yang, and Parr’s[12] correlation functional under 631+G(d,p) basis set The optimized molecular structure has been visualized using GaussView program.[13] The highest occupied molecular orbital energy (EHOMO) and lowest unoccupied molecular orbital energy (ELUMO), the energy gap between HOMO and LUMO (E) value were obtained All calculations were carried out using the GAUSSIAN 16 suite of program.[14] RESULTS AND DISCUSSION 3.1 Characterization of AgNPs The reduction of silver salt to AgNPs exposure to aqueous extract of Muntingia calabura leaf could be followed by the change of color were shown in Figures 1a and 1b UV-Vis spectroscopy has proven to be a useful spectroscopic method for the detection of synthesized metallic nanoparticles The change in the colors and UV-Vis measurement of the concentration-effect of extracts on the synthesis of AgNPs are shown in figures and 3a 2.1.4 Synthesis of green silver nanoparticles (AgNPs) Add mL solution A, mL of 0.03 M AgNO3, 20 mL PVP % into a 100-mL beaker, the mixture is stirred on a magnetic stirrer at a speed of 400 rpm, temperature of 35 oC in 30 minutes 2.1.5 UV-Vis spectra analysis The reduction of silver ions was observed by Figure 1: (a) Aqueous extract of Muntingia calabura leaf with silver nitrate solution before and (b) after the formation of silver nanoparticle © 2021 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 607 Vietnam Journal of Chemistry Figure shows the color change in the formation of AgNPs The biomolecules such as quercetin in Muntingia calabura leaf extract for the reduction of silver ions to AgNPs with PVP that act as stabilization and against agglomeratio As the concentration of the extract increases, the amount of reducing agent will increase correspondingly The absorbance increases but wavelengths of absorbance have no change, therefore the amount of the produced AgNPs increases but the particle size changes not significantly (figure 3a) Figure 2: Colors of silver nanoparticle at different concentrations of Muntingia calabura leaf extract Study on synthesizing silver nanoparticles… Figure 3b shows that the surface plasmon resonance band for AgNPs absorbed at 427 nm, which belongs to the characteristic region of AgNPs (range from 400 to 440 nm, the smaller the AgNPs are, the lower wavelength absorption they have).[15] However, after storage of 2.5 months at room temperature (protected from light), the samples with extract concentration of 1.5 %, %, and 2.5 % turn dark brown, opaque It showed that when the concentration of AgNPs in the reaction mixture increased, the probability of AgNPs colliding and agglomerating with each other was higher, thereby forming the larger silver nanoparticles The % sample remained the same color as the original, with no precipitation or cloudiness Its maximum absorption wavelength is increased not significantly (from 427 to 430 nm) Therefore, the extract concentration of % is chosen for synthesizing of AgNPs (a) (b) Figure 3: (a) UV-Vis spectra of silver nanoparticle at different concentrations of Muntingia calabura leaf extract and (b) before and after 2.5 months of strorage The results of TEM image analysis (figure 4) showed that the spherical AgNPs have the size from 6-16 nm, the average size was 11±5 nm In comparison with AgNPs synthesized by using Muntingia calabura extract in previous research, these AgNPs have smaller sizes and lower wavelength of maximum absorption In the research of Inija Udhaya et al (2018), AgNPs have the size 28-43 nm and the maximum absorption at 443 nm.[10] A recent study of Mohd Azlan Ahmad et al (2020) showed that AgNPs synthesized by using Muntingia calabura extract have the maximum absorption at 425-430 nm, the size ranges from 22 to 37 nm.[8] 3.2 DFT calculations The molecular orbital (MO) is a very important concept in quantum chemistry It is used to describe the behavior of electrons in a molecule The highest occupied molecular orbital (HOMO) and lower unoccupied molecular orbital (LUMO) are the two most important molecular orbitals in a molecule as both are used to describe various chemical properties such as reactivity and kinetics Several chemical parameters, such as ionization potential, electron affinity, electronic chemical potentials, global hardnesses, electrophilicity, electronegativity and chemical softnessess can be evaluated from the HOMO, LUMO energy.[16,17] In addition, the value of E provides a measure for the stability of the formed complex on the metal surface The molecular geometry optimization calculation was performed with the Gaussian 16 suite of program by using DFT method with B3LYP/6-31+G(d,p) basis set (Figure 5a) The HOMO-LUMO energy gap of quercetin calculated by DFT methods at the same basis set, and their image is displayed by GaussView © 2021 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 608 Vietnam Journal of Chemistry software as shown in figure 5b that the positive and negative phase is represented in red and green color, Truong Tan Trung et al respectively Figure 4: The TEM image and size distribution of the synthesized silver nanoparticle (a) (b) Figure 5: Pictures of (a) the optimized structures and (b) HOMO-LUMO energy gap of the quercetin molecules calculated by DFT methods at the B3LYP/6-31+G(d,p) level As seen in figure 5b, the EHOMO value is -6.04 eV indicates that quercetin is the greater ease of electron-donating to the unoccupied d orbital of silver metal and the reduction of Ag+ to Ag0 occurs when quercetin gets absorbed on the surface of AgNO3 salt, which is in good agreement with the mechanism proposed from previously reported by Jain et al [9] The HOMO orbital is residing on O−H groups of the quercetin and gives a clear explanation that the electron-donating ability is enhanced by the electron lone pair of the oxygen atom This is the reason why there were dispersion and stabilization of AgNPs interconnected as interconnected silver particles was the presence of the chemical bond among the electron-rich oxygen that exists in the quercetin and the silver orbital through their sole pair electrons.[18] The ELUMO value is -2.09 eV indicates that these compound can be electronacceptors through a charge transfer mechanism In the pattern of the LUMO orbital, the electron density is completely focused on an aromatic ring Another parameter to be given importance is the E energy gap The lower value of E(EHOMO - ELUMO) indicates high reactivity of quercetin and the need only minimum of energy (-3.96 eV) is required to remove the electron from the oxygen atom which results in increased reducing ability to reduce Ag+ to Ag0 Besides, the chemical properties of quercetin such as ionization potential (I), electron affinity (A), electronic chemical potentials (), global hardness (), electrophilicity () also provides through the value of EHOMO and ELUMO are tabulated in table © 2021 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 609 Vietnam Journal of Chemistry Study on synthesizing silver nanoparticles… Table 1: Frontier molecular orbital energies (in eV unit) and global reactivity descriptors of quercetin by the B3LYP/6-31+G(d,p) basis set EHOMO -6.04 a,b,c ELUMO -2.09 E -3.96 I = -EHOMO 6.04 A = - ELUMO 2.09 = (I-A)/2 a 1.98 = -(I+A)/2 b -4.07 = 2/2 c 4.18 Taken from Ref [16], [17] From table 1, the chemical potential () is negative (-4.07 eV) indicating that the quercetin is stable and does not decompose spontaneously into other compound Similarly, the electrophilicity () plays an excellent role in describing the chemical reactivity of a compound Table shows that the index (4.18 eV) is strongly electrophilic in quercetin compound, which is in good agreement with the obtained results from Song et al when the O−H group is considered the most reactive site in the quercetin compound.[19] CONCLUSION The reduction of Ag+ ions to AgNPs by the leaf extract from the M calabura has been successfully performed The formation of silver nanoparticles is confirmed by UV-Vis and TEM measurements The synthesized AgNPs exhibited a strong absorption at 427 nm The particle size from to 16 nm of AgNPs was determined by TEM analysis with an average size of 11±5 nm The DFT studies reveal that the quercetin presented in the M calabura plays an important role in reduc silver ions to silver nanoparticles and provide stability against agglomeration Acknowledgments The research is a part of the project LHU-RF-MP-18-02-09, funded by Lac Hong University Various Ethanol Concentration, J Food Pharm Sci., 2020, 8(1), 174-184 Z A Zakaria, A S Sufian, K Ramasamy, N Ahmat, M R Sulaiman, A K Arifah, A Zuraini, M N Somchit In vitro antimicrobial activity of Muntingia calabura extracts and fractions, Afr J Microbiol Res., 2010, 4(4), 304-308 E C B A Alegria, A P C Ribeiro, M Mendes, A M Ferraria, A M B Rego, and A J L Pombeiro., Effect of phenolic compounds on the synthesis of gold nanoparticles and its catalytic activity in the reduction of nitro compounds, Nanomaterials, 2018, 8(5), 320 A W Wahab, A Karim, N La Nafie, Nurafni, and I W Sutapa Synthesis of silver nanoparticles using Muntingia calabura L Leaf extract as bioreductor and applied as glucose nanosensor, Orient J Chem., 2018, 34(6), 3088 M A Ahmad, S Salmiati, M Marpongahtun, M R Salim, J A Lolo, A Syafiuddin Green Synthesis of Silver Nanoparticles Using Muntingia calabura Leaf Extract and Evaluation of Antibacterial Activities, Biointerface Res Appl Chem., 2020, 10, 6253-6261 S Jain, M S Mehata Medicinal plant leaf extract and pure flavonoid mediated green synthesis of silver nanoparticles and their enhanced antibacterial property, Sci Rep., 2017, 7(1), 1-13 10 C Iniya Udhaya Biosynthesis of Silver Nanoparticles using Aqueous Leaf Extract of Muntingia calabura Linn, Int J Nanobiotechnolo., 2018, 4(1), 1-7 11 A D Becke Density-functional exchange-energy approximation with correct asymptotic behavior, Phys Rev A, 1988, 38(6), 3098 REFERENCES M Rath, S S Panda, N K Dhal Synthesis of silver nano particles from plant extract and its application in cancer treatment: A review, Int J Plant Anim Environ Sci., 2014, 4(3), 137-145 12 C Lee, W Yang, R G Parr Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density, Phys Rev B, 1988, 37(2), 785 T C Dakal, A Kumar, R S Majumdar, V Yadav Mechanistic basis of antimicrobial actions of silver nanoparticles, J Front Microbiol., 2016, 7, 1831 13 R Dennington, T A Keith, J M Millam, KS, USA, GaussView 6.0 16, 2016 S Ayesha, K B Premakumari, S Roukiya, Vithya, Savitha Antioxidant activity and estimation of total phenolic content of Muntingia Calabura by colorimetry, Inte J ChemTech Res., 2010, 2(1), 205208 R D Pertiwi, Suwaldi, R Martien, E P Setyowati Radical Scavenging Activity and Quercetin Content of Muntingia calabura L Leaves Extracted by 14 M Frisch, G W Trucks, H B Schlegel, G E Scuseria, M A Robb, J R Cheeseman, G Scalmani, V Barone, B Mennucci, G A Petersson, H Nakatsuji, M Caricato, X Li, H P Hratchian, A F Izmaylov, J Bloino, G Zheng, J L Sonnenberg, M Hada, M Ehara, K Toyota, R Fukuda, J Hasegawa, M Ishida, T Nakajima, Y Honda, O Kitao, H Nakai, T Vreven, J A Montgomery, J E Peralta, F Ogliaro, M Bearpark, J J Heyd, E Brothers, K N © 2021 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 610 Vietnam Journal of Chemistry Kudin, V N Staroverov, R Kobayashi, J Normand, K Raghavachari, A Rendell, J C Burant, S S Iyengar, J Tomasi, M Cossi, N Rega, J M Millam, M Klene, J E Knox, J B Cross, V Bakken, C Adamo, J Jaramillo, R Gomperts, R.E Stratmann, O Yazyev, A J Austin, R Cammi, C Pomelli, J W Ochterski, R L Martin, K Morokuma, V G Zakrzewski, G A Voth, P Salvador, J J Dannenberg, S Dapprich, A D Daniels, Ö Farkas, J B Foresman, J V Ortiz, J Cioslowski, D J Fox Gaussian 16, Wallingford CT., Gaussian Inc, 2016 15 O Długosz and M Banach Continuous production of silver nanoparticles and process control, J Clust Sci., 2019, 30(3), 541-552 16 R G Pearson Chemical hardness and density Truong Tan Trung et al functional theory, J Chem Sci., 2005, 117(5), 369377 17 R G Pearson Absolute electronegativity and hardness correlated with molecular orbital theory, Proc Natl Acad Sci USA., 1986, 83(22), 84408441 18 S B Aziz, G Hussein, M A Brza, S J Mohammed, R T Abdulwahid, S R Saeed, A Hassanzadeh Fabrication of interconnected plasmonic spherical silver nanoparticles with enhanced localized surface plasmon resonance (LSPR) peaks using quince leaf extract solution, Nanomaterials, 2019, 9(11), 1557 19 X Song, Y Wang, L Gao Mechanism of antioxidant properties of quercetin and quercetinDNA complex, J Mol Model., 2020, 26, 1-8 Corresponding authors: Truong Tan Trung Institute of Research and Applied Technological Science Dong Nai Technology University Nguyen Khuyen, Trang Dai, Bien Hoa, Dong Nai 76000, Viet Nam E-mail: truongtantrung@dntu.edu.vn Cao Van Du Faculty of Pharmacy, Lac Hong University 10 Huynh Van Nghe, Buu Long, Bien Hoa, Dong Nai 76000, Viet Nam E-mail: caovandulhu@gmail.com © 2021 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 611 ... Colors of silver nanoparticle at different concentrations of Muntingia calabura leaf extract Study on synthesizing silver nanoparticles? ?? Figure 3b shows that the surface plasmon resonance band for... compound.[19] CONCLUSION The reduction of Ag+ ions to AgNPs by the leaf extract from the M calabura has been successfully performed The formation of silver nanoparticles is confirmed by UV-Vis and TEM... analysis The reduction of silver ions was observed by Figure 1: (a) Aqueous extract of Muntingia calabura leaf with silver nitrate solution before and (b) after the formation of silver nanoparticle