ISSN 00125016, Doklady Physical Chemistry, 2015, Vol. 464, Part 2, pp. 234–237. © Pleiades Publishing, Ltd., 2015. Original Russian Text © L.N. Shirokova, V.A. Alexandrova, 2015, published in Doklady Akademii Nauk, 2015, Vol. 464, No. 4, pp. 440–443.
PHYSICAL CHEMISTRY
RadiationChemical Synthesis of Silver Nanoparticles in Carboxymethyl Chitin L. N. Shirokova and V. A. Alexandrova Presented by Academician S.N. Khadzhiev March 3, 2015 Received May 18, 2015
Abstract—New radiationinduced bactericide metal–polymer nanosystems based on 6Ocarboxymethyl chitin and silver nanoparticles were prepared. Variation in exposure dose and extent of filling with silver ions allowed the preparation of macromolecular systems with silver nanoparticles of controllable size (1–5 nm). DOI: 10.1134/S0012501615100036
Unique electrophysical, catalytic, and other prop erties of metal–polymer nanocomposite materials determine the interest of researchers to develop meth ods of synthesis of metal nanoparticles immediately within the polymer matrix [1, 2]. Macromolecular compounds [3], in particular chitin derivatives, can not only behave as stabilizers of resulting metal nano particles but also directly participate in the process of nanoparticle formation and act as a polymer matrix that control the size and shape of nanoparticles [4–6]. In spite of the expected growth of metal binding ability for carboxymethylated chitosan, such a behav ior has not been revealed [4]. It should be taken into account, however, that the preparation of metal nano particles in the carboxymethyl chitosan matrix was carried out in an acidic medium (2% acetic acid) [4]. In an acidic medium, carboxylic groups do not disso ciate, and macromolecules in solution adopt a shape of a dense coil that hampers the process of uniform distribution of silver and other metal ions across the macromolecule. It is recommended to maintain pH 8–9 for efficient reduction of metal ions into nanopar ticles in these systems [3, 7]. Carboxylic groups in an alkaline medium are dissociated, and macromolecules have a shape of a loose coil, which favors the uniform distribution of silver ions over the carboxylic groups of a macromolecule to form metal–polymer complexes [3]. Thus, carboxymethyl chitosan macromolecule at different pH values changes its conformation that has different effect on the stability of resulting metal nano particles, which was confirmed in [6]. In the present paper, we report the synthesis of new radiationinduced bactericide metal–polymer nano
Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, Leninskii pr. 29, Moscow, 119991 Russia email:
[email protected],
[email protected]
systems based on 6Ocarboxymethyl chitin and silver nanoparticles at ambient pH 8.5. It is known that nontoxic [8] biodegradable water soluble chitin derivative, 6Ocarboxymethyl chitin, is used as a biosensor [9], drug carrier [10], implant in tissue engineering for bone tissue restoration [11], etc. The presence of carboxylic groups in the side chain of 6Ocarboxymethyl chitin causes the ability of this polyelectrolyte to form complex selforganizing sys tems with metal ions. Taking this feature into account, the aim of this work is to study the effect of filling of a 6Ocarboxymethyl chitin macromolecules with silver ions and exposure dose on the size and shape of silver nanoparticles formed in the course of radiation chemical reduction of the ions. The method of radiationchemical reduction of ions into nanoparticles in aqueous solutions has a number of considerable advantages as compared with chemical reduction: the lack of admixtures of chemi cal reducing agents and byproducts of their transfor mations in the resulting nanoparticles and polymer matrix, as well as the possibility to control radiation chemical reduction processes. This leads to the prepa ration of nanoparticles of prescribed size. Moreover, solvated electron (eaq) generated from the radiolysis of water is a pure and efficient reducing agent (E0 = –2.9 V) [6]. The monitoring of formation of silver nanoparti cles in a colloid solution and the assessment of their stability was carried out by UV–Vis spectrophotome try from the change in the absorbance at the plasmon resonance maximum of the resulting silver nanoparti cles at 420 nm (Figs. 1a, 1c). The size and shape of sil ver nanoparticles were studied by transmission elec tron microscopy. The initial silver ion concentration is known to affect essentially the process of silver nanoparticles formation; therefore, in this work, for the radiation chemical synthesis of nanosized particles, we studied
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2.5 2.0 1.5
20 µm
3 2
Absorbance, arb. units
1.0 1 0.5 (a) 300
400
500
600
700
800
(b)
50 nm
2.5 2.0 1.5 20 µm
3' 1.0
2' 1'
0.5 (c) 300
400
500
600
700
800 λ, nm
(d)
50 nm
Fig. 1. Electronic absorption spectra of silver nanoparticles prepared in a 0.5 wt % aqueous solution of 6Ocarboxymethyl chitin at absorbed dose of (a) 2 and (c) 10 kGy with the extent of filling with silver ions of (1, 1') 0.2, (2, 2') 0.4, and (3, 3') 0.6; and TEM images of silver nanoparticles prepared in the matrix of 6Ocarboxymethyl chitin with the extent of filling with silver ions of 0.2 at an absorbed dose of (b) 2 and (d) 10 kGy.
three filling degrees of 6Ocarboxymethyl chitin polyelectrolyte macromolecules with silver ions—0.2, 0.4, and 0.6—of the maximal possible filling (0.65) in accordance with the sorption isotherm of silver ions by the polymer. Figure 1a shows the electronic spectra of macro molecular systems, which contain silver nanoparticles prepared on the basis of 6Ocarboxymethyl chitin with the extent of filling with silver ions of 0.2 (1), 0.4 (2), and 0.6 (3) at an exposure dose of 2 kGy. For all described systems, absorption bands in the range 340–550 nm are identical, and the absorbance of silver nanoparticles increases with filling extent. Absorption bands in the region 340–550 nm are related to Agn oli gomeric clusters containing different numbers of metal atoms [7, 12]. DOKLADY PHYSICAL CHEMISTRY
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Analysis of the results allows us to draw a conclu sion that 6Ocarboxymethyl chitin can stabilize intermediate silver clusters of different nuclearity with a particle size of 1–5 nm (Fig. 1b) resulting from radi ationchemical reduction and acting as precursors of metal nanoparticles. Figure 1c shows the electronic spectra of nanosys tems obtained with the use of 6Ocarboxymethyl chitin with the extent of macromolecule filling with silver ions of 0.2 (1'), 0.4 (2 '), and 0.6 (3 ') at an expo sure dose of 10 kGy. The spectra confirm that the radi ationchemical reduction of silver ions into nanopar ticles in the studied polyelectrolytes proceeds efficiently, the absorbance reaching 2.3–2.4 (at λmax = 420 nm). The TEM image of nanosystems shows that spher ical silver nanoparticles 1–5 nm in size are formed at 2015
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an exposure dose of 10 kGy for 6Ocarboxymethyl chitin at the filling extent with silver ions of 0.2 (Fig. 1d) and 0.4. An increase in the extent of macromolecule filling with silver ions to 0.6 leads to formation of larger particles of ellipsoid shape up to 10–15 nm in size. Microdiffractograms show reflections corresponding to the crystal lattice of silver (Figs. 1b and 1d). Thus, in the radiationchemical synthesis of silver nanoparticles from silver ions, the polymer matrix of 6Ocarboxymethyl chitin serves as a microreactor where the ions preliminary uniformly distributed over the carboxylic groups of the polymer are reduced at pH 8.5 to give silver clusters and then nanoparticles. Variation in exposure dose and the extent of macro molecule filling with silver ions afforded the prepara tion of macromolecular systems with silver nanoparti cles of controllable size. These nanoparticles sepa rated from each other by macromolecule structural fragments display high stability. It was established in invivo experiments that the designed biodegradable colloidal solutions of silver nanoparticles exhibit a pronounced concentration dependent bactericidal activity toward the strains of both grampositive Staphylococcus aureus and gram negative Salmonella tythimurium bacteria [13, 15].
The obtained new macromolecular nanosystems can be used as antibacterial medium, in particular, in designing bactericidal liquid plasters, as a component for materials for bone tissue restoration in reparative medicine, and in electronics and optoelectronic appli cations (conducting ink). EXPERIMENTAL Chitin ((1 → 4)2acetamido2deoxyβDglu can) used in the work (Bioprogress, Russia) was obtained from crab shells and claws and had a molec ular weight of (40–45) × 104. Sodium hydroxide (reagent grade), isopropanol CH3CH(OH)CH3 (high purity grade), monochloroacetic acid ClCH2COOH (reagent grade), and silver nitrate AgNO3 (reagent grade) were used as received. Watersoluble polymer 6Ocarboxymethyl chitin was obtained from chitin by the method described in [14]. Preliminary activated chitin was treated in the presence of an NaOH excess with ClCH2COOH as a carboxylating agent in an aqueous alcohol medium at elevated temperature. The resultant 6Ocarboxyme thyl chitin had a weightaverage molecular weight of 7 × 104 and a carboxylation degree of 1.0 (Scheme 1).
HOH H O
O HO
O HO
NaOH ClCH2COOH
NH
H H O
C
HOCH2COONa H O NH
H H
H
O
CH3
C
H CH3
n
m
Scheme 1.
Free (unbound) silver ions concentration [Ag+]f was determined by potentiometry with the use of an ELIS131Ag ionselective electrode and a glass refer ence electrode filled with 0.1 M KNO3. Potentiomet ric titration was performed on a Radiometer PHM 82 Standard pHmeter (Canada) at 20°С. To prepare working solutions, a definite amount of 0.1 M AgNO3 solution and 2 mL of 1.0 M KNO3 supporting electro lyte was added to 10 mL of 0.5 wt % solution of 6O carboxymethyl chitin in water at pH 8.5. The extent of macromolecule filling with silver ions (Θbound) was cal culated from the measurement results [3]: Θbound = (cAg – [Ag+]f)/[CMC], where cAg is total silver concentration in solution, M; [Ag+]f is free silver ions concentration, M; [CMC] is the normality of 6Ocarboxymethyl chitin in solu tion, basemol/L. Electronic absorption spectra were recorded on a Carl Zeiss Specord M40 UV–Vis spectrophotometer
(Germany) in a quartz cuvette with the 1mm optical path length at 20°С, bidistilled water was used as a ref erence solution. Electron microscopy images were obtained on a FEI Tecnai electron microscope (USA). The microscope included an Xray spectral microanalysis unit. Radiationchemical synthesis of silver nanoparticles in 6Ocarboxymethyl chitin matrix [13, 15]. Isopro panol CH3CH(OH)CH3 (0.05 mL) and an aqueous solution of AgNO3 were added to 3 mL of 0.5 wt % solution of 6Ocarboxymethyl chitin in water until a concentration of 3.5, 7.0, and 10.1 mM in a 6Ocar boxymethyl chitin solution. The obtained solution containing 6Ocarboxymethyl chitin and AgNO3 was purged with argon for 1.5 h and carefully sealed. Then, the solution was exposed to γ radiation from 60Co using a RKhMγ20 isotope radiationchemical installation (Russia) with dose from 2 to 10 kGy at absorbed dose rate 0.14 ± 0.01 Gy/s.
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ACKNOWLEDGMENTS We are grateful to the Shared Facility Center, Mos cow State University, for providing TEM analysis and Xray microanalysis. REFERENCES 1. Dos Santos, C.A., Seckler, M.M., Ingle, A.P., Gupta, I., Galdiero, S., Galdiero, M., Gade, A., and Rai, M., J. Pharm. Sci., 2014, vol. 103, no. 7, pp. 1931–1944. 2. Lai, C.Y., Cheong, C.F., Mandeep, J.S., Abdullah, H.B., Amin, N., and Lai, K.W., J. Mater. Eng. Perform., 2014, vol. 23, no. 10, pp. 3541–3550. 3. Kiryukhin, M.V., Sergeev, B.M., Sergeyev, V.G., and Prusov, A.N., Polym. Sci. Ser. B, 2000, vol. 42, no. 5/6, pp. 158–162. 4. Laudenslager, M.J., Schiffman, J.D., and Schauer, C.L., Biomacromolecules, 2008, vol. 9, no. 10, pp. 2682– 2685. 5. Wei, D. and Qian, W., Colloids Surf. B: Biointerfaces, 2008, vol. 62, no. 1, pp. 136–142. 6. Zhang, Q., Zhai, M., Peng, J., Hao, Y., and Li, J., Nucl. Instr. Meth. Phys. Res. B, 2012, vol. 286, no. 1, pp. 334– 340.
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Translated by I. Kudryavtsev
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