Green fabrication of ferromagnetic Fe3O4 ...

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Green fabrication of ferromagnetic Fe3O4 nanoparticles and their novel catalytic applications for the synthesis of biologically interesting benzoxazinone and benzthioxazinone derivatives Nagaraj Basavegowda, Krishna Bahadur Somai Magar, Kanchan Mishra and Yong Rok Lee* This paper demonstrates a novel and green approach for the synthesis of Fe3O4 nanoparticles using the leaf extract of Artemisia annua (A. annua), which is widely distributed in Asia as a medicinal plant. The formation of Fe3O4 nanoparticles was observed by UV-Vis spectroscopy. The synthesized nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray

Received (in Montpellier, France) 10th July 2014, Accepted 28th August 2014

analysis (EDAX), Fourier transform infrared (FT-IR) spectroscopy, vibrating sample magnetometry (VSM), and

DOI: 10.1039/c4nj01155d

shape with an average size of 6 nm. The synthesized Fe3O4 nanoparticles were used as a catalyst for the

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preparation of biologically interesting benzoxazinone and benzthioxazinone derivatives in high yields. These results showed that the synthesized Fe3O4 nanoparticles could be used as a catalyst in organic synthesis.

thermogravimetric analysis (TGA). TEM analysis of Fe3O4 nanoparticles showed that they were spherical in

1. Introduction Fe3O4 nanoparticles have attracted considerable attention because of their fundamental properties and applications in medical diagnosis and therapy,1 drug delivery,2 magnetic resonance imaging,3 and cancer hyperthermia treatment.4 Several methods for synthesizing Fe3O4 nanoparticles have been reported by chemical precipitation using NaOH,5 ammonia solutions,6 thermal decomposition of organic iron precursors in organic solvents,7 the sol–gel method,8 sonochemical synthesis,9 surfactants,10 solvothermal synthesis,11 mechano-chemical processes,12 hydrothermal synthesis,13 and emulsion techniques.14 As a facile and eco-friendly method, a green protocol for the synthesis of Fe3O4 nanoparticles using tea polyphenols was recently developed.15 This method reduced the environmental hazards through the use of non-toxic chemicals and renewable materials.16 Although several synthetic methods for Fe3O4 nanoparticles have been described, there is still a demand for a rapid, non-toxic, and green synthesis that can provide Fe3O4 nanoparticles efficiently. Despite this, a green approach for the synthesis of Fe3O4 nanoparticles using the Artemisia annua (A. annua) leaf extract has not been reported so far. School of Chemical Engineering, Yeungnam University, Gyeongsan 712-749, Republic of Korea. E-mail: [email protected]; Fax: +82-53-810-4631; Tel: +82-53-810-2529

Recently, Fe3O4 nanoparticles have emerged as a new type of catalyst, which show higher catalytic activity than conventional heterogeneous catalysts due to their high surface area and chemical stability. These materials have been widely used as mild and efficient catalysts for many organic transformations including Suzuki reaction,17 Friedel–Crafts acylation,18 Sonogashira– Hagihara reaction,19 Paal–Knorr reaction,20 thiolysis of epoxides,21 dehydrogenation of ethylbenzene,22 N-Boc protection of amines,23 and syntheses of heterocycles,24 a-aminonitriles,25 sulphonamides,26 and quinoxalines.27 Although a number of Fe3O4 nanoparticlescatalyzed reactions have been well developed for producing many useful molecules, the synthesis using Fe3O4 nanoparticles for biologically interesting benzoxazinone and benzthioxazinone derivatives has not yet been reported. Molecules bearing benzoxazinones and benzthioxazinones have received considerable attention because of their pharmacological activities. They exhibited a variety of biological activities such as antiulcer,28 antipyretic,29 antihypertensive,30 anti-inflammatory,31 and antifungal activities.32 Some of these compounds also exhibited several important biological activities including DP receptor antagonism,33 integrin antagonism,34 calmodulin antagonism,35 platelet fibrinogen receptor antagonism,36 and inhibition of the transforming growth factor b (TGF-b) signaling pathway.37 This paper reports the biosynthesis of Fe3O4 nanoparticles from an aqueous solution of iron(III) chloride (FeCl3) using A. annua leaf extracts. Further, the synthesized Fe3O4 nanoparticles were used as

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a catalyst for the preparation of biologically interesting benzoxazinone and benzthioxazinone derivatives through multicomponent reaction of 2-naphthol with aromatic aldehydes and ureas.

2. Experimental section


2.1.

Chemicals

Iron(III) chloride, 2-naphthol, aromatic aldehydes, and ureas were obtained from Sigma-Aldrich. All glassware was washed with distilled water and dried in an oven before use. Dried leaves of A. annua were obtained at a local market in Yeongchon, South Korea. 2.2.

Preparation of the A. annua extract

Dried A. annua leaves were crushed to fine powder and then sieved through 20#mesh. The aqueous extract was prepared by adding 5 g of powdered leaves to 200 mL of double distilled water and boiling for 10 minutes. The broth solution was filtered through a 0.2 mm filter and stored at 4 1C for further use within a week. 2.3.

The synthesis of Fe3O4 nanoparticles

An aqueous solution of 2 mM iron(III) chloride (FeCl3) was used to synthesize Fe3O4 nanoparticles. 5 mL of A. annua extract was added to 50 mL of previously prepared 2 mM salt solutions. Bioreduction occurred just after the addition of the plant extract indicating the formation of Fe3O4 nanoparticles. The nanoparticles thus obtained were purified by centrifugation in a Beckman Coulter’s Avanti J-E centrifuge (USA) at 10 000 rpm for 20 minutes. 2.4.

Characterization of the synthesized Fe3O4 nanoparticles

Bioreduction of iron salts was monitored by using an Optizen 3220 (double beam) UV-Vis spectrophotometer with a quartz cuvette and distilled water as a reference. The UV-Vis spectra of Fe3O4 nanoparticles were recorded in the range of 200–600 nm. FT-IR (JASCO FT-IR) analysis was performed to characterize the biomolecules present in the A. annua extract which may be accountable for the reduction of the metals and even for the stabilization of nanoparticles. The resulting solutions were centrifuged at 10 000 rpm for 20 minutes at 4 1C. The particles were then dried completely in a vacuum oven at 40 1C for 2 h and ground with potassium bromide to produce pellets, which was examined over the wavelength range 400–4000 cm 1. The shape, size and morphology of Fe3O4 nanoparticles were characterized by TEM (FEI Tecnai G2 F20 ST FE-TEM). The sample was prepared by placing a drop of the Fe3O4 nanoparticle solutions on carbon-coated copper grids and allowing the solvent to evaporate in air at ambient temperature. TEM was performed at 200 kV with a point resolution of 0.24 nm, and a Cs of 1.2 mm. The chemical composition of the Fe3O4 nanoparticles was analyzed using a Genesis liquid nitrogen cooled EDAX detector using an ultrathin window. The Fe3O4 nanoparticles were subjected to XRD (PANalytical X’Pert MRD). The nanoparticles were dried at 40 1C in a vacuum

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oven and hand-ground gently to fine powder. The powder XRD was performed at 30 kV and 40 mA with Cu Ka radians (l = 1.5406 Å) at 2y angle configuration scanning from 201 to 901. The magnetic properties of Fe3O4 nanoparticles were measured by using VSM (Lake Shore Cryotronics, Inc., Idea-VSM, model 662 with 735 VSM controller). The thermal properties of the Fe3O4 nanoparticles were analysed by TGA (TG-DTA, SDT-Q600 V20.5 Build 15). The synthesized nanoparticles (5 mg) were placed in a platinum sample pan and heated under a N2 atmosphere to 1000 1C at a heating rate of 10 1C min 1. 2.5.

Catalytic activity

The synthesized Fe3O4 nanoparticles were used as a catalyst for the synthesis of benzoxazinone and benzthioxazinone derivatives. 2.6.

General procedure for the synthesis of compounds 4a–4f.

Fe3O4 nanoparticles (0.05 mmol) were added to a mixture of 2-naphthol (1, 1.0 mmol), aldehyde (2, 1.2 mmol), and urea or thiourea (3, 1.2 mmol) in toluene (5.0 mL) under a N2 atmosphere. The reaction mixture was heated under reflux for 10–12 h. After the reaction was completed, as indicated by TLC, the solvent was removed in a reduced pressure evaporator. The residue was purified by column chromatography on silica gel to afford the final product. 2.7.

Characterization data

1-Phenyl-1,2-dihydro-3H-naphtho[1,2-e][1,3]oxazin-3-one(4a)38,39. Yield 93% as a white solid; mp 177–179 1C; 1H NMR (300 MHz, CDCl3 + DMSO-d6) d 8.45 (1H, br s), 7.81–7.75 (2H, m), 7.60–7.54 (1H, m), 7.37–7.30 (2H, m), 7.25–7.17 (6H, m), 5.99 (1H, s); 13C NMR (75 MHz, CDCl3 + DMSO-d6) d 149.0, 146.8, 141.5, 129.7, 129.3, 128.3, 128.0, 127.8, 127.2, 126.3, 126.2, 124.0, 121.7, 115.9, 112.5, 54.0; IR (KBr) 3453, 2376, 2280, 1729, 1395, 1222, 1176, 1110, 827 cm 1. 1-(p-Tolyl)-1,2-dihydro-3H-naphtho[1,2-e][1,3]oxazin-3-one(4b)38,39. Yield 94% as a white solid; mp 170–172 1C; 1H NMR (300 MHz, DMSO-d6) d 8.84 (1H, s), 7.97–7.90 (2H, m), 7.79–7.76 (1H, m), 7.48–7.41 (2H, m), 7.36 (1H, d, J = 9.0 Hz), 7.19 (2H, d, J = 8.1 Hz), 7.10 (2H, d, J = 8.1 Hz), 6.14 (1H, d, J = 3.0 Hz), 2.19 (3H, s); 13C NMR (75 MHz, DMSO-d6) d 149.4, 147.4, 140.0, 137.4, 130.4, 130.2, 129.5, 129.0, 128.7, 127.4, 126.9, 125.1, 123.2, 116.9, 114.2, 53.6, 20.7; IR (KBr) 3240, 2362, 1725, 1514, 1391, 1225, 1112, 817 cm 1. 1-(3-Methoxyphenyl)-1,2-dihydro-3H-naphtho[1,2-e][1,3]oxazin3-one (4c)38,39. Yield 90% as a white solid; mp 206–208 1C; 1 H NMR (300 MHz, CDCl3 + DMSO-d6) d 8.31 (1H, br s), 7.80– 7.75 (2H, m), 7.55–7.53 (1H, m), 7.37–7.30 (2H, m), 7.23 (1H, d, J = 8.7 Hz), 7.14 (1H, t, J = 8.1 Hz), 6.81–6.79 (2H, m), 6.72–6.69 (1H, m), 5.95 (1H, d, J = 2.4 Hz), 3.65 (3H, s); 13C NMR (75 MHz, CDCl3 + DMSO-d6) d 159.2, 149.4, 147.1, 130.0, 129.5, 129.3, 128.6, 127.9, 126.6, 124.3, 122.0, 118.6, 116.2, 112.6, 112.4, 112.3, 54.4, 54.3; IR (KBr) 2960, 1731, 1512, 1385, 1256, 1227, 1174, 1112, 1027, 834 cm 1. 1-(4-Nitrophenyl)-1,2-dihydro-3H-naphtho[1,2-e][1,3]oxazin-3one (4d)38,39. Yield 88% as a white solid; mp 172–174 1C; 1 H NMR (300 MHz, CDCl3 + DMSO-d6) d 8.61 (1H, br s), 8.04 (2H, d, J = 8.4 Hz), 7.83–7.72 (2H, m), 7.43–7.33 (3H, m),


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7.36–7.33 (2H, m), 7.24 (1H, d, J = 8.4 Hz), 6.12 (1H, d, J = 2.4 Hz); 13 C NMR (75 MHz, CDCl3 + DMSO-d6) d 149.0, 148.2, 147.3, 146.7, 130.0, 129.9, 128.2, 128.1, 127.5, 126.9, 124.5, 123.3, 121.5, 116.2, 111.3, 53.3; IR (KBr) 2955, 1736, 1525, 1340, 1227, 1115, 924, 826 cm 1. 1-Phenyl-1,2-dihydro-3H-naphtho[1,2-e][1,3]oxazine-3-thione(4e)39. Yield 80% as a yellowish solid; mp 208–210 1C; 1H NMR (300 MHz, CDCl3) d 8.37 (1H, br), 7.82–7.75 (2H, m), 7.46–7.43 (1H, m), 7.35–7.32 (3H, m), 7.21–7.18 (5H, m), 5.95 (1H, s); 13C NMR (75 MHz, CDCl3) d 181.4, 146.5, 140.2, 131.4, 130.9, 129.5, 129.1, 129.0, 128.9, 127.7, 127.3, 125.7, 122.7, 116.6, 56.3; IR (KBr) 3057, 2365, 1635, 1558, 1514, 1402, 1309, 1182 cm 1. 1-(4-Nitrophenyl)-1,2-dihydro-3H-naphtho[1,2-e][1,3]oxazine-3thione (4f)39. Yield 85% as a whitish solid; mp 136–138 1C; 1 H NMR (300 MHz, CDCl3) d 9.13 (1H, br), 8.11 (2H, d, J = 8.4 Hz), 7.91 (1H, d, J = 9.0 Hz), 7.87–7.84 (1H, m), 7.45–7.37 (6H, m), 6.14 (1H, d, J = 2.7 Hz); 13C NMR (75 MHz, CDCl3) d 181.4, 148.0, 146.5, 146.5, 131.6, 131.5, 129.2, 128.5, 128.4, 128.2, 126.1, 124.7, 122.1, 116.4, 110.6, 54.5; IR (KBr) 2942, 1609, 1524, 1344, 1166, 828, 740 cm 1.

The shape, size, and morphology of the Fe3O4 nanoparticles were analyzed by using transmission electron microscopy. Aliquots of Fe3O4 nanoparticle solution were placed on a carbon coated copper grid and allowed to dry under ambient conditions. Fig. 2a and b shows the TEM image of Fe3O4 nanoparticles, which were mainly spherical with a size of 3–10 nm. A particle size distribution histogram based on the size of 82 particles was measured from the TEM image as shown in Fig. 2c. The mean particle size was 6.4 nm with the standard deviation of 2.7. The particle size was quite close to the calculated crystallite size of 6 nm, suggesting that the majority of the observed spherical nanoparticles might be single crystals. EDAX (Fig. 2d) revealed iron & oxygen, which confirmed the formation of Fe3O4 nanoparticles, and a typical optical absorption peak at B0.5 keV due to surface plasmon resonance was observed. The presence of C and Cu was attributed to the carbon coated copper grid used for sample preparation.

3. Results and discussion 3.1.

Characterization of the Fe3O4 nanoparticles

UV-Vis spectroscopy was conducted to pinpoint the formation of Fe3O4 nanoparticles. Owing to the reaction of FeCl3 solution and the leaf extract, the reaction mixture became black immediately, indicating the formation of Fe3O4 nanoparticles. Aliquots of the reaction mixture were withdrawn and scanned using a spectrophotometer. The formation of Fe3O4 nanoparticles can be explained by comparison with the related mechanism through reduction of FeCl3 using bioactive phyto-molecules.40 On the basis of this mechanism, the hydroxyl groups of bioactive molecules in plant extracts first bind to Fe3+ to give ferric hydroxide, which is partially reduced by other bioactive materials to form Fe3O4 particles (Fig. 1).41 The Fe3O4 nanoparticles did not show any strong absorption in the visible region.42 The observed absorption peak of Fe3O4 nanoparticles shifted slightly towards 250 nm, which further confirmed that the Fe3O4 nanoparticles were formed.

Fig. 1 UV-Vis spectra and inset diagram showing color changes. (a) FeCl3 solution and (b) Fe3O4 nanoparticle solution.

Fig. 2 TEM images of the Fe3O4 nanoparticles at different magnifications: scale bar at (a) 10 nm and (b) 5 nm, (c) size distribution histogram, and (d) EDAX result showing the formation of Fe3O4 nanoparticles.

Fig. 3 shows XRD patterns of the synthesized Fe3O4 nanoparticles. A series of characteristic diffraction peaks were observed at 22.701, 30.031, 35.371, 49.361, 56.851, and 62.431 2y, which were assigned to the (111), (220), (311), (422), (511), and (440) Bragg reflections, respectively and were also comparable with standard magnetite XRD patterns (JCPDS card no.: 19-0629).43 The estimated mean size of the Fe3O4 nanoparticles

Fig. 3

XRD Patterns of Fe3O4 nanoparticles.


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Fig. 4 FT-IR spectra of (a) the A. annua leaf extract and (b) Fe3O4 nanoparticles synthesized from the A. annua leaf extract.

was approximately 6 nm. From the wide-angle XRD pattern, all the peaks could be readily identified as the pure cubic phase of Fe3O4. No impurity peak was observed, indicating that high purity crystalline Fe3O4 was successfully synthesized. An extra sharp unassigned peak observed at 61.351 2y was attributed to the crystallization of some bio-organic compounds on the surfaces of the Fe3O4 nanoparticles, which concurs with previous reports.44 FT-IR spectroscopy was carried out to identify probable biomolecules present in the A. annua leaf extract responsible for the reduction and stabilization of Fe3O4 nanoparticles. The spectra of the A. annua leaf extract showed strong bands at 3400, 2939, 2279, 1609, 1403, 1272, and 1070 cm 1 (Fig. 4(a)), whereas those of Fe3O4 nanoparticles were observed at 3410, 2925, 2367, 1632, 1424, 1271, and 1071 cm 1 (Fig. 4(b)). The band at 3400 cm 1 in the A. annua leaf extract was assigned to O–H stretching vibration. This band was shifted to 3410 cm 1 in Fe3O4 nanoparticles most likely because of biomaterial binding. The absorption peaks at 2939 cm 1 were assigned to the C–H stretching band, and the absorption peaks at 1609 cm1 were attributed to the CQC stretching vibrations of biomolecules.43 The magnetic properties of the Fe3O4 nanoparticles were examined by VSM at 300 K (Fig. 5). The hysteresis loops indicated that the Fe3O4 nanoparticles were ferromagnetic in nature. The coercivity (Hc), saturation magnetization (Ms) at 7000 G and remanent magnetization (Mr) values were 230 G, 20.73 emu g 1, and 3.76 emu g 1 respectively. The VSM results of Fe3O4 nanoparticles were similar to the results of other studies.40 TGA of Fe3O4 nanoparticles revealed three significant weight loss steps from room temperature to 1000 1C (Fig. 6). The weight loss in the first, second, and third steps was 5.79%, 28.76%, and 21.83% respectively, giving an overall weight loss of 56.38%. This indicates that the bioactive molecules capped on Fe3O4 nanoparticles were degraded completely at high temperature. The residual mass at 990.47 1C was 43.62%. 3.2.

Catalytic activity of the Fe3O4 nanoparticles

Because of the importance of benzoxazinones and benzthioxazinones, several synthetic approaches have been devised for the synthesis of benzoxazinones and benzthioxazinones.38,39,45,46

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Fig. 5 Magnetization curve of the synthesized Fe3O4 nanoparticles at 300 K and inset diagram: Isolation of the dispersed magnetic NPs (left) with the aid of an external magnet (right) from the reaction mixture.

Fig. 6

TGA traces of the Fe3O4 nanoparticles.

To examine the catalytic ability of the synthesized Fe3O4 nanoparticles, their catalytic efficacy for the multicomponent synthesis of 1-phenyl-1,2-dihydro-3H-naphtho[1,2-e][1,3]oxazin-3-one (4a) in different solvents was first studied. The reaction of 2-naphthol (1, 1.0 mmol) with benzaldehyde (2, 1.2 mmol) and urea (3, 1.2 mmol) was examined in the presence of 5 mol% of Fe3O4 nanoparticles in several solvents. With benzene, fluorobenzene and DMF under reflux for 16 h, the expected cycloadduct 4a was produced in 53, 58 and 81% yields, respectively. On the other hand, when toluene was used under reflux for 12 h, expected product 4a was isolated in high yield (93%). Compound 4a was determined by analysis of its spectral data and by direct comparison with the reported data.39 To evaluate the usefulness of a multicomponent reaction for the synthesis of a range of 1-aryl-1,2-dihydro-3H-naphtho[1,2-e][1,3]oxazin-3-ones and 1-aryl-1,2-dihydro-3H-naphtho[1,2-e][1,3]oxazine-3-thiones, further reactions of compound 1 with several aromatic aldehydes and urea or thiourea in the presence of the Fe3O4 nanoparticles in refluxing toluene for 10–12 h were examined. The results are summarized in Table 1. Treatment of compound 1 with 4-methylbenzaldehyde and urea in the presence of 5 mol% of Fe3O4 nanoparticles for 10 h gave 4b in 94% yield, whereas that of 3-methoxybenzaldehyde afforded the desired product 4c in 90% yield. Similarly, a reaction of compound 1 with 4-nitrobenzaldehyde with urea


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Table 1 Synthesis of 1-aryl-1,2-dihydro-3H-naphtho[1,2-e][1,3]oxazin3-ones 4a–4d and 1-aryl-1,2-dihydro-3H-naphtho[1,2-e][1,3]oxazine3-thiones 4e–4f using Fe3O4 nanoparticles as a catalysta

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and XRD and EDAX confirmed their structure and elemental composition, respectively. The Fe3O4 nanoparticles had spherical shapes with mean particle sizes of 6 nm. VSM showed that the Fe3O4 nanoparticles were ferromagnetic in nature. Overall, the proposed green synthetic method is simple and eco-friendly because it does not require any extra surfactants or reductants. These findings highlighted the above method for the production of excellent catalysts for use in a range of organic syntheses.

Acknowledgements This study was supported by the Nano Material Technology Development Program of the Korean National Research Foundation (NRF) funded by the Korean Ministry of Education, Science, and Technology (2012M3A7B4049675).

Notes and references a

Reaction conditions: 1 (1.0 mmol), 2 (1.2 mmol), 3 (1.2 mmol), Fe3O4 nanoparticles (0.05 mmol) in toluene (5.0 ml), reflux for 10–12 h.

provided compound 4d in 88% yield. The desired products were also obtained when thiourea was used in place of urea. The reaction of compound 1 between benzaldehyde or 4-nitrobenzaldehyde and thiourea in refluxing toluene for 12 h gave compounds 4e and 4f in 80 and 85% yield, respectively. The reactions of aromatic aldehydes bearing electron-donating as well as electron-withdrawing groups were also successful. The Fe3O4 nanoparticles-catalysed multicomponent reactions provided a rapid synthetic route to various 1-aryl-1,2-dihydro3H-naphtho[1,2-e][1,3]oxazin-3-ones 4a–4d and 1-aryl-1,2-dihydro3H-naphtho[1,2-e][1,3]oxazine-3-thiones 4e–4f in good to excellent yield. The synthesized Fe3O4 nanoparticles-catalyzed reactions for biologically interesting benzoxazinone and benzthioxazinone derivatives provided several advantages of low catalyst loading (5 mol%), short reaction times (10–12 h), and high yields (80–93%) by comparing with other reported reactions using H3Mo12O40P (10 mol%),45 RuCl2(PPh3)3 (10–20 h),39 and TMSCl (49–83%)46 as catalysts.

4. Conclusions A facile and green approach to the synthesis of Fe3O4 nanoparticles from aqueous iron(III) chloride (FeCl3) solution using an aqueous extract of A. annua was described. The synthesized Fe3O4 nanoparticles exhibited strong catalytic activity for the synthesis of biologically interesting benzoxazinone and benzthioxazinone derivatives. FT-IR spectroscopy showed that the biomolecules present in the aqueous extract of A. annua were responsible for reducing FeCl3 and capping the active molecules in the Fe3O4 nanoparticles. UV-visible spectroscopy and TEM suggested that the produced nanoparticles were stable,

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