Extracts of leaf from five native Chilean weeds were evaluated in the biosynthesis of silver nanoparticles. The synthesis was monitored by UV-Vis spectra at 420 nm by typical formation of surface plasmon resonance. Moreover, the extract with major potential for the formation of nanoparticles was used to optimize the synthesis processes by response surface methodology, to obtain nanoparticles of small sizes by combination of three parameters (AgNO 3 and leaf extract concentrations and pH). Characterization of AgNPs was made by TEM, XRD, and DLS. The inhibitory activity was evaluated by disk diffusion method and minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were determined. Only two out of five extracts evaluated (Hypericum perforatum and Malva nicaensis) showed capacity to biosynthesize AgNPs. pH 10, AgNO 3 (1 mM), and leaf extract at 5% vv −1 were the optimal conditions to synthesize small AgNPs (< 40 nm). Inhibition zone from diffusion disk assay, MIC (30 μg mL −1) and MBC (40 μg mL −1), revealed a high antibacterial activity of AgNPs against Ralstonia solanacearum. Based on the results, the AgNPs biosynthesized from the leaf extract of H. perforatum is a promising antibacterial agent for its use in the control of R. solanacearum.
This study aimed to evaluate the toxicity of superparamagnetic iron oxide nanoparticles (SPIONs) synthesized by biogenic (BS) and chemical (CH) routes. The nanoparticles were characterized by X-ray diffraction (XRD), X-ray spectroscopy (XPS), atomic force microscopy (AFM), vibrating-sample magnetometry (VSM-SQUID), Fourier-transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM). The toxicity of SPIONs was evaluated using Artemia salina as model aquatic organisms and Raphanus sativus and Lactuca sativa as model plants to evaluate their phytotoxicity. The results obtained from XRD, XPS, and AFM confirmed the formation of spherical nanoparticles of 41.9 ± 1.00 nm (BS route) and 19.8 ± 0.47 nm (CH route). VSM-SQUID demonstrated the superparamagnetic behavior of both nanoparticles, and FT-IR provided evidence of the differences in the surface of SPIONs, suggesting the presence of phenolic compounds on the surface of BS-SPIONs. For the assays with Artemia salina, the results demonstrated (i) nonsignificant differences of BS-SPIONs in mortality rates, and (ii) significant toxicity (p < 0.05) was observed for CH-SPIONs at 300 and 400 mg L−1. The Raphanus sativa plant assay tests showed (i) BS-SPIONs and CH-SPIONs improved the root elongation of seedlings. However, BS-SPIONs demonstrated significant activity on root seedling elongation (p < 0.05) in the range of 300 mg L−1 to 600 mg L−1. To the best of our knowledge, this is the first report to compare the toxicity of chemically and biogenically synthesized SPIONs. In conclusion, although BS-SPIONs and CH-SPIONs present similar structures, their characteristics of magnetic saturation and surface structure are nonidentical, providing differences in their biological activity.
Para disminuir el peso de los componentes utilizados en la industria aeroespacial se han desarrollado a nivel mundial aleaciones de aluminio de alta resistencia con litio como aleante principal. Este aleante reduce considerablemente el peso final de la aleación y además mejora las propiedades mecánicas al convertir a esta aleación en termotratable. Actualmente, estos materiales no se producen en el país y es difícil su importación ya que se trata de materiales estratégicos. El objetivo del presente trabajo es mostrar los resultados obtenidos en el estudio de los efectos del control de la velocidad de enfriamiento de una aleacion AA2195. El análisis y evaluación de los resultados se realizó a través de micrografías y ensayos de dureza. Se observa la aparición de estructuras de Widmanstätten de interfase incoherente al enfriar lentamente luego del recocido total, lo que hace inviable el conformado plástico posterior. Utilizando el temple luego del recocido, se inhibe la formación de estructuras de Widmanstätten, con lo que se mejora enormemente la trabajabilidad de la aleación.
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