Síntese verde de nanopartículas de prata mediada por extratos de Paullinia cupana (Guaraná)

Abstract

In addition to the unique properties that nanometric dimensions have, nanotechnology aims to study and improve the characteristics of materials, in addition to assigning new functionalities. Silver nanoparticles (AgNPs) belong to this set which, which have been widely investigated, demonstrate bactericidal properties. As an alternative to traditional synthesis methods, Green Chemistry results in a more sustainable methodology due to the use of materials that are potentially less harmful to the environment. In this scenario, the components present in plant extracts facilitate the synthesis of metallic nanoparticles, considering that the bioactive substances present in plants, such as those present in guarana (Paullinia cupana), demonstrate the capacity to mediate the production and stabilization of nanoparticles.The AgNPs were produced through different synthesis conditions, in order to obtain the best reaction conditions and, subsequently, to analyze the microbicidal potential of the produced dispersions. The characterization of the aqueous extract of guarana was carried out through electronic UV-Vis spectroscopy, making it possible to relate the spectrum found with the electronic transitions present in the structures of the plant extract. The surface plasmon band (RPS) was identified and monitored for the other AgNPs synthesis conditions. The conditions of synthesis in alkaline medium using more diluted concentrations of aqueous extract of guarana showed bands related to the formation of more intense and symmetrical nanostructures, indicating the occurrence of nanoparticles with smaller diameters and uniforms in relation to acidic and neutral media. Furthermore, increasing the temperature of the reaction medium did not cause considerable effects in terms of the amounts of nanoparticles produced, but favored the complexation effects in relation to the synthesis performed at room temperature. Analysis through transmission electron microscopy (TEM) analyzes confirmed the behavior of the RPS band obtained for the synthesis conditions in acidic and basic medium, signaling the production of monodisperse and spheroidal nanoparticles, which together with the information obtained by dynamic light scattering (DLS) and Zeta potential, suggest even more monodisperse structures with reduced hydrodynamic diameter with increasing temperature for AgNPs produced at pH 9.0. Sensitivity of S. aureus and E.coli microorganisms against AgNPs was observed in synthesis using a higher dilution concentration of guarana extract (condition 1) at pH 9.0 at room temperature, being metallic nanostructures with a hydrodynamic diameter of 32.0 ± 0.6 nm.