Avaliação da atividade anticorrosiva e antioxidante dos extratos etanólicos de espécies de Senna Mill. nativas do nordeste do brasil

Abstract

The genus Senna is a source of bioactive compounds mainly anthraquinones and alkaloids that present diverse biological activities such as antitumor, antimalarial, antipsoriatic, molluscicidal, bactericidal, antiparasitic and antimicrobial. In addition to the above activities, it is known that compounds that have multiple bonds, such as flavonoids and anthraquinones, can act as corrosion inhibitors due to the bond formed between the electron cloud of electrons π of the donor atoms and the metal surface, reducing the attack corrosive. The literature reports various applications of plant extracts as organic inhibitors. The objective of this work was to evaluate the ethanolic extracts of the leaves of two species of Senna, S. gardneri and S. trachypus, as their action as a corrosion inhibitor of 1020 carbon steel in 0.5 mol L-1 HCl medium and its activity antioxidant. Additionally, the content of phenolic and flavonoid compounds was determined and the chromatographic profile by HPLC-DAD of all extracts studied was obtained. The antioxidant capacity was evaluated using the DPPH radical sequestration method and to obtain the phenolic compounds content, the Folin-Ciocalteu spectrophotometric method was used, while the flavonoid content was determined by reaction with AlCl 3. In order to evaluate the inhibitory effect of the extracts in the corrosion of the carbon steel, gravimetric and electrochemical tests were carried out, composed of mass loss tests, potentiodynamic polarization and electrochemical impedance spectroscopy. The chemical study allowed to identify the presence of phenolic acids, anthraquinones and flavonoids, the latter being the class present in both extracts. The evaluation of the antioxidant activity made it possible to identify Senna gardneri extract with a higher phenolic content (274.21 mg EAG / g dry extract) while the Senna trachypus extract had the highest flavonoid content (53.53 mg ER / g of dry extract). The mass loss test showed that the two extracts act to decrease the mass loss significantly after 1 hour of immersion in 0.5 mol / L HCl medium. The polarization curve obtained in the electrochemical test indicated that the presence of the extracts promoted the displacement of 25 mV of the corrosion potential in relation to the blanck and the Nyquist graph obtained by electrochemical impedance spectroscopy showed that the extracts present properties of mixed inhibitors.These results allow to conclude that the extracts of S. gardneri and S. trachypus studied have properties of corrosion inhibitors, being able to be source of future applications in this sector.