The inhibitory ability of an oxazinoquinoxaline derivative (OAQX) against the corrosion of AISI 1018 mild steel induced by aqueous 0.6 mol L -1 NaCl solution is herein evaluated. Linear polarization resistance studies showed the inhibitory efficiency of OAQX varying from 62.75% to 75.93% with OAQX concentration ranged from 0.259 x 10 -4 mol L -1 to 3.243 x 10 -4 mol L -1 . Aiming at to investigate the Tafel curves on the OAQX electrochemical behavior at saline (0.6 mol L -1 NaCl) aqueous media the linear Tafel segments of anodic and cathodic curves were extrapolated to the intersection point which afforded corrosion potential (E corr ) and corrosion current density (i corr ) data. By applying Tafel approach the efficiency of OAQX ranges from 55.30% to 87.60%. In both analysis Langmuir isotherm lead to optimized adsorption parameter. The adsorption mechanism of OAQX is proposed from FTIR experiments and quantum calculations. The theoretical employed method is hybrid B3LYP combined with 6-311++G(d,p). Theoretical results showed OAQX as a promising inhibitor that form a stable protective metal-ligand film on metal surfaces, and differs from several heterocyclic compounds due to its solubility in small amount of DMSO (0.627 x 10 -4 mol L -1 ) which is resistant to a saline aqueous media (0.6 mol L -1 NaCl).Keywords: oxazinoquinoxaline derivative; corrosion inhibitor; linear polarization resistance; FTIR analysis; modeling studies. INTRODUÇÃOCorrosion is one of the main problems found in several industrial processes since it leads to material failure and this damage cause several consequences, including pollution, risks of accidents and financial losses. [1][2][3][4][5] Mild steels have been extensively employed in many industrial fields due to their interesting properties, easy fabrication and low cost. 6 However, they are sensitive to corrosion phenomenon, and become an environmental problem. In this sense, it is important to focuses on the demand for fossil fuels from which a major application of mild steels arrives from their use in the petroleum industry. Since the largest oil sources are located underground in oceans and seas, corrosion of these materials by saline conditions has been attracting considerable attention. [7][8][9][10] The addition of a corrosion inhibitor in the corrosive medium is one of the most common approaches to control corrosion process. 11 In this context, since mild steels are basically composed of metallic atoms (iron, manganese, copper, among others) the choice of a corrosion inhibitor especially comes from its electron donation ability or electrostatic interaction. The chemical structure of organic compounds contain elements like oxygen, sulfur, nitrogen as well as π bonds, which shows high electron density. In fact, heterocyclic compounds containing nitrogen, oxygen sulfur, and phosphorous have been extensively reported for their effectiveness in this field. 2,4,[12][13][14][15][16][17][18][19][20][21][22][23][24][25] Such important characteristic contributes to the adsorption phenom...

ResumoO mercado farmacêutico atual, volta sua atenção para medicamentos de origem vegetal e suas inovações tecnológicas. Neste contexto, inclui-se a espécie Azadirachta indica A. Juss. (Meliaceae) popularmente conhecida como neem, uma planta nativa da Índia, com ampla aplicação fitoterápica. Neste trabalho, aspectos químicos e farmacológicos desta planta são discutidos, bem como sua propriedade antioxidante e métodos usados para determinar micro e macronutrientes. Para tanto, obteve-se o extrato hidroalcoólico das folhas de A. indica (EAI) e a propriedade antioxidante foi avaliada pelo método do fosfomolibdênio de amônio. O resultado obtido (26,5 %) foi relacionado com a propriedade antioxidante do ácido ascórbico, podendo ser justificado pela presença de compostos polares presentes no extrato EAI, com destaque para azadiractina, nimbina e salanina. Os resultados obtidos para a determinação dos teores de umidade, cinzas e minerais (cálcio, chumbo, cobre, cromo, ferro, magnésio, manganês, níquel, potássio, sódio e zinco) nas folhas de A. indica, foram 68,0 % de umidade, 12,3 % de cinzas e dentre os minerais detectados, o cálcio apresentou maior percentual (73,0 %), seguido de potássio (15,0 %), magnésio (11,0 %), e sódio (1,0 %). Aspectos correlacionados com os teores de minerais e suas importâncias nos metabolismos dos vegetais, também são objetos de discussão. Palavras-chave: Azadirachta indica; Extrato Hidroalcoólico; Aspectos Químicos e Farmacológicos. AbstractThe pharmaceutical industry turned its attention to medicines of plant origin, which include plant extracts. In this context, it becomes significant to complete characterization of species for medical use, for example, Azadirachta indica A. Juss. (Meliaceae) popularly known as neem, a native plant of India, with significant medicinal applications. In this work, chemical and pharmaceutical aspects of this plant are discussed and, an antioxidant property and methods to determine micronutrients and macronutrients were applied to its leaves. The antioxidant property evaluation was realized by analysis of the hydroalcoholic extract of the leaves of A. indica (EAI) using the phosphomolybdenum method. Ascorbic acid was considered to be the maximal (100 %) antioxidant value. The obtained result for EAI was 26 % of the antioxidant activity of ascorbic acid, which can be explained by the presence of polar compounds such as azadirachtin, nimbin and salannin. The results for determination of humidity, ashes and