The screening of natural flavonoids for their bioactivity as antioxidants is usually carried out by determinination of their profile as chain-breaking antioxidants, by the evaluation of their direct free radical-scavenging activity as hydrogen- or electron-donating compounds. Since this may not be the only mechanism underlying the antioxidant activity it is important to check the ability of these compounds to act as chelators of transition metal ions. Accordingly, in the present study the acidity constants of catechin and taxifolin, as well as the formation constants of the corresponding copper (II) complexes, were investigated by potentiometry and/or spectrophotometry. Moreover, a detailed quantitative examination of the coordination species formed is presented. In addition, the partition coefficients of both catechin and taxifolin in a biomimetic system (micelles) were determined, since these properties may also contribute to the antioxidant behavior of this type of compound. The log P values determined depend on the electrostatic interactions of the compounds with the differently charged micelles (the highest values were obtained for zwitterionic and cationic micelles). The prooxidant behavior of the compounds was assessed through the oxidation of 2'-deoxyguanosine, induced by a Fenton reaction, catalyzed by copper. The data obtained reveal that the flavonoids under study did not present prooxidant activity, in this particular system. The results obtained are evidence of a clear difference among the pKa, the complexation properties, and the lipophilicity of the flavonoids studied, which can partially explain their distinct antioxidant activity. The most stable geometries of the free compounds were determined by theoretical (ab initio) methods, in order to properly account for the electron correlation effects which occur in these systems, thus allowing a better interpretation of the experimental data.

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Most herbicides applied in crop field, stay in the soil for a period, affecting next crop or even the plants using as green manure. Nowadays, the use of herbicides grow to increase productivity, mainly in the grain producing region north of Rio Grande do Sul state. The objective of this study was to evaluate the effects of herbicides fomesafen and sulfentrazone on antioxidant system in Avena sativa1, Vicia sativa2, Raphanus sativus and Lupinus albus. The plants were exposed to varying concentrations of fomesafen3 (0, 0.125, 0.25 and 0.5 kg ha -1) and sulfentrazone (0, 0.3, 0.6 and 1.2 kg ha-1). For this, the activities of, ascorbat peroxidase, catalase and guaiacol enzymes were analyzed, and the levels of MDA were quantificated. Fomesafen and sulfentrazone promoted alterations in balance of plants generating oxidative stress and elicited the response of the antioxidant system of plants, mainly in the high doses of fomesafen, for the species V. sativa and R. sativus. At the same time, the 1,2 kg ha -1 dose of sulfentrazone generated lipid peroxidation for V. sativa, R. sativus and L. albus. Additionally, A. sativa was the species that demonstrated low alterations on antioxidant system with the exposure to herbicide fomesafen and sulfentrazone. Thus, we can we can suggest that the species present a better response in defense of the oxidative stress generated by the herbicides.

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Copper (Cu) is an essential metal and it is important for metabolism. However, in high concentrations, it becomes toxic. Metal‐induced toxicity is the cause of many neurodegenerative diseases. So it is necessary to search mechanisms to find ways of healthy aging. Natural compounds and diets based on fruits are increasingly common and could lead to a healthy life. Pitaya (Hylocereus undatus) is a tropical and Latin American, fruit that is gaining more popularity due to its antioxidant properties. Here, we evaluate the preventive and curative effect of different doses of microencapsulated pulp H. undatus extract on copper‐induced toxicity. For this we use the nematode Caenorhabditis elegans, to investigate the effects of pitaya extract on behavior, lipid peroxidation, antioxidant chaperon, and cholinergic nervous system (ColNS). Results showed behavioral changes, decreased cell death biomarkers, and lipid peroxidation caused by copper, and these toxic effects were prevented and reverted by Pitaya's extract. After all, the extract can be used in diet as a supplement and studied to treat or prevent specific diseases, some of them linked to contamination and senility‐related conditions. Practical applications This research has been aimed to provide the uses of Hylocereus undatus microencapsulated pulp extract for the prevention and treatment of copper‐induced toxicity. We have been shown that Pitaya is a good source of antioxidant compounds that can ameliorate the antioxidant system as well as the cholinergic nervous system avoiding behavior changes before and after the metal toxicity of copper. Therefore, the potential applications and common use of this extract can serve as food supplementation to prevent metal oxidative damage as well as to repair clinical cases of copper poisoning.

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