Phenolic compounds: a theoretic-computation study of antioxidant capacity of cardanol and eugenol

Abstract

The study and development of antioxidants has an important role in technological and health areas. Naphthenic mineral oil and biodiesel modifies its physical and chemical properties due to action of reactive oxygen species (ROS) over time, affecting their performance. Our body tends to maintain a balance between antioxidant and radical species. However, as we age, the number of radicals increases, the balance is broken resulting in a condition known as oxidative stress. This condition is associated with thrombosis, heart attack, depression and cancer. Therefore, it is important the study of antioxidants and the development of new compounds with antiradical activity to increase storage time of naphthenic mineral oil and biodiesel, and avoid conditions associated with excess radicals in the body. In this context, in this work we carried out two studies. In the first, the antioxidant activity of saturated cardanol, monoene, diene and triene was computationally evaluated, with the functional hybrid B3LYP with the base set 6-31G(d,p). Using chemical quantum descriptors, the HAT, SPLET and SET-PT mechanisms were evaluated. The data obtained suggest that the HAT mechanism is the main form of action of these molecules. The analysis of the Fukui index confirms the experimental data of the best antioxidant profile of cardanol monoene. The global reactivity analysis shows that the greater the number of unsaturations in the cardanol side chain, the greater its overall reactivity. In the second study, the effect of acetylation and nitration on the antioxidant potential of eugenol and its results were evaluated. For this study, the hybrid functional M06-2X with a set of bases 6-31+G(d,p) was used to simulate the mechanism of HAT with the HO, HOO, CH3O, DPPH radicals. The thermodynamic data showed a dependence of the formation of p-quinomethanes (27, 28 and 29) to make the reaction spontaneous with DPPH, revealing the need for two steps of HAT. The kinetic data that showed the preferred site for hydrogen transfer depends on the instability of the attacking radical. The computational data corroborated the experimental data, confirming the antioxidant profile of (1, 4-allyl-2-methoxyphenol), and nitro-derivative 7 (5-allyl-3-nitrobenzene-1,2-diol) in the DPPH assay. Finally, this study showed that the nitro compound 6 (4-allyl-2-methoxy-6-nitrophenol) has antiradical activity with HO, HOO and CH3O radicals, but the repulsion between the nitro groups with DPPH makes it difficult to approach the DPPH molecule making the reaction be slow and undetectable experimentally.