Proposta de um modelo mecânico-quântico para avaliar a atividade antioxidante de compostos fenólicos dos extratos aquosos de Curcuma longa L., Piper nigrum L. e Cuminum cyminum empregando teoria funcional da densidade

Abstract

Since ancient times, it has been reported the use of medicinal plants that are characterized by having properties such as: anti-inflammatory, antibacterial, anticarcinogenic, anti-hypertensive, antioxidant, among others. Therefore, the purpose of this study is to create a computational model by the Functional Density Theory, based on the Prieto method, to evaluate the antioxidant activity of the phenolic compounds curcumin, thymol and capsaicin, present in the aqueous extracts of the plants Curcuma longa, Cuminum cyminum and Piper nigrum, respectively. To investigate the reactivity of antioxidant species, their three-dimensional structures were designed and optimized with the theoretical level B3LYP/6-31+G(d,p). Frequency calculations have also been made to confirm that the optimized geometries correspond to a minimum on the potential energy surface or transition states. Electronic property calculations were performed to acquire the energies of the frontier orbitals in order to obtain the reactivity descriptors. A disagreement of these descriptors regarding the order of antioxidant potential, made it necessary to create another model. Prieto’s method was used as a starting point to create a new computational model to evaluate the antioxidant activity of phenolic compounds by reducing a species of Mo (VI) to Mo (V) forming a phosphate-molybdenum complex. Molybdenum has been optimized with the same functional as the phenolic compounds, but with a different base set, LANL2DZ. Understanding the frontier orbitals in terms of reactivity, the model successfully described the transfer of electrons from phenolic compounds to molybdenum, allowing to classify these compounds in order of reactivity, concluding that thymol has the greatest antioxidant potential. Thus, the computational model created can serve to reduce costs and time and predict the antioxidant activity of later studies.