Índice de figuras

Abstract

I n the last decade the study of active oxygen and nitrogen species and their role in a large number of chronicle diseases, including cancer, heart disease and even aging itself, revealed that natural and synthetic antioxidants are able to prevent the effects caused by oxidative stress. Several methods can be used to evaluate the total antioxidant activity in body fluids, complex mixtures and isolated substances. Simple trapping assays can quantify the total antioxidant content in a sample, which is expressed as TRAP (total radical-trapping potentíal) or TEAC (trolox equivalent antioxidant capacity) and these indexes are well accepted due to its high sensitivity and operational facilities. The determination of the antioxidant potential of plant extracts and isolated natural products may constitute a simple tool to evaluate the potential biological activity of plant constituents. The chemiluminescence reaction of luminol and hydrogen peroxide in the presence of hemin as catalyst has been used as the method to evaluate the antioxidant activity, since the chemiluminescence emission can be suppressed by antioxidants, and a linear relationship between antioxidant concentration and the observed induction time is obtained. A kinetic study was performed to establish the ideal experimental conditions for the assay. The reactant concentrations were varied in the absence and the presence of antioxidants, and the results lead to a better understanding of the system. A new method for data treatment is al80 used, which allows the correlation of the antioxidant effect to the number of photons suppressed. Several well-known antioxidants (trolox, ascorbic and uric acid) were used to establish the methodology. TRAP values were calculated from the correlations between the number ofphotons suppressed and the antioxidant concentration, using trolox as reference compound. Using this methodology we were able to determine the antioxidant activity of Photomorphe umbellata extracts, and of its isolated major compound, 4-nerolidylcatechol. C(frações de 17 a23 e (O)) fração cromatográfica D(frações de 24 a 30). São apresentadas as intensidades dos picos, obtidos por detecção espectroscópica de UV-Visivel em 254 nm (em cima) e índice de refração (em baixo). Os tempos de retenção podem mostrar pequenas variações.