Novel kinetic method for expressing the ability of antioxidant to scavenge radicals

Abstract

A method was developed to treat the result from an antioxidant trapping radicals including 2,2′-azinobis (3-ethylbenzothiazoline-6-sulfonate) cationic radical(ABTS+·), 2,2′-diphenyl-1-picrylhydrazyl radical(DPPH), and galvinoxyl radical. In the presence of a certain concentration of an antioxidant, the decrease of the concentration of a kind of radicals follows the second order exponential function with the increase of the reaction time(t), viz., [radical]=Ae−t/a+Be−t/b+C, the derivation operation of which obtains the differential style, −d[radical]/dt= (A/a)e−t/a+(B/b)e−t/b, revealing the relationship between the reaction rate(r=-d[radical]/dt) and the reaction time(t). Thus, the reaction rate at the beginning of the reaction(r0) can be calculated by assigning t=0 in the equation of -d[radical]/dt-t. Based on the concept of the reaction rate, r=k[radical][antioxidant], the rate constant(k) can be calculated based on r0 and the initial concentrations of radical and antioxidant, k=r0/([radical]0[antioxidant]0). The k means the rate of a fresh antioxidant molecule to trap a fresh radical. This method was used to treat the interactions of ABTS+·, DPPH, and galvinoxyl radicals with three homoisoflavonoids, four pyrazoles, and three ferrocenyl Schiff bases. It was found that ferrocenyl group is beneficial for antioxidants to reduce ABTS+·, and ortho-hydroxyl group is beneficial for antioxidants to donate hydrogen atom in phenolic hydroxyl group to DPPH and galvinoxyl radicals.