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(r ₀) 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 r ₀ and the initial concentrations of radical and antioxidant, k=r ₀/([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.

Keywords

Rate constant / Radical-scavenging ability / Antioxidant capacity / Chemical kinetics

References

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