Perturbations of an Acetone-Based Briggs-Rauscher System by α-Tocopherol (Vitamin E)

The malonic acid (MA)-based oscillating Briggs–Rauscher reaction (BR) in batch mode has been shown to be sensitive to various hydrophilic polyphenol antioxidants. Several of these have been shown to cause cessation of oscillations for a period of time before a restart occurs. The length of time before oscillations restart is related to the type of antioxidant and its concentration. Procedures have been devised to use this method as a tool for measuring antioxidant activity from pure compounds and from extracts of natural sources. The antioxidant activity has been related to the reaction of the antioxidants with HOO. radicals present in the oscillating system. Vitamin E (α-tocopherol), a typical highly lipophilic antioxidant containing an phenolic OH group, is soluble in acetone that also is a suitable substrate for the BR reaction. Perturbations of a highly concentrated acetone-based BR oscillator by acetonic solutions of vitamin E were studied. The inhibitory effects were found similar to those provoked by hydrophilic polyphenols in the MA-based oscillator, but to obtain reasonable inhibition times, the concentration of vitamin E must be at the mM level instead μM. However, there is a region of concentrations where there is a nearly linear relation between concentration and inhibition time. A comparison with a hydrophilic diphenol (2,6-dihydroxybenzoic acid) in the acetone-based oscillator showed that the inhibitory reaction is much slower in this system than in the MA one. We were able to model the perturbations by vitamin E assuming its reaction with HOO. radicals by using the FCA mechanism previously reported with some little modifications.