Inhibitory Effects by Antioxidants on the Oscillations of the Briggs-Rauscher Reaction in Mixed EtOH/H2O Medium

Abstract

The Briggs-Rauscher (BR) oscillating reaction in mixed 20% EtOH/H 2 O (v/v) medium is studied together with the inhibitory effects by the addition of hydroalcoholic solutions of antioxidants on its oscillatory regime. As in aqueous BR mixtures, the inhibitory effect consists of an immediate cessation of oscillations, an inhibitory time that linearly depends on the concentration of the antioxidant added, and subsequent regeneration of oscillations. The effects of several water-insoluble and water-soluble antioxidants were investigated: at a parity of concentration of antioxidant added, inhibition times in the mixed EtOH/H 2 O medium are 2 ± 3 times lower than those reported previously in aqueous solution. However, the mechanism of the BR reaction, as far as that of the inhibitory effect, seems to be the same in either aqueous or mixed medium. The findings reported and discussed here are an indication that the analytical procedure to assess the activity of free radical scavengers based on the BR reaction can be extended to lipophilic antioxidants. Introduction. ± This paper is the third of a series [1] [2] concerning the inhibitory effects by antioxidants on the oscillations of the Briggs-Rauscher (BR) reaction [3], which consists of the iodination and oxidation of an organic substrate (in general, malonic acid (MA) or its derivatives) by acidic iodate in the presence of H 2 O 2 and with the Mn 2 ion as catalyst. The inhibitory effect consists of an immediate cessation of oscillations, an inhibition time that linearly depends on the concentration of the antioxidant added, and subsequent regeneration of oscillations.Among the main intermediates for which concentrations oscillate in the BR mixture, there is the hydroperoxyl radical HOO . . It was well-established that phenolic OH group(s) attached to ring structures present in several components of plants as well as in synthetic compounds are responsible for the antioxidant activity [4] against free radicals of oxygen. We have ascribed inhibitory effects on the oscillations of the BR reaction to scavenging of HOO . radicals by phenolic OH contained in the antioxidants added to an active BR mixture [1] [2]. The dependence of the inhibition time (i.e., the time elapsed between the cessation and the regeneration of the oscillatory regime) on the concentration of antioxidants added was found to be linear over a wide range of concentration [2].On the basis of inhibition times, it was possible to set up a new method (the BRreaction method) to assess the relative antioxidant activity with respect to a substance chosen as a standard [2]. This new method has been successfully tested on 16 German

Optimization of the Measurement of Italian Monocultivar Extra Virgin Olive Oil Antioxidant Power Via the Briggs–Rauscher Reaction

“…For this topic, there is a dearth in the literature. In fact, there is only one paper that deals with a hydroalcoholic medium to test the antioxidant activity of water-insoluble antioxidants; it was found that the mechanism was the same in either aqueous or mixed medium (Cervellati et al 2002). Early scouts indicated that the olive oil has to be dissolved in a suitable solvent to give reproducible inhibition times: emulsions of EVOO samples with ethanol or isopropylic alcohol were ruled out because the inhibition time of the perfectly shaken emulsion changed as the emulsion was settling down.…”

“…Compared to other methods, the BR assay has many advantages: it is easy, inexpensive and rapid, and has often been successfully used to test the antioxidant activity (Cervellati et al 2002;Höner and Cervellati 2003;Prenesti et al 2005).…”

The first quantitative rating system of the antioxidant capacity of beauty creams via the Briggs–Rauscher reaction: a crucial step towards evidence-based cosmetics

“…involves many reactions working together. [16][17][18][19][20] The reaction can follow both a radical and a non-radical path, according to the low or high iodide concentration. Each reaction path creates the conditions that favor the alternative path, hence the concentration of iodide and the reaction electrochemical potential oscillate.…”

“…Compared to other methods, the BR assay has not only theoretical advantages but also many practical advantages: it is easy, inexpensive and rapid and has often been successfully used to test the antioxidant activity. [15][16][17][18] To standardize the antioxidant capacity of a sample a standard antioxidant molecule must be used. We already successfully tested gallic acid as reference compound: the equation parameters of the straight line optimized for gallic acid at 20.0 C are t in ¼ 5890GA + 13.9, R ¼ 0.9973, where GA represents the mass of gallic acid added to the BR mixture (ranging from 0.02 to 0.04 mg).…”

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

“…1 and 2, the concentration of vitamin E in the mixture has to be at mm level in order to obtain reasonable inhibition times, while for hydrophilic antioxidants in the malonic acid-based BR oscillator, very high inhibition times were obtained at mm level [2 -5] 4 ).…”