Inhibitory Effects by Soy Antioxidants on the Oscillations of theBriggs-Rauscher Reaction

Abstract

Inhibitory effects by addition of aqueous extracts of soy flour to an active Briggs-Rauscher mixture are reported. The effect consists of an immediate cessation of oscillations, but, after some time, the oscillatory behavior is regenerated with amplitude and frequency different from those observed in a reference mixture. The inhibition time depends linearly on the concentration of substances contained in the extract in a wide range of concentration. The inhibitory effects are due to the high free-radical scavenging activity of substances contained in the soy flour. Two preponderant products contained in the soy flour extract were identified and characterized as malonyldaidzin and malonylgenistin. The antioxidant activity of these isoflavones contained in the extracts was determined on the basis of the inhibition time. A qualitative mechanistic explanation of the inhibitory effects is given. Our findings are decisive indirect evidence of involvement and important role played by HOO . radicals in establishing oscillations in the Briggs-Rauscher (BR) system. The linear relationship between the inhibition time and the whole-mass concentration of antioxidant contained in soy extracts added to a BR mixture is an indication of the possibility to develop and implement an analytical procedure for monitoring the activity of antioxidant scavengers of free radicals based on the oscillating Briggs-Rauscher reaction.1. Introduction. ± As stated by Furrow and Noyes [1], the most dramatic oscillating reaction in solution is probably that discovered by Briggs and Rauscher [2], now referred to as the BR reaction. When appropriate amounts of H 2 O 2 , acidic iodate, manganous salt, malonic acid (MA), and starch indicator are mixed in aqueous solution, the system repeats the sequence colorless 3 yellow 3 blue several times.The mechanism of the BR reaction is quite complex; a skeleton mechanism, proposed in 1982 by Noyes and Furrow [3], reproduces some of the basic features of the oscillations in the system in closed reactors (batch conditions). At the same time, De Kepper and Epstein [4] developed a qualitatively similar mechanism that, taking into account flow terms, is able to model, besides oscillations, a variety of phenomena that appear in continuously stirred tank reactors (open conditions).The main intermediates in these mechanisms are: iodine, iodide ion, the oxyiodine species HOI, HOIO, and IO . 2 , and the hydroperoxyl radical HOO . . It is to be noted that IO .2 and HOO . radicals were not detected in BR mixtures: their presence and the important role they play in the onset of oscillations were proposed in analogy with the well-established mechanism for the Belousov-Zhabotinsky (BZ) reaction [5] and with a mechanism proposed for the Bray-Liebhafsky (BL) reaction [6].In a qualitative study, Franz [7] found that the addition of a crumbled superoxide dismutase pellet (health food, 2000 SOD units per pellet) to an actively reacting BR mixture caused an immediate cessation of oscillations (initial concentrations in the

Measurements of the antioxidant capacity of fruits and vegetables using the BR reaction method

“…It has been discussed recently that below a certain concentration of the extract added (different for each extract) the behaviour deviates from linearity. In fact, at low concentration of extract added, the inhibition times become too low to be measured, as shown in reference [25]. There is a threshold under which inhibition times cannot be detected.…”

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

“…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].…”

“…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.…”

TheBriggs-Rauscher Reaction as a Test to Measure the Activity of Antioxidants

“…Recently, we reported [4] the inhibitory effects of soy antioxidants on an oscillating reaction, the Briggs-Rauscher (BR) reaction [5]. The BR oscillating system 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.…”

“…Decisive indirect evidence for the involvement and important role played by HOO . radicals in the onset of oscillations is given by the inhibitory effects observed when glycosides contained in the soy wholeflour (as malonyldaidzin or malonylgenistin) are added to an active BR mixture [4]. The effect consists of an immediate cessation of oscillations, but, after some time, the oscillatory behavior is regenerated with amplitude, frequency, and duration different from those observed in a reference mixture.…”