The Influence Of Halide And Pseudo-Halide Antioxidants In Fenton-Like Reaction Systems

Jasna Malešič,*a Jana Kolar,a Matija Strličb and Slovenko Polancb

a National and University library, Turjaška 1, SI-1000 Ljubljana, Slovenia. Fax: 00386(1)5861311; Tel: 00386(1)5861300;
b University of Ljubljana, Faculty of Chemistry and Chemical Technology, Aškerčeva 5, SI-1000 Ljubljana, Slovenia.

An application of the N,N'-(5-nitro-1,3-phenylene)bisglutaramide (NPG) hydroxylation assay for spectrophotometric determination of the rate of oxidising species generation in Fenton-like systems in the presence of halide and pseudo-halide antioxidants was evaluated. Using ion chromatography it was demonstrated that the concentration of antioxidants did not decrease during the course of the experiment. Although the stoichiometry was not constant, determination of the rate constant of NPG hydroxylation was not significantly affected. Consequently, a reasonably good correlation was obtained between the kinetic data obtained spectrophotometrically by studying the reaction mixtures at 432 nm and the sum of concentrations of p- and o- hydroxylated NPG derivatives determined chromatographically. This indicates that the less time consuming spectrophotometric N,N'-(5-nitro-1,3-phenylene)bisglutaramide hydroxylation assay may be used for facile determination of the rate of oxidising species generation in Fenton-like systems containing various halide and pseudo-halide antioxidants. Employing the assay, it was demonstrated that the efficiency of the antioxidants is affected by their concentration and decreases in the order I- > SCN- ³ Br-. In addition, the effect of the corresponding cations was also studied. It was shown that there is a pronounced effect on the rate of hydroxyl radical production, with quaternary ammonium bromides being more effective than potassium bromide or methyltriphenylphosphonium bromide.

Keywords: fenton reaction, hydroxylation, antioxidant, halide, pseudo-halide