Subsecond time-resolved spin trapping followed by stopped-flow EPR of Fenton reaction products

Determination of antioxidant activity of phenolic antioxidants in a Fenton-type reaction system by chemiluminescence assay

“…In the present work, a rapid, convenient and reliable assay was developed to assess the hydroxylradical-scavenging activity of phenolic compounds by taking advantage of the transient properties of the Fenton reaction [28,29] and chemiluminescent reaction between · OH and luminol. Since the measurement time was reduced to its minimum and, in addition, this assay was performed under de-aerated conditions, the pro-oxidant actions [12,13,14,15,16,17] of some phenolic compounds could be attenuated effectively.…”

“…1 Chemical structures of the selected phenolic antioxidants: 1 o-coumaric acid, R 1 =OH; 2 p-coumaric acid, R 3 =OH; 3 ferulic acid, R 2 =OCH 3 , R 3 =OH; 4 caffeic acid, R 2 =R 3 =OH; 5 catechol, R 4 =OH; 6 pyrogallol, R 4 =R 5 =OH; 7 phloroglucinal, R 5 =R 7 =OH; 8 resorcinol, R 5 =OH; 9 hydroquinone, R 6 =OH; 10 p-aminophenol, R 6 =NH 2 ; 11 protocatechuic acid, R 9 =R 10 =OH; 12 gallic acid, R 9 =R 10 =R 11 =OH; 13 salicylic acid, R 8 =OH; 14 m-hydroxybenzoic acid, R 9 =OH; 15 p-hydroxybenzoic acid, R 10 =OH; other substituents are hydrogen atoms unless noted would make it impossible to produce adequate CL signal for evaluating hydroxyl-radical-quenching effects. It is known that the Fenton reaction was completed transiently [28,29], and hydroxyl radicals are short-lived (less that 10 -4 s) under aqueous conditions. Therefore, the generated hydroxyl radicals had already vanished if H 2 O2 was premixed with Fe 2+ -EDTA before luminol was added to start the CL reaction, and only very weak light emission was recorded.…”

“…In their report, Jiang et al [28] performed a subsecond time-resolved investigation on the rapid spin-trapping kinetics of Fenton reaction products, by applying loop-gap resonator technology to optical stop-flow ESR (electron spin resonance), and found that the total second-order rates for the Fenton reaction were equal to or greater than 10 4 M -1 s -1 . Evidently, under most of the experimental conditions in which the concentration of H 2 O 2 or Fe(II) is less than 0.1 mM, the Fenton reaction might finish within 1 s. Further supporting evidence [29] was published to indicate that no increase in hydroxyl radical formation and 2-deoxyribose degradation was observed 5 s after the initiation of the Fenton reaction.…”

The pollution of water resources and interventions to mitigate and control environmental impact

“…It is well known that hydroxyl radical (HO -) [7][8][9] is one of the most powerful oxidant universally recognized. The mechanism of oxidation of (1) …”

An advanced EPR stopped-flow apparatus based on a dielectric ring resonator

“…Radicals that are not EPR-detectable in the liquid state due to short relaxation times T 1 (linewidth broadening), as e.g., hydroxyl (OH Å ), superoxide ðO ÅÀ 2 Þ, or alkyl thiyl (R-S Å ), cannot be studied directly by EPR-SF techniques. Nevertheless, the spin-adducts of these radicals with nitrones, yielding nitroxide-type radicals, are EPR-active and their kinetics can be monitored also by EPR-SF [6,7]. The kinetics of reduction of a protein-associated tyrosine radical in the R2 protein of Escherichia coli and mouse ribonucleotide reductase (RNR) by inhibitor-based reductants, as hydroxyurea [8] and para-alkoxyphenols [9], have been investigated.…”