Determination of rate constants of the spin trap 3,5-dibromo-4- nitrosobenzenesulfonic acid with various radicals by pulse radiolysis and competition kinetics.

The spin-trapping reactions of the aromatic nitroso compound 3,5-dibromo-4-nitrosobenzene-sulfonic acid (DBNBS) with a number of inorganic [.OH, .N3, CO2 .-, O 2 .-, (SCN)2.-] and organic radicals (methyl, hydroxymethyl, hydroxyethyl, 2-hydroxypropyl, 2-hydroxy-2-methylpropyl) have been studied by both pulse radiolysis and EPR spectroscopy. Direct kinetic as well as competition kinetic methods have been used to determine the respective rate constants. In the case of CO2 .- and O 2 .-, no corresponding spin adduct is observed, while with .OH and (SCN)2 .- only unspecific nine-line EPR signals occur. At neutral pH, only hyperfine splitting constants of spin adducts consistent with trapping of primary (β-hydroxyalkyl) radicals can be determined, while strongly acidic solutions are required to trap secondary and tertiary (α-hydroxyalkyl) radicals

Radical species produced from the photolytic and pulse-radiolytic degradation of tert-butyl hydroperoxide. An EPR spin trapping investigation.

The radicals generated during the photolysis of tert-butyl hydroperoxide have been identified by comparison with those generated by reductive pulse radiolysis of the same compound, by photolysis of di-tert-butyl peroxide, and by oxidative degradation of dimethyl sulfoxide. While ButO. can definitely be identified as the primary alkoxyl radical intermediate, the identity of the predominantly-formed peroxyl radical is dependent on the generation system

Antioxidant mechanisms of polyphenolic caffeic acid oligomers, constituents of Salvia officinalis.

Caffeic acid, rosmarinic acid and oligomers of caffeic acid with multiple catechol groups are all constituents of Salvia officinalis. Their antioxidant potential was investigated with regard to their radical scavenging activity and the stability and structure of the intermediate radicals. Pulse-radiolytic studies revealed very high rate constants with hydroxyl radicals. Evidence from kinetic modeling calculations suggested an unusual complex behavior due to the presence of both O4- and O3-semiquinones and formation and decay of a hydroxyl radical adduct at the vinyl side chain. The radical structures observed by EPR spectroscopy after autoxidation in slightly alkaline solutions were only partially identified due to their instability and generally represented dissociated O4-semiquinones. Hybrid density-functional calculations of the potential radical structures showed distinct differences between the resonance stabilization of the O4- and O3-semiquinones of caffeic and dihydrocaffeic acids, reflected also in the considerably faster decay of the O3-semiquinone observed by pulse radiolysis. No evidence was found for dimerization reactions via Cbeta radicals typical for lignin biosynthesis