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

Abstract

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˙^–, O₂˙^–, (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 O₂˙^–, 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.