The generation of hydroxyl radicals in the reaction of molecular oxygen with polyphosphate complexes of ferrous ion.

The reaction of Fe2+ with molecular oxygen (autoxidation) was investigated in 20 mM phosphate buffer (pH 7.4) at 37 degrees C using a fluorescent OH probe, coumarin-3-carboxylic acid. The autoxidation of unchelated Fe2+ produces OH radicals. Polyphosphatic chelators (pyrophosphate and tri- and tetrapoly phosphate) enhanced the generation of radicals. This effect was explained by an alteration of the reaction mechanism. The two-electron reduction of the oxygen molecule and the generation of hydrogen peroxide intermediates are the major reactions during Fe2+ autoxidation. The polyphosphatic complexes of ferrous ion reduce molecular oxygen and reactive oxygen intermediates by a one-electron mechanism. The chelation of ferrous ion increases the generation of the superoxide radical and production of OH during ferrous ion autoxidation and in the Fenton reaction. The results consider the ferrous ion-polyphosphate system as a convenient model for the generation of hydroxyl radical in biological systems.