engleski

Influence of medium on oxidation kinetics of iron(II) ion with tert-butyl hydroperoxide

The aim of investigations of hydroperoxide reactivity with iron was to explain the role of free radicals in lipid peroxidation processes. Our study conducted on the oxidation of iron(II) with tert-butyl hydroperoxide (t-BuOOH) in the absence of oxygen suggested that possible involvement of iron in lipid peroxidation in biological systems depends on pre-existing lipid hydroperoxides. It has been shown experimentally that the rate of oxidation of iron(II) with t-BuOOH measured as [FeCl]2+ complex in dichloromethane-methanol solvent mixture was slow at acid medium, about 150 M-1 s-1, increased with decreasing the acid concentration and approaching the physiological conditions the rate constant attained the value of an order of magnitude of 103 M-1 s-1. For all that, very little alteraton of stoichiometry of the oxidation reaction was observed throughout the acidity range. Increasing solvent polarity from the dichloromethane-methanol mixture to water at constant acid concentration of 0.8 mM HCl resulted in hundred-fold decreasing the rate constant of oxidation of iron(II) with t-BuOOH. Further, in the presence of thiocyanate the rate of the oxidation was approximately twice as high as the rate of the oxidation in the presence chloride. Based on these results, a possible mechanism of the effect of solvent, acidity and ligand type on the rate constant is discussed.

iron; hydroperoxide; free radicals; oxidation rate; solvent polarity; chloride; thiocyanate

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