Searching for an absolute kinetic scale of antioxidant activity against lipid peroxidation

- An absolute scale for antioxidant activity of natural and synthetic molecules is proposed.
- The scale is based on the measure of the inhibition of lipid peroxidation in SDS micelles.
- Experimental results well fit with equation for competitive kinetics.
- Measures of the time of total oxygen consumption well agree with initial rate of oxygen consumption.

The inhibition properties of a number of antioxidants against peroxidation, started by a 2,2′-azobis[2-(2-imidazolin-2-yl)propane] radical initiator, of linoleic acid in sodium dodecyl sulfate micelles, have been determined in terms of oxygen consumption by a Clark electrode in an oxygen-tight cell. For the 31 antioxidants investigated at variable concentrations, the experimental results well fit the kinetic equation for competitive reactions.The ratio between the initial rates, monitored in the absence and in the presence of antioxidants, depends linearly on their concentration. From the slopes of these straight lines, an absolute scale of inhibition properties of the lipid peroxidation can be devised. Furthermore, the little difference of the time of complete oxygen consumption on concentration of different antioxidants has been found, indicating a restricted difference towards chemical structure and stoichiometric ratio.Some considerations regarding the mechanisms of inhibition of the lipid peroxidation in micelles, in view of bibliographic data, have been made.