How meaningful is the assessment of antioxidant activities in microheterogeneous media?

Ignoring environmental factors in microheterogeneous solutions of antioxidants may lead to significant distortions and inconsistencies in the assessment of their activities. The importance of the hydrophobicity of the antioxidants and of the assaying radicals in such media is illustrated by comparing the reactivities of three phenols of different hydrophobicity, 3,5-di-t-butyl-4-hydroxytoluene (BHT), 6-hydroxy-2,5,7,8-tetramethylchromane-2-carboxylic acid (Trolox) and Quercetin compared to radicals TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) and 4-amino-TEMPO in micellar solutions of variable acidity of reduced Triton-X 100. The relative reactivities of these radicals, measured by EPR spectroscopy, indicated that the hydrophobicity of the involved species is a factor that should always be considered in the evaluation of antioxidants, with the risk of arriving at wrong conclusions regarding their activities.