Importance of solvent association in the estimation of antioxidant properties of phenolic compounds by DPPH method.

The presented paper shows the influence of temperature increase in the range typically used during antioxidant measurements (15-35 °C) on the estimation of antioxidant properties of phenolic compounds (caffeic acid, ferulic acid, gallic acid, trolox, butylhydroxyanisole, butylhydroxytoluene and 2,6-diisopropylphenol) in associating and non-associating solvents. A significant influence of temperature on the DPPH(•)/antioxidant reaction kinetic is observed for strongly associating solvents (e.g. methanol). This trend is less marked for non-associating solvents (e.g. dioxane, ethyl acetate). The performed experiments prove that the change of solvent structure, caused by temperature increase, influences the estimation of antioxidant properties of phenolic compounds much more than the increase of kinetic energy of reacting molecules and/or the increase of the dissociation degree of hydroxyl groups occurring in antioxidants.