Substituted aminophenols and flavonoids as potential components for test-systems for total antioxidant activity

Kinetics of ortho-phenylenediamine (PDA) oxidation has been investigated in the “pseudoperoxidase” system, Methemalbumin-H₂O₂, in the presence of 2-amino-4-tert-butylphenol (ATBP), 2-amino-4,6-ditert-butylphenol (ADTBP) and its four N-acyl derivates, as well as flavonoids (quercetin, morin, silibin, hesperidin and naringin). Under standard experimental conditions (20°C, phosphate buffered saline, pH 7.4, containing 5.25% ethanol and DMF) ATBP, ADTBP and two its N-acyl-derivatives and also all five flavonoids inhibited PDA oxidation with different efficiency, which was characterized in terms of the inhibition constants, K_i, M, or the percent of inhibition degree at the maximal concentrations of these inhibitors. Quercetin (K_i = 7.7 × 10^?5 M) and ATBP (K_i = 1.26 × 10^?4 M) were the most effective antioxidants. Using these characteristics and other required criteria, the pairs PDA-quercetin and PDA-ATBP were proposed for a practical application in the test-systems for evaluation of total antioxidant activity of biological objects.