Evaluation of the influence of structural features of selected antioxidants on the reduction of Iron ions in the Fe–TPTZ complex

Recent studies have demonstrated that methods for determining antioxidant activity based on the chromogenic change of transition metal complexes following the reduction of the metal ion oxidation state may, in biological matrices, reflect the potential pro-oxidant activity of compounds through Fenton and so called Fenton-like reactions. Fenton and Fenton-like reactions comprise the redox reactions of iron, copper, cobalt, manganese, chromium, vanadium, titanium, nickel, and other transition metal ions. In addition to hydrogen peroxide, these reactions may proceed in the presence of oxidants such as peroxymonosulfates, persulfates (peroxydisulfates), hypochlorides, organic hydroperoxides, and lipid hydroperoxides. The physiological impact of these reactions on biological and other complex chemical systems is significant. Therefore, understanding the mechanisms governing these reactions is essential. The aim of this study was to validate an improved methodology for the Ferric Reducing Antioxidant Power (FRAP) assay, followed by the evaluation of ten model antioxidant compounds and the interpretation of the obtained results. The ability of these compounds to reduce Fe³⁺ ions in the 2,4,6-tris(2-pyridyl)-s-triazine (TPTZ) complex was found to be influenced primarily by molecular complexity (from database sources), further the number of heteroatoms, and secondarily by the number of aromatic rings and double bonds within the molecular structure of tested antioxidants.