The study of aminophenazone radical cation and its interaction with some antioxidants

The purpose of this study was to identify both the possibilities of in vitro generation of 1-phenyl-2,3-dimethyl-4-dimethylamino-5-pyrazolone (aminophenazone) radical cation (abbreviated APH*+) and the mechanisms of interaction with different antioxidants.The chromophore radical cation APH*+ was obtained by oxidizing APH with ammonium persulfate. The stages of the oxidation reaction and the production of the intermediate compounds were studied by spectrophotometrical and potentiometric titration. As standard antioxidant there was used a catechin solution in distilled water with concentrations ranging between 50-250 microg/mL, in weak alkaline environment.The oxidation of APH with ammonium persulfate developed in four stages, involving the production of some intermediate compounds with different colorations. A mechanism for this reaction has been proposed. The radical cation forms to an APH - ammonium persulfate molar ratio of 2 : 1. In the presence of an antioxidant (catechin) the radical cation APH*+ forms to a molar ratio APH-ammonium persulfate of 1:1, in weak alkaline environment. It has an absorbtion maxima at lambda = 540 nm. The molar extinction coefficient of APH*+ at lambda = 540 nm has been calculated. Its absorbance was proportional with catechin concentration in the range 50-250 microg/mL (r2 = 0.9988).The APH-ammonium persulfate system can be used for spectrophotometric determination of total polyphenols in different systems.