Electrochemical properties and antioxidant activity of tetraphenylporphyrin derivatives

Abstract

The method of cyclic voltammetry is used to estimate antioxidant activity of tetraphenylporphyrin (H2TPhP), 5,10,15,20-tetrakis(4'-hydroxyphenyl)porphyrin (H2T(4-OHPh)P), and 5,10,15,20-tetrakis(4'-hydroxy-3'5'-di-tert-butylphenyl)porphyrin (H2T(4-OH-3,5-di-t-BuPh)P) in the reaction with 2,2-diphe-nyl-1-picrylhydrazyl (DPPH). It is found that two of the three studied compounds, i.e., 5,10,15,20-tet-rakis(4'-hydroxyphenyl)porphyrin and 5,10,15,20-tetrakis(4'-hydroxy-3'5'-di-tert-butylphenyl)porphyrin are characterized by antioxidant activity with respect to the stable 2,2-diphenyl-1-picryl-hydrazyl radical that increases in the following series: H2TPhP < H2T(4-OH-3,5-di-t-BuPh)P < H2T(4-OHPh)P. At the same time, tetraphenylporphyrin possesses practically no antiradical properties. The results obtained in this work indicate that, similar to the mechanism for phenol antioxidants as substances with a mobile hydrogen atom (proton donors), one of the mechanisms of the antioxidant effect of the studied porphyrins is related to their interaction with free radicals, particularly with DPPH according to the following reaction: AH + DPPH{sn•}→ A{sn•} + DPPH-H. A change in the structure of the H2T(4-OH-3,5-di-t-BuPh)P molecule due to formation of a sterically hindered phenol fragment resulting from introduction of two tert-butyl substituents causes a decrease in the antioxidant activity of the studied porphyrins.