Substituent position influence on the electrochemical properties and antioxidant activity of tetra(aminophenyl)porphyrins

摘要

Free radicals and reactive oxygen species (ROS) are important intermediate products in physiological processes. In the healthy cell, they are generated and regulated by enzymes and low molecular weight antioxidants. Overproduction of ROS leads to a large list of diseases, so the determination of antioxidant activity of perspective natural and synthetic compounds is necessary for drugs development. In this paper cyclic voltammetry (CV) method was applied to the electrochemical and superoxide scavenging properties of 5,10,15,20-tetrakis(4′-aminophenyl)porphyrin (H_2T(p-NH_2Ph) P) and 5,10,15,20-tetrakis(3′-aminophenyl)porphyrin (H_2T(m-NH_2Ph)P) investigation. It is shown that the studied porphyrins have very similar electrochemical behavior and slight effect on the quantity of superoxide produced during first CV cycle therefore the estimation of superoxide scavenging properties may be performed by the O_2~(· -) oxidation peak current monitoring. The antioxidant properties of porphyrins were estimated in terms of binding constants. The strong effect of NH_2 group position on the superoxide scavenging activity are shown: the H_2T(p-NH_2Ph)P (k_b = 12.7 × 10~2 mol~(-1)) demonstrates the significant superoxide scavenging activities whereas H_2T(m-NH_2Ph)P (kb = 0.83 × 10~2 mol~(-1)) — negligible. The most probable mechanism of superoxide scavenges explaining the observed differences are the H-atoms transfer due to N–H bond breaking in the aminophenyl substituent.