Kuz’min, SM; Chulovskaya, SA; Tesakova, MV; Semeikin, AS; Parfenyuk, VI; ,
Antioxidant properties of tetraphenylporphyrin (H-2 TPhP), 5,10,15,20-tetrakis(4-hydroxy-3,5-di-tert-butylphenyl) porphyrin (H2T(4-OH-3,5-di-t-BuPh) P), 5,10,15,20-tetrakis(3-hydroxyphenyl) porphyrin (H2T(3-OHPh)P), 5,10,5,20-tetrakis( 4-hydroxyphenyl) porphyrin (H2T(4-OHPh)P), 5,10,15,20-tetrakis(3-aminophenyl) porphyrin (H2T(3-NH2Ph)P) and 5,10,15,20-tetrakis(4-aminophenyl) porphyrin (H2T(4-NH2Ph)P) were examined using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and superoxide radicals. The modified DPPH assay was used because of high absorption coefficient of porphyrins that leads to inaccuracy in the spectrophotometric data of DPPH center dot concentration. The amperometric response during cyclic voltammetry (CV) allows us to investigate the antioxidant properties of chromophores at sufficiently high concentration of the components.The antioxidant activity of porphyrins was evaluated using equation A=(I-0-I)/I-0, where I-0 and I are current peak values of DPPH center dot oxidation (reduction) at initial moment and after 10 min interaction of radical with antioxidants, correspondingly. The DPPH assay shows that antioxidant activity increases in the following series: H2TPhP < H2T(4-OH- 3,5-di-t-BuPh)P < H2T(3-OHPh)P < H2T(4-OHPh)P. The synthetic DPPH radical is a traditional standard for the antioxidant activity studying but the high antiradical ability to natural radicals is more important for the practical application. Superoxide anion radical (O-2(center dot-)), arising as a living and lifeless nature, plays a key role in many oxidative processes so the interaction of O-2(center dot-) and the macrocyclic compounds was studied. Electroreduction of oxygen in oxygen saturated media during first CV cicle enable us to fix the well reproducible current peak of O-2(center dot-) oxidation. The changing in the O-2(center dot-) oxidation current value indicates the interaction of studied porphyrins with superoxide. The decay of O-2(center dot-) oxidation current with increasing of the porphyrin concentration was used for IC50 parameter (corresponds to the porphyrin concentration was needed to halve the O-2(center dot-) reduction current) and binding constant (K) estimation. The K value was found according relation: lg(1/C)= lgK+lg(I/I-0-I), where C - the porphyrin concentration, I - O-2(center dot-) oxidation peak current, I-0 - O-2(center dot-) oxidation peak current without the porphyrin. The obtained parameters show that antioxidant activity increase in following series: H2TPhP < H2T(3-NH2Ph)P < H2T(3-OHPh)P < H2T(4-NH2Ph)P < H2T(4-OHPh)P. It is clear that the used tests lead to similar antiradical activity series: para-substituted tetraphenylporphyrins have higher activity than the meta-substituted. The antioxidant properties of porphyrins in comparison with properties of other type antioxidant compounds demonstrate that H2T(4-NH2Ph)P and H2T(4-OHPh)P are promising molecular forms with high antioxidant activity.