Журнал "Макрогетероциклы"

S. M. Kuz’min,^а@ S. A. Chulovskaya,^а M. V. Tesakova,^а A. S. Semeikin,^b and V. I. Parfenyuk^а

Dedicated to Prof. O. I. Koifman on the occasion of his 70-th Anniversary

^аG.A. Krestov Institute of Solution Chemistry of Russian Academy of Sciences, 153045 Ivanovo, Russia

^bIvanovo State University of Chemistry and Technology, 153000 Ivanovo, Russia

^@Corresponding author E-mail: smk@isc-ras.ru

DOI: 10.6060/mhc140511k
Macroheterocycles 2014 7(3)

Antioxidant properties of tetraphenylporphyrin (H₂TPhP), 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^• 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=(I₀-I)/I₀, where I₀ and I are current peak values of DPPH^• 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 (O₂^•–), arising as a living and lifeless nature, plays a key role in many oxidative processes so the interaction of O₂^•– 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 O₂^•– oxidation. The changing in the O₂^•– oxidation current value indicates the interaction of studied porphyrins with superoxide. The decay of O₂^•– oxidation current with increasing of the porphyrin concentration was used for IC₅₀ parameter (corresponds to the porphyrin concentration was needed to halve the O₂^•– reduction current) and binding constant (K) estimation. The K value was found according relation: lg(1/C)=lgK+lg(I/I₀-I), where C – the porphyrin concentration, I – O₂^•– oxidationpeak current, I₀ – O₂^•– oxidation peak current without the porphyrin. The obtained parameters show that antioxidant activity increase in following series: H₂TPhP < H₂T(3-NH₂Ph)P < H₂T(3-ОНPh)P < H₂T(4-NH₂Ph)P < H₂T(4-ОНPh)P. It is clear that the used tests lead to similar antiradical activity series: para-substituted tetraphenylporphyrinshave 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.

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