Acceleration of lopid peroxidation in cells and production of active oxigen forms and free
radicals leads to destruction of the cells membranes and aging of organisms. Search of new
antiodidants capable “to quench” free radicals and prevent oxidative stress is a very important
problem. Studiy of antioxidant properties of porphyrin compounds is of particular interest.
It is widely known that natural porphyrins are macroheterocyclic compounds which play
an important role in metabolism of living organisms, for example, iron containing blood heme
porphyrin (hemoglobin) or magnesium containing porphyrin (chlorine) which was found in
chloroplasts. In the presen work tetraphenylporphin and its derivatives such as 5,10,15,20-
tetrakis(4’-hydroxyphenyl)porphyrin and 5,10,15,20-tetrakis(4’-hydroxy-3’,5’-di-tretbutylphenyl)
porphyrin were synthesized and their antioxodant activity was estimated. The
antioxidant activity of the porphyrins was tested in their reaction with free radicals of 2,2-
dipheny-l-picrylhydrazyl (DPPH) by cyclic voltammetry method and on the basis of oxidation
potentials of the studied compounds. Table 1 shows the oxidation potential values (Eox,V),
oxidation-reducntion potential values (Eox/red, V) and the indexex of efficiency of antioxidant
action (A1, A2) of the porphyrins in organic solvents.

It has been found that 5,10,15,20-tetrakis(4’-hydroxyphenyl)porphyrin and 5,10,15,20-
tetrakis(4’-hydroxy-3’,5’-di-tret-butylphenyl)porphyrin exhibit the antioxidant activity
increasing in the following order: H2TPhP < H2T(4’-ОН-3’,5’-di-t-BuPh)P < H2T(4’-ОНPh)P.
Among the studied compounds, H2T(4’-ОНPh)P has the lowest oxidation potential. This
confirms a fact that redox potentials are direct measure of antioxidant activity of chemical
compounds. The porphyrins “guench” free radicals due to hydrogen donating ability of hydroxyl
group of phenyl ring. The presence of spatially hindered phenol fragment in the H2T(4’-ОН-
3’,5’-di-t-BuPh)P molecules results in the decreasing antioxidant activity of the porphyrin.