ANTIOXIDANT ACTIVITY OF ASCORBIC ACID AND 2,2,5,7,8-PENTAMETHYL-6-CHROMANOL IN A MODEL SYSTEM OF TETRAHYDROFURAN RADICAL CHAIN OXIDATION IN AN AQUEOUS MEDIUM

In this work, a detailed comparative study of the antioxidant activity of two known compounds with different solubility has been conducted: ascorbic acid (AscH), which is a antioxidant, and 2,2,5,7,8-pentamethyl-6-chromanol (PMX), a water-soluble analog of vitamin E, often used as a model for lipid-soluble antioxidants. The study aimed to evaluate the effectiveness of these compounds against peroxyl radicals in tetrahydrofuran (THF), an organic solvent often used in chemical and biological research. THF oxidation was initiated using a water-soluble radical polymerization initiator, 2,2’-azo-bis-(2-amidinopropane) dihydrochloride (ABAP), in the presence of atmospheric oxygen, which allowed to create controlled conditions for the generation of free radicals. The reaction was carried out in an aqueous medium without the use of buffer solutions at a temperature of 310 K (37 °C), which brings the experimental conditions closer to physiological ones. The reaction was monitored using the differential pressure gauge method, which makes it possible to quantify the rate of oxygen consumption during the inhibited chain reaction of tetrahydrofuran oxidation. To quantify the activity of ascorbic acid and 2,2,5,7,8-pentamethyl-6-chromanol, the effective inhibition rate constant (fk7, l mol–1 s–1) was measured): (3.8 ± 0.2) · 104 and (5.7 ± 0.3) · 105, respectively, and the stoichiometric coefficient of inhibition f: (0.13 ± 0.01) and (2.05 ± 0.2), respectively. The results obtained clearly indicate a significantly higher antioxidant efficiency of PMX compared to AscH in this water-tetrahydrofuran system. It is important to note that this difference is primarily due to a significant decrease in the stoichiometric inhibition coefficient for ascorbic acid in this medium, which indicates a change in the mechanism of its action and/or a decrease in its ability to effectively interact with free radicals in this solvent. It has been shown that the model system of radical chain oxidation of tetrahydrofuran in an aqueous medium can be used to quantify both water- and lipid-soluble inhibitors. For citation: Migranov A.R., Yakupova L.R., Safiullin R.L. Antioxidant activity of ascorbic acid and 2,2,5,7,8-pentamethyl-6-chromanol in a model system of tetrahydrofuran radical chain oxidation in an aqueous medium. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2026. V. 69. N 3. P. 23-29. DOI: 10.6060/ivkkt.20266903.7298.