Effect of flavonols on radiation-induced reactions with the participation of α-hydroxyl-containing organic radicals

Abstract

1 Flavonols, which are plant polyphenols, are widely used for the regulation of free-radical oxidation processes in biological systems [1][2][3][4]. The antioxidant activity of flavonols, as well as a number of other flavonoids, is responsible for their useful therapeutic properties. Because of this, it is of considerable interest to study the properties of this class of compounds.Previously [5][6][7][8], it was found that biologically important molecules exposed to γ -radiation and other initiators of free-radical processes can be damaged not only by oxidation but also as a result of fragmentation. In the latter process, the step of degradation of α -hydroxyl-containing radicals plays a key role. It was also found [9, 10] that carbonyl-containing compounds and quinones affect free-radical processes that involve α -hydroxyl-containing carbon-centered organic radicals. As regards flavonoids, only a few publications [11][12][13][14] have been devoted to their reactivity toward carbon-centered radicals.In this paper, we report data that allow us to judge the probabilities and reaction pathways of flavonols and structurally related model compounds with organic radicals formed in the radiolysis of ethanol and aqueous ethylene glycol and 2-methoxyethanol solutions. EXPERIMENTALThe figure summarizes the structural formulas of compounds used in this study. Commercial quercetin (more than 95% purity), rutin (more than 95% purity), morin (more than 95% purity), maltol (more than 98% purity), and kojic acid (more than 98% purity) from Aldrich were used without additional purification. Ethanol (96 vol %) was purified using Wolfen Zeosorb LA zeolite and distilled using a 3-m rectification column. 1 Ethylene glycol and 2-methoxyethanol were purified by double distillation. The purity of the substances was monitored by chromatography.Before dissolving samples, ethanol was sparged with high-purity argon (99.9%) for 50 min. All of the subsequent procedures up to sealing ampules with solutions were performed in an argon atmosphere.Ethylene glycol and 2-methoxyethanol solutions at a concentration of 3 mol/l were prepared with twicedistilled water, fresh solutions being used for each particular set of experiments. Required concentrations of additives in the resulting solutions were obtained by introducing weighed portions of test substances into the solutions. Oxygen was removed by five freezingpumping-thawing cycles. Next, the ampules were sealed under vacuum.The γ -radiation of 137 Cs was used as an initiator of free-radical processes in model systems. Irradiation was performed in sealed ampules (inner diameter, 6 mm; height, 40 mm; sample volume, 0.7 ml). The dose rate was 0.31 ± 0.01 Gy/s; the absorbed dose range 0.2-3.5 kGy was used.All of the data given were obtained by averaging the results of no less than three sets of experiments. The radiation-chemical yields of formation of substances were determined from the dose dependence of the buildup of these substances.The concentrations of acetaldehyde, 2,3-butanediol, and methano...

Gamma-radiolysis of the ethanol-water binary system in the presence of oxygen

“…Aqueous ethanol solutions are widely used in stud ies of radioprotectant, antioxidant, and other proper ties of biologically active substances (e.g., vitamins) and their substituted synthetic analogues [1][2][3][4][5]. The activity of these compounds in processes involving free radicals is assessed by measuring the radiation chem ical yield of a certain stable radiolytic product, usually generated by gamma radiation.…”