S. D. Brinkevich

Effect of ascorbic acid and its derivatives on the radiation-chemical transformations of hydroxyl-containing organic compounds

The effect of ascorbic acid, 5,6-O-isopropylidyl-2,3-O-dimethylascorbic acid, and 2-O-glucopyranosylascorbic acid on the formation of main radiolysis products of ethanol and aqueous ethanol, ethylene glycol, α-methylglucopyranoside, and maltose solutions was studied by means of continuous radiolysis. The obtained results indicate that ascorbic acid effectively reacts with the carbon-centered hydroxyl-containing radicals derived from the substrates, thus decreasing the yield of their recombination and fragmentation products. It was found that the interaction of ascorbic acid and its derivatives with the carbon-centered radicals during the radiolysis of deaerated ethanol and its aqueous solutions may occur via both reducing and oxidizing mechanisms and that ascorbic acid in the aerated solutions acts as a hydrogen donor, reducing mainly the HO2· radical to hydrogen peroxide.

Effects of indole and imidazole derivatives on the radiation- and peroxide-induced transformations of ethanol

The interaction of indole, imidazole, and their derivatives with α-hydroxyethyl radicals has been studied by the radiation and peroxide initiation of free-radical processes. The enthalpies of H-atom addition to the multiple bonds of the test compounds, which characterize their oxidation properties, have been calculated within the framework of the density functional theory. The set of experimental and theoretically calculated data indicate that serotonin or β-carboline alkaloids (harmine, harman, and harmaline) inhibit the formation of 2,3-butanediol—the main radiolysis product of deaerated ethanol—mainly due to reduction and addition or the oxidation of α-hydroxyethyl radicals, respectively. Enhancement of oxidation properties in the above order of β-carboline alkaloids has been observed. Pyrrole, indole, melatonin, imidazole, 1-methylimidazole, and 2-mercapto-1-methylimidazole exhibit low reactivity toward α-hydroxyethyl radicals.

Effects of B vitamins on the radiation-induced transformations of hydroxyl-containing organic compounds

In this work, the interaction of B vitamins with α-hydroxyl-containing carbon-centered radicals formed upon the irradiation of deaerated aqueous solutions of ethanol, ethylene glycol, α-methylglycoside, maltose, and α-glycerophosphate at pH 7 was studied by means of continuous radiolysis. Within the framework of the density functional theory, the homolytic bond dissociation enthalpies (BDEs) of -C-H, -O-H, and -N-H bonds and H-atom addition enthalpies (HAEs) at the -C=O and -C=N groups of the test compounds were calculated. The set of the experimental and theoretically calculated data suggests that vitamin B2, nicotinamide and pyridoxal phosphate effectively oxidize α-hydroxyl-containing carbon-centered radicals, whereas vitamins B1 and B6 reduce these radicals to prevent their recombination and fragmentation reactions.

Interaction of tryptophan and its derivatives with oxygen- and nitrogen-centered radicals

The interaction of tryptophan and its derivatives with the nitrogen-centered 2,2-diphenyl-1-picrylhydrazyl radical and oxygen-centered radicals formed during the radiolysis of oxygen-saturated ethanol and its aqueous solutions has been studied. It has been found that unlike pyrrole, indole, or melatonin, tryptophan, 5-hydroxytryptophan, serotonin, harman, harmine, and harmaline are capable of reducing oxygen-centered radicals by electron transfer from the lone pairs of nitrogen atoms. It has been shown that serotonin and 5-hydroxytryptophan reduce the 2,2-diphenyl-1-picrylhydrazyl radical via the transfer of hydrogen atoms from the hydroxyl groups of the molecules. In this case, pyrrole, indole, tryptophan, melatonin, harman, harmine, and harmaline, which do not contain phenolic hydroxyl groups in their structures, do not interact with the 2,2-diphenyl-1-picrylhydrazyl radical. The final molecular products of the reaction of serotonin and 5-hydroxytryptophan with 2,2-diphenyl-1-picrylhydrazyl radicals have been identified by chromatography-mass spectrometry.

IR spectra of benzaldehyde and its derivatives in different aggregate states

We have measured the IR Fourier-transform spectra of biologically active benzaldehyde and its derivatives in the gas and liquid phases. For compounds of this class, the role played by C=O, OH, and CH groups in intra- and intermolecular has been analyzed. We have revealed spectral features that characterize the participation of C=O groups of unsubstituted benzaldehyde molecules in the occurrence of intermolecular hydrogen bonds C=O...H-C with the formation of molecular dimers of different types. For 2-hydroxybenzaldehyde molecules, spectral data have been obtained that are indicative of the occurrence of intramolecular hydrogen bonds of the C=O...H-C type in solutions. In 2-methoxybenzaldehyde molecules, no intramolecular hydrogen bonds have been observed.

Interaction of hydroxyaryl aldehydes with α-hydroxyethyl radicals

The effect of some hydroxylated aromatic aldehydes on the radiation-chemical transformations of deaerated ethanol during continuous radiolysis has been studied. The data obtained show that these compounds effectively inhibit radiation-induced processes involving α-hydroxyethyl radicals (α-HER). Benzaldehyde and its hydroxylated derivatives (II, III) predominantly oxidize, and compounds containing the cinnamic moiety, (IV–VI), add α-HER to a carbonyl group or -C=C bond.

Effects of coenzyme Q0, ascorbic acid, and its glycoside on the radiation-induced dephosphorylation of organic phosphates in aqueous solutions

The effects of coenzyme Q0, ascorbic acid, and 2-O-α-D-glucopyranosylascorbic acid on the radiation-induced dephosphorylation of 1-glycerophosphate, glucose-1-phosphate, and glucose-6-phosphate in deaerated aqueous solutions at pH 7 were studied by means of continuous radiolysis. It was found that the test compounds efficiently suppressed the radiation-induced dephosphorylation of organic phosphates in equimolar concentrations by interactions with water radiolysis products. At an organic phosphate to additive concentration ratio of 100: 1, ascorbic acid and coenzyme Q0 can suppress the radiation-induced dephosphorylation of the initial substances in aqueous solutions by the reduction and oxidation of hydroxyl-containing carbon-centered radicals, respectively.