RESUMEN
The coenzymes Q and Vitamin K(3), as well as their synthetic analogues, have been found to inhibit free-radical processes of fragmentation of hydroxyl-containing organic compounds and oxidation of the latter by molecular oxygen. It has been established that the observed effects are due to the ability of quinones to oxidize the alpha-hydroxyl-containing carbon-centered radicals formed from the starting compounds.
Asunto(s)
Radicales Libres , Compuestos Orgánicos/química , Oxígeno/química , Quinonas/química , Cinética , Estructura Molecular , Oxidación-ReducciónRESUMEN
PURPOSE: To investigate regularities observed in the course of reactions involving cleavage of C-N bonds on the radiolysis of amino-containing organic compounds and their derivatives in aqueous solutions. MATERIALS AND METHODS: Aqueous solutions of amino-containing compounds, saturated with Ar or O(2), were exposed to gamma-radiation from a (137)Cs source. The absorbed dose-rate was 0.33 Gy s(-1), the absorbed dose range was 0.1-7.5 kGy. Analyses for ammonia and amino-containing organic compounds were performed using an amino acid analyser, and analyses for other radiolysis products were made by gas-liquid chromatography. RESULTS: The presence of a hydroxyl group in the beta-position to the amino group promotes deamination of amino alcohols, amino acids, di- and tripeptides, these processes being associated with the possible occurrence of monomolecular fragmentation of the respective radicals. Oxygen inhibits the deamination of alpha,beta-amino alcohols and hydroxyl-containing amino acids. The presence of alkyl substituents in the amino group favours C-N bond cleavage on the radiolysis of amino alcohols, whereas the presence of an acyl group sharply suppresses this process. Replacement of the hydroxyl group in molecules of the initial amino alcohols by a hydrogen atom (i.e. a changeover to alkylamines) or by a methoxy group decreases the efficiency of deamination sharply. The presence of hydroxyl groups in side residues of di- and tripeptides promotes destruction of the peptide chain with formation of amides of amino acids, while suppression of deamination and main chain destruction processes in these compounds is observed in the presence of oxygen. CONCLUSIONS: The most effective processes leading to the C-N bond cleavage on the radiolysis of aqueous solutions of amino-containing organic compounds are those in which the key role is played by reactions of monomolecular decomposition of radicals of the initial compounds.
Asunto(s)
Aminas/química , Aminas/efectos de la radiación , Aminoácidos/química , Aminoácidos/efectos de la radiación , Amino Alcoholes/química , Amino Alcoholes/efectos de la radiación , Rayos gamma , Enlace de Hidrógeno , Concentración de Iones de Hidrógeno , Técnicas In Vitro , Péptidos/química , Péptidos/efectos de la radiación , Soluciones , AguaRESUMEN
Effects of a number of quinones and diphenols of various structures on free-radical fragmentation processes taking place in alpha-diols, glycerol, 2-aminoethanol, glycero-1-phosphate, ethylene glycol monobutyrate, maltose, and some lipids were investigated. Quinone additions have been found to change the direction of free-radical transformations of the compounds cited above by inhibiting formation of the respective fragmentation products owing to oxidation of radicals of the starting compounds. The results obtained and literature data available allow a suggestion to be made that the system quinone/diphenol is able to not only deactivate or generate such active species as O2.- but also control the realization probability of free-radical processes of peroxidation and fragmentation in biologically important molecules.