7-Ethyl-2,3,5,6,8-pentahydroxy-1,4-naphthoquinone (echinochrome A): a DFT study of the antioxidant mechanism. 3.* The structures of dianions and disodium salts of echinochrome A and their reactions with the hydroperoxyl radical

摘要

Quantum chemical calculations and the conformational analysis of dianions, radical dianions, disodium salts, and radicals of disodium salts of 7-ethyl-2,3,5,6,8-pentahydroxy-1,4-naphthoquinone (echinochrome A) were carried out at the (U)B3LYP/6-31G(d) and (U)B3LYP/6-311G(d) levels of theory. The heats of reactions of the hydroperoxyl radical (HOO") with the isomers of dianions and disodium salts of echinochrome A with the lowest Gibbs free energies were estimated. All reactions of these isomers of dianions and disodium salts of echinochrome A with HOO' in the gas phase are exothermic. The isomer of the dianion of echinochrome A with the lowest Gibbs free energy, which is formed by the heterolysis of the 2β- and 6β-OH groups, is the more effective antioxidant than the isomer of the 2,6-disodium salt with the lowest Gibbs free energy.