Kinetic modeling of the reversal of antioxidant potency of α-, ß-, γ- and δ-tocopherols in methyl linoleate peroxidation.

Extended, chemically detailed kinetic models at the molecular basis are constructed to identify the reactions involved in the reversal of the antioxidant action of α-, ß-, γ- and δ-tocopherols during methyl linoleate oxidation. The reaction mechanisms were numerically simulated and subjected to analysis to quantify the significance of individual chemical steps by the value-based method. Results of the obtained kinetic models agreed well with the experimental data. The significant individual reactions contributing to the observed antioxidant and pro-oxidant behavior of the different tocopherols were identified. It is revealed that the reverse order of antioxidant potency and a complex nonlinear dependency of the antioxidant potency of tocopherols with the increase in their concentration are due to the increasing contribution of pro-oxidant relative to the antioxidant reactions. Once the approach presented here can be applied to more complex systems, engineered optimization of antioxidant protection strategies may be reached.

Antioxidant Properties of Selenophene, Thiophene and Their Aminocarbonitrile Derivatives.

The oxygen radical absorbance capacity (ORAC) method was used to detect the antiperoxyradical ability of organoselenium compounds: selenophene and its derivative, 2-amino-4,5,6,7-tetrahydro-1-selenophene-3-carbonitrile (ATSe); while as a comparison, the sulfur-containing analogue of selenophene-thiophene and its derivative-2-amino-4,5,6,7-tetrahydro-1-thiophene-3-carbonitrile (ATS)-was selected. Cyclic voltammetry (CV), differential pulse voltammetry (DPV) and squarewave voltammetry (SWV) methods were used to determine the redox characteristics of organoselenium and organosulfur compounds. The antiradical activity and capacity of the studied compounds were also measured by using stable radical 2,2'-diphenyl-1-picrylhydrazyl (DPPH). Detected anodic peaks of the oxidation of selenophene, thiophene and their derivatives in CV, DPV and SWV in the interval of -1200 ÷ (+1600) mV potentials in regard to the Ag/Ag⁺ medium of acetonitrile prove the presence of antiperoxyradical activity in regard to oxidizers, i.e., peroxyradicals. The chemical mechanism of the antiperoxyradical ability of selenophene, thiophene and their organic derivatives is proposed.

Numerical revelation of the kinetic significance of individual steps in the reaction mechanism of methyl linoleate peroxidation inhibited by alpha-tocopherol.

A kinetic model was constructed to describe the reactions involved in the oxidation of methyl linoleate (ML) inhibited by alpha-tocopherol (TH). The initial model of the reaction mechanism included 53 individual steps, which were numerically analyzed by the value method based on Hamiltonian systematization of kinetic equations. Good accord was obtained with experimental data at 40 and 50 degrees C. The dominant steps responsible for the antioxidant and pro-oxidant properties of TH in the process of ML peroxidation were revealed. Tocopherol-mediated peroxidation (TMP) and generation of alkoxyl radicals as a result of the reduction of hydroperoxides by TH or the decomposition tocopherol alkyl peroxides are the dominant reactions responsible for the pro-oxidant activities of alpha-tocopherol. The extreme behavior of reaction induction period in relation to TH initial concentration is related to the increase in the ratios of [tocopheroxyl radical]/[peroxyl radical] and the TMP rate/rate of termination by combination of tocopheroxyl and peroxyl radicals.