Abstract
dl-alpha-Tocopherol spread on an acidic subphase as a gaseous monolayer was oxidized slowly to a derivative that was identified by thin-layer chromatography as alpha-tocopherylquinone. The derivative generated the same II-A isotherm as alpha-tocopherylquinone. When the subphase contained gold chloride, alpha-tocopherol was oxidized rapidly and quantitatively to alpha-tocopherylquinone. dl-alpha-Tocopherol spread on a basic subphase as a gaseous monolayer was oxidized slowly to a mixture that contained alpha-tocopherol, a quinone, and a nonpolar derivative. The mixture generated a II-A isotherm with an inflection point below the equilibrium spreading pressure of either alpha-tocopherol or alpha-tocopherylquinone. When potassium ferricyanide was added to the alkaline subphase, alpha-tocopherol was oxidized rapidly to a mixture that contained both the nonpolar derivative (major product) and the quinone (minor product). The nonpolar derivative was isolated by thin-layer chromatography and identified as the spirodienone ether by ultraviolet, infrared, and chemical ionization mass spectra. The spirodienone ether had a low equilibrium spreading pressure that explained the inflection point in the II-A isotherm generated by alpha-tocopherol on an alkaline subphase. Surface area data showed that dl-alpha-tocopherol formed immiscible films with stearyl alcohol and miscible films with oleyl alcohol. II-A isotherms showed that alpha-tocopherol in both immiscible and miscible mixtures was oxidized rapidly on an alkaline potassium ferricyanide subphase to the spirodienone ether. Collapse pressure data showed that the spirodienone ether formed an immiscible film with stearyl alcohol and a miscible film with oleyl alcohol. Interfacial oxidation experiments showed that alpha-tocopherol is oxidized either to tocopherylquinone (acidic subphase) or to the spirodienone ether (alkaline subphase). The natural occurrence of both tocopherylquinone and the spirodienone ether suggests that several types of oxidant stress are found in biological systems. One type of oxidant stress may involve the peroxy radical generating tocopherylquinone; a second type may involve hydroxyl radical-hydroxide ion generating the spirodienone ether.
Highlights
Miscible and immiscible films * peroxy and hydroxyl radicals ticalwith the compound obtained by the oxidation of a-tocopherol with alkaline potassium ferricyanide
The interfacial oxidation of a-tocopherol to tocopherylquinone and the spirodienone ether, and the surface properties of these oxidation products are examined in the present study
Thin-layer chromatography (TLC) was usedto establish the initial purity of a-tocopherol and a-tocopherylquinone and to identify these compounds in lipid film
Summary
The interfacial oxidation of a-tocopherol to tocopherylquinone and the spirodienone ether, and the surface properties of these oxidation products are examined in the present study. When DL-a-tocopherol was spread on subphase at pH 7 and pH 12.8 and the ll-A isotherm was generated, the isotherm was expanded at lower surface pressures (Fig. 3). The inflection point in the II-A isotherm suggests thata newfilm component with a lower collapse pressure is formed when a-tocopherol is spread on a neutral oralkaline subphase.The film was collected and analyzed to investigate this possibility.TLC analysis showed that the film contained a-tocopherol (R,0.65) and two minor components, a-tocopherylquinone ( R f0.3) and a new component (R, 0.9).
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