Oxidation/reduction studies and quantitation analysis of alpha-tocopherol

This research involves an extensive study of alpha-tocopherol oxidation by cupric chloride both in protic (ethanol) and aprotic (hexane) solvents. In aqueous ethanol solution, the dissolution of CuCl2 formed a homogenous reaction system. Oxidation of alpha-tocopherol was carried out at four different Cu(II) concentrations. The time course of the reaction was followed by UV and HPLC. The reaction rate was dependent on Cu(II) concentration. The alpha-tocopherol was almost quantitatively converted to alpha-tocopherylquinone, probably via the intermediate 8a-substituted-alpha-tocopherone. While in hexane, the oxidation took place at the interface between the liquid phase and the solid phase of insoluble CuCl2·2H2O or anhydrous CuCl2. With CuCl2·2H2O, alpha-tocopherylquinone and other products were produced. With anhydrous CuCl2 as the oxidizing reagent in hexane, a relatively stable non-UV-absorbing intermediate was formed, and partly converted to alpha-tocopherylquinone quickly upon treatment with aqueous ethanol.; Polymeric nanomicelles formed by self-assembly of an amphiphilic copolymer in aqueous medium, are potential drug delivery vehicles for hydrophobic and partially hydrophilic drugs. The ability of the nanomicelle to protect alpha-tocopherol against oxidation by Cu(II), air and light under room temperature was evaluated by measuring the residual alpha-tocopherol at different reaction times during the oxidation process, and compared with that of an aqueous alcohol solution of alpha-tocopherol at the same concentration which underwent the same oxidation process. The oxidation of alpha-tocopherol by Cu(II) was suppressed significantly by encapsulation in the nanomicelle. But it did not seem to have a protective effect against air and light.; The reduction of alpha-tocopherylquinone by stannous chloride was also studied. In hexane, alpha-tocopherylquinone, was reduced by solid SnCl 2 or SnCl2·2H2O to alpha-tocopherol via the intermediate alpha-tocopherylhydroquinone at a yield of 80%. The choice of SnCl2 or SnCl2·2H2O considerably affected the reaction rate. In methanol the reduction was carried out at two Sn2+ concentration levels. The alpha-tocopherol yield was also 80%, and the reaction rate was not affected by the Sn2+ concentration.; The last part of the study was to determine the tocopherols in vegetable oils. A new sample preparation method was developed which involved extracting tocopherols from vegetable oils with methanol. This method offers the advantage of rapidness, convenience and compatibility with the mobile phase and column for reverse-phase HPLC, but the recovery was low, less than 80% for alpha-tocopherol.