Abstract
The reaction of α-tocopherol (α-T) with superoxide anion (O −2 ) in both dry acetonitrile and in aqueous acetonitrile solution is described. The O −2 was generated by the electrochemical reduction of molecular oxygen in acetonitrile, using tetrabutylammonium bromide as an electrolyte. α-T was reacted with O −2 either in dry acetonitrile or in a 10% aqueous acetonitrile solution. In dry acetonitrile, α-T was oxidized to a very unstable primary intermediate, which was further oxidized to a secondary, more stable intermediate. The formation of the secondary intermediate depended upon the presence of molecular oxygen. This intermediate readily converted into two compounds in equimolar amounts (designated A and B). The primary, very unstable intermediate was readily reduced again to α-T by treatment with LiAlH4 or ascorbic acid. However, the secondary intermediate or the stable oxidation products could not be reduced to α-T. In the 10% aqueous acetonitrile, α-T was oxidized to α-tocopheryl quinone, α-tocopherol dimer and α-tocopherol dihydroxy dimer, and an unknown compound. In the aqueous medium, no intermediates were formed by the action of O −2 . The results of this study indicate that the reaction of α-T with O −2 under aprotic conditions is different from that observed under protic conditions.
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Abbreviations
- α-T:
-
α-tocopherol
- D:
-
α-T dimer
- DHD:
-
α-T dihydroxy dimer
- HPLC:
-
high-performance liquid chromatography
- O −2 :
-
superoxide anion
- O.D.:
-
optical density
- TBAB:
-
tetrabutylammonium bromide
- TQ:
-
α-tocopheryl quinone
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Csallany, A.S., Ha, Y.L. α-tocopherol oxidation mediated by superoxide anion (O −2 ) I. Reactions in aprotic and protic conditions. Lipids 27, 195–200 (1992). https://doi.org/10.1007/BF02536178
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DOI: https://doi.org/10.1007/BF02536178