Characterization of inclusion complex of vitamin E compound with 2,6-di-O-methylated β-cyclodextrin as the solubility enhancer and its kinetic determination for radical scavenging ability

The structure of the inclusion complex of α-tocopherol (vitamin E compound) with 2,6-di-O-methylated β-cyclodextrin (DM-β-CD) was characterized by 2D ROESY NMR measurements, suggesting that DM-β-CD includes the side-chain moiety of α-tocopherol. The inclusion complexation of DM-β-CD showed the usefulness of water solubilizer for the radical scavenging assay of vitamin E compounds in aqueous solution. Using the electron paramagnetic resonance (EPR) competitive spin trapping method, we determined the oxygen radical (RO∙) scavenging abilities of seven vitamin E compounds (tocopherols and tocotrienols), which were solubilized by DM-β-CD in water. The order of the RO∙ radical scavenging abilities for vitamin E compounds solubilized by DM-β-CD are α- > β- ≈ γ- > δ-, which is in agreement with the oxidation potential values of antioxidants. It is noted that the RO∙ radical scavenging abilities of tocotrienols are comparable to those of tocopherols. Based on the results, the mechanism of the antioxidant reaction of vitamin E compounds with the RO∙ radical is discussed.