Electrochemistry of α-Tocopherol (Vitamin E) and α-Tocopherol Quinone Films Deposited on Electrode Surfaces in the Presence and Absence of Lipid Multilayers

Water insoluble α-tocopherol films were deposited on the surface of gold, glassy carbon and platinum electrodes and their voltammetric behavior examined in aqueous solutions between pH 3 and 13. The voltammetric mechanism involved α-tocopherol being oxidized in a −2e⁻/−H⁺ process to form a phenoxonium cation, which underwent rapid reaction with water (or ⁻OH at pH > 7) and rearrangement to form α-tocopherol quinone in a chemically irreversible process. The identity of α-tocopherol quinone was determined by reflectance-FTIR spectroscopy of the product on the glassy carbon electrode surface and from comparison of the voltammetric data obtained with a sample of the α-tocopherol quinone model compound. α-Tocopherol quinone films could be voltammetrically reduced at negative potentials to form α-tocopherol hydroquinone in a +2e⁻/+2H⁺ chemically reversible process. Experiments were also conducted by incorporating α-tocopherol into lipid (lecithin) multilayers deposited onto the electrode surfaces and the electrochemical results compared with voltammetric data obtained from α-tocopherol films that were directly in contact with aqueous buffered solutions.