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 alpha-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 alpha-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 alpha-tocopherol quinone in a chemically irreversible process. The identity of alpha-tocopherol quinone was determined by reflectance-FTIR spectroscopy of the product oil the glassy carbon electrode surface and from comparison of the voltammetric data obtained with a sample of the alpha-tocopherol quinone model compound. alpha-Tocopherol quinone films could be voltammetrically reduced at negative potentials to form alpha-tocopherol hydroquinone in a +2e(-)/+2H(+) chemically reversible process. Experiments were also conducted by incorporating alpha-tocopherol into lipid (lecithin) multilayers deposited onto the electrode Surfaces and the electrochemical results compared with voltammetric data obtained from alpha-tocopherol films that were directly in contact with aqueous buffered solutions.