title: Electron-transfer reactions between the diamagnetic cation of α-tocopherol (vitamin E) and β-carotene.
abstract: β-Carotene (β-Car) was chemically oxidized in a -2e(-) process using 2 mol equiv of NOSbF(6) in a 4:1 ratio (v/v) of dichloromethane:acetonitrile to form the β-carotene dication (β-Car(2+)). Voltammetric monitoring of the chemical oxidation experiments over a range of temperatures indicated that the half-life of β-Car(2+) was approximately 20 min at -60 °C, and approximately 1 min at -30 °C. α-Tocopherol (α-TOH) was chemically oxidized in a -2e(-)/-H(+) process using 2 mol equiv of NOSbF(6) to form the diamagnetic cation (α-TO(+)) which survives indefinitely at -60 °C in a 4:1 ratio (v/v) of dichloromethane:acetonitrile. Cyclic voltammetry experiments indicated that the oxidative peak potential for α-TOH was approximately +0.4 V more positive than the oxidative peak potential of β-Car. When solutions of α-TO(+)/H(+) (prepared by chemical oxidation of α-TOH with 2 NO(+)) were reacted with solutions containing equal molar amounts of β-Car, voltammetric monitoring indicated that α-TOH was quantitatively regenerated and β-Car(2+) was formed in high yield in a homogeneous two-electron transfer, according to the reaction α-TO(+) + H(+) + β-Car → α-TOH + β-Car(2+).
authors.affiliation: Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371.
authors.forename: Ying Shan
authors.initials: YS
authors.lastname: Tan
authors.forename: Richard D
authors.initials: RD
authors.lastname: Webster
mesh_terms: D000097:Acetonitriles / Q000737:chemistry; D002338:Carotenoids / Q000737:chemistry; D002412:Cations / Q000737:chemistry; D055664:Electrochemical Techniques; D004579:Electron Transport; D006207:Half-Life; D008752:Methylene Chloride / Q000737:chemistry; D010084:Oxidation-Reduction; D024502:alpha-Tocopherol / Q000737:chemistry*; D019207:beta Carotene / Q000737:chemistry*
chemical_list: D000097:Acetonitriles; D002412:Cations; D019207:beta Carotene; D002338:Carotenoids; C041635:alpha-carotene; D008752:Methylene Chloride; D024502:alpha-Tocopherol; C032159:acetonitrile