Kinetic studies of the free radical-scavenging actions of tocopherol metabolites (alpha-, gamma-, and delta-carboxyethyl-6-hydroxychroman) and Trolox in ethanol and micellar solutions.
The reaction rates ( k s) of tocopherol metabolites (alpha-, gamma-, and delta-CEHC) and Trolox with aroxyl radical have been measured in ethanol and micellar solution by a stopped-flow spectrophotometer, and the k s values obtained were compared with those reported for tocopherols (alpha-, beta-, gamma-, and delta-tocopherol, TocH) and tocol. The rate constants ( k s) increased in the order of Tocol < delta-CEHC < delta-TocH < gamma-CEHC < Trolox approximately gamma-TocH approximately beta-TocH < alpha-CEHC < alpha-TocH in ethanol. The antioxidants that have lower oxidation potentials ( E p) showed higher reactivities. The k s values of alpha-, beta-, gamma-, and delta-tocopherol and tocol in micelle remained constant between pH 4 and pH 10 and decreased rapidly at pH 11~12 by increasing pH value. On the other hand, the k s values of alpha-CEHC, gamma-CEHC, and Trolox showed notable pH dependence. As a result of the detailed analysis of the pH dependence of the rate constants ( k s), the structure-activity relationship in the free radical-scavenging action of the tocopherol metabolites and Trolox has been clarified.
Mitarai
Akiko
A
Department of Chemistry, Faculty of Science, Ehime University, Matsuyama, Japan.
Ouchi
Aya
A
Mukai
Kyohei
K
Tokunaga
Aiko
A
Mukai
Kazuo
K
Abe
Kouichi
K
D002839:Chromans / Q000737:chemistry*; D000431:Ethanol; D016166:Free Radical Scavengers / Q000737:chemistry*; D007700:Kinetics; D008823:Micelles; D012996:Solutions; D013053:Spectrophotometry; D024505:Tocopherols / Q000378:metabolism*
D002839:Chromans; D016166:Free Radical Scavengers; D008823:Micelles; D012996:Solutions; C483420:carboxyethyl-hydroxychroman; D000431:Ethanol; D024505:Tocopherols; C010643:6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid