Reactivities of Vitamin E with Alkyl and Peroxy Radicals

Methods: The activity of VE was evaluated by the induction period method from the kinetics of polymerization of methyl methacrylate (MMA) initiated by AIBN (R .) or BPO (PhCOO .), using DSC. MMA, 9.4 mol; initiator, 1.0 mol%; VE, 0.001-0.05 mol%; 70 ¢XC.

Results: The ratio of the rate-constant of inhibition to that of propagation (kinh/kp) for each VE was about 10 in a system with a molar ratio of AIBN to VE of 100:1 (or 10), whereas in the corresponding BPO system kinh/kp declined in the order ƒÑ (47) > ƒ" (15) > ƒ× (10)> ƒÔ (7). In contrast, with AIBN the number of free radicals trapped by the phenolic moiety (n) declined in the order ƒÔ (3.0) > ƒ× (2.5) > ƒÑ (2.2) > ƒ" (1.6), whereas with BPO n declined in the order ƒÔ (1.9) > ƒ× (1.4) > ƒ" (1.0) > ƒÑ (0.3). The scavenging-activity of VE to diphenylpicryhydrazyradical (ID50 mM) declined in the order ƒÔ (0.182) > ƒ× (0.148) > ƒÑ (0.023)> ƒ" (0.013). The order was similar to that of n values of corresponding VE for R ..

Conclusion: The radical-scavenging activity of VE differs markedly between PhCOO . and R ., and is affected by the number and position of the methyl groups in the benzene nucleus of VE. The great kinh/kp of Ą for PhCOO . suggested a potent reactivity with poly-unsaturated fatty acid radicals in vivo.