ANTIOXIDANT ACTIVITIES OF VITAMIN-E ANALOGS IN WATER AND A KAMLET-TAFT BETA-VALUE FOR WATER

Rate constants for hydrogen atom abstraction from two water-soluble al pha-tocopherol (alpha-TOH, vitamin E) analogues by tert-butoxyl radica ls have been measured at room temperature in four solvents, including water. The results imply that H-atom abstraction from alpha-TOH is 3.9 times slower in water than in benzene and yield a ''reliable'' Kamlet -Taft beta solvent parameter for water of 0.31. Literature rate consta nts for H-atom abstraction by peroxyl radicals from alpha-TOH in SDS m icelles and in phospholipid micelles are, respectively, about 100 and 1000 times lower than int styrene. Since only a small fraction of the observed rate diminution can be attributed to hydrogen bonding of alph a-TOH to water it is concluded that in these heterogeneous systems muc h of the alpha-TOH is physically inaccessible to the attacking radical s. Whether this is also true for alpha-TOH in the biological membranes in living animals remains to be determined.