REMARKABLE ENHANCEMENT OF ANTIOXIDANT ACTIVITY OF VITAMIN-C IN AN ARTIFICIAL BILAYER BY MAKING IT LIPO-SOLUBLE

The reaction kinetics between -palmitoyloxy-2,2,6,6-tetramethylpiperid ine-1-oxyl (TEMPO-16) and vitamin C (VC) and its lipophilic derivative ascorbyl-6-palmitate (VC-16) was studied by stopped-flow ESR spectros copy in a synthetic surfactant vesicle sodium 1-pentadecyl hexadecyl s ulfate (SPHS). TEMPO-16 reacted with VC very slowly and showed a bipha sic first-order kinetics with rate constants of 9.6 x 10(-4) and 2.5 x 10(-4) s(-1), corresponding to diffusion of TEMPO-16 from the externa l monolayer of SPHS to the bulk water and flip-flop of TEMPO-16 from t he internal to external monolayer of the vesicle, respectively. On the other hand, the reaction of TEMPO-16 with VC-16 was second-order and over three orders of magnitude faster than that with VC, presumably du e to VC-16 induced fusion of the vesicle.