Pulse Radiolysis Studies in Model Lipid Systems. The Influence of Aggregation on Kinetic Behavior of OH Induced Radicals in Aqueous Sodium Linoleate

The kinetic and spectral behavior of radicals formed by hydroxyl radical attack on linoleate anions has been studied by pulse radiolysis. Reactivity of ·OH toward this surfactant is an order of magnitude greater in monomeric form [ k ·OH+linoleate = 8.0 ± 10 9 M −1 sec −1 ] than in micellar form [ k ·OH+lin(micelle) = 1.0 ± 10 9 M −1 sec −1 ]. Abstraction of a hydrogen atom from the doubly allylic position gives rise to an intense absorption in the UV region (δ max = 282–286 nm, ε 3·10 4 M −1 cm −1 ) which may be used as a probe of radical activity at that site. This abstraction may occur, to a small extent, directly via ·OH attack. However, greater than 90% of initial attack occurs at other sites. Subsequent secondary abstraction of doubly allylic H atoms appears to occur predominantly by: (1) intramolecular processes in monomers, (2) intermolecular processes in micelles. Disappearance of radicals by secondary processes is slower in the micellar pseudo phase than in monomeric solution.