Reactions of Radicals with Lecithin Bilayers

Abstract

The kinetics of reaction of •OH and $e{}_{{\rm aq}}{}^{-}$ with lecithin bilayers have been measured. The rate for •OH + lecithin is $5.1\pm 0.9\times 10^{8} M^{-1} {\rm sec}^{-1}$ while the $e{}_{{\rm aq}}{}^{-}$ + lecithin rate is very slow. When a solute such as pyrene is solubilized in the bilayer, •OH and $e{}_{{\rm aq}}{}^{-}$ may react with the solute; rates of $1.65\pm 0.12\times 10^{9} M^{-1} {\rm sec}^{-1}$ and $7\times 10^{7} M^{-1} {\rm sec}^{-1}$ have been measured for reaction of •OH and $e{}_{{\rm aq}}{}^{-}$ , respectively, with pyrene in lecithin. These rates are lower than those observed for similar reactions in homogeneous systems. This is explained in terms of (a) the protective effect of the bilayer, this being especially true for $e{}_{{\rm aq}}{}^{-}$ which does not readily leave the aqueous phase, and (b) in ter...