Reactions of Radicals with Lecithin Bilayers

Abstract

The kinetics of reaction of .**GRAPHIC**. and eaq- [hydrated electrons] with lecithin bilayers were measured. The rate for .**GRAPHIC**. + lecithin was 5.1 .+-. 0.9 .times. 108 M-1 s-1 while the eaq- + lecithin rate was very slow. When a solute such as pyrene was solubilized in the bilayer, .**GRAPHIC**. and eaq- may react with the solute; rates of 1.65 .+-. 0.12 .times. 109 M-1 s-1 and 7 .times. 107 M-1 s-1 were measured for reaction of .**GRAPHIC**. and eaq-, respectively, with pyrene in lecithin. These rates were lower than those observed for similar reactions in homogeneous systems. This was explained in terms of the protective effect of the bilayer, this was especially true for eaq- which did not readily leave the aqueous phase and in terms of the restricted diffusion imposed on the reactive species by the bilayer. The kinetics in these model systems were relevant to reactions of radicals with membranes. Long-term alteration in the model membrane following .**GRAPHIC**. attack was manifested in terms of damage to the head group, increasing water penetration of the bilayer and of cross-linking with the membrane, thereby restricting motion in the interior of the bilayer. Increased rigidity and leakiness of membranes was an expected consequence of radiation damage.