Kinetics of lipid peroxidation in compartmentalized systems initiated by awater-soluble free radical source

Kinetic rate Laws arising from theoretical expectations for the oxidation o f lipids initiated by water-soluble free radicals in compartmentalized syst ems under different experimental conditions are deduced. In particular, the predictions for the kinetic reaction orders in: (a) intra-particle oxidiza ble compound concentration (at fixed number of particles and particle size) , alpha; (b) number of particles or analytical lipid concentration (at fixe d intra-particle concentration and particle size), beta and (c) initiator, gamma, are obtained. The reaction orders beta and gamma are determined by t he fraction of initiator derived radicals captured by the particles (f) and the mean number of chain carrying radicals per particle ([n]) when the sys tem reaches the steady state condition. Predicted orders in initiator range from 0 ([n] = 0.5) to 0.5 (f --> I; [n] > > 1), while the order in number of particles ranges between 0.5 (f -->, 1; [n] > > 1) and 1. These predicti ons are tested by measuring the kinetic law for the oxidation of SUV's egg yolk phosphatidylcholine vesicles initiated by the thermal decomposition of ABAP. The results indicate that, under the conditions employed, beta = 0.6 8 +/- 0.05 and gamma = 0.46 +/- 0.04. These values are close to those expec ted for a system in which [n] > > 1 and the efficiency of capture is relati vely high. This last condition is confirmed by estimating the efficiency of capture from a comparison of induction times elicited by similar concentra tions of Trolox and alpha-tocopherol. (C) 2000 Elsevier Science Ireland Ltd . All rights reserved.