Kinetics of peroxidation of linoleic acid incorporated into DPPC vesicles initiated by the thermal decomposition of 2,2 '-azobis(2-amidinopropane) dihydrochloride

In a previous work [Chem. Phys. Lipids 104 (2000) 49], we have derived the following rate law for the oxidation of lipids in compartmentalized systems : R-T = (k(1)/k(t))(0.5) k(p) [In](0.5) c(0.5) [LH], where, R-T is the tota l rate of oxidation, k(1) is the rate constant for the production of free r adicals, k(t) and k(p) are the intra-particle rate constants for the termin ation and propagation sets, respectively, [In] is the concentration of a wa ter-soluble initiator, c is the concentration of particles, and [LH] is the intra-particle concentration of oxidable lipid. In the present work, we ha ve investigated on the applicability of the proposed kinetic rate law for a system where it takes place the oxidation of a reactive lipid incorporated into an inert matrix. With this purpose, we have measured the rate of oxid ation of linoleic acid incorporated into dipalmitoylphosphatidylcholine ves icles initiated by the thermal decomposition of 2,2'-azobis(2-amidinopropan e) dihydrochloride as a function of the initiator, particles, and intra-par ticle LH concentrations. The experimentally determined kinetic orders obtai ned were 0.54 +/-0.02, 0.48 +/-0.05 and 0.83 +/-0.04 for the dependence of the oxidation rate with initiator, particles, and LH intra-particle concent rations, respectively, in agreement with those theoretically predicted. The lower value obtained for the kinetic order in LH is attributed to a change in kt with the increase in oxidable lipid intra-particle concentration. Th e main point to be emphasized from the results here obtained is that the ki netic rate law for the oxidation of lipids in compartmentalized systems can be significantly different than that observed when to the oxidation takes place in homogeneous solution. (C) 2001 Elsevier Science Ireland Ltd. All r ights reserved.