The characteristics of the visible luminescence that follows the lipid peroxidative process were investigated either in the autoxidation of rat brain homogenates or in the azo-bis-amidinopropane initiated lipid peroxidation of erythrocyte plasma membranes and liver microsomes. In these systems the luminescence decay observed after total inhibition of the lipid peroxidation is not an iron-catalyzed process, and follows a complex kinetics comprising fast and slow components. The slow component of the decay lasts for several hours at 27 degrees C and amounts to nearly half of the total intensity measured prior to the inhibition of the oxidative process by propyl gallate. The addition of thiols (diethyldithiocarbamate, penicillamine or dithiothreitol) to a lipid peroxidizing system inhibits the chain oxidation and catalyzes the dark decomposition of one (or several) of the luminescence precursors, following first order kinetics. The effect of temperature on the slow luminescence decay corresponds to an activation energy of 18.5 kcal/mol.

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Fluorescence quenching by oxygen of cationic [pyrene-(CH2)nN(CH3)3+; n = 1, 4, and 11] and anionic [pyrene-(CH2)nCO2-, n = 3, 8, 11, and 15] probes was investigated in erythrocyte plasma membranes (leaky) in order to assess the ability of oxygen molecules to interact with solutes located at different positions in the membrane. The pseudounimolecular quenching rate constants measured increase, both for cationic and anionic probes, when n increases. These results are interpreted in terms of an increased oxygen solubility toward the center of the membrane interior, and imply that lateral diffusion contributes more than transverse diffusion to total oxygen mobility. For all of the probes considered, quenching rates increase when n-alkanols are added. The effect observed increases when n decreases and when the size of the n-alkanol alkyl chain increases. Arrhenius-type plots for the quenching rate constants show noticeable downward curvatures. Average (0-40 degrees C) activation energies are approximately 6 kcal/mol.

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The autooxidation of diethy1 hydroxylamine (DEHA) has been studied both in solution and in the gas phase between 0" and 60°C. The results obtained are interpreted in terms of a nonchain free radical mechanism in which reaction (1) (1)is the rate-determining step. This reaction is followed by the reaction of H02 radicals with DEHA to give hydrogen peroxide. The initial stoichiometry is given by 2DEHA + 0 2 -2 nitrone + 2H20 which implies that the hydrogen peroxide reacts with DEHA to give water and diethyl nitroxide radicals.The activation energy of reaction (I) is 16.5 f 2 kcal/moI, leading to a dissociation energy of 69.5 i 2 kcal for the 0-H bond in DEHA.The oxidation of DEHA in the gas phase is nearly ten times slower than that observed in chlorobenzene solution under similar experimental conditions. This result is related to the stabilization of the free radicals produced by the solvent.