sodium-dodecyl-sulfate and 2-2--azobis(2-amidinopropane)

The rates of radical generation, R(i), by two water soluble initiators: 2,2'-azobis(2-methylpropionamidine) and 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide], and the lipid soluble 2,2'-azobisisobutyronitrile were measured in an SDS micellar system over a pH range of 4-10. Enhanced values of R(i) at low pH are attributed to Coulombic repulsion of protonated radicals.

Topics: Amidines; Hydrogen-Ion Concentration; Kinetics; Lipids; Micelles; Oxidation-Reduction; Oxygen; Sodium Dodecyl Sulfate

The rate of accumulation of conjugated dienes of polyunsaturated fatty acids was measured during free-radical oxidation of linoleic acid (18:2n-6, LA), alpha-linolenic acid (18:3n-3, alpha-LNA), and gamma-linolenic acid (18:3n-6, gamma-LNA) initiated by 2,2;-azo-bis-(2-amidinopropane) hydrochloride in aqueous micellar solutions of sodium dodecyl sulfate and sodium cholate. It was shown that, unlike homogeneous solutions, the oxidative stability of PUFAs in aqueous dispersions increased with an increase in the extent of unsaturation. The rate of LA oxidation was more than tenfold greater than that of alpha- and gamma-LNA. The antioxidant activity of beta-carotene, in contrast to homogeneous solutions, in both micellar systems studied depended on the degree of PUFA unsaturation. We found that 5 micro M beta-carotene effectively inhibited the LA oxidation (almost by 90%), whereas the oxidation of alpha-LNA and gamma-LNA was not inhibited by beta-carotene even at much greater concentration (30 micro M). The paradoxical discrepancy between the extent of unsaturation and the PUFA oxidation rate, as well as a decrease in the efficiency of beta-carotene-dependent inhibition of oxidation of more polyunsaturated fatty acids in reactions conducted in aqueous dispersions is consistent with the model according to which the peroxyl radicals of LA and fatty acids with the double-bond number greater than two exhibit different polarity.

Topics: Amidines; Antioxidants; beta Carotene; Free Radicals; Kinetics; Linoleic Acid; Linolenic Acids; Micelles; Oxidation-Reduction; Sodium Cholate; Sodium Dodecyl Sulfate; Solutions; Water

(E)-Retinoic acid (RA) was shown to stimulate the rate of 2,2'-azobis(2-amidinopropane) (AAPH)-initiated autoxidation of linoleic acid (18:2) in sodium dodecyl sulfate (SDS) micelles. RA-dependent stimulation of 18:2 autoxidation was characterized by enhanced rates of dioxygen uptake which were linear with retinoid concentration. In contrast, 5,6-epoxy-RA, a major oxidation product of RA, failed to affect the rate of dioxygen consumption at all concentrations tested. RA was also shown to stimulate peroxyl radical-dependent oxidation of styrene to the corresponding oxirane when styrene was included in the micellar system as a molecular probe. Furthermore, unequivocal evidence of RA-dependent stimulation of 18:2 autoxidation was obtained by relative quantitation of 13-hydroxy-(9Z, 11E)-octadecadienoic acid (13-HODE) plus 9-hydroxy-(10E,12Z)-octadecadienoic acid (9-HODE) production. In addition, enhanced carbon-centered radical formation was demonstrated in the presence of RA by EPR spectroscopy using alpha-(4-pyridyl 1-oxide)-N-tert-butylnitrone (4-POBN) as a spin trap. Analysis and quantitation of RA oxidation products indicated that RA was oxidized to one primary product, 5,6-epoxy-RA, which was identified on the basis of cochromatography with synthetic standard (in a reverse-phase HPLC system), electronic absorption spectroscopy, and positive chemical ionization mass spectrometry of the corresponding methyl ester. Other minor oxidation products were also detected but not characterized. In contrast, reaction mixtures devoid of 18:2 failed to demonstrate significant retinoid oxidation. Mechanisms are proposed to account for the prooxidant effects of RA in this system.

Topics: Amidines; Humans; Linoleic Acid; Lipid Peroxidation; Micelles; Mutagens; Oxidation-Reduction; Sodium Dodecyl Sulfate; Spin Trapping; Tretinoin