No abstract

A study was made of the effect of the inhibitors ascorbic acid (C), a-tocopherol (E), and 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylate (Trolox, T) on the autoxidation of linoleic acid in 0.50 M sodium dodecyl sulfate (SDS) micelles at pH 7.0 in phosphate buffer. Reactions were thermally initiated at 30°C in the SDS micelles by a micelle-soluble initiator, di-tert-butylhyponitrite (DBHN). Although water-soluble C alone is an inefficient inhibitor, when combined with micellesoluble E, it acts synergistically with the latter to extend the efficient antioxidant action of E beyond the sum of the induction periods of C and E acting separately. Similarly C acts synergistically with the water-soluble antioxidant, T. Quantitative studies of these effects under controlled rates of initiation (R,) reveal that C functions to regenerate a mole of E (or T) per mole of C used. Kinetic studies show that the rate of autoxidation is first order in micellar linoleic acid and one-half order in micellar DBHN concentrations. Therefore, the classical rate law, -

Can. J. Chcm. 61, 1288 ( 1 983). The kinctics of thermally (30°C) initiatctl autoxidations of unsaturated lipids, linolcic acid, and mcthyl linolcatc arc studiccl in 0.50 M sodium dodecyl sulfatc (SDS) micelles. The ratc of chain initiation, R,, was controlled by using known amounts of the thermal initiator, di-ter.t-butylhyponitritc (DBHN). Thc initiator cfficicncy, e. dctcrniincd by the induction period method with %-tocopherol, was 0.30 for linoleic acid and varied (0.30 to 0.36) for mcthyl linoleate autoxiation as the concentration of thc ester increased. The ratc of autoxidation of linoleic acid follows thc classical rate law since it is proportional to the substrate concentration and to the squarc root of chain initiation. The oxidizability of linoleic acid measured in micelles is 4.09 X lo-' M -I / ' sC"'. The oxidizability of methyl linoleate varied from 2.37 X lo-' to 6.92 X loC' M -' / %~' / ' as the amount of solubilized ester increased. The lattcr results are indicative of pooling of the cster in the micellar phase. Additions of aqueous solutions of ascorbic acid to 1-tocopherol-inhibitcd micellar autoxidations result in vcry significant extensions of the efficient inhibition pcriod compared to that obtained with %-tocopherol alone. The mechanism of this synergism is briefly discussed.LAWRENCE ROSS COATES BARCLAY, STEVEN JEFFREY LOCKE et JOSEPH MARK MACNEIL. Can. J. Chcm. 61, 1288 (1983). On a ttudit la cinttique de I'autoxydation initiCe thermiqucment (30°C) des lipides insaturts, I'acidc linoltique et le linoltate de mtthyle, dans des micelles de sulfate de dodtcyl sodium (SDS) (0,50 M). On a contrblt la vitesse d'initiation de la chaine, R,, en utilisant des quantitts connues de l'initiateur thermique, le di-terr-butylhyponitrite (DBHN). L'efficaeitC de I'initiateur, e, dtterminte par la rntthode de la pCriode d'induction avec I'a-tocophtrol, est dc 0,30 pour I'acide linoltique et varie (de 0,30 a 0,36) pour I'autoxydation du linoleate de mtthyle lorsquc la concentration de I'ester augmente. La vitesse d'autoxyclation de I'acide linoltique obtit a la loi de vitesse classique puisqu'elle cst proportionnelle a la concentration du substrat et 2 la racine carrte de I'initiation de la chaine. L'oxydabilitt de I'acide linoltique mesurte dans des micelles est de 4,09 X lo-' M-'I' s-"" LL'oxydabilitt du linoltate de mCthyle varie de 2,37 x lo-' i 6,92 X lo-' M-'I' s-'I' lorsque la quantitt d'ester solubilist augmente. Ces derniers rtsultats sont une indication de I'entassement de I'ester dans la phase micellaire. Des additions de solutions aqueuses d'acide aseorbique a l'autoxydation micellaire inhibee par l'a-tocophtrol conduisent 5 une augmentation marqute de I'efficacitC de la ptriode d'induction par rapport a celle obtenue avec l'a-tocophtrol seul. On discute brikvement du mtcanisme de ce synergisme.[Traduit par le journal]The free radical autoxidation of organic molecules organized in amphiphilic microenvironments is important to various biological processes, but has been lacking in quarztitarivc kin...

Chem. 63, 2633 (1985).The kinetics of autoxidation of linoleic acid in dimyristoylphosphatidylcholine (DMPC) bilayers were studied at 30°C and pH 7 under 760 Torr 02. Reactions were initiated using either the lipid-soluble di-tert-butylhyponitrite (DBHN) or watersoluble azobis(2-amidinopropane) . HCI (ABAP). Rates of chain initiation, R i , were measured with a lipid-soluble antioxidant, a-tocopherol, or a water-soluble one, 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxyate (Trolox). The slightly higher oxidizability pbtained (kp/2k$ = 2.76 x lo-' M-i s-4 compared to methyl linoleate in chlombenzene (kp/2k$ = 2.18 x ]0-2 M-i -2 s 3 is attributed to a moderate polar solvent effect on ionized linoleate near the bilayer surface. A low initiator efficiency, e = 0.0895 for DBHN in DMPC, is attributed to the cage effect in the bilayer of high microviscosity. Similar autoxidation experiments on methyl linoleate in DMPC bilayers gave a lower oxidizability (kp/2k) = 1.79 x lo-' M-i s-i), indicating that the ester is sequestered deeper in the hydrophobic region of DMPC than is ionized linoleate. Some absolute rate constants are determined using the rotating sector technique for linoleic acid in 0.50 M SDS micelles, and egg lecithin and dilinoleoylphosphatidylcholine (DLPC) bilayers. A hundredfold decrease in the termination rate constant, 2k,, for DLPC bilayer compared to homogeneous solution is attributed to chain termination in a bilayer region of high polarity. A concomitant reduction (up to tenfold) in the propagation rate constant, k,, is attributed to diffusion of polar peroxyl radicals away from the oxidizable region of the bilayer.LAWRENCE ROSS COATES BARCLAY, STEVEN JEFFREY LOCKE, JOSEPH MARK MACNEIL et JOANN VANKESSEL. Can. J. Chem. 63, 2633 (1985).Opt5rant h 30°C, i un pH de 7 et sous une pression de 760 Torr d'02, on a ttudiC la cinktique de I'auto-oxydation de I'acide IinolCique dans des couches doubles de dimyristoylphosphatidylcholine (DMPC). On a initie les reactions i I'aide soit de I'hyponitrite du di-tert-butyle (HNDB) qui est soluble dans les lipides soit le chlorhydrate de I'azo bis(amidin0-2 propane) (ABAP) qui est soluble dans I'eau. On a mesure les vitesses d'initiation de chaines, Ri, en presence d'un antioxydant soluble dans I'eau, I'a-tocophCrol, ainsi que d'un antioxydant soluble days I'eau, I'hydroxy-q tt5pamethyl-2,5,7,8 chromanecarboxylate-2 (Trolox). L'oxyd,abifite est 1Cgkrement supt5rieure (k,/2k? = 2,76 x lo-' M-7 s-3 h celle du linoleate de mCthyle (kp/2k,3 = 2,18 x lo-' M-i s-3; on attribue ce resultat h une influence modCree du solvant polaire sur le linoltate ionis6 prks de la surface i couche double. On attribue la faible efficacitk comme initiateur, e = 0,0895, du HNDB dans le DMPC i un effet de cage dans la double couche qui aurait une microviscositC ClevCe. Des experiences semblables d'a~to~oxydation sur le linolkate de mCthyle dans des doubles couches de DMPC donnent lieu i des oxydabilites plus faibles (kp/2k,5 = 1,79 x M-f s-$; ce rksultat indiquerait que I'ester est plus sequ...

Mittels 31P‐ NMR‐Spektroskopie bei Verwendung von Pr3+ als Verschiebungsreagens wird gezeigt, daß die Phospholipide Dipalmitoylphosphatidylcholin (I), Dilinoleoylphosphatidylcholin (II) und Eilecithine (III) in den organischen Lösungsmitteln Benzol, Chlorbenzol und o‐Dichlorbenzol aggregieren, und zwar mit einer Aggregationszahl von 80‐100, wenn das molare Verhältnis von H2O/Phospholipid 20/1 beträgt.