Benzophenone-photosensitized autoxidation of linoleate in solution and sodium dodecyl sulfate micelles

1987 ◽  
Vol 65 (11) ◽  
pp. 2529-2540 ◽  
Author(s):  
Lawrence Ross Coates Barclay ◽  
Kimberly Ann Baskin ◽  
Steven Jeffrey Locke ◽  
Tanya Diane Schaefer
Keyword(s):  
Linoleic Acid ◽  
Rate Constants ◽  
Sodium Dodecyl ◽  
Kinetic Studies ◽  
Water Soluble ◽  
Peroxyl Radicals ◽  
Phenolic Antioxidants ◽  
Radical Chain ◽  
Geometrical Isomers ◽  
Chain Reactions

Diffusion studies show that benzophenone (BP), linoleic acid, and methyl linoleate partition completely into the micelles of phosphate buffer/0.10 M SDS. Water-soluble compounds 4-sulphomethylbenzophenone, sodium salt (BP−), azobis(2-amidinopropane•HCl) (ABAP) and 2,5,7,8-tetramethyl-6-hydroxychroman-2-carboxylate (Trolox) show partial partitioning into the micelles. BP- and BP−-photosensitized oxidation of linoleic acid in 0.50 M SDS exhibited characteristics of free radical chain reactions including: (1) inhibition by phenolic antioxidants, (2) no retardation by singlet oxygen quenchers, and (3) the formation of conjugated hydroperoxides with cis,trans to trans,trans ratios of geometrical isomers typical of autoxidation. Quantitative kinetic studies of the order in substrate, RH, and the rate of chain initiation, Ri, show that the classical rate law, −d[O2]/dt = kp/2kt1/2[RH]Ri1/2 applies to BP-photoinitiated autoxidation of linoleic acid in SDS and the oxidizability (kp/2kt1/2 = 4.42 × 10−2 M−1/2 s−1/2) is the same as that found with a thermal initiator. The rotating sector method gave absolute rate constants for linoleic acid autoxidation in 0.50 M SDS for propagation (kp = 36.2 M−1 s−1) and termination (2kt = 3.52 × 105 M−1 s−1), significantly lower than values in polar organic solvents; attributed to solvation of polar peroxyls in aqueous SDS. Depressed inhibition rate constants (kinh) for α-tocopherol, Trolox, and pentamefhylhydroxychroman (PMHC) in 0.50 M SDS compared to kinh in tert-butyl alcohol are attributed to hydrogen bonding effects on the peroxyl radicals and on the inhibitors.

The antioxidant activities of phenolic antioxidants in free radical peroxidation of phospholipid membranes

1990 ◽  
Vol 68 (12) ◽  
pp. 2258-2269 ◽  
Author(s):  
Lawrence Ross Coates Barclay ◽  
Kimberly Ann Baskin ◽  
Kelly Andrea Dakin ◽  
Steven Jefffrey Locke ◽  
Melinda Ruth Vinqvist
Keyword(s):  
Hydrogen Bonding ◽  
Free Radical ◽  
Rate Constants ◽  
Antioxidant Activities ◽  
Hydrogen Abstraction ◽  
Peroxyl Radicals ◽  
Phenolic Antioxidants ◽  
Inhibition Rate ◽  
Radical Chain ◽  
Tert Butyl

Autoxidation of dilinoleoylphosphatidylcholine (DLPC) bilayers photoinitiated by benzophenone takes place by a free radical chain mechanism according to product studies of the cis, trans and trans, trans-9- and -13-linoleate hydroperoxides formed and kinetic studies of the reaction order as a function of light intensity. The absolute rate constant for hydrogen abstraction from DLPC bilayers by peroxyl radicals is found to be 36.1 M−1 s−1 at 37 °C. Preliminary measurements of activities of phenolic antioxidants, α-tocopherol (α-T), 2,2,5,7,8-pentamethyl-6-hydroxychroman (PMHC), 2,5,7,8-tetramethyl-6-hydroxychroman-2-carboxylate (Trolox), and 2,6-di-tert-butyl-4-methylphenol (BHT) by oxygen uptake studies during inhibition periods using photoinitiation gave uncorrected inhibition rate constants, Kinh, for α-T, PMHC, and Trolox several orders of magnitude lower than observed earlier in chlorobenzene. Three series of phenolic antioxidants, (a) polyalkyl-6-hydroxychromans, (b) polyalkyl-4-methoxyphenols, and (c) trialkylphenols, were examined for their antioxidant activities in DLPC membranes during thermally initiated autoxidation by azobis-2,4-dimethylvaleronitrile (DMVN). The corrected inhibition rate constants, kinh, observed in (a), α-T (5.8 × 103), PMHC (17.8 × 103), Trolox (5.8 × 103), 2,2-dimethyl-5,7-diisopropyl-6-hydroxychroman, 4a (55 × 103), and 2,2,5-trimethyl-7-tert-butyl-6-hydroxychroman, 5a (61 × 103) M−1 s−1, are dramatically lower, by several orders of magnitude, than those measured earlier in chlorobenzene and significantly lower (about 1/40–1/10) than those measured in solution in tert-butyl alcohol and less than kinh measurements (1/2–1/5) in aqueous SDS micelles. The kinh values for series (b) were 2,3,5,6-tetramethyl-4-methoxyphenol (TTMMP) (2.1 × 103), 2,3,6-trimethyl-4-methoxyphenol (TMMP) (10.4 × 103), and 2,6-di-tert-butyl-4-methoxyphenol (DBHA) (27.5 × 103) M−1 s−1 and for (c) were 2,6-di-tert-butyl-4-methylphenol (BHT) (3.7 × 103) and 2,4,6-trimethylphenol (TMP) (0.56 × 103) M−1 s−1. The results show an overall leveling and depression of antioxidant activities in DLPC membranes in the series (a), (b), (c) compared to those reported in solution in chlorobenzene, where large differences were attributed to steroelectronic effects of the para ether oxygen stabilizing the derived phenoxyl radicals in (a) and (b) types. The results in aqueous micellar and membrane systems are interpreted in terms of polar solvation effects. Hydrogen bonding by water at both the ether and phenolic groups decreases the activity of the (a) series. Hydrogen bonding at the phenolic hydroxyl appears to be the more significant factor since steric hindrance to H-bonding at hydroxyl allows 4a and 5a to be the most active antioxidants of the α-tocopherol series (a) and DBHA to be the most active antioxidant of the (b) series. Keywords: antioxidant activities, phenols, membranes, peroxidation, kinetics.

Quantitative studies of the autoxidation of linoleate monomers sequestered in phosphatidylcholine bilayers. Absolute rate constants in bilayers

1985 ◽  
Vol 63 (10) ◽  
pp. 2633-2638 ◽  
Author(s):  
Lawrence Ross Coates Barclay ◽  
Steven Jeffrey Locke ◽  
Joseph Mark MacNeil ◽  
Joann Vankessel
Keyword(s):  
Linoleic Acid ◽  
Methyl Linoleate ◽  
Rate Constant ◽  
Rate Constants ◽  
Homogeneous Solution ◽  
Propagation Rate ◽  
Water Soluble ◽  
Peroxyl Radicals ◽  
Absolute Rate ◽  
Hydrophobic Region

The kinetics of autoxidation of linoleic acid in dimyristoylphosphatidylcholine (DMPC) bilayers were studied at 30 °C and pH 7 under 760 Torr O2. Reactions were initiated using either the lipid-soluble di-tert-butylhyponitrite (DBHN) or water-soluble azobis(2-amidinopropane)•HCl (ABAP). Rates of chain initiation, Ri, were measured with a lipid-soluble antioxidant, a-tocopherol, or a water-soluble one, 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylate (Trolox). The slightly higher oxidizability obtained [Formula: see text] compared to methyl linoleate in chlorobenzene [Formula: see text] 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 [Formula: see text], 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, 2kt 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, kp, is attributed to diffusion of polar peroxyl radicals away from the oxidizable region of the bilayer.

Autoxidation in micelles. Synergism of vitamin C with lipid-soluble vitamin E and water-soluble Trolox

1985 ◽  
Vol 63 (2) ◽  
pp. 366-374 ◽  
Author(s):  
Lawrence Ross. Coates. Barclay ◽  
Steven Jeffrey. Locke ◽  
Joseph Mark MacNeil
Keyword(s):  
Linoleic Acid ◽  
Sodium Dodecyl ◽  
Homogeneous Solution ◽  
Kinetic Studies ◽  
Water Soluble ◽  
Interfacial Region ◽  
Induction Periods ◽  
Quantitative Studies ◽  
Sds Micelles ◽  
Soluble C

A study was made of the effect of the inhibitors ascorbic acid (C), α-tocopherol (E), and 6-hydroxy-2,5,7,8-tetramethyl-chroman-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 micelle-soluble 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 (Ri,) 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, −dO2/dt = kp[R—H] (Ri)1/2/(2k1)1/2 is followed. The higher oxidizability (kp/2kt1/2 = 4.48 × 10−2 M−1/2 s−1/2) of linoleate in micelles compared to that in homogeneous solution in chlorobenzene (kp/2kt1/2 = 2.30 × 10−2 M−1/2 s−1/2) is interpreted in terms of the effect of the polar interfacial region of the micelles on a dipolar transition state, R—OŌ: H•R, of the propagation reaction.

Article

1998 ◽  
Vol 76 (12) ◽  
pp. 1805-1816
Author(s):  
L Ross C Barclay ◽  
Jennifer K Grandy ◽  
Heather D MacKinnon ◽  
Heather C Nichol ◽  
Melinda R Vinqvist
Keyword(s):  
Oxygen Uptake ◽  
Singlet Oxygen ◽  
Sodium Azide ◽  
Lignin Content ◽  
Sodium Dodecyl ◽  
Kinetic Studies ◽  
Product Distribution ◽  
Geometrical Isomers ◽  
Photo Oxidation ◽  
Tert Butyl

3,5-Di-tert-butyl-ortho-quinone, 6, and 1-(3,4-dimethoxyphenyl-2-(2-methoxyphenoxy)-1-propanone, 7, models for oxidized lignin and for lignin, were used as sensitizers of photo-oxidation. Product studies by HPLC from oxidation of methyl linoleate in solution sensitized by 6 or 7, and in sodium dodecyl sulfate (SDS) sensitized by 6, showed a product distribution of six hydroperoxides, the four conjugated 9- and 13-hydroperoxides of the geometrical isomers: trans-10, cis-12 (2), cis-9, trans-11 (3), trans-10, trans-12 (4), and trans-9, trans-11 (5)-octadecadienoates plus two nonconjugated hydroperoxides. The higher cis/trans to trans/trans (ct/tt) of geometrical isomers (2 + 3//4 + 5) compared to ct/tt from known thermal free-radical peroxidations (Type 1) indicate that singlet oxygen (Type 2) oxidation occurs in reactions sensitized by 6 or 7. Kinetic studies by oxygen uptake are reported on oxidations of hydrocarbons 1-phenyl-2-methylpropene,8, and trans-stilbene,9, sensitized by the quinone, 6, or by a dye, Rose Bengal. Quenching studies imply singlet oxygen reactions. Milled wood lignin undergoes self-initiated photo-oxidation in water, and oxygen uptake was quenched by sodium azide. Cellobiose, a cellulose model, undergoes sensitized photo-oxidation using model quinone, 6, in a mixture of tert-butyl alcohol and water or using the sensitizers benzophenone or the lignin model, 7, delivered on a solid support, silica gel, and these oxidations were quenched with sodium azide. These results implicate singlet oxygen in the photo-yellowing of high lignin content wood pulps.Key words: lignin models, ortho-quinone, photo-oxidation, singlet oxygen, lignin, cellobiose.

The cytoprotective effect of Trolox demonstrated with three types of human cells

1990 ◽  
Vol 68 (10) ◽  
pp. 1189-1194 ◽  
Author(s):  
Tai-Wing Wu ◽  
Noriaki Hashimoto ◽  
Jun Wu ◽  
Doug Carey ◽  
Ren-Ke Li ◽  
...  
Keyword(s):  
Xanthine Oxidase ◽  
Ventricular Myocytes ◽  
Sodium Dodecyl ◽  
Optimal Level ◽  
Human Cells ◽  
Water Soluble ◽  
Peroxyl Radicals ◽  
Azo Initiator ◽  
Dose Dependent ◽  
In Cells

Trolox, a hydrophilic analogue of α-tocopherol, was reported to scavenge peroxyl radicals better than vitamin E in sodium dodecyl sulfate micelles and in liposomes. However, it was not known if Trolox protects human cells against oxyradical damage or if it acts as an antioxidant there. Here we demonstrate that Trolox prolonged substantially the survival of human ventricular myocytes and hepatocytes against oxyradicals generated with xanthine oxidase plus hypoxanthine, and prevented lysis of red cells exposed to an azo-initiator (2,2′-azo-bis(2-amidinopropane) HCl. Note that Trolox did not inhibit xanthine oxidase. In each cell type, the protection by Trolox was dose dependent and surpassed those given by such water-soluble antioxidants as ascorbic acid, superoxide dismutase, and (or) catalase, each examined at or near its optimal level in the same system. Using hepatocytes as a model, we further observed that Trolox reduced markedly the quantity of phospholipid conjugated dienes (a chemical imprint of oxyradical damage) in cells despite their exposure to oxyradicals. These data suggested that Trolox behaves as an antioxidant in cells as illustrated in hepatocytes.Key words: oxyradicals, cytoprotection, hepatocytes, myocytes, erythrocytes.

ChemInform Abstract: Concise Syntheses of L-Selenomethionine and of L-Selenocystine Using Radical Chain Reactions.

ChemInform ◽  
1987 ◽  
Vol 18 (4) ◽  
Author(s):  
D. H. R. BARTON ◽  
D. BRIDON ◽  
Y. HERVE ◽  
P. POTIER ◽  
J. THIERRY ◽  
...  
Keyword(s):  
Radical Chain ◽  
Chain Reactions

scholarly journals The detection and inhibition of free radical chain reactions

1942 ◽  
Vol 180 (982) ◽  
pp. 237-256 ◽  
Keyword(s):  
Nitric Oxide ◽  
Free Radical ◽  
Chemical Analysis ◽  
Diethyl Ether ◽  
Pressure Increase ◽  
Stationary States ◽  
Decomposition Rates ◽  
Radical Chain ◽  
Chain Reactions ◽  
Limiting Values

Part I. Comparison of nitric oxide and propylene as inhibitors The reduction by propylene of the rate of pressure increase in the decomposition of propaldehyde at 550° has been shown by chemical analysis to represent a true inhibition of the reaction, and not to be due n an important degree to an induced polymerization of the propylene. With propaldehyde and with diethyl ether the limiting values to which the decomposition rates are reduced by nitric oxide and by propylene respectively are the same, although much more propylene is required to produce a given degree of inhibition. From this it is concluded that the limiting rates are more probably those of independent non-chain processes, than those characteristic of stationary states where the inhibitor starts and stops chains with equal efficiency.

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