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.

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 Free Radical Photooximation of Alkanes by Nitrosyl Chloride

1971 ◽  
Vol 49 (1) ◽  
pp. 28-34 ◽  
Author(s):  
Melvyn W. Mosher ◽  
N. J. Bunce
Keyword(s):  
Free Radical ◽  
Hydrogen Abstraction ◽  
Chain Process ◽  
Nitrosyl Chloride ◽  
Deuterium Isotope Effect ◽  
Radical Chain ◽  
Elemental Chlorine ◽  
Probable Reaction ◽  
Radical Initiators ◽  
Atomic Chlorine

The mechanism of the photooximation of alkanes with nitrosyl chloride has been reinvestigated. The lack of initiation of the reaction with free radical initiators suggests that a free radical chain pathway is not involved. Nevertheless, the relative reactivities of hydrocarbons of different structure and the deuterium isotope effect are very similar to those obtained in chlorinations with elemental chlorine, and in particular, primary and tertiary hydrogens are not inert to photooximation as has been previously supposed. A probable reaction mechanism involves hydrogen abstraction from the substrate by atomic chlorine in a free radical non-chain process. This hydrogen abstraction step is shown not to be significantly reversible.

Hydrogen Abstraction Reactions from Phenolic Compounds by Peroxyl Radicals: Multireference Character and Density Functional Theory Rate Constants

2015 ◽  
Vol 120 (27) ◽  
pp. 4634-4642 ◽  
Author(s):  
Annia Galano ◽  
Leonardo Muñoz-Rugeles ◽  
Juan Raul Alvarez-Idaboy ◽  
Junwei Lucas Bao ◽  
Donald G. Truhlar
Keyword(s):  
Density Functional Theory ◽  
Phenolic Compounds ◽  
Rate Constants ◽  
Density Functional ◽  
Hydrogen Abstraction ◽  
Peroxyl Radicals ◽  
Functional Theory

Pyrolysis of Aryl Azides.X. Effects of Azide Concentration on Rate Constants and Product Yields

1990 ◽  
Vol 43 (6) ◽  
pp. 997 ◽  
Author(s):  
LK Dyall ◽  
PAS Smith
Keyword(s):  
Free Radical ◽  
Rate Constants ◽  
Aryl Azides ◽  
Radical Chain ◽  
Initial Concentration ◽  
Azo Compound ◽  
Product Yields ◽  
First Order ◽  
Induced Decomposition ◽  
Group Effects

First-order rate constants (k1) have been measured for pyrolysis of azidobenzenes in decalin solution, in the presence of a free-radical chain inhibitor to prevent any induced decomposition. The new values of k1 for the spontaneous unimolecular thermolysis are lower than previously reported ones, and require revision of published neighbouring group effects. Product yields ( azo compound and primary amine) vary with initial concentration of azide in ways which suggest the species responsible for induced decomposition is not triplet arylnitrene , but a solvent-derived free radical. There is no evidence for induced decomposition when nitrobenzene is the solvent. For aryl azides with no neighbouring group effects operating in their pyrolysis, the Arrhenius parameters Eact and ΔSactobey a precise linear relationship.

Derivation of rate constants for steps in the free-radical chain decomposition of paraffins

1962 ◽  
Vol 268 (1332) ◽  
pp. 36-45 ◽  
Keyword(s):  
Nitric Oxide ◽  
Free Radical ◽  
Rate Constants ◽  
High Pressures ◽  
Radical Mechanism ◽  
Methyl Radicals ◽  
Saturated Hydrocarbons ◽  
Radical Chain ◽  
Free Radical Mechanism ◽  
Standard Values

The Rice-Herzfeld free-radical mechanism for the thermal decomposition of saturated hydrocarbons, including both the uninhibited reaction and that partially inhibited by nitric oxide, involves the rate constants of various individual steps. If standard values are assumed for the rate constants of H -abstraction from n -pentane by methyl radicals, alkyl radical recombination, and addition of methyl to nitric oxide, then those of all the steps for a series of paraffins can be found. The method depends on measurements of the rate constant in the region where the chain reaction is of the first order, the inhibitory action of nitric oxide as a function of paraffin pressure, and the acceleration of paraffin decomposition rate produced by high pressures of nitric oxide. Values are derived for propane, three pentanes ( neo -, iso - and normal pentane) and three octanes ( normal octane, 2:3:4-trimethyl pentane and 2:2:4-trimethyl pentane), and the variations of the several rate constants with structure are discussed.

IRRADIATION OF AQUEOUS CHLORAL HYDRATE WITH Sr90–Y90 BETA RAYS

1959 ◽  
Vol 37 (6) ◽  
pp. 1022-1028 ◽  
Author(s):  
R. F. Platford ◽  
J. W. T. Spinks
Keyword(s):  
Free Radical ◽  
Rate Constants ◽  
Chloral Hydrate ◽  
Average Lifetime ◽  
Chain Reaction ◽  
Radical Chain ◽  
Acid Yield ◽  
Initial Concentration ◽  
Free Radical Chain Reaction ◽  
Radical Chain Reaction

Air-saturated aqueous chloral hydrate has been irradiated with beta rays and the acid yield as determined by titration has been studied as a function of dose rate, temperature, and initial concentration of the chloral hydrate.The average lifetime of the intermediates has been found, by means of the rotating sector technique, to be about 0.5 second. Propagation and termination rate constants for the reaction have been calculated and an effort has been made to explain the results observed in terms of a free radical chain reaction.

Free Radical Bromination of Saturated Hydrocarbons using Bromine and Mercuric Oxide

1972 ◽  
Vol 50 (19) ◽  
pp. 3109-3116 ◽  
Author(s):  
N. J. Bunce
Keyword(s):  
Free Radical ◽  
Hydrogen Abstraction ◽  
Chain Process ◽  
Mercuric Oxide ◽  
Saturated Hydrocarbons ◽  
Radical Chain ◽  
Radical Bromination ◽  
Mercury Oxide ◽  
Alkyl Bromides ◽  
Radical Chain Process

The reaction of alkanes with a mixture of bromine and mercuric oxide gives alkyl bromides in preparatively useful yields. The reagent is significantly more reactive than elemental bromine, and it is believed that bromine monoxide, formed insitu by the interaction of bromine and mercury oxide, is the reactive intermediate. Bromination by bromine monoxide is a free radical chain process in which hydrogen abstraction is carried out predominantly by bromoxy (BrO•) radicals, and to a lesser extent by bromine atoms.

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