Peroxidation Of Methyl Linoleate Research Articles

Kinetic modeling of the reversal of antioxidant potency of α-, β-, γ- and δ-tocopherols in methyl linoleate peroxidation

Extended, chemically detailed kinetic models at the molecular basis are constructed to identify the reactions involved in the reversal of the antioxidant action of α-, β-, γ- and δ-tocopherols during methyl linoleate oxidation. The reaction mechanisms were numerically simulated and subjected to analysis to quantify the significance of individual chemical steps by the value-based method. Results of the obtained kinetic models agreed well with the experimental data. The significant individual reactions contributing to the observed antioxidant and pro-oxidant behavior of the different tocopherols were identified. It is revealed that the reverse order of antioxidant potency and a complex nonlinear dependency of the antioxidant potency of tocopherols with the increase in their concentration are due to the increasing contribution of pro-oxidant relative to the antioxidant reactions. Once the approach presented here can be applied to more complex systems, engineered optimization of antioxidant protection strategies may be reached.

Unexpected Role of pH and Microenvironment on the Antioxidant and Synergistic Activity of Resveratrol in Model Micellar and Liposomal Systems.

Experimental and theoretical studies indicate that resveratrol (RSV, dietary polyphenol that effectively reduces cellular oxidative stress) is a good scavenger of hydroxyl, alkoxyl, and peroxyl radicals in homogeneous systems. However, the role of RSV as a chain-breaking antioxidant is still questioned. Here, we describe pH dependent effectiveness of RSV as an inhibitor of peroxidation of methyl linoleate in Triton X-100 micelles and in 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) liposomes, with the best effectiveness at pH 6 (stoichiometric factors, n, are 4.9 and 5.6, and the rate constants for reaction with peroxyl radicals, kinh, are 1200 and 3300 M–1 s–1 in micellar and liposomal systems, respectively). We propose the mechanism in which RSV-derived radicals are coupled to dimers with recovered ability to trap lipidperoxyl radicals. The formation of such dimers is facilitated due to increased local concentration of RSV at the lipid–water interface. Good synergy of RSV with α-tocopherol analogue in micelles and liposomes is in contrast to the previously reported lack of synergy in non-polar solvents; however, the increased persistency of tocopheroxyl radicals in dispersed lipid/water systems and proximal localization of both antioxidants greatly facilitate the possible recovery of α-TOH by RSV.

Hydroxycinnamyl Derived BODIPY as a Lipophilic Fluorescence Probe for Peroxyl Radicals.

Herein, we describe the synthesis of a fluorescent probe NB-2 and its use for the detection of peroxyl radicals. This probe is composed of two receptor segments (4-hydroxycinnamyl moieties) sensitive towards peroxyl radicals that are conjugated with a fluorescent reporter, dipyrrometheneboron difluoride (BODIPY), whose emission changes depend on the oxidation state of the receptors. The measurement of the rate of peroxidation of methyl linoleate in a micellar system in the presence of 1.0 µM NB-2 confirmed its ability to trap lipid peroxyl radicals with the rate constant kinh = 1000 M−1·s−1, which is ten-fold smaller than for pentamethylchromanol (an analog of α-tocopherol). The reaction of NB-2 with peroxyl radicals was further studied via fluorescence measurements in methanol, with α,α′-azobisisobutyronitrile (AIBN) used as a source of radicals generated by photolysis or thermolysis, and in the micellar system at pH 7.4, with 2,2′-azobis(2-amidinopropane) (ABAP) used as a thermal source of the radicals. The reaction of NB-2 receptors with peroxyl radicals manifests itself by the strong increase of a fluorescence with a maximum at 612–616 nm, with a 14-fold enhancement of emission in methanol and a 4-fold enhancement in the micelles, as compared to the unoxidized probe. Our preliminary results indicate that NB-2 behaves as a “switch on” fluorescent probe that is suitable for sensing peroxyl radicals in an organic lipid environment and in bi-phasic dispersed lipid systems.

Antioxidant Activity of Metal Nanoparticles Coated with Tocopherol-Like Residues-The Importance of Studies in Homo- and Heterogeneous Systems.

Functionalized nanoparticles (NPs) attract great attention in pharmacy, diagnostics, and biomedical areas due to benefits like localization and unique interactions of NPs with biocomponents of living cells. In the present paper, we prepared and characterized two kinds of gold nanoparticles (AuNPs) coated with α-tocopherol-like residues: 1A were soluble in non-polar solvents and their antioxidant activity was tested during the peroxidation of a model hydrocarbon in a homogeneous system, whereas nanoparticles 1B were soluble in polar solvents and were applied as antioxidants in micellar and liposomal systems. The effectiveness of 1A is comparable to 2,2,5,7,8-pentamethylchroman-6-ol (PMHC, an analogue of α-tocopherol). Taking the results of the kinetic measurements, we calculated an average number of 2150 chromanol residues per one NP, suggesting a thick organic coating around the metal core. In heterogeneous systems, the peroxidation of methyl linoleate dispersed in Triton X-100 micelles or DMPC liposomes resulted in the observation that 1B (545 chromanol residues per one NP) was active enough to effectively inhibit peroxidation in a micellar system, but in a liposomal system, 1B behaved as a retardant (no clear induction period). The importance of microenvironment in heterogeneous systems on the overall antioxidant activity of nanoparticles is discussed.

Antioxidant activity of dopamine and L-DOPA in lipid micelles and their cooperation with an analogue of α-tocopherol

Oxidative stress contributes to the progression of neurodegenerative diseases and considerable attention has been given to the development of new antioxidant-based therapies aimed at limiting neuronal cell damage. Structural analysis of catecholamine neurotransmitters indicates that these molecules can exhibit antioxidant activity due to the presence of a catechol moiety. This hypothesis is confirmed in cell culture experiments but the mechanism of antioxidant action of catecholamines is not described. Herein, we present quantitative kinetic studies on the effect of dopamine (DA) and L-3,4-dihydroxyphenylalanine (L-DOPA) on the peroxidation of methyl linoleate dispersed in Triton X-100 micelles as a model heterogeneous lipid system. Experiments were performed at extended pH range 4.0–10.0 in order to study how protonation/deprotonation of catecholamine affect its antioxidant activity. At pH 4.0–7.0, the activity of catecholamines is limited to retardation of lipid peroxidation (caused by the reaction of catecholamines with initiating radicals in the aqueous phase). The effective suppression of lipid peroxidation can be achieved by applying catecholamines together with an analogue of α-tocopherol (2,2,5,7,8-pentamethyl-6-hydroxychroman, PMHC). For example, a mixture of 1μM PMHC with 10μM L-DOPA causes 18-fold elongation of suppression time as compared to 1μM PMHC used alone. We suggest that catecholamines together with α-tocopherol efficiently enhance the protection of biological systems from oxidative stress. At pH above 8.0 a prooxidative effect caused by reaction of semiquinone radical anions with molecular oxygen is observed. However, this toxic action can be completely suppressed by PMHC acting as an agent removing the potentially harmful semiquinone radicals from the reaction environment.

The Antioxidative Effect of Fullerenes during the Peroxidation of Methyl Linoleate in Toluene

The antioxidative effect of fullerenes C(60) and C(70) was examined by measuring the inhibition of methyl linoleate (MeL) peroxidation in toluene initiated by 2,2'-azobis(2,4-dimethylvaleronitrile) (AMVN). The fullerenes retarded the formation of MeL hydroperoxides and lowered the rate of propagation. The reaction rates of fullerenes with AMVN-derived peroxyl radicals were much higher than that of MeL. These results indicate that fullerenes can act as retarders of lipid peroxidation, though their activity is low compared with that of α-tocopherol.

Natural polyphenols as chain‐breaking antioxidants during methyl linoleate peroxidation

A technique based on monitoring oxygen consumption was applied to study 11 natural and model polyphenols (PP, QH2) as well as four typical monophenolics as a chain-breaking antioxidant during the controlled chain oxidation of methyl linoleate (ML) in bulk at 37°C. The antioxidant activities of QH2 were characterized by two parameters: the rate constant k1 for reaction of QH2 with the peroxy radical : (i) QH2 + → + LOOH and the stoichiometric factor of inhibition, f, which shows how many kinetic chains may be terminated by one molecule of QH2. The rate constant k1 were reduced significantly by factor of 4 –28 as compared to these determined during the oxidation of styrene in bulk; the effect was typically more pronounced for catechol derivatives than for pyrogallol derivatives. At the same time, f for QH2 was found to be close to two independent of the number of active OH groups, similar to that determined earlier during the inhibited oxidation of styrene. The formation of H bond between OH group of QH2 and carboxyl group of ML is suggested as a reason for reducing effect of ML on k1. Practical applications: This work reports rate constants for the reaction of lipid peroxyl radical with phenolics and stoichiometric coefficient of inhibition, which characterize the antioxidant activity (AOA) of 15 natural and model PP, QH2 during the controlled peroxidation of ML. The reactivity of PP, QH2 during the oxidation of ML is routinely lower than the reactivity during the oxidation of non-polar model hydrocarbons. This information may be useful to estimate the AOA of natural PP, QH2 in real systems of practical significance including plant oils, fats, food-stuffs, biological objects, and similar.

Photosensitizing properties of chlorins in solution and in membrane-mimicking systems

The photosensitizing properties of three chlorins, meso-tetra(3-hydroxyphenyl)chlorin (m-THPC), chlorin e6 (Ce6) and meso-tetraphenylchlorin substituted by two adjacent sulfonated groups (TPCS(2a)) are compared in solution and when incorporated in dioleoyl-sn-phosphatidylcholine (DOPC) liposomes. In solution, the three chlorins possess a similar efficacy to generate singlet oxygen (quantum yield approximately 0.65). The formation of conjugated dienes was used to determine their ability to induce the peroxidation of methyl linoleate as a target of singlet oxygen. In ethanol solution, the apparent quantum yield for this process is the same for the three chlorins and its value agrees with that expected from the known rates for the decay of singlet oxygen and its reaction with methyl linoleate. When incorporated in liposomes, the order of efficacy is m-THPC > TPCS(2a) > Ce6. This order is tentatively assigned to the relative embedment of the photosensitizer within the lipidic bilayer, TPCS(2a) and Ce6 being anchored by their negative chains nearer to the water-lipid interface. The photoinduced permeation of the lipidic bilayer by these chlorins was investigated by measuring the release of carboxyfluorescein entrapped into DOPC liposomes. The charged chlorins, in particular TPCS(2a), are the most efficient, a result discussed in relation with the technology of photochemical internalization, PCI.

Chain-breaking antioxidant activity of reduced forms ofmitochondria-targeted quinones, a novel type of geroprotectors

The chain-breaking antioxidant activities of reduced form of novel type of geroprotectors, mitochondria-targeted quinones (QH(2)) have quantitatively been measured for the first time. To this end, the chain peroxidation of methyl linoleate (ML) in Triton micelles was used as a kinetic testing model. The studied QH(2) were lipophilic triphenylphosphonium cations conjugated by an aliphatic linker to an antioxidant, i.e. a ubiquinol moiety (MitoQH(2)) or plastoquinol moiety (SkQH(2)). The antioxidant activity was characterized by the rate constant k(1) for the reaction between QH(2) and the lipid peroxyl radical (LO(2) (.)) originated from ML: QH(2) + LO(2) (.) --> HQ(.) + LOOH. All the tested QH(2) displayed a pronounced antioxidant activity. The oxidized forms of the same compounds did not inhibit ML peroxidation. The value of k(1) for SkQH(2) far exceeded k(1) for MitoQH(2). For the biologically active geroprotectors SkQ1H(2), the k(1) value found to be as high as 2.2 x 10(5) M(-) (1)s(-) (1), whereas for MitoQH(2), it was 0.58 x 10(5) M(-) (1)s(-) (1). The kinetic behavior of QH(2) suggested that SkQ1H(2) can rather easily diffuse through lipid-water microheterogeneous systems.

Numerical revelation of the kinetic significance of individual steps in the reaction mechanism of methyl linoleate peroxidation inhibited by α-tocopherol

A kinetic model was constructed to describe the reactions involved in the oxidation of methyl linoleate (ML) inhibited by α-tocopherol (TH). The initial model of the reaction mechanism included 53 individual steps, which were numerically analyzed by the value method based on Hamiltonian systematization of kinetic equations. Good accord was obtained with experimental data at 40 and 50 °C. The dominant steps responsible for the antioxidant and pro-oxidant properties of TH in the process of ML peroxidation were revealed. Tocopherol-mediated peroxidation (TMP) and generation of alkoxyl radicals as a result of the reduction of hydroperoxides by TH or the decomposition tocopherol alkyl peroxides are the dominant reactions responsible for the pro-oxidant activities of α-tocopherol. The extreme behavior of reaction induction period in relation to TH initial concentration is related to the increase in the ratios of [tocopheroxyl radical]/[peroxyl radical] and the TMP rate/rate of termination by combination of tocopheroxyl and peroxyl radicals.

Antioxidative Activity of Philippine Salt-Fermented Shrimp and Variation of Its Constituents during Fermentation

Shrimp (Acetes sp.) was mixed with salt in a ratio of 3:1 and allowed to ferment at room temperature (28-30°C). From the shrimp paste samples collected at the initial (1 day) and end (10 days) of fermentation, 85% ethanol extracts were prepared for their antioxidative assays. Both extracts exhibited high free radical scavenging property against 1,1 diphenyl 2-picrylhydrazyl and suppressed peroxidation of methyl linoleate initiated by 2,2′azobis 2-amidinopropane dihydrochloride. These antioxidative activities, however, did not change significantly during fermentation for 10 days, thus suggesting that the observed antioxidative activities could have mainly due to original antioxidants present in shrimp but not to its fermentative products. The salt-fermented shrimp samples contained large amount of polyunsaturated fatty acids including EPA and DHA, although the polar lipids like phospholipids were hydrolyzed during fermentation to produce the corresponding amount of free fatty acids. In addition, free amino acids of the shrimp sample significantly increased during the fermentation and could be responsible for the unique flavor of salt-fermented shrimp paste. Since the salt-fermented shrimp paste was found to obtain potent antioxidative substances and large amount of EPA, DHA, and amino acids, it is expected to act as an effective antioxidant in our body and to be a good source of these nutrients.

Antioxidant synergy and regeneration effect of quercetin, (-)-epicatechin, and (+)-catechin on alpha-tocopherol in homogeneous solutions of peroxidating methyl linoleate.

Antioxidant interactions between flavonoids and alpha-tocopherol have been demonstrated by oximetry (oxygen concentration measured by ESR signal line width). In tert-butyl alcohol, a solvent in which flavonoids are weak retarders of peroxidation of methyl linoleate when initiated by alpha,alpha'-azoisobutyronitrile, quercetin and (-)-epicatechin were found to act synergistically with the chain-breaking antioxidant alpha-tocopherol. In chlorobenzene, a solvent in which flavonoids are chain-breaking antioxidants, quercetin and (+)-catechin each regenerated alpha-tocopherol, resulting in a co-antioxidant effect. The stoichiometric factor of the flavonoids as chain-breaking antioxidants in 1:1 mixtures with alpha-tocopherol was measured to be close to 1 for quercetin and slightly smaller for the catechins. The apparent inhibition rate constant, k(inh), for the mixture quercetin/alpha-tocopherol was measured to be 4.1 x 10(5) and 2.6 x 10(6) M(-1) s(-1) in tert-butyl alcohol and chlorobenzene, respectively, at 50 degrees C. A k(inh) of 4.4 x 10(5) M(-1) s(-1) was measured for (+)-catechin alone in chlorobenzene at 50 degrees C.

Chain-Breaking Antioxidant Capability of Some Beverages as Determined by the Clark Electrode Technique

The protective effects of red wine, tea, and coffee on cancer, atheroclerosis, and other diseases are attributed to the antioxidant activity (AOA) of polyphenols, which are abundant in those beverages. We present a rational procedure for determining the total chain-breaking AOA of beverages with the use of the Clark electrode technique. The procedure is based on the steady monitoring of oxygen consumption accompanying the chain peroxidation of methyl linoleate in Triton X-100 aqueous micelles induced by 2,2'-azobis(2-amidinopropan) dihydrochloride as a source of active free radicals. AOA was characterized by the number of kinetic chains (expressed in concentration units) that could be terminated by a beverage. The procedure was applied to determine the AOA of nine red wines and single samples of green and black teas, white wine, beer, and soluble coffee. The addition of any of the studied beverages to the testing system resulted in pronounced retardation of methyl linoleate oxidation. The period of increase in the oxidation rate with time caused by antioxidant consumption was preceded by a period when the oxidation rate was visibly decreased with time (increase in inhibition). The release of polyphenols from their complexes with other components of beverages was suggested as the most probable mechanism of this event, which was observed for the first time in this study.

Antioxidant activities of phycocyanobilin prepared from Spirulina platensis

The antioxidative activity of phycocyanobilin fromSpirulina platensis was evaluated againstoxidation of methyl linoleate in a hydrophobic systemor with phosphatidylcholine liposomes. Phycocyanobilin as well as phytochemicals includingα-tocopherol, caffeic acid and zeaxanthin,effectively inhibited the peroxidation of methyllinoleate and produced a prolonged induction period.Oxidation of phosphatidylcholine liposomes was alsocontrolled markedly by adding phycocyanobilin orα-tocopherol. Phycocyanobilin was distributedoutside in the liposomes to scavenge radicals fromAAPH and to prevent initiation of radical chainreactions. When the concentrations of phycocyanin andphycocyanobilin in the reaction mixture were adjustedequally on a phycocyanobilin basis, the activity ofphycocyanobilin was almost the same as that ofphycocyanin in the AAPH-containing reaction mixture.The antioxidizing action of phycocyanin prepared fromspray-dried Spirulina almost agreed with thatfrom fresh Spirulina in the AAPH-containingreaction mixture. These results suggest thatphycocyanobilin is responsible for the majority of theantioxidative activity of phycocyanin and may act asan effective antioxidant in a living human body.

Products Formed by Peroxyl Radical-Mediated Oxidation of Canthaxanthin in Benzene and in Methyl Linoleate

Canthaxanthin was reacted with peroxyl radicals generated by thermolysis of 2,2‘-azobis(2,4-dimethylvaleronitrile) (AMVN) in benzene. The reaction products were separated by reversed-phase high-performance liquid chromatography, and their structures were identified as a mixture of 12-formyl-11-nor-β,β-carotene-4,4‘-dione (1a) and 15‘-formyl-15-nor-β,β-carotene-4,4‘-dione (1b), 15‘,13-epoxyvinyleno-13,15‘-dihydro-14,15-dinor-β,β-carotene-4,4‘-dione (2), 13,15‘-epoxyvinyleno-13,15‘-dihydro-14,15-dinor-β,β-carotene-4,4‘-dione (3), and 11,15‘-dihydrooxepino-β,β-carotene-4,4‘-dione (4). Compounds 1−4 could be accounted for almost all the consumed canthaxanthin at an early stage of the reaction mixture. The peroxidation of methyl linoleate initiated by AMVN in bulk phase was suppressed by the addition of canthaxanthin. The reaction products of canthaxanthin, 1−4, were also formed during the antioxidant process of canthaxanthin, although their yields were low. The result indicates that the peroxyl radical addition occurred in the antioxidant process of canthaxanthin during the AMVN-initiated peroxidation of methyl linoleate. Keywords: Canthaxanthin; carotenoids; lipid peroxidation; antioxidant; free radical

Article

The antioxidant activities, kinh, of catechol, 1, 4-tert-butylcatechol, 2, and 3,5-di-tert-butylcatechol (DTBC), 3, determined by the inhibited oxygen-uptake method during peroxidation of styrene initiated by AIBN are 55.0 x 104, 88.4 x 104, and 149 x 104M-1s-1, respectively, and the stoichiometric factors (n) were 2.1-2.3. A decrease by 50-fold in kinhfor 3 and a drop of 1.1-1.4 in n observed during inhibited peroxidation of methyl linoleate in aqueous sodium dodecyl sulfate (SDS) initiated by di-tert-butylhyponitrile (DBHN) is attributed to hydrogen bonding by water on the antioxidant and on the intermediate di-tert-butylsemiquinone radical, 5, formed in the inhibition step. Combinations of ascorbyl palmitate with 3 exhibited cooperative (not synergistic) antioxidant effects during inhibited peroxidation of styrene in solution. Combinations of ascorbic acid with 3 exhibited synergistic effects during inhibited peroxidation of methyl linoleate initiated by DBHN in SDS micelles. A profile of the effect of concentration of ascorbate on this synergism indicates a mole of 3 is regenerated per mole of ascorbate. The thiols, homocysteine, and polyethylene glycol thiol (polythiol) also exhibited synergistic effects with DTBC in this inhibition. Either ascorbate or polythiol rapidly reduces di-tert-butyl-ortho-quinone (DTBQ), 4, to 3 in methanol or in SDS micelles, and the combination of 3 + ascorbate acted as an efficient inhibitor in this medium. The esr studies indicate the semiquinone radical, 5, produced photochemically from 3 or spontaneously from 3 + 4 in solution, to be very persistent at room temperature. A pathway, mediated by 5, is proposed to account for the cooperative and synergistic effects observed and for the additional combination effect discovered when the three inhibitors: 3, ascorbate, and a thiol are used in the SDS medium. Combinations of such antioxidants are expected to be useful for inhibition of yellowing of pulps and paper with high lignin content, and to be significant in the in vivo reductions of ortho-quinones and semiquinone radicals formed during oxidations of various biomolecules.Key words: catechols, ascorbate, thiols, radicals, antioxidants.

Oxidation Products of β-Carotene during the Peroxidation of Methyl Linoleate in the Bulk Phase.

Methyl linoleate containing β-carotene was autoxidized or photooxidized at 37°C in the bulk phase, and the oxidation products of β-carotene were analyzed by high-performance liquid chromatography. Formyl β-carotenes, β-carotene 5,6-epoxide, and cyclic ethers of β-carotene were detected as the oxidation products during the peroxidation of methyl linoleate initiated by a free radical initiator. These products, which were also detected in the methyl linoleate autoxidized without an initiator, were detectable only in much smaller amounts than the consumed β-carotene. In the chlorophyll-sensitized photooxidation process, the products were β-carotene 5,8-endoperoxide and β-carotene 5,6-epoxide. α-Tocopherol partially inhibited the formation of the 5,6-epoxide, but had no effect on the main product, the 5,8-endoperoxide. These results indicate that β-carotene reacted with singlet oxygen to form the 5,8-endoperoxide as the primary product during the photooxidation of methyl linoleate, and that β-carotene trapped lipid-peroxyl radicals to form oxygenated products which decomposed immediately during the autoxidation process.

Photo-initiated peroxidation of lipids in micelles by azaaromatics.

The monoazaaromatics, pyridine (1), hexyl nicotinate (2), and quinoline (3) and diazaaromatics, pyrimidine (4) and purine (5), readily act as photo-initiators for the peroxidation of methyl linoleate in 0.50 M SDS at 37 degrees C giving free radical chain oxidations of linoleate. Quantitative kinetic runs on the order in substate, RH, and in the rate of chain initiation, Ri, showed that the classical rate law for autoxidation, -d[O2]/dt = (kp/(2 kt 1/2))[RH] x Ri 1/2, is applicable to these photo-initiated oxidations. The oxidizability of methyl linoleate under these conditions is 2.92 x 10(-2) M-1/2 s-1/2. These peroxidations were inhibited by chromanol phenolic antioxidants of the vitamin E class, such as lipid-soluble 2,2,5,7,8-pentamethyl-6-hydroxychroman (PMHC) and water-soluble 2-carboxy- 2,5,7,8-tetramethyl-6-hydroxychroman (Trolox) and derived rate constants for inhibition of peroxidation were kinh (PMHC) = 4.35 x 10(4) M-1 s-1 and k(inh) (Trolox) = 2.81 x 10(4) M-1 s-1 during inhibited oxidation of methyl linoleate photo-initiated by 4. The products from photo-initiated peroxidation of methyl linoleate by 1 through 5 were determined by reduction and high-performance liquid chromatography analyses to be the 9- and 13-positional hydroperoxides of the four geometrical isomers: cis-9, trans-11 (6), trans-10, cis-12 (7), trans-9, trans-11 (8), and trans-10, trans-12 (9)-octadecadienoates typical of the free radical chain mechanism of lipid peroxidation. Products from dye-sensitized oxidation by Methylene Blue or Rose Bengal of methyl linoleate gave a product distribution of six hydroperoxides typical of oxidation by singlet oxygen. Thermal or photo-initiated peroxidation of methyl linoleate in SDS gave some selectivity of oxidation at the 13-position of the linoleate chain. The ratio of 13- to 9-oxidation varied in the range 1.23 to 1.14 as the cis/trans to trans/trans ratio of geometrical isomers varied from 0.44 to 1.25 during photooxidation of increased amounts of linoleate in SDS. This selectivity is attributed to loss of the pseudo symmetry around the pentadienyl system in the lipid chain in the SDS system during the peroxidation.

Moderate antioxidative efficiencies of flavonoids during peroxidation of methyl linoleate in homogeneous and micellar solutions

AbstractThe relative reactivities as well as the stoichiometric coefficients for a number of flavonoids, catechols, and—for comparison—standard phenolic antioxidants were determined by analyzing the kinetics of oxygen consumption in organic and micellar systems, with peroxidation initiated by lipid‐ and water‐soluble azo initiators. The results demonstrated that the flavonoids did not behave as classic phenolic antioxidants such as α‐tocopherol, but showed only moderate chain‐breaking activities. The results were in line with other structure‐activity relationship studies on the importance of the B‐ring catechol structure, the 2,3‐double bond, and the 3,5‐hydroxy groups. The data are discussed in view of possible explanations of the deviations flavonoids reveal in their behavior compared with regular phenolic antioxidants.

A potent chain-breaking antioxidant activity of the cardiovascular drug dipyridamole

The antioxidant properties of the antithrombotic drug dipyridamole have been studied using lipid oxidation assays based on the generation of peroxy radicals by azo compounds. Dipyridamole was observed to prevent both peroxidation of arachidonic acid micelles in aqueous solution and peroxidation of methyl linoleate in organic solvents; in contrast to vitamin E, dipyridamole was found to scavenge both hydrophilic and hydrophobic radicals. The rate constant for the reaction of dipyridamole with methyl linoleate peroxyl radicals at 37°C was calculated as 2 × 10 6 M −1 s −1, in comparison to 1 × 10 6 M −1 s −1 of vitamin E under the same conditions. The antioxidant efficiency of the drug was confirmed in experiments with radiolysis-induced oxidation and through measurements of malondialdehyde production and diene formation. As a result of radical scavenging, a relatively stable dipyridamole radical was formed that could be detected by electron spin resonance spectroscopy. The particular antioxidant properties of dipyridamole may explain the vasodilating and antiplatelet effects of this cardiovascular drug