Search

Lipid peroxidation (LP) is the most important type of oxidative-radical damage in biological systems, owing to its interplay with ferroptosis and to its role in secondary damage to other biomolecules, such as proteins. The chemistry of LP and its biological consequences are reviewed with focus on the kinetics of the various processes, which helps understand the mechanisms and efficacy of antioxidant strategies. The main types of antioxidants are discussed in terms of structure–activity rationalization, with focus on mechanism and kinetics, as well as on their potential role in modulating ferroptosis. Phenols, pyri(mi)dinols, antioxidants based on heavy chalcogens (Se and Te), diarylamines, ascorbate and others are addressed, along with the latest unconventional antioxidant strategies based on the double-sided role of the superoxide/hydroperoxyl radical system. [ABSTRACT FROM AUTHOR]

Phenols with intramolecular hydrogen bond between a pendant base and the phenolic OH group react differently in polar and non-polar environments with electron/proton acceptors. This was demonstrated by using time resolved chemically induced dynamic nuclear polarization (TR CIDNP) and theoretical calculations. In benzene, those phenols undergo a concerted electron-proton transfer (EPT) that yields neutral ketyl and phenoxyl radicals. In polar acetonitrile, the reaction mechanism turns into an electron transfer from the phenol to the triplet ketone, accompanied by the shift of a proton from the phenolic OH group to the nitrogen atom of the pendant base to form a distonic radical cation. This behavior is similar to that of tyrosine H-bonded to basic residues in some radical enzymes. This solvent-induced mechanism switch in proton-coupled electron transfers is important in different biological systems, in which the same metabolites and intermediates can react differently depending on the specific local environments. [ABSTRACT FROM AUTHOR]

Conspectus: Hydrocarbon autoxidation, the archetype free radical chain reaction, challenges the longevity of both living organisms and petroleum-derived products. The most important strategy in slowing this process is via the intervention of radical-trapping antioxidants (RTAs), which are abundant in nature and included as additives to almost every petroleum-derived product as well as several other commercial products. Accordingly, a longstanding objective of many academic and industrial scientists has been the design and development of novel RTAs that can outperform natural and industrial standards, such as α-tocopherol, the most biologically active form of vitamin E, and dialkylated diphenylamines, respectively. Some time ago we recognized that attempts to maximize the reactivity of phenolic RTAs had largely failed because substitution of the phenolic ring with electron-donating groups to weaken the O-H bond and accelerate the rate of H atom transfer to radicals leads to compounds that are unstable in air. We surmised that incorporating nitrogen into the phenolic ring would render them more stable to one-electron oxidation, enabling their substitution with strong electron-donating groups. Guided by computational chemistry, we demonstrated that replacing the phenyl ring in very electron-rich phenols with either 3-pyridyl or 5-pyrimidyl rings leads to phenolic-like RTAs with good air stability and great reactivity. In fact, rate constants determined for the reactions of some compounds with peroxyl radicals were almost 2 orders of magnitude greater than those for α-tocopherol and implied that the reactions proceeded without an enthalpic barrier. Following extensive thermochemical and kinetic characterization, we took our studies of these compounds to more physiologically relevant media, such as lipid bilayers and human low density lipoproteins, where the heterocyclic analogues of vitamin E shone, displaying unparalleled abilities to inhibit lipid peroxidation and prompting their current investigation in animal models of degenerative disease. Moreover, we carried out studies of these compounds in several industrially relevant contexts and in particular demonstrated that they could be used synergistically with less reactive, less expensive, phenolic RTAs. More recently, our attention has turned to the application of these ideas to maximizing the reactivity of diarylamine RTAs that are common in additives to petroleum-derived products, such as lubricating oils, transmission and hydraulic fluids, and rubber. In doing so, we have developed the most reactive diarylamines ever reported. The 3-pyridyl- and 5-pyrimidyl-containing diarylamines are easily accessed using Pd- and/or Cu-catalyzed cross-coupling reactions, and display an ideal compromise between reactivity and stability. The most reactive compounds are characterized by rate constants for reactions with peroxyl radicals that are independent of temperature, implying that as for the most reactive heterocyclic phenols these reactions proceed without an enthalpic barrier. Unprecedented reactivity was also observed when hydrocarbon autoxidations were carried out at elevated temperatures, real-world conditions where diarylamines are uniquely effective because of a catalytic RTA activity that makes use of the hydrocarbon substrate as a sacrificial reductant. Our studies to date suggest that heterocyclic diarylamines have real potential to increase the longevity of petroleum-derived products in a variety of applications where diphenylamines are currently used. [ABSTRACT FROM AUTHOR]

5-S-Lipoylhydroxytyrosol (1), the parent member of a novel group of bioinspired multidefense antioxidants, is shown herein to exhibit potent peroxyl radical scavenging properties that are controlled in a solvent-dependent manner by the sulfur center adjacent to the active o-diphenol moiety. With respect to the parent hydroxytyrosol (HTy), 1 proved to be a more potent inhibitor of model autoxidation processes in a polar solvent (acetonitrile), due to a lower susceptibility to the adverse effects of hydrogen bonding with the solvent. Determination of O-H bond dissociation enthalpies (BDE) in t-butanol by EPR radical equilibration technique consistently indicated a ca. 1.5 kcal/mol lower value for 1 relative to HTy. In good agreement, DFT calculations of the BDEOH using an explicit methanol molecule to mimic solvent effects predicted a 1.2 kcal/mol lower value for 1 relative to HTy. Forcing the geometry of the -S-R group to coplanarity with the aromatic ring resulted in a dramatic decrease in the computed BDEOH values suggesting a potentially higher activity than the reference antioxidant α-tocopherol, depending on geometrical constrains in microheterogeneous environments. These results point to sulfur substitution as an expedient tool to tailor the chain-breaking antioxidant properties of catechol derivatives in a rational and predictable fashion. [ABSTRACT FROM AUTHOR]

Hydroxyaryl alkyl tellurides are effective antioxidants both in organic solution and aqueous biphasic systems. They react by an unconventional mechanism with ROO. radicals with rate constants as high as 107 M−1 s−1 at 303 K, outperforming common phenols. The reactions proceed by oxygen atom transfer to tellurium followed by hydrogen atom transfer to the resulting RO. radical from the phenolic OH. The reaction rates do not reflect the electronic properties of the ring substituents and, because the reactions occur in a solvent cage, quenching is more efficient when the OH and TeR groups have an ortho arrangement. In the presence of thiols, hydroxyaryl alkyl tellurides act as catalytic antioxidants towards both hydroperoxides (mimicking the glutathione peroxidases) and peroxyl radicals. The high efficiency of the quenching of the peroxyl radicals and hydroperoxides could be advantageous under normal cellular conditions, but pro-oxidative (thiol depletion) when thiol concentrations are low. [ABSTRACT FROM AUTHOR]

We recently reported a preliminary account of our efforts to develop novel diarylamine radical-trapping antioxidants (Hanthorn, J. J. et al. J. Am. Chem. Soc 2012,134, 8306-8309) wherein we demonstrated that the incorporation of ring nitrogens into diphenylamines affords compounds which display a compromise between H-atom transfer reactivity to peroxyl radicals and stability to one-electron oxidation. Herein we provide the details of the synthetic efforts associated with that report, which have been substantially expanded to produce a library of substituted heterocyclic diarylammes that we have used to provide further insight into the structure--reactivity relationships of these compounds as antioxidants (see the accompanying paper, DOI: 10.1021/jo301012x). The diarylamines were prepared in short, modular sequences from 2-aminopyridine and 2- aminopyrimidine wherein aminations of intermediate pyri(mi)dyl bromides and then Pd-catalyzed cross-coupling reactions of the amines and precursor bromides were the key steps to yield the diarylammes. The cross-coupling reactions were found to proceed best with Pd(η³-1-PhC3H4)(η5-C5H5) as precatalyst, which gave higher yields than the conventional Pd source, Pd2(dba)3. [ABSTRACT FROM AUTHOR]

Essential oils (EOs) are mixtures of volatile molecules endowed with health-promoting biological activities that go beyond their role as aromas and natural preservatives and can be exploited to develop functional foods and diet supplements. Their composition is briefly addressed along with regulatory aspects. The potential health benefit of human diet supplementation with EOs is outlined through a review of the recent literature on available clinical trials and preclinical research concerning EOs activity towards: (1) irritable bowel syndrome; (2) inflammatory bowel disease; (3) regulation of microbiota; (4) gastroprotection; (5) hepatoprotection; (6) protection of the urinary tract and diuresis; (7) management of metabolic disorders including hyperglycemia and hyperlipidemia; (8) anti-inflammatory and pain control; (9) immunomodulation and protection from influenza; and (10) neuroprotection and modulation of mood and cognitive performance. The emerging potential in such activities of selected EOs is given focus, particularly green and black cumin, bergamot, orange, myrtle, peppermint, sage, eucalyptus, lavender, thyme, lemon balm, ginger, and garlic. [ABSTRACT FROM AUTHOR]

The incorporation of nitrogen atoms into the aryl rings of conventional diphenylamine antioxidants enables the preparation of readily accessible, air-stable analogues, several of which have temperature-independent radical-trapping activities up to 200-fold greater than those of typical commercial diphenylamines. Amazingly, the nitrogen atoms raise the oxidation potentials of the amines without greatly changing their radical-trapping (H-atom transfer) reactivity. [ABSTRACT FROM AUTHOR]

Hydroquinones (benzene-1,4-diols) are naturally occurring chain-breaking antioxidants, whose reactions with peroxyl radicals yield 1,4-semiquinone radicals. Unlike the 1,2-semiquinone radicals derived from catechols (benzene-l,2-diols), the 1,4-semiquinone radicals do not always trap another peroxyl radical, and instead the stoichiometric factor of hydroquinones varies widely between 0 and 2 as a function of ring-substitution and reaction conditions. This variable antioxidant behavior has been attributed to the competing reaction of the 1,4-semiquinone radical with molecular oxygen. Herein we report the results of experiments and theoretical calculations focused on understanding this key reaction. Our experiments, which include detailed kinetic and mechanistic investigations by laser flash photolysis and inhibited autoxidation studies, and our theoretical calculations, which include detailed studies of the reactions of both 1,4-semiquinones and 1,2-semiquinones with O2, provide many important insights. They show that the reaction of O2 with 2,5-di-tert-butyl-1,4-semiquinone radical (used as model compound) has a rate constant of 2.4 4 ⊥ 0.9 × 105 M-1 s-1 in acetonitrile and as high as 2.0 ± 0.9 × 106 M-1 s-1 in chlorobenzene, i.e., similar to that previously reported in water at pH ~7. These results, considered alongside our theoretical calculations, suggest that the reaction occurs by an unusual hydrogen atom abstraction mechanism, taking place in a two-step process consisting first of addition of O2 to the semiquinone radical and second an intramolecular H-atom transfer concerted with elimination of hydroperoxyl to yield the quinone. This reaction appears to be much more facile for 1,4-semiquinones than for their 1,2-isomers. [ABSTRACT FROM AUTHOR]

Assessment of oxidative stress status (OSS) in human tissues is still troublesome. Using an innovative EPR-radical-probe we successfully measured the instantaneous concentration of ROS directly in peripheral blood of athletes and normally active workers during 60 min controlled exercise. The probe employed was bis(1-hydroxy-2,2,6,6-tetramethyl-4-piperidinyl)decandioate, which quantitatively and instantaneously reacts with oxygen-centered radicals (including superoxide) to yield the parent nitroxide, which is sufficiently persistent to be measured by EPR. Our measurements suggest that while at rest normally active individuals may benefit more from antioxidant supplementation than athletes; conversely, during exercise athletes may benefit more from supplementation. Our method allows reliable, quick, and non-invasive quantitative determination of OSS in human peripheral blood. [ABSTRACT FROM AUTHOR]

The role of reactive oxygen species (ROS) in liver disease is controversial. This mostly reflects the difficulties to quantify ROS in vivo , particularly in humans. We aimed to measure the presence of ROS in diseased human liver and identify possible relations between ROS levels and etiology, histology and hepatocyte proliferation. Liver biopsy specimens from 102 individuals: 18 healthy controls and 84 patients (42 HCV chronic hepatitis (CHC), 19 HBV chronic hepatitis (CHB), 7 PBC, 4 PSC, 4 HCV relapsing hepatitis after liver transplantation, 3 autoimmune hepatitis, 3 hepatocellular carcinoma, 2 alcoholic hepatitis) underwent analysis by radical-probe electron paramagnetic resonance (EPR). ROS in patients (median=5×10 -6 mmol/mg) were higher than in controls (median=3×10 -11 mmol/mg) ( p <0.001). Progressively increasing levels of ROS were recorded passing from control values to CHB (median=4×10 -7 mmol/mg), CHC (median=3×10 -6 mmol/mg) and PBC (median=2×10 -5 mmol/mg), the differences being significant ( p <0.001). ROS in CHC positively correlated with histological disease activity ( r =0.92; p <0.001). No correlation was found between ROS and hepatocyte proliferation rate, presence/degree of steatosis, serum ferritin levels and aminotransferases. ROS overproduction in liver appears to be a common thread linking different pathologic conditions and seems to be influenced by diseases' etiologies. [ABSTRACT FROM AUTHOR]

Chamazulene (CA) is an intensely blue molecule with a wealth of biological properties. In cosmetics, chamazulene is exploited as a natural coloring and soothing agent. CA is unstable and tends to spontaneously degrade, accelerated by light. We studied the photodegradation of CA upon controlled exposure to UVB-UVA irradiation by multiple techniques, including GC-MS, UHPLC-PDA-ESI-MS/MS and by direct infusion in ESI-MSn, which were matched to in silico mass spectral simulations to identify degradation products. Seven byproducts formed upon UVA exposure for 3 h at 70 mW/cm2 (blue-to-green color change) were identified, including CA dimers and CA benzenoid, which were not found on extended 6 h irradiation (green-to-yellow fading). Photostability tests with reduced irradiance conducted in various solvents in the presence/absence of air indicated highest degradation in acetonitrile in the presence of oxygen, suggesting a photo-oxidative mechanism. Testing in the presence of antioxidants (tocopherol, ascorbyl palmitate, hydroxytyrosol, bakuchiol, γ-terpinene, TEMPO and their combinations) indicated the highest protection by tocopherol and TEMPO. Sunscreens ethylhexyl methoxycinnamate and particularly Tinosorb® S (but not octocrylene) showed good CA photoprotection. Thermal stability tests indicated no degradation of CA in acetonitrile at 50 °C in the dark for 50 days; however, accelerated degradation occurred in the presence of ascorbyl palmitate. [ABSTRACT FROM AUTHOR]

Focuses on the solvent effects on the reactivity and free spin distribution of 2,2-diphenyl-1-picrylhydrazyl radicals. Kinetic measurements; Abstraction of a hydrogen atom from substrate molecules; Absolute rate constants for hydrogen atom abstraction.

Presents an experiment in which the rates constant for hydrogen atom abstraction from vitamin E analogues in four solvents was measured. Comparison of abstraction rate in water to that in benzene; Abstraction rates for other solvents; Inaccessibility of heterogeneous systems to attacking radicals; Determination of accesibility in the biological membranes of living animals.

Measures rate constants in several solvents for the abstraction of the phenolic hydrogen atom by various abstracting radicals. Radicals utilized; Variations over a range of solvents; Kinetic solvent effect; Absolute magnitudes of the rate constants; Evidence of a unifying principle for free radical chemistry in solution.

Investigates the solvent effects on the antioxidant activity of vitamin E (alpha-tocopherol), a major radical-trapping, lipid-soluble antioxidant in mammals. Inhibition of lipid peroxidation; Facile transfer of the phenolic hydrogen atom of alpha-tocopherol (TOH) to peroxyl radicals; Hydrogen atom abstraction from TOH and phenol.

Sulfur chemistry plays a central role in cellular redox homeostasis and cysteine-derived antioxidants like glutathione are the most abundant in biological systems. Inspired by Nature, the insertion of divalent sulfur as a substituent in phenolic antioxidants, e.g in thiatocopherol, seeking for improved antioxidant performance, has been an important strategy for long time. Replacement of sulfur with heavier chalcogens like Selenium and Tellurium has brought to even more performing antioxidants, able to quench peroxyl radical in a catalytic fashion and to express unusually high reactivity. On the other hand, natural bioactive compounds like plant-derived thiosulfinates (R-S(O)S-R) own their exceptional antioxidant properties to the ability of releasing sulfenic acids, whose antioxidant behavior has only recently been clarified. The chemistry and redox properties of unstable sulfenic acids (R-SOH), and analogous selenenic acids (R-SeOH) have also recently been elucidated, to better understand the properties of chalcogen-based natural antioxidants, and to develop novel bio-inspired compounds. This fascinating chemistry will be reviewed and the most significant achievement will be presented. [ABSTRACT FROM AUTHOR]

Review: 37 refs. [ABSTRACT FROM AUTHOR]

A number of title compounds are prepared in order to get information about structure-reactivity relationships. [ABSTRACT FROM AUTHOR]

Review: 79 refs. [ABSTRACT FROM AUTHOR]

The measure of O2 consumption during the inhibited autoxidation of an easily oxidizable substrate is one of the most reliable and predictive methods to assess antioxidant activity, especially for structure-activity relationship studies, for food and industrial applications. The differential oxygen uptake apparatus described herein represents a powerful and cost-effective way to obtain antioxidant activity from inhibited autoxidation studies. These experiments provide the rate constant and the stoichiometry of the reaction between antioxidants and peroxyl radicals (ROO∙), which are involved in the propagation of radical damage. We show the operation principles and the utility of this instrumentation in the bioorganic laboratory, with regard to the recent advances in this field, ranging from the study of natural antioxidants in biomimetic system, to the use of substrates generating hydroperoxyl radicals, and to the evaluation of novel nanoantioxidants. [ABSTRACT FROM AUTHOR]

[Display omitted] • Chem/phys cross over study on suspended melanin precursors and Sepia pigment in Imidazolium – based ionic liquids is shown. • Ionic charge transport is tuned by ionic liquid chemical features, steric hindrance and type of melanin. • A high order correlation is found between ionic charge densities and Debye lengths. Melanins (mel) are a class of pigments that are nearly ubiquitous and among the oldest compounds found in nature. However, their practical application has been limited due to their low solubility in water and in most organic solvents. Recent research on polydopamine has revealed that ionic liquids (ILs) not only enhance melanin's dissolution but also fine-tune its redox properties through specific dipolar interactions. In this study, we expand upon previous investigations by customizing new suspensions on a broader range of melanins. Concerning ILs, we focus on imidazolium based ILs, tailoring their chemical properties (pKa) and structural characteristics (cation radius, anion radius). The melanins under consideration include synthetic polymers derived from the oxidative polymerization of 5,6-dihydroxyindole (DHI) and its 2-carboxylic acid counterpart (DHICA), as well as the natural pigment Sepiomelanin (Sepiomel), which is isolated from the ink sack of cuttlefish. Our comparative analysis between neat ILs and ILs-mel responses reveals several key findings: the increase in solubility, the tuning of the redox ability, the decrease of the ionic charge resistance (from MΩ τo kΩ); the partial removal of the electrical polarization effects and the delocalized ionic charge hopping mechanisms in conductivity; the increase of the free ionic diffusion mobility and Debye lengths. Notably, electrical transport is influenced by both the chemical features and the steric hindrance in the ILs as well as the specific type of melanin employed. These factors contribute to the high order correlation between free ionic charge densities and their corresponding Debye lengths. Consequently, our findings suggest that for these complex systems, an improved model extending beyond a simplified electrostatic interaction mechanism is required. [ABSTRACT FROM AUTHOR]

The reactivities of novel heterocyclic diarylamine radical-trapping antioxidants (RTAs) are profiled in a heavy hydrocarbon at 160 °C, conditions representative of those at which diphenylamine RTAs are used industrially. While carboxylic acids produced during the autoxidation are shown to deactivate these more basic RTAs, the addition of a sacrificial base leads to efficacies that are unprecedented in the decades of academic and industrial research in this area. [ABSTRACT FROM AUTHOR]

To verfy their difference from isolated fatty acids, the absolute kinetics of peroxidation was studied for seven triglyceride-based oils of olive (OLI-1, OLI-2), high-oleic sunflower (SUN-HO), high-oleic and high-linoleic safflower (SAF-HO, SAF-HL) grapeseed (GRA) and borage (BOR), by oxygen uptake monitoring, using 2,6-di- tert -butyl-4-methoxyphenol and 2,2,5,7,8-pentamethyl-6-chromanol as reference inhibitors. Propagation constants (k p /M−1 s−1 at 303 K in PhCl) were respectively 34.8 ± 2.3, 35.1 ± 1.8, 40.6 ± 5.5, 36.0 ± 7.7, 160.8 ± 5.1, 145.1 ± 24.5, 275.1 ± 63.8, while oxidizability responded to empirical equation k p (2 k t)-½/M-½s-½ = 1.63 × 10−3[allyl >CH 2 /M] + 1.82 × 10−2[bisallyl >CH 2 /M], based on fatty acids residues assessed by GC–MS. Peroxidation kinetics was markedly different from that of isolated fatty acids. The H-bond basicity of all oils was measured by FT-IR affording Abraham's βH 2 values in the range 0.55 ± 0.03. H-bonding explained the protection of oils measured for seven reference phenolic antioxidants, except for the catechols quercetin and caffeic acid phenethyl ester, which were 2-to-4-folds more effective than expected, supporting a proposed different mechanism. • k p and 2 k t constants for triglycerides differ from those of their main fatty acids. • MUFA-rich triglycerides oxidize 40-folds faster than their isolated MUFAs. • A linear empirical equation predicted oxidizability from FAME analysis (r 2 = 0.992). • Protection and k i nh for antioxidants were explained by H-bonding to triglycerides. • Catechols quercetin and CAPE gave exceptional protection via different mechanisms. [ABSTRACT FROM AUTHOR]

We recently reported a preliminary account of our efforts to develop novel diarylamine radical-trapping antioxidants (Hanthom et al. J. Am. Chem. Soc. 2012, 134, 8306-8309), wherein we demonstrated that die incorporation of ring nitrogens into diphenylamines affords compounds that display a compromise between H-atom transfer reactivity to peroxyl radicals and stability to one-electron oxidation. Herein, we report the results of thermochemical and kinetic experiments on an expanded set of diarylamines (see the accompanying paper, DOI: 10.1021/jo301013c), which provide a more complete picture of the structure--reactivity relationships of these compounds as antioxidants. Nitrogen incoporation into a series of alkyl-, alkoxyl-, and dialkylamino-substituted diphenylamines raises their oxidation potentials systematically with the number of nitrogen atoms, resulting in overall increases of 0.3-0.S V on going from the diphenylamines to the dipyrimidylamines. At the same time, the effect of nitrogen incorporation on their reactivity toward peroxyl radicals was comparatively small (a decrease of only 6-fold at most), which is also reflected in their N--H bond dissociation enthalpies. Rate constants for reactions of dialkylamino-substituted diarylamines with peroxyl radicals were found to be >107 M-1 s-1 which correspond to the pre-exponential factors that we obtained for a representative trio of compounds (log A ~ 7), indicating that the activation energies (Ea) are negligible for these reactions. Comparison of our thermokinetic data for reactions of the diarylamines with peroxyl radicals with literature data for reactions of phenols with peroxyl radicals clearly reveals that diarylamines have higher inherent reactivities, which can be explained by a proton-coupled electron-transfer mechanism for these reactions, which is supported by theoretical calculations. A similar comparison of the reactivities of diarylamines and phenols with alkyl radicals, which must take place by a H-atom transfer mechanism, clearly reveals the importance of die polar effect in the reactions of the more acidic phenols, which makes phenols comparatively more reactive. [ABSTRACT FROM AUTHOR]

Abstract: A liquid chromatographic method with UV detection (HPLC-DAD) and a gas chromatographic method coupled with mass spectrometry (GC–MS) have been developed for the determination of guaiazulene (GA) in complex matrices such as creams and toothpastes. A solid phase extraction (SPE) sample pre-treatment on a polymeric sorbent (Strata-X polymer) was applied before the HPLC analyses, which were performed on a XTerra™ C8 stationary phase, using a mobile phase consisting of acetonitrile–water 50:50 (v/v). For GC–MS analyses, solid–liquid extraction (creams) and SPE (toothpastes) were applied. The proposed methods, based on techniques with different selectivity, were validated and both proved to be suitable to obtain an unambiguous identification and reliable determination of GA in commercial health care products (creams and toothpastes), giving concordant results. Moreover, the described methods can offer a useful analytical support for photostability studies of GA, a photolabile natural compound, in creams. [Copyright &y& Elsevier]

6-(Ethylthio)-, 6-(ethylseleno)-, and 6-(ethyltelluro)-2,2,4-trimethyl-1,2-dihydroquinoline-three heavier chalcogen analogues of ethoxyquin—were prepared by dilithiation of the corresponding 6-bromodihydroquinoline followed either by treatment with the corresponding diethyl dichalcogenide (sulfur derivative) or by insertion of selenium/tellurium into the carbon-lithium bond, oxidation to a diaryl dichalcogenide, borohydride reduction, and finally alkylation of the resulting areneselenolate/arenetellurolate. Ethoxyquin, its heavier chalcogen analogues, and the corresponding 6-PhS, 6-PhSe, and 6-PhTe derivatives were assayed for both their chain-breaking antioxidative capacity and their ability to catalyze reduction of hydrogen peroxide in the presence of a stoichiometric amount of a thiol reducing agent (thiol peroxidase activity). Ethoxyquin itself turned out to be the best inhibitor of azo-initiated peroxidation of linoleic acid in a water/chlorobenzene two-phase system. In the absence of N-acetylcysteine as a coantioxidant in the aqueous phase, it inhibited peroxidation as efficiently as a-tocopherol but with a more than 2-fold longer inhibition time. In the presence of 0.25 mM coantioxidant in the aqueous phase, the inhibition time was further increased by almost a factor of 2. This is probably due to thiol-mediated regeneration of the active antioxidant across the lipid-aqueous interphase. The ethyltelluro analogue id of ethoxyquin was a similarly efficient quencher of peroxyl radicals compared to the parent in the two-phase system, but less regenerable. Ethoxyquin was found to inhibit azo-initiated oxidation of styrene in the homogeneous phase (chlorobenzene) almost as efficiently (kinh = (2.0 ± 0.2) × 106 M-1 s-1) as α-tocopherol with a stoichiometric factor n = 2.2 ± 0.1. At the end of the inhibition period, autoxidation was additionally retarded, probably by ethoxyquin nitroxide formed during the course of peroxidation. The N-H bond dissociation enthalpy of ethoxyquin (81.3 ± 0.3 kcal/mol) was determined by a radical equilibration method using 2,6-dimethoxyphenol and 2,6-di-tert-butyl-4-methylphenol as equilibration partners. Among the investigated compounds, only the tellurium analogues id and, less efficiently, 1g had a capacity to catalyze reduction of hydrogen peroxide in the presence of thiophenol. Therefore, analogue id is the only antioxidant which is multifunctional (chain-breaking and preventive) in character and which can act in a truly catalytic fashion to decompose both peroxyl radicals and organic hydroperoxides in the presence of suitable thiol reducing agents. [ABSTRACT FROM AUTHOR]

Examines the substituent effects of the bond dissociation enthalpies of aromatic amines. Employment of electrochemical methods; Use of closed thermodynamic cycles in determining the acidities of anilines; Weakening effect of electron-donating Y.

Evaluates the thermochemical and kinetic properties of bisphenol antioxidant. Identification of radicals by the abstraction of hydroxylic hydrogen; Determination of hydrogen bond dissociation energy; Action of bisphenol.

Melanins are stable and non‐toxic biomaterials with a great potential as chemopreventive agents for diseases connected with oxidative stress, but the mechanism of their antioxidant action is unclear. Herein, we show that polydopamine (PDA), a well‐known synthetic melanin, becomes an excellent trap for alkylperoxyl radicals (ROO., typically formed during autoxidation of lipid substrates) in the presence of hydroperoxyl radicals (HOO.). The key reaction explaining this peculiar antioxidant activity is the reduction of the ortho‐quinone moieties present in PDA by the reaction with HOO.. This reaction occurs via a H‐atom transfer mechanism, as demonstrated by the large kinetic solvent effect of the reaction of a model quinone (3,5‐di‐tert‐butyl‐1,2‐benzoquinone) with HOO. (k=1.5×107 and 1.1×105 M−1 s−1 in PhCl and MeCN). The chemistry disclosed herein is an important step to rationalize the redox‐mediated bioactivity of melanins and of quinones. [ABSTRACT FROM AUTHOR]

Melanins are stable and non‐toxic biomaterials with a great potential as chemopreventive agents for diseases connected with oxidative stress, but the mechanism of their antioxidant action is unclear. Herein, we show that polydopamine (PDA), a well‐known synthetic melanin, becomes an excellent trap for alkylperoxyl radicals (ROO., typically formed during autoxidation of lipid substrates) in the presence of hydroperoxyl radicals (HOO.). The key reaction explaining this peculiar antioxidant activity is the reduction of the ortho‐quinone moieties present in PDA by the reaction with HOO.. This reaction occurs via a H‐atom transfer mechanism, as demonstrated by the large kinetic solvent effect of the reaction of a model quinone (3,5‐di‐tert‐butyl‐1,2‐benzoquinone) with HOO. (k=1.5×107 and 1.1×105 M−1 s−1 in PhCl and MeCN). The chemistry disclosed herein is an important step to rationalize the redox‐mediated bioactivity of melanins and of quinones. [ABSTRACT FROM AUTHOR]

Presents a study which investigated the impact of oxidation by the molecular oxygen of lipids, on the structural and functional properties of biomembranes. Identification of the pathological events related to the membrane damage by lipid peroxidation; Autoxidation of the lipids; Methodology used to conduct the study; Results of the study.

A persistent triptycenyl sulfenic acid is used as a model for cysteine-derived and other biologically relevant sulfenic acids in experiments which define their redox chemistry. EPR spectroscopy reveals that sulfinyl radicals are persistent and unreactive toward O2, allowing the O-H bonding dissociation enthalpy (BDE) of the sulfenic acid to be readily determined by equilibration with TEMPO as 71.9 kcal/mol. The Eo (RSO∙/RSO-) and pKa of this sulfenic acid are also reported. [ABSTRACT FROM AUTHOR]

Developing effective strategies to increase the chemical stability and to fine‐tune the physico‐chemical properties of melanin biopolymers by rational control of π‐electron conjugation is an important goal in materials science for biomedical and technological applications. Herein we report that poly‐1,8‐dihydroxynaphthalene (pDHN), a non‐nitrogenous, catechol‐free fungal melanin mimic, displays a high degree of structural integrity (from MALDI‐MS and CP/MAS 13C NMR analysis), a strong radical scavenging capacity (DPPH and FRAP assays), and an unusually intense EPR signal (g=2.0030). Morphological and spectral characterization of pDHN, along with deassembly experiments in ionic liquids, indicated amorphous aggregates of small globular structures with an estimated stacking distance of 3.9 Å and broadband absorption throughout the visible range. These results indicate that DHN‐based melanins exhibit a high structural integrity and enhanced antioxidant and free‐radical properties of potentially greater biomedical and technological relevance than for typical indole‐based eumelanins. [ABSTRACT FROM AUTHOR]

Symmetrical ditocopheryl disulfides (Toc)2S2 and symmetrical and unsymmetrical ditocopheryl sulfides (Toc)2S were simply prepared under remarkably mild conditions with complete control of the regiochemistry by using δ‐, γ‐, and β‐tocopheryl‐N‐thiophthalimides (Toc‐NSPht) as common starting materials. The roles of sulfur atom(s), H‐bond and aryl ring substitution pattern on the antioxidant profile of these new compounds, which were assembled by linking together two tocopheryl units, are also discussed. [ABSTRACT FROM AUTHOR]

Abstract: Metal nanoparticles are reported to be toxic due to the generation of free radicals at their surface. Relatively inert thiol‐capped gold nanoparticles (AuNPs) have been reported to induce radical formation in the presence of hydroperoxides, which would conflict with their potential use as inert scaffolds for the design of novel nano‐antioxidants. With the aim of clarifying this aspect, we investigated the pro‐oxidant activity of dodecanethiol‐capped AuNPs (∼5 nm diameter), prepared through the Brust–Schiffrin synthesis, by oxygen‐uptake kinetic studies. The pro‐oxidant activity was found to be proportional to the impurities of the transfer agent tetraoctylammonium bromide (TOAB) left from the synthesis and decreased on repeated washing of the nanoparticles. Under identical settings similar batches of AuNP (∼9 nm diameter) prepared through the Ulman method without onium salts showed no pro‐oxidant behavior. The alternative onium phase‐transfer agents Oct4NBF4 (Oct=octyl), Hex4NBF4 (Hex=hexyl), and Hex4NPF6 were comparatively investigated and showed lower pro‐oxidant activity depending on the counterion (Br−>PF6−>BF4−). [ABSTRACT FROM AUTHOR]

Alzheimer's disease (AD) is a multifactorial pathology that requires multifaceted agents able to address its peculiar nature. In recent years, a plethora of proteins and biochemical pathways has been proposed as possible targets to counteract neurotoxicity. Although the complex scenario is not completely elucidated, close relationships are emerging among some of these actors. In particular, increasing evidence has shown that aggregation of amyloid beta (Aβ), glycogen synthase kinase 3β (GSK-3β) and oxidative stress are strictly interconnected and their concomitant modulation may have a positive and synergic effect in contrasting AD-related impairments. We designed compound 3 which demonstrated the ability to inhibit both GSK-3β (IC 50 = 24.36 ± 0.01 μM) and Aβ 42 self-aggregation (IC 50 = 9.0 ± 1.4 μM), to chelate copper (II) and to act as exceptionally strong radical scavenger ( k inh = 6.8 ± 0.5 · 10 5 M −1 s −1 ) even in phosphate buffer at pH 7.4 (k inh = 3.2 ± 0.5 · 10 5 M −1 s −1 ). Importantly, compound 3 showed high-predicted blood-brain barrier permeability, did not exert any significant cytotoxic effects in immature cortical neurons up to 50 μM and showed neuroprotective properties at micromolar concentration against toxic insult induced by glutamate. [ABSTRACT FROM AUTHOR]

Limonene, linalool and citral are common non-phenolic terpenoid components of essential oils, with attributed controversial antioxidant properties. The kinetics of their antioxidant activity was investigated using the inhibited autoxidation of a standard model substrate. Results indicate that antioxidant behavior of limonene, linalool and citral occurs by co-oxidation with the substrate, due to very fast self-termination and cross-termination of the oxidative chain. Rate constants k p and 2 k t , (M −1 s −1 ) at 30 °C were 4.5 and 3.5 × 10 6 for limonene, 2.2 and 9.0 × 10 5 for linalool and 39 and 1.0 × 10 8 for citral. Behavior is bimodal antioxidant/pro-oxidant depending on the concentration. Calculations at the M05/6-311+g(2df,2p) level indicate that citral reacts selectively at the aldehyde C–H having activation enthalpy and energy respectively lower by 1.3 and 1.8 kcal/mol compared to the most activated allyl position. Their termination-enhancing antioxidant chemistry might be relevant in food preservation and could be exploited under appropriate settings. [ABSTRACT FROM AUTHOR]

[Display omitted] • Bakuchiol from P. corylifolia is an emerging skin-care active against photoaging. • It is a competitive tyrosinase inhibitor with K i ∼ 7 and ∼ 1 µM for mono- di-phenolase. • It traps peroxyl radicals with k inh (104M−1s−1) 18.1 in solution and 0.16 in micelles. • Its antioxidant activity stems from the OH group with a BDE of 81.7 ± 0.1 kcal/mol. • Combined antioxidant and antityrosinase potency prompt its use as food preservative. Bakuchiol is gaining major interest for treatments against skin photoaging. The kinetics of mushroom tyrosinase inhibition by bakuchiol, by real-time oxygen sensing and UV–vis monitoring (475 nm), showed competitive inhibition with average K i constant (µM, 30 °C, pH 6.8) of 6.71 ± 1.23 and 1.15 ± 0.34 for monophenolase and diphenolase reactions respectively, with respective IC 50 37.22 ± 5.18 and 6.91 ± 0.96 ∼ at 1 mM substrate, compared to kojic acid IC 50 34.02 ± 5.51 and 16.86 ± 3.28 μM. Fluorescence quenching showed a single binding mode with formation constant K a 1.02 × 106 M−1. The antioxidant activity was studied by inhibited autoxidation of styrene and cumene (PhCl, 30 °C) affording inhibition constant k inh = 18.1 ± 6.6 (104M−1s−1, 30 °C) and of MeLin in Triton™ X-100 micelles giving k inh = 0.16 ± 0.03 (104M−1s−1, 37 °C). Stoichiometric factor was 1.9 ± 0.1. ReqEPR spectroscopy afforded the BDE(OH) as 81.7 ± 0.1 kcal/mol. Bakuchiol is a potent tyrosinase inhibitor with good antioxidant activity having major potential as natural food preservative against oxidation and food-browning. [ABSTRACT FROM AUTHOR]

Despite the growing scientific and technological relevance of polydopamine (PDA), a eumelanin-like adhesive material widely used for surface functionalization and coating, knowledge of its structural and physicochemical properties, including in particular the origin of paramagnetic behavior, is still far from being complete. Herein, we disclose the unique ability of ionic liquids (ILs) to disassemble PDA, either as a suspension or as a thin film, up to the nanoscale, and to establish specific interactions with the free radical centers exposed by deaggregation of potential investigative value. Immersion of PDA-coated glasses into four different ILs ([C1C1im][(CH3O)HPO2], [C1C1im][(CH3O)CH3PO2], [C1C1im][(CH3O)2PO2], [N1888][C18:1]) at room temperature caused the fast and virtually complete removal of the coating as determined by UV-visible spectroscopy and scanning electron microscopy (SEM). Transmission electron microscopy (TEM) analysis of the colored supernatants from PDA suspensions in ILs revealed the presence of nanostructures not exceeding 50 nm in diameter. Electron paramagnetic resonance (EPR) analysis indicated profound IL-dependent modifications in signal intensity, line-width, and g-factor values of PDA. These differences were interpreted in terms of a partial conversion of C-centered radicals into O-centered semiquinone-type components following destacking and interaction with the anion component in ILs. The discovery of ILs as a powerful tool to disassemble PDA under mild conditions provides a new entry both to detailed investigations of this biopolymer on the nanoscale and to mild removal of coatings from functionalized surfaces, greatly expanding the scope of PDA-based surface functionalization strategies. [ABSTRACT FROM AUTHOR]

• A new method of real-time oxygen sensing allows monitoring tyrosinase reaction. • The method matches conventional spectrophotometry to study enzyme inhibition. • The new method prompted revision of mechanism and potency of reference Glabridin. • Glabridin from G. glabra has nearly competitive mixed-type inhibition mechanism. • Activity is 30000-folds higher than reported and 1000-folds higher than Kojic acid. A new method for studying tyrosinase kinetics and inhibition by oxygen sensing is described and matched to the conventional spectrophotometric approach. The stoichiometric ratio of O 2 uptake to dopachrome formation was 1.5 ± 0.2 for substrate l -tyrosine and 1.0 ± 0.1 for l -DOPA. With both methods, we reinvestigated mushroom tyrosinase inhibition by glabridin from Glycyrrhiza glabra. The two methods agreed showing mixed-type inhibition for monophenolase and diphenolase activities, at variance with previous literature. Average K I (K SI) values for glabridin were 13.6 ± 3.5 (281 ± 89) nM and 57 ± 8 (1312 ± 550) nM, for monophenolase and diphenolase inhibition, respectively, with IC 50 of 80 ± 8 nM and 294 ± 25 nM, respectively, at 1 mM substrate. For reference kojic acid K I (K SI) were 10.9 ± 8 (217 ± 55) µM and 9.9 ± 1.4 (21.0 ± 5.2) µM, for monophenolase and diphenolase, respectively, with respective IC 50 of 33 ± 8 μM and 17 ± 3 μM. Glabridin's activity is among the highest in nature, being about three orders of magnitude higher than previously reported. [ABSTRACT FROM AUTHOR]

Thiols are well known for their role in cellular redox homeostasis, while aromatic amines and phenols are the best known classes of chain-breaking antioxidants. On the other hand, thiyl radicals are known to catalyse the double bond isomerization in PUFA. We investigated the role and interplay of 2-mercaptoethanol and diphenylamine in the parallel processes of peroxidation and cis–trans isomerization of linoleic acid (LA) during gamma radiolysis, both in solution and micelles. Both compounds, used alone were able to protect LA from oxidation; however pro-oxidant activity and enhanced isomerization was observed when they were used together, depending on the experimental settings. Instead, α-tocopherol protected LA from both oxidation and isomerization in the presence of thiols under any tested settings. The mechanistic scenario is discussed highlighting the role of diphenylaminyl radicals in promoting thiyl-radical-induced cis–trans isomerization in the presence of oxygen. [ABSTRACT FROM AUTHOR]

The reactions of alkylperoxyl radicals with phenols have remained difficult to investigate in water. We describe herein a simple and reliable method based on the inhibited autoxidation of water/THF mixtures, which we calibrated against pulse radiolysis. With this method we measured the rate constants kinh for the reactions of 2-tetrahydrofuranylperoxyl radicals with reference compounds: urate, ascorbate, ferrocenes, 2,2,5,7,8-pentamethyl-6-chromanol, Trolox, 6-hydroxy-2,5,7,8-tetramethylchroman-2-acetic acid, 2,6-di-tert-butyl-4-methoxyphenol, 4-methoxyphenol, catechol and 3,5-di-tert-butylcatechol. The role of pH was investigated: the value of kinh for Trolox and 4-methoxyphenol increased 11- and 50-fold from pH 2.1 to 12, respectively, which indicate the occurrence of a SPLET-like mechanism. H(D) kinetic isotope effects combined with pH and solvent effects suggest that different types of proton-coupled electron transfer (PCET) mechanisms are involved in water: less electron-rich phenols react at low pH by concerted electron-proton transfer (EPT) to the peroxyl radical, whereas more electron-rich phenols and phenoxide anions react by multi-site EPT in which water acts as proton relay. [ABSTRACT FROM AUTHOR]

The reactions of alkylperoxyl radicals with phenols have remained difficult to investigate in water. We describe herein a simple and reliable method based on the inhibited autoxidation of water/THF mixtures, which we calibrated against pulse radiolysis. With this method we measured the rate constants kinh for the reactions of 2-tetrahydrofuranylperoxyl radicals with reference compounds: urate, ascorbate, ferrocenes, 2,2,5,7,8-pentamethyl-6-chromanol, Trolox, 6-hydroxy-2,5,7,8-tetramethylchroman-2-acetic acid, 2,6-di- tert-butyl-4-methoxyphenol, 4-methoxyphenol, catechol and 3,5-di- tert-butylcatechol. The role of pH was investigated: the value of kinh for Trolox and 4-methoxyphenol increased 11- and 50-fold from pH 2.1 to 12, respectively, which indicate the occurrence of a SPLET-like mechanism. H(D) kinetic isotope effects combined with pH and solvent effects suggest that different types of proton-coupled electron transfer (PCET) mechanisms are involved in water: less electron-rich phenols react at low pH by concerted electron-proton transfer (EPT) to the peroxyl radical, whereas more electron-rich phenols and phenoxide anions react by multi-site EPT in which water acts as proton relay. [ABSTRACT FROM AUTHOR]

Persistent dialkylnitroxides (e.g., 2,2,6,6-tetramethylpiperidin-1-oxyl, TEMPO) play a central role in the activity of hindered amine light stabilizers (HALS)--additives that inhibit the (photo)oxidative degradation of consumer and industrial products. The accepted mechanism of HALS comprises a catalytic cycle involving the rapid combination of a nitroxide with an alkyl radical to yield an alkoxyamine that subsequently reacts with a peroxyl radical to eventually re-form the nitroxide. Herein, we offer evidence in favor of an alternative reaction mechanism involving the acid-catalyzed reaction of a nitroxide with a peroxyl radical to yield an oxoammonium ion followed by electron transfer from an alkyl radical to the oxoammonium ion to re-form the nitroxide. In preliminary work, we showed that TEMPO reacts with peroxyl radicals at diffusion-controlled rates in the presence of acids. Now, we show that TEMPO can be regenerated from its oxoammonium ion by reaction with alkyl radicals. We have determined that this reaction, which has been proposed to be a key step in TEMPO-catalyzed synthetic transformations, occurs with k ~ 1-3 × 1010 M-1 s-1, thereby enabling it to compete with O2 for alkyl radicals. The addition of weak acids facilitates this reaction, whereas the addition of strong acids slows it by enabling back electron transfer. The chemistry is shown to occur in hydrocarbon autoxidations at elevated temperatures without added acid due to the in situ formation of carboxylic acids, accounting for the long-known catalytic radical-trapping antioxidant activity of TEMPO that prompted the development of HALS. [ABSTRACT FROM AUTHOR]

Magnolol and honokiol, the bioactive phytochemicals contained in Magnolia officinalis, are uncommon antioxidants bearing isomeric bisphenol cores substituted with allyl functions. We have elucidated the chemistry behind their antioxidant activity by experimental and computational methods. In the inhibited autoxidation of cumene and styrene at 303 K, magnolol trapped four peroxyl radicals, with a kinh of 6.1 × 104 M-1 s-1 in chlorobenzene and 6.0 × 10³ M-1 s-1 in acetonitrile, and honokiol trapped two peroxyl radicals in chlorobenzene (kinh = 3.8 × 104 M-1 s-1) and four peroxyl radicals in acetonitrile (kinh = 9.5 × 10³ M-1 s-1). Their different behavior arises from a combination of intramolecular hydrogen bonding among the reactive OH groups (in magnolol) and of the OH groups with the aromatic and allyl π-systems, as confirmed by FT-IR spectroscopy and DFT calculations. Comparison with structurally related 3,3′,5,5′-tetramethylbiphenyl-4,4′-diol, 2-allylphenol, and 2-allylanisole allowed us to exclude that the antioxidant behavior of magnolol and honokiol is due to the allyl groups. The reaction of the allyl group with a peroxyl radical (C-H hydrogen abstraction) proceeds with rate constant of 1.1 M-1 s-1 at 303 K. Magnolol and honokiol radicals do not react with molecular oxygen and produce no superoxide radical under the typical settings of inhibited autoxidations. [ABSTRACT FROM AUTHOR]

We report a newly developed synthesis of a number of alditol thiacrowns using an eco-friendly and versatile two-step strategy: the regioselective thioallyletherification of a polyhydroxylated alditol followed by a ring closing metathesis using the Grubbs second generation catalyst. This approach allows a series of target thiacrown products to be obtained in acceptable to good yields, from the corresponding α,ω-dithioallylether alditol starting materials featuring either the xylo , ribo , threo , erythro , d - manno or d - gluco configurations. The per- O -acetylated d -mannitol dithioallyether 10 , easily obtained on a large scale using this approach, was selected for evaluation as both an antibacterial and an antioxidant. Although no antibacterial activity was observed for the bacterial strains investigated, compound 10 is shown to be an antioxidant, and able to quench hydrogen peroxide in a stoichiometric fashion. [ABSTRACT FROM AUTHOR]

Despite more than 50 years of investigations into the free radical theory, the direct role of oxidative stress (OS) in aging and age-related diseases remains unproven. Little progress in identifying antioxidant drugs promoting longevity has been made, likely due to selectivity toward one or few radical species, variable efficacy in vivo, inherent pro-oxidant behavior of such drugs, or lack of synergism with metabolic redox homeostasis. Silencing the wide range of reactive free radicals has a great impact on OS-linked outcomes and age-related disorders. Here we show that an innovative, redox-active, multi-radical-scavenger catalytic drug delays the age-associated decline in physiological processes and markedly prolongs the mean lifespan of the adult freshwater annelids Aeolosoma viride by 170%. This unprecedented extension is associated with a decreased OS status. Consistently, treatment of annelids increases their natural resistance to oxygen-derived damage without affecting mitochondrial respiration or reproductive activity. Conversely, the superoxide dismutase (SOD)-mimetic EUK 134 that we selected as a positive control led to an increase in lifespan of ~50%, the same increase previously observed in nematodes. Our results show that reduction of the global network of OS has a profound impact on aging, prompting the development of a possible redox-based therapeutic intervention to counteract the progression of aging. [ABSTRACT FROM AUTHOR]

A novel method for the UHPLC–MS/MS analysis of ( E )-4-hydroxynonenal (4-HNE) is described. The method is based on derivatization of 4-HNE with pentafluorophenylhydrazine ( 1 ) or 4-trifluoromethylphenylhydrazine ( 2 ) in acetonitrile in the presence of trifluoroacetic acid as catalyst at room temperature and allows complete analysis of one sample of vegetable oil in only 21 min, including sample preparation and chromatography. The method involving hydrazine 1 , implemented in an ion trap instrument with analysis of the transition m/z 337 → 154 showed LOD = 10.9 nM, average accuracy of 101% and precision ranging 2.5–4.0% RSD intra-day (2.7–4.1% RSD inter-day), with 4-HNE standard solutions. Average recovery from lipid matrices was 96.3% from vaseline oil, 91.3% from sweet almond oil and 105.3% from olive oil. The method was tested on the assessment of safety and oxidative degradation of seven samples of dietary oil (soybean, mixed seeds, corn, peanut, sunflower, olive) and six cosmetic-grade oils (avocado, blackcurrant, apricot kernel, echium, sesame, wheat germ) and effectively detected increased 4-HNE levels in response to chemical (Fenton reaction), photochemical, or thermal stress and aging, aimed at mimicking typical oxidation associated with storage or industrial processing. The method is a convenient, cost-effective and reliable tool to assess quality and safety of vegetable oils. [ABSTRACT FROM AUTHOR]