Reactions Of Peroxyl Radicals Research Articles

Theoretical Study of Intramolecular H-Migration Reactions of Peroxyl Radicals of JP-10 (Exo-Tetrahydrodicyclopentadiene)

ABSTRACT Intramolecular H-migration reactions of peroxyl radicals of JP-10 (C10H15OO•) play an important role in developing the oxidation mechanism of JP-10 at low temperature. However, accurate rate coefficients for these reactions are lacking in the literature. Therefore, 33 H-migration reactions of C10H15OO•, which belong to six series of reactions, were investigated. Quantum chemical computations at the CBS-QB3 level reveal that C10H15OO• do not obey the rule that the energy barrier of 1,4-H migration reaction is higher than that of 1,5-H migration reaction because of the special steric cyclic structure of C10H15OO• and the ring strain in the transition state. The transition state theory and Rice-Ramsberger-Kassel-Marcus/Master-Equation theory were used to obtain high-pressure limit rate coefficients and pressure-dependent rate coefficients, respectively. The results show that H-migration reactions of C10H15OO• have obvious pressure-dependent effect. The most competitive reaction was obtained among 33 reactions. Moreover, branching ratios of each series of reactions were used as weight ratios to lump this series of reactions. Six series of reactions were lumped as six lumped reactions by the isomer lumping method. This will provide accurate rate coefficients for constructing a mechanism with the low number of species and suitability for computational fluid dynamics simulation.

Triterpenoids and ultrasound dual-catalytic nanoreactor ignites long-lived hypertoxic reactive species storm for deep tumor treatment

Inducing redox imbalance in cancer cells aided by external stimuli is a promising strategy to treat cancer. However, maximizing efficacious reactive species content with durable effects in deep tumors remains to be challenging. Here, we report an herbal medicine-based nanoreactor (OH7) self-assembled by oleanolic acid (OA) and two sonosensitizers. OH7 couples two cascade reactions under sonication, including dual-sonosensitizer-participated consecutive reactions for generating long-living peroxyl radical (ROO•) and OA-participated serial reactions for forming highly cytotoxic peroxynitrite (ONOO−). The site-directed reactive species burst exerts excellent cytotoxicity on two-dimensional cancer cell cultures and multicellular tumor spheroids. The high elasticity of OH7 for deep tumor transportation, the enhanced intratumoral convection by ultrasound, and the formation of ONOO− to destroy extracellular matrix jointly facilitate satisfactory penetration depth of sonosensitizers. Of note, the deep penetration and the long-lived hypertoxic reactive species generating ability can realize effective tumor inhibition by systemic administration. This study opens up new insights into the reactive species-related bioactive mechanisms to support green development of biocompatible high-performance sonocatalytic nanoreactor for potential clinical applications.

On ‘Is vitamin E the only lipid-soluble, chain-breaking antioxidant in human blood plasma and erythrocyte membranes?’ by Graham W. Burton, Anne Joyce, Keith U. Ingold

Application of a time-tested quantitative method of measuring peroxyl radical production in conjunction with the determination of the stoichiometry of the reaction of peroxyl radicals with α-tocopherol has permitted the conclusion that α-tocopherol is the major lipid-soluble chain-breaking antioxidant in human plasma and red cell membranes.

Reactions of methyl, hydroxyl and peroxyl radicals with the DOTA chelating agent used in medical imaging

The mechanism of reaction of DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) with ·CH3, CH3O2· and ·OH radicals were studied. The radicals were formed in situ radiolytically. The methyl radicals react orders of magnitude slower with DOTA and with MIII(DOTA)- than the hydroxyl radicals. The various final products were identified and mechanisms for their formation are proposed. CH3O2· radicals do not react, or react too slowly to be observed, with DOTA and with MIII(DOTA)- as long as the central cation is not oxidized by the peroxyl radical. The results imply that synthesis of the MIII(DOTA)-(MIII = radioisotope) complexes in a water-organic solvent (ethanol or 2-propanol or acetonitrile) mixture is not only kinetically desired but the so formed complex also decreases the radiolytic decomposition of DOTA.

Computational Investigation of the Formation of Peroxide (ROOR) Accretion Products in the OH- and NO3-Initiated Oxidation of α-Pinene.

The formation of accretion products (“dimers”) from recombination reactions of peroxyl radicals (RO2) is a key step in the gas-phase generation of low-volatility vapors, leading to atmospheric aerosol particles. We have recently demonstrated that this recombination reaction very likely proceeds via an intermediate complex of two alkoxy radicals (RO···OR′) and that the accretion product pathway involves an intersystem crossing (ISC) of this complex from the triplet to the singlet surface. However, ISC rates have hitherto not been computed for large and chemically complex RO···OR′ systems actually relevant to atmospheric aerosol formation. Here, we carry out systematic conformational sampling and ISC rate calculations on 3(RO···OR′) clusters formed in the recombination reactions of different diastereomers of the first-generation peroxyl radicals originating in both OH- and NO3-initiated reactions of α-pinene, a key biogenic hydrocarbon for atmospheric aerosol formation. While we find large differences between the ISC rates of different diastereomer pairs, all systems have ISC rates of at least 106 s–1, and many have rates exceeding 1010 s–1. Especially the latter value demonstrates that accretion product formation via the suggested pathway is a competitive process also for α-pinene-derived RO2 and likely explains the experimentally observed gas-phase formation of C20 compounds in α-pinene oxidation.

Insight into the formation of organosulfur compounds from the reaction of methyl vinyl ketone with sulfite radical in atmospheric aqueous phase

The formation of organosulfur compounds through the reaction of organic species with sulfoxy radicals produced from the metal-catalyzed oxidation of S(IV) has become of recent concern, but the detailed formation mechanism still remains unanswered. In this work, we studied the mechanism of the initial reaction of methyl vinyl ketone (MVK) by SO3− radical and the subsequent sulfonate formation processes using DFT calculation. The results show that dissolved O2 addition to the initial product is more favorable than the addition of MVK to the initial product due to its lower activation free energy (6.19 kcal mol−1). The produced peroxyl radical can undergo bimolecular self-reactions, unimolecular decay and bimolecular reaction with other species (HSO3− and H2O) to form alcohols and ketones. Among them, two pathways are most likely to occur: one belongs to bimolecular self-reactions, whose activation free energy is 16.20 kcal mol−1; the other is derived from bimolecular reaction of peroxyl radical with HSO3−, which needs to overcome the activation free energy of 18.47 kcal mol−1. This work displays a complete description of the formation process of sulfonates and thus can provide some insights into the further study on the formation of organosulfur compounds.

Elucidating the Elementary Reaction Pathways and Kinetics of Hydroxyl Radical-Induced Acetone Degradation in Aqueous Phase Advanced Oxidation Processes.

Advanced oxidation processes (AOPs) that produce highly reactive hydroxyl radicals are promising methods to destroy aqueous organic contaminants. Hydroxyl radicals react rapidly and nonselectively with organic contaminants and degrade them into intermediates and transformation byproducts. Past studies have indicated that peroxyl radical reactions are responsible for the formation of many intermediate radicals and transformation byproducts. However, complex peroxyl radical reactions that produce identical transformation products make it difficult to experimentally study the elementary reaction pathways and kinetics. In this study, we used ab initio quantum mechanical calculations to identify the thermodynamically preferable elementary reaction pathways of hydroxyl radical-induced acetone degradation by calculating the free energies of the reaction and predicting the corresponding reaction rate constants by calculating the free energies of activation. In addition, we solved the ordinary differential equations for each species participating in the elementary reactions to predict the concentration profiles for acetone and its transformation byproducts in an aqueous phase UV/hydrogen peroxide AOP. Our ab initio quantum mechanical calculations found an insignificant contribution of Russell reaction mechanisms of peroxyl radicals, but significant involvement of HO2• in the peroxyl radical reactions. The predicted concentration profiles were compared with experiments in the literature, validating our elementary reaction-based kinetic model.

Thinking outside the classical chain reaction box of lipid oxidation: Evidence for alternate pathways and the importance of epoxides

SummaryLipid oxidation has always been viewed as a simple free radical chain reaction with straightforward sequence of radicals → hydroperoxides → products. The first paper in this series proposed that alternate reactions of lipid peroxyl and alkoxyl radicals compete with hydrogen abstraction to make the process much more complex. This article provides experimental evidence for formation of epoxides as major products and shows how monitoring a broad spectrum of products is critical for accurate assessment of the extent of lipid oxidation, elucidating reaction pathways, and anticipating potential toxicity.

Quantum-chemical analysis of the disproportionation of nitroxyl and peroxyl radicals in oxidizing organic compounds

The enthalpy change of disproportionation reaction of nitroxyl and peroxyl radicals was calculated by the DFT B3LYP/cc-pVDZ method. The regeneration of the corresponding hydroxylamine during the oxidation of unsaturated compounds inhibited by nitroxyl radicals is shown to be associated with the disproportionation of the nitroxyl and peroxyl radicals.

Peroxyl Radical Reactions in Water Solution: A Gym for Proton-Coupled Electron-Transfer Theories.

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.

Peroxyl radical reactions with carotenoids in microemulsions: Influence of microemulsion composition and the nature of peroxyl radical precursor

The reactions of acetylperoxyl radicals with different carotenoids (7,7′-dihydro-β-carotene and ζ-carotene) in SDS and CTAC microemulsions of different compositions were investigated using laser flash photolysis (LFP) coupled with kinetic absorption spectroscopy. The primary objective of this study was to explore the influence of microemulsion composition and the type of surfactant used on the yields and kinetics of various transients formed from the reaction of acetylperoxyl radicals with carotenoids. Also, the influence of the site (hydrocarbon phases or aqueous phase) of generation of the peroxyl radical precursor was examined by using 4-acetyl-4-phenylpiperidine hydrochloride (APPHCl) and 1,1-diphenylacetone (11DPA) as water-soluble and lipid-soluble peroxyl radical precursors, respectively. LFP of peroxyl radical precursors with 7,7′-dihydro-β-carotene (77DH) in different microemulsions gives rise to the formation of three distinct transients namely addition radical (λmax=460nm), near infrared transient1 (NIR, λmax=700nm) and 7,7′-dihydro-β-carotene radical cation (77DH•+, λmax=770nm). In addition, for ζ-carotene (ZETA) two transients (near infrared transient1 (NIR1, λmax=660nm) and ζ-carotene radical cation (ZETA•+, λmax=730–740nm)) are generated following LFP of peroxyl radical precursors in the presence of ζ-carotene (ZETA) in different microemulsions. The results show that the composition of the microemulsion strongly influences the observed yield and kinetics of the transients formed from the reactions of peroxyl radicals (acetylperoxyl radicals) with carotenoids (77DH and ZETA). Also, the type of surfactant used in the microemulsions influences the yield of the transients formed. The dependence of the transient yields and kinetics on microemulsion composition (or the type of surfactant used in the microemulsion) can be attributed to the change of the polarity of the microenvironment of the carotenoid. Furthermore, the nature of the peroxyl radical precursor used (water-soluble or lipid-soluble peroxyl radical precursors) has little influence on the yields and kinetics of the transients formed from the reaction of peroxyl radicals with carotenoids. In the context of the interest in carotenoids as radical scavenging antioxidants, the fates of the addition radicals (formed from the reaction of carotenoid with peroxyl radicals) and carotenoid radical cations are discussed.

Effect of layer-by-layer coatings and localization of antioxidant on oxidative stability of a model encapsulated bioactive compound in oil-in-water emulsions

Oxidation of encapsulated bioactives in emulsions is one of the key challenges that limit shelf-life of many emulsion containing products. This study seeks to quantify the role of layer-by-layer coatings and localization of antioxidant molecules at the emulsion interface in influencing oxidation of the encapsulated bioactives. Oxidative barrier properties of the emulsions were simulated by measuring the rate of reaction of peroxyl radicals generated in the aqueous phase with the encapsulated radical sensitive dye in the lipid core of the emulsions. The results of peroxyl radical permeation were compared to the stability of encapsulated retinol (model bioactive) in emulsions. To evaluate the role of layer-by-layer coatings in influencing oxidative barrier properties, radical permeation rates and retinol stability were evaluated in emulsion formulations of SDS emulsion and SDS emulsion with one or two layers of polymers (ϵ-polylysine and dextran sulfate) coated at the interface. To localize antioxidant molecules to the interface, gallic acid (GA) was chemically conjugated with ϵ-polylysine and subsequently deposited on SDS emulsion based on electrostatic interactions. Emulsion formulations with localized GA molecules at the interface were compared with SDS emulsion with GA molecules in the bulk aqueous phase. The results of this study demonstrate the advantage of localization of antioxidant at the interface and the limited impact of short chain polymer coatings at the interface of emulsions in reducing permeation of radicals and oxidation of a model encapsulated bioactive in oil-in-water emulsions.

The role of peroxyl radicals in polyester degradation--a mass spectrometric product and kinetic study using the distonic radical ion approach.

Mass spectrometric techniques were used to obtain detailed insight into the reactions of peroxyl radicals with model systems of (damaged) polyesters. Using a distonic radical ion approach, it was shown that N-methylpyridinium peroxyl radical cations, Pyr(+)OO˙, do not react with non-activated C-H bonds typically present in polyesters that resist degradation. Structural damage in the polymer, for example small amounts of alkene moieties formed during the manufacturing process, is required to enable reaction with Pyr(+)OO˙, which proceeds with high preference through addition to the π system rather than via allylic hydrogen atom abstraction (kadd/kHAT > 20 for internal alkenes). This is due to the very fast and strongly exothermic subsequent fragmentation of the peroxyl-alkene radical adduct to epoxides and highly reactive Pyr(+)O˙, which both could promote further degradation of the polymer through non-radical and radical pathways. This work provides essential experimental support that the basic autoxidation mechanism is a too simplistic model to rationalize radical mediated degradation of polymers under ambient conditions.

Development of linear free energy relationships for aqueous phase radical-involved chemical reactions.

Aqueous phase advanced oxidation processes (AOPs) produce hydroxyl radicals (HO•) which can completely oxidize electron rich organic compounds. The proper design and operation of AOPs require that we predict the formation and fate of the byproducts and their associated toxicity. Accordingly, there is a need to develop a first-principles kinetic model that can predict the dominant reaction pathways that potentially produce toxic byproducts. We have published some of our efforts on predicting the elementary reaction pathways and the HO• rate constants. Here we develop linear free energy relationships (LFERs) that predict the rate constants for aqueous phase radical reactions. The LFERs relate experimentally obtained kinetic rate constants to quantum mechanically calculated aqueous phase free energies of activation. The LFERs have been applied to 101 reactions, including (1) HO• addition to 15 aromatic compounds; (2) addition of molecular oxygen to 65 carbon-centered aliphatic and cyclohexadienyl radicals; (3) disproportionation of 10 peroxyl radicals, and (4) unimolecular decay of nine peroxyl radicals. The LFERs correlations predict the rate constants within a factor of 2 from the experimental values for HO• reactions and molecular oxygen addition, and a factor of 5 for peroxyl radical reactions. The LFERs and the elementary reaction pathways will enable us to predict the formation and initial fate of the byproducts in AOPs. Furthermore, our methodology can be applied to other environmental processes in which aqueous phase radical-involved reactions occur.

Pulse radiolysis studies of 3,5-dimethyl pyrazole derivatives of selenoethers.

One electron redox reaction of two asymmetric 3,5-dimethyl pyrazole derivatives of selenoethers attached to ethanoic acid (DPSeEA) and propionic acid (DPSePA) were studied by pulse radiolysis technique using transient absorption detection. The reaction of the hydroxyl ((•)OH) radical with DPSeEA or DPSePA at pH 7 produced transients absorbing at 500 nm and at 300 nm, respectively. The absorbance at 500 nm increased with increasing parent concentration indicating formation of dimer radical cations. From the absorbance changes, the equilibrium constants for the formation of dimer radical cation of DPSeEA and DPSePA were estimated as 2020 and 1608 M(-1), respectively. The rate constants at pH 7 for the reaction of the (•)OH radical with DPSeEA and DPSePA were determined to be 9.6 × 10(9) and 1.4 × 10(10) M(-1) s(-1), respectively. The dimer radical cation of DPSeEA and DPSePA decayed by first order kinetics with a rate constant of 2.8 × 10(4) and 5.5 × 10(3) s(-1), respectively. The yield of radical cations of DPSeEA and DPSePA were estimated from the secondary electron transfer reaction, which corresponds to 38% and 48% of (•)OH radical yield, respectively. Some fraction of monomer radical cation undergoes decarboxylation reaction, and the yield of decarboxylation was 25% and 20% for DPSeEA and DPSePA, respectively. These results have implication in understanding their antioxidant activity. The reaction of trichloromethyl peroxyl radical, glutathione, and ascorbic acid further support their antioxidant behavior.

Characteristics of n-butane weak flames at elevated pressures in a micro flow reactor with a controlled temperature profile

The very first successful experiments at elevated pressures up to 1.2MPa by an “in-pressure-chamber”-type micro flow reactor with a controlled temperature profile are demonstrated. n-Butane was applied to the micro flow reactor and the ignition characteristics at pressures of 0.1–1.2MPa were investigated by observing weak flames. Among three kinds of separated weak flames which can be observed by the present reactor, the blue flame was only observed at pressures higher than 0.2MPa and the cool flame was only observed at pressures higher than 0.3MPa. This interprets the multi-stage oxidation for n-butane was confirmed experimentally and computationally. The positions of the blue and cool flames shifted towards the lower temperature side along with the increase of pressure in the experiment. Computation results reproduced the experimental tendency of the blue and cool flames. The wall temperature value at the cool flame position in the experiment agreed with that in the computation at all pressures studied, and that at 1.0MPa agreed with the compressed temperature at which the cool flame was observed in the rapid compression machine at a compression pressure of 10bar. The computational weak flame structure at 0.1MPa was compared with that of 1.0MPa. High-temperature oxidation is important at 0.1MPa while low temperature oxidation is important at high pressures. At 1.0MPa, most of the fuel is consumed at the cool flame. Separated cool flames were found at 1.2MPa and four-stage oxidation was produced in the computation. Rate of production analysis indicated that the first cool flame was formed by fuel oxidation through low-temperature oxidation while the second one was formed by reaction of peroxyl radicals with H2O2.

Singlet molecular oxygen generated by biological hydroperoxides

The chemistry behind the phenomenon of ultra-weak photon emission has been subject of considerable interest for decades. Great progress has been made on the understanding of the chemical generation of electronically excited states that are involved in these processes. Proposed mechanisms implicated the production of excited carbonyl species and singlet molecular oxygen in the mechanism of generation of chemiluminescence in biological system. In particular, attention has been focused on the potential generation of singlet molecular oxygen in the recombination reaction of peroxyl radicals by the Russell mechanism. In the last ten years, our group has demonstrated the generation of singlet molecular oxygen from reactions involving the decomposition of biologically relevant hydroperoxides, especially from lipid hydroperoxides in the presence of metal ions, peroxynitrite, HOCl and cytochrome c. In this review we will discuss details on the chemical aspects related to the mechanism of singlet molecular oxygen generation from different biological hydroperoxides.

WEISS LECTURECarbohydrate radicals: from ethylene glycol to DNA strand breakage

Radiation-induced DNA strand breakage results from the reactions of radicals formed at the sugar moiety of DNA. In order to elucidate the mechanism of this reaction investigations were first performed on low molecular weight model systems. Results from studies on deoxygenated aqueous solutions of ethylene glycol, 2-deoxy-d-ribose and other carbohydrates and, more relevantly, of d-ribose-5-phosphate have shown that substituents can be eliminated from the β-position of the radical site either proton and base-assisted (as in the case of the OH substituent), or spontaneously (as in the case of the phosphate substituent). In DNA the C(4’) radical undergoes strand breakage via this type of reaction. In the presence of oxygen the carbon-centred radicals are rapidly converted into the corresponding peroxyl radicals. Again, low molecular weights models have been investigated to elucidate the key reactions. A typical reaction of DNA peroxyl radicals is the fragmentation of the C(4’)-C(S’) bond, a reaction not observed in the absence of oxygen. Although OH radicals may be the important direct precursors of the sugar radicals of DNA, results obtained with poly(U) indicate that base radicals may well be of even greater importance. The base radicals, formed by addition of the water radicals (H and OH) to the bases would in their turn attack the sugar moiety to produce sugar radicals which then give rise to strand breakage and base release. For a better understanding of strand break formation it is therefore necessary to investigate in more detail the reactions of the base radicals. For a start, the radiolysis of uracil in oxygenated solutions has been reinvestigated, and it has been shown that the major peroxyl radical in this system undergoes base-catalysed elimination of , a reaction that involves the proton at N(l). In the nucleic acids the pyrimidines are bound at N(l) to the sugar moiety and this type of reaction can no longer occur. Therefore, with respect to the nucleic acids, pyrimidines are good models only in acid solutions where the elimination reaction is too slow to compete with the bimolecular reactions of the peroxyl radicals. Moreover, the long lifetime of the radical sites on the nucleic acid strand may allow reactions to occur which are kinetically of first order, and which cannot be studied in model systems at ordinary dose rates. It is therefore suggested to extend model system studies to low dose rates and to oligonucleo-tides. Such studies might eventually reveal the key reactions in radical-induced DNA degradation.

Mass Spectrometric and Computational Studies on the Reaction of Aromatic Peroxyl Radicals with Phenylacetylene Using the Distonic Radical Ion Approach

Product and mechanistic studies were performed for the reaction of aromatic distonic peroxyl radical cations 4-PyrOO(•+) and 3-PyrOO(•+) with phenylacetylene (7) in the gas phase using mass spectrometric and computational techniques. PyrOO(•+) was generated through reaction of the respective distonic aryl radical cation Pyr(•+) with O2 in the ion source of the mass spectrometer. For the reaction involving the more electrophilic 4-PyrOO(•+), a rate coefficient of k1 = (2.2 ± 0.6) × 10(-10) cm(3) molecule(-1) s(-1) was determined at 298 K, while a value of k2 = (8.2 ± 2.1) × 10(-11) cm(3) molecule(-1) s(-1) was obtained for the reaction involving the less electrophilic 3-PyrOO(•+). This highlights the role of polar effects in these reactions, which are likely of high relevance for processes in combustions and atmospheric transformations. The mechanism was studied by computational methods, which showed that radical addition occurs exclusively at the less substituted alkyne site to give the distonic vinyl radical cation 8. The latter undergoes a series of subsequent rearrangements/fragmentations that are similar for both isomeric PyrOO(•+). γ-Fragmentation in 8 leads to the distonic aryloxyl radical cation PyrO(•+) and a singlet carbene 10. The product association complex [PyrO(•+) - 10] is the starting point for two important subsequent reactions, e.g., (i) rapid hydrogen transfer to form ketenyl radical 11 and the closed-shell species PyrOH(+), and (ii) oxygen transfer from PyrO(•+) to 10 that leads to α-keto aldehyde 13 and Pyr(•+), followed by hydrogen abstraction to give acyl radical 14 and PyrH(+). Additional major products are the closed-shell aromatic carbonyl compounds 20 and 30 that result from multistep rearrangements in vinyl radical 8, which are terminated by homolytic bond scission and release of neutral acyl radicals.

Dissociation energies of O-H, N-H, and S-H bonds in sulfur-containing antioxidants

The dissociation energies of O-H bonds (DO-H) of 48 phenol sulfides and N-H bonds (DN-H) of five amino sulfides were determined from experimental data. The dissociation energies of the bonds were estimated by the method of crossing parabolas from the kinetic data (the rate constants of reactions of peroxyl radicals with these antioxidants). The O-H, S-H, and N-H bond dissociation energies were determined for three hybrid antioxidants (two hydroxythiophenols and one aminophenol): DO-H = 335.9 kJ mol−1 and DS-H = 340.8 kJ mol−1 for 2-hydroxy-3,5-bis-(1′-phenylethyl)thiophenol, DO-H = 337.7 kJ mol−1 and DS-H = 344.2 kJ mol−1 for 3,5-bis-(1′-phenylethyl)-4-hydroxythiophenol, and DO-H = 338.6 kJ mol−1 and DN-H = 366.2 kJ mol−1 for 1-(N-phenylamino)-2-thiol-3-thio-(3′,5′-bis-di-tert-butyl-4′-hydroxyphenyl)-propane.