Journal articles: 'Autoxidative reactions'

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Wolff, S. P., and R. T. Dean. "Glucose autoxidation and protein modification. The potential role of ‘autoxidative glycosylation’ in diabetes." Biochemical Journal 245, no. 1 (July 1, 1987): 243–50. http://dx.doi.org/10.1042/bj2450243.

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Monosaccharide autoxidation (a transition metal-catalysed process that generates H2O2 and ketoaldehydes) appears to contribute to protein modification by glucose in vitro. The metal-chelating agent diethylenetriaminepenta-acetic acid (DETAPAC), which inhibits glucose autoxidation, also reduces the covalent attachment of glucose to bovine serum albumin. A maximal 45% inhibition of covalent attachment was observed, but this varied with glucose and DETAPAC concentrations in a complex fashion, suggesting at least two modes of attachment. The extent of inhibition of the metal-catalysed pathway correlated with the extent of inhibition of glycosylation-associated chromo- and fluorophore development. DETAPAC also inhibited tryptophan fluorescence quenching associated with glycosylation. Conversely, ketoaldehydes analogous to those produced by glucose autoxidation, but generated by 60Co irradiation, bound avidly to albumin and accelerated browning reactions. It is therefore suggested that a component of protein glycosylation is dependent upon glucose autoxidation and subsequent covalent attachment of ketoaldehydes. The process of glucose autoxidation, or ketoaldehydes derived therefrom, appear to be important in chromophoric and fluorophoric alterations. It is noted, consistent with these observations, that the chemical evidence for the currently accepted ‘Amadori’ product derived from the reaction of glucose with protein amino groups is consistent also with the structure expected for the attachment of a glucose-derived ketoaldehyde to protein. The concept of ‘autoxidative glycosylation’ is briefly discussed in relation to oxidative stress in diabetes mellitus.

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Cilliers, Johannes J. L., and Vernon L. Singleton. "Nonenzymic Autoxidative Reactions of Caffeic Acid in Wine." American Journal of Enology and Viticulture 41, no. 1 (1990): 84–86. http://dx.doi.org/10.5344/ajev.1990.41.1.84.

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Cilliers, Johannes J. L., and Vernon L. Singleton. "Nonenzymic autoxidative phenolic browning reactions in a caffeic acid model system." Journal of Agricultural and Food Chemistry 37, no. 4 (July 1989): 890–96. http://dx.doi.org/10.1021/jf00088a013.

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Cilliers, Johannes J. L., and Vernon L. Singleton. "Characterization of the products of nonenzymic autoxidative phenolic reactions in a caffeic acid model system." Journal of Agricultural and Food Chemistry 39, no. 7 (July 1991): 1298–303. http://dx.doi.org/10.1021/jf00007a021.

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Field, J. A., and G. Lettinga. "Treatment and Detoxification of Aqueous Spruce Bark Extracts by Aspergillus niger." Water Science and Technology 24, no. 3-4 (August 1, 1991): 127–37. http://dx.doi.org/10.2166/wst.1991.0469.

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Debarking effluents of the forest industry are severely toxic waste streams due to their high tannin content. The objectives of this study were to evaluate the treatment and detoxification of debarking wastewater with tannin tolerant fungi. For this purpose, Aspergillus niger was cultivated on aqueous bark extracts and the toxicity was assayed utilizing methanogenic bacteria as the test organism. Sterilized aqueous extracts of spruce bark were diluted to 5.2 g COD L−1 (containing 2.7 g tannin COD L−1) in either citrate or tartrate buffer and inoculated with A. niger spores. During four day aerobic fermentations with citrate buffer, the elimination of unfiltered and soluble COD was 28 and 63%, respectively. The apparent yield of biomass averaged 34% of the extract COD; however, 12% of the extract COD was tannins adsorbed on the fungal biomass. The decrease in the tannin concentratio was 50%. According to gel chromatography results, the original oligomeric tannins that resisted biodegradation were those of the highest MW. The toxicity was consequently only partially reduced by the fermentation. During the tartrate buffered fermentations, the pH rose due to the metabolism of the organic acid in the buffer. The rise in pH beyond 6 promoted autoxidative reactions that caused extensive polymerization of the tannins which resisted biodegradation. This resulted not only in an enhanced elimination of the tannins but also in a complete detoxification of the extracts. Similar levels of detoxification could be obtained in sterile un-inoculated extracts by autoxidation alone (raising the pH and aerating the extracts). Likewise, extracts fermented in citrate buffer could be completely detoxified by a subsequent autoxidation treatment. The exclusion peak of the gel chromatograms (MW > 30,000 g mole−1) obtained from the highly autoxidized samples accounted for 53% of the UV absorbance, whereas no exclusion peak was present in the unoxidized extracts. For the biological treatment and detoxification of debarking wastewaters, we recommend the cultivation of tannin tolerant fungi followed by short autoxidation treatments that polymerize the oligomeric tannin fraction resisting biodegradation to non-toxic high molecular weight polymers.

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Ballesteros, Daniel, Hugh W. Pritchard, and Christina Walters. "Dry architecture: towards the understanding of the variation of longevity in desiccation-tolerant germplasm." Seed Science Research 30, no. 2 (June 2020): 142–55. http://dx.doi.org/10.1017/s0960258520000239.

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AbstractDesiccation-tolerant (DT) plant germplasm (i.e. seeds, pollen and spores) survive drying to low moisture contents, when cytoplasm solidifies, forming a glass, and chemical reactions are slowed. DT germplasm may survive for long periods in this state, though inter-specific and intra-specific variation occurs and is not currently explained. Such variability has consequences for agriculture, forestry and biodiversity conservation. Longevity was previously considered in the context of morphological features, cellular constituents or habitat characteristics. We suggest, however, that a biophysical perspective, which considers the molecular organization – or structure – within dried cytoplasm, can provide a more integrated understanding of the fundamental mechanisms that control ageing rates, hence the variation of longevity among species and cell types. Based on biochemical composition and physical–chemical properties of dried materials, we explore three types of the interplay between structural conformations of dried cytoplasm and ageing: (1) cells that lack chlorophyll and contain few storage lipids may exhibit long shelf life, with ageing probably occurring through slow autoxidative processes within the glassy matrix as it relaxes; (2) cells with active chlorophyll may die quickly, possibly because they are prone to oxidative stress promoted by the photosynthetic pigments in the absence of metabolic water and (3) cells that lack chloroplasts but contain high storage lipids may die quickly during storage at −20°C, possibly because lipids crystallize and destabilize the glassy matrix. Understanding the complex variation in structural conformation in space and time may help to design strategies that increase longevity in germplasm with generally poor shelf life.

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Zeng, Meirong, Nadja Heine, and Kevin R. Wilson. "Evidence that Criegee intermediates drive autoxidation in unsaturated lipids." Proceedings of the National Academy of Sciences 117, no. 9 (February 18, 2020): 4486–90. http://dx.doi.org/10.1073/pnas.1920765117.

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Autoxidation is an autocatalytic free-radical chain reaction responsible for the oxidative destruction of organic molecules in biological cells, foods, plastics, petrochemicals, fuels, and the environment. In cellular membranes, lipid autoxidation (peroxidation) is linked with oxidative stress, age-related diseases, and cancers. The established mechanism of autoxidation proceeds via H-atom abstraction through a cyclic network of peroxy–hydroperoxide-mediated free-radical chain reactions. For a series of model unsaturated lipids, we present evidence for an autoxidation mechanism, initiated by hydroxyl radical (OH) addition to C=C bonds and propagated by chain reactions involving Criegee intermediates (CIs). This mechanism leads to unexpectedly rapid autoxidation even in the presence of water, implying that as reactive intermediates, CI could play a much more prominent role in chemistries beyond the atmosphere.

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Veselinović, Aleksandar, Ružica Nikolić, and Goran Nikolić. "Application of multivariate curve resolution-alternating least squares (MCR-ALS) for resolving pyrogallol autoxidation in weakly alkaline aqueous solutions." Open Chemistry 10, no. 6 (December 1, 2012): 1942–48. http://dx.doi.org/10.2478/s11532-012-0125-z.

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AbstractMultivariate curve resolution — alternating least squares (MCR-ALS) has been applied to data collected from UV/Vis spectrophotometric analysis of the autoxidation process of pyrogallol in weakly alkaline aqueous solutions. The MCR-ALS analysis was able to explain the autoxidation kinetics of pyrogallol at pH 7.4 and 8.0, allowing deduction of the pure spectra and concentration changes of different species present throughout the entire process. The autoxidation process at pH 7.4 was found to follow a first-order reaction model, with formation of purpurogallin as the sole and terminal product. Changing the pH to 8.0 not only accelerated autoxidation of pyrogallol to purpurogallin but also introduced a further autoxidation of purpurogallin. At pH 8.0 the process fits a model of two consecutive first-order reactions. The first step is formation of purpurogallin, which reacts in a further autoxidation to form a yellow colored substance, most probably purpurogallin polymer.

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Griesser, Markus, Jean-Philippe R. Chauvin, and Derek A. Pratt. "The hydrogen atom transfer reactivity of sulfinic acids." Chemical Science 9, no. 36 (2018): 7218–29. http://dx.doi.org/10.1039/c8sc02400f.

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Sulfinic acids are characterized to be very good H-atom donors to each of alkyl and alkoxyl radicals. In order to participate in useful radical chain reactions, the sulfonyl radicals must undergo fast propagating reactions to avoid autoxidation, which is surprisingly rate-limited by the reaction of sulfonyl radicals with oxygen.

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Xu, Ruochong, Joel A. Thornton, Ben H. Lee, Yanxu Zhang, Lyatt Jaeglé, Felipe D. Lopez-Hilfiker, Pekka Rantala, and Tuukka Petäjä. "Global simulations of monoterpene-derived peroxy radical fates and the distributions of highly oxygenated organic molecules (HOMs) and accretion products." Atmospheric Chemistry and Physics 22, no. 8 (April 26, 2022): 5477–94. http://dx.doi.org/10.5194/acp-22-5477-2022.

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Abstract. We evaluate monoterpene-derived peroxy radical (MT-RO2) unimolecular autoxidation and self- and cross-reactions with other RO2 species in the GEOS-Chem global chemical transport model. The formation of associated highly oxygenated organic molecules (HOMs) and accretion products are tracked in competition with other bimolecular reactions. Autoxidation is the dominant fate up to 6–8 km for first-generation MT-RO2, which can undergo unimolecular H shifts. Reaction with NO can be a more common fate for H-shift rate constants < 0.1 s−1 or at altitudes higher than 8 km due to the imposed Arrhenius temperature dependence of unimolecular H shifts. For MT-derived HOM-RO2, generated by multistep autoxidation of first-generation MT-RO2, reaction with other RO2 species is predicted to be the major fate throughout most of the boreal and tropical forest regions, whereas reaction with NO dominates in the temperate and subtropical forests of the Northern Hemisphere. The newly added reactions result in an approximate 4 % global average decrease in HO2 and RO2, mainly due to faster self-/cross-reactions of MT-RO2, but the impact upon HO2, OH, and NOx abundances is only important in the planetary boundary layer (PBL) over portions of tropical forests. Predicted HOM concentrations in MT-rich regions and seasons can exceed total organic aerosol predicted by the standard version of the GEOS-Chem model depending on the parameters used. Comparisons to observations reveal that large uncertainties remain for key reaction parameters and processes, especially with respect to the photochemical lifetime and volatility of HOMs as well as the rates and branching of associated RO2 accretion products. Further observations and laboratory studies related to MT-RO2-derived HOMs and gas-phase RO2 accretion product formation kinetics – especially their atmospheric fate, such as gas–particle partitioning, multiphase chemistry, and net secondary organic aerosol formation – are needed.

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Xu, Ruochong, Joel A. Thornton, Ben H. Lee, Yanxu Zhang, Lyatt Jaeglé, Felipe D. Lopez-Hilfiker, Pekka Rantala, and Tuukka Petäjä. "Global simulations of monoterpene-derived peroxy radical fates and the distributions of highly oxygenated organic molecules (HOMs) and accretion products." Atmospheric Chemistry and Physics 22, no. 8 (April 26, 2022): 5477–94. http://dx.doi.org/10.5194/acp-22-5477-2022.

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Abstract. We evaluate monoterpene-derived peroxy radical (MT-RO2) unimolecular autoxidation and self- and cross-reactions with other RO2 species in the GEOS-Chem global chemical transport model. The formation of associated highly oxygenated organic molecules (HOMs) and accretion products are tracked in competition with other bimolecular reactions. Autoxidation is the dominant fate up to 6–8 km for first-generation MT-RO2, which can undergo unimolecular H shifts. Reaction with NO can be a more common fate for H-shift rate constants < 0.1 s−1 or at altitudes higher than 8 km due to the imposed Arrhenius temperature dependence of unimolecular H shifts. For MT-derived HOM-RO2, generated by multistep autoxidation of first-generation MT-RO2, reaction with other RO2 species is predicted to be the major fate throughout most of the boreal and tropical forest regions, whereas reaction with NO dominates in the temperate and subtropical forests of the Northern Hemisphere. The newly added reactions result in an approximate 4 % global average decrease in HO2 and RO2, mainly due to faster self-/cross-reactions of MT-RO2, but the impact upon HO2, OH, and NOx abundances is only important in the planetary boundary layer (PBL) over portions of tropical forests. Predicted HOM concentrations in MT-rich regions and seasons can exceed total organic aerosol predicted by the standard version of the GEOS-Chem model depending on the parameters used. Comparisons to observations reveal that large uncertainties remain for key reaction parameters and processes, especially with respect to the photochemical lifetime and volatility of HOMs as well as the rates and branching of associated RO2 accretion products. Further observations and laboratory studies related to MT-RO2-derived HOMs and gas-phase RO2 accretion product formation kinetics – especially their atmospheric fate, such as gas–particle partitioning, multiphase chemistry, and net secondary organic aerosol formation – are needed.

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12

Guillén, Francisco, Carmen Muñoz, Víctor Gómez-Toribio, Angel T. Martínez, and María Jesús Martínez. "Oxygen Activation during Oxidation of Methoxyhydroquinones by Laccase from Pleurotus eryngii." Applied and Environmental Microbiology 66, no. 1 (January 1, 2000): 170–75. http://dx.doi.org/10.1128/aem.66.1.170-175.2000.

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ABSTRACT Oxygen activation during oxidation of the lignin-derived hydroquinones 2-methoxy-1,4-benzohydroquinone (MBQH2) and 2,6-dimethoxy-1,4-benzohydroquinone (DBQH2) by laccase fromPleurotus eryngii was examined. Laccase oxidized DBQH2 more efficiently than it oxidized MBQH2; both the affinity and maximal velocity of oxidation were higher for DBQH2 than for MBQH2. Autoxidation of the semiquinones produced by laccase led to the activation of oxygen, producing superoxide anion radicals (Q·− + O2 ↔ Q + O2 ·−). As this reaction is reversible, its existence was first noted in studies of the effect of systems consuming and producing O2 ·− on quinone formation rates. Then, the production of H2O2 in laccase reactions, as a consequence of O2 ·− dismutation, confirmed that semiquinones autoxidized. The highest H2O2levels were obtained with DBQH2, indicating that DBQ·− autoxidized to a greater extent than did MBQ·−. Besides undergoing autoxidation, semiquinones were found to be transformed into quinones via dismutation and laccase oxidation. Two ways of favoring semiquinone autoxidation over dismutation and laccase oxidation were increasing the rate of O2 ·− consumption with superoxide dismutase (SOD) and recycling of quinones with diaphorase (a reductase catalyzing the divalent reduction of quinones). These two strategies made the laccase reaction conditions more natural, since O2 ·−, besides undergoing dismutation, reacts with Mn2+, Fe3+, and aromatic radicals. In addition, quinones are continuously reduced by the mycelium of white-rot fungi. The presence of SOD in laccase reactions increased the extent of autoxidation of 100 μM concentrations of MBQ·− and DBQ·− from 4.5 to 30.6% and from 19.6 to 40.0%, respectively. With diaphorase, the extent of MBQ·− autoxidation rose to 13.8% and that of DBQ·− increased to 39.9%.

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Schervish, Meredith, and Neil M. Donahue. "Peroxy radical chemistry and the volatility basis set." Atmospheric Chemistry and Physics 20, no. 2 (January 31, 2020): 1183–99. http://dx.doi.org/10.5194/acp-20-1183-2020.

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Abstract. Gas-phase autoxidation of organics can generate highly oxygenated organic molecules (HOMs) and thus increase secondary organic aerosol production and enable new-particle formation. Here we present a new implementation of the volatility basis set (VBS) that explicitly resolves peroxy radical (RO2) products formed via autoxidation. The model includes a strong temperature dependence for autoxidation as well as explicit termination of RO2, including reactions with NO, HO2, and other RO2. The RO2 cross-reactions can produce dimers (ROOR). We explore the temperature and NOx dependence of this chemistry, showing that temperature strongly influences the intrinsic volatility distribution and that NO can suppress autoxidation under conditions typically found in the atmosphere.

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Ordoñez, I. D., and E. Cadenas. "Thiol oxidation coupled to DT-diaphorase-catalysed reduction of diaziquone. Reductive and oxidative pathways of diaziquone semiquinone modulated by glutathione and superoxide dismutase." Biochemical Journal 286, no. 2 (September 1, 1992): 481–90. http://dx.doi.org/10.1042/bj2860481.

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DT-diaphorase [NAD(P)H:quinone oxidoreductase; EC 1.6.99.2] catalysed the two-electron reduction of the anti-tumour quinone 2,5-bis-(1-aziridinyl)-3,6-bis(ethoxycarbonylamino)-1,4-benzoquino ne (AZQ) to the hydroquinone form (AZQH2). Although DT-diaphorase catalysis of AZQ was not significantly affected by pH, the hydroquinone product was effectively stabilized by protonation at pH values below 7, whereas, above that pH, hyroquinone autoxidation, evaluated in terms of H2O2 production, increased exponentially. The autoxidation of AZQH2 entailed the formation of diverse radicals, such as O2-.,HO., and the semiquinone form of AZQ (AZQ-.), which contributed to different extents to the e.p.r. spectrum. Superoxide dismutase enhanced the autoxidation of AZQH2 and suppressed the e.p.r. signal ascribed to AZQ-., in agreement with a displacement of the equilibrium of the semiquinone autoxidation reaction (AZQ-.+O2 in equilibrium with AZQ+O2-.) upon enzymic withdrawal of O2-.. GSH increased the steady-state concentration of AZQH2 formed during DT-diaphorase catalysis and inhibited temporarily its autoxidation. This effect was accompanied by oxidation of the thiol to the disulphide within a process involving glutathionyl radical (GS.) formation, the relative contribution of which to the e.p.r. spectrum was enhanced by increasing GSH concentrations. GS. formation in this experimental model can be rationalized as originating from the reaction of GSH with AZQ-., rather than with O2-. or HO., for thiol oxidation was not affected significantly by superoxide dismutase, and GS. formation was insensitive to catalase. In addition, GSH suppressed the e.p.r. signal attributed to AZQ-.. No glutathionyl-quinone conjugate was detected during the DT-diaphorase-catalysed reduction of AZQ; although the chemical requirements for alkylation were partly fulfilled (quinone ring aromatization and acid-assisted aziridinyl ring opening), the negligible dissociation of GSH (GS(-)+H+ in equilibrium with GSH) at low pH prevented any nucleophilic addition to occur. Therefore the redox transitions of AZQ during DT-diaphorase catalysis seemed to be centred on the semiquinone species, the fate of which was inversely affected by catalytic amounts of superoxide dismutase and large amounts of GSH: the former enhanced AZQ-. autoxidation and the latter favoured AZQ-. reduction. Accordingly, superoxide dismutase and GSH suppressed the semiquinone e.p.r. signal. These results are discussed in terms of three interdependent redox transitions (comprising one-electron transfer reactions involving the quinone, oxygen and the thiol) and the thermodynamic and kinetic properties of the reactions involved.

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Praske, Eric, Rasmus V. Otkjær, John D. Crounse, J. Caleb Hethcox, Brian M. Stoltz, Henrik G. Kjaergaard, and Paul O. Wennberg. "Atmospheric autoxidation is increasingly important in urban and suburban North America." Proceedings of the National Academy of Sciences 115, no. 1 (December 18, 2017): 64–69. http://dx.doi.org/10.1073/pnas.1715540115.

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Gas-phase autoxidation—regenerative peroxy radical formation following intramolecular hydrogen shifts—is known to be important in the combustion of organic materials. The relevance of this chemistry in the oxidation of organics in the atmosphere has received less attention due, in part, to the lack of kinetic data at relevant temperatures. Here, we combine computational and experimental approaches to investigate the rate of autoxidation for organic peroxy radicals (RO2) produced in the oxidation of a prototypical atmospheric pollutant, n-hexane. We find that the reaction rate depends critically on the molecular configuration of the RO2 radical undergoing hydrogen transfer (H-shift). RO2 H-shift rate coefficients via transition states involving six- and seven-membered rings (1,5 and 1,6 H-shifts, respectively) of α-OH hydrogens (HOC-H) formed in this system are of order 0.1 s−1 at 296 K, while the 1,4 H-shift is calculated to be orders of magnitude slower. Consistent with H-shift reactions over a substantial energetic barrier, we find that the rate coefficients of these reactions increase rapidly with temperature and exhibit a large, primary, kinetic isotope effect. The observed H-shift rate coefficients are sufficiently fast that, as a result of ongoing NOx emission reductions, autoxidation is now competing with bimolecular chemistry even in the most polluted North American cities, particularly during summer afternoons when NO levels are low and temperatures are elevated.

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Fábián, István, and Gábor Lente. "Light-induced multistep redox reactions: The diode-array spectrophotometer as a photoreactor." Pure and Applied Chemistry 82, no. 10 (June 23, 2010): 1957–73. http://dx.doi.org/10.1351/pac-con-09-11-16.

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The light source of a photometer may induce chemical reactions in photosensitive reactive systems. Diode-array spectrophotometers are particularly suitable for producing such phenomena. This paper provides an overview on how this equipment can be used as a photoreactor. The principles of various techniques to control the intensity and spectral region of the illuminating light are discussed in detail. It will be shown that the quantum yields of various photochemically induced redox reactions can be determined by exploiting specific features of diode-array spectrophotometers. Kinetic coupling between primary photo-chemical and secondary thermally activated reaction steps are utilized to explore intimate details of composite redox reactions. Key aspects of the method applied are demonstrated via the photoreactions of 2,6-dichloro-1,4-benzoquinone (DCQ), the photoinduced autoxidation of S(IV) and a photochemically activated redox reaction of the chlorate ion.

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Limpanuparb, Taweetham, Pakpong Roongruangsree, and Cherprang Areekul. "A DFT investigation of the blue bottle experiment: E ∘ half-cell analysis of autoxidation catalysed by redox indicators." Royal Society Open Science 4, no. 11 (November 2017): 170708. http://dx.doi.org/10.1098/rsos.170708.

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The blue bottle experiment is a collective term for autoxidation reactions catalysed by redox indicators. The reactions are characterized by their repeatable cycle of colour changes when shaken/left to stand and intricate chemical pattern formation. The blue bottle experiment is studied based on calculated solution-phase half-cell reduction potential of related reactions. Our investigation confirms that the reaction in various versions of the blue bottle experiment published to date is mainly the oxidation of an acyloin to a 1,2-dicarbonyl structure. In the light of the calculations, we also propose new non-acyloin reducing agents for the experiment. These results can help guide future experimental studies on the blue bottle experiment.

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Milano, Francesco, Marco Lopresti, Danilo Vona, Gabrielle Buscemi, Mariangela Cantore, Gianluca M. Farinola, and Massimo Trotta. "Activity of photosynthetic Reaction Centers coated with polydopamine." MRS Advances 5, no. 45 (2020): 2299–307. http://dx.doi.org/10.1557/adv.2020.275.

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Dilute aqueous solutions of dopamine buffered to an alkaline pH and in the presence of dissolved oxygen undergo to a series of autoxidation and rearrangement reactions that lead to the formation of a dark insoluble material called polydopamine (PDA) with melanin reminiscent properties. In this work we carried out this reaction in the presence of the photosynthetic reaction center (RC), a transmembrane pigment-protein complex responsible for the first light-induced reactions in the photosynthetic process. We have found that PDA grows in colloidal form around the RC and in the appropriate conditions the protein is entrapped in the PDA matrix without loss of functionality. The protein is still capable to perform its natural photocycle leading to the generation of photocurrents and the ubiquinone acceptor complex function is modulated by the PDA/RC ratio.

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Endalew, Abebe K., and Yohannes Kiros. "Catalytic Autoxidation of Fatty Acid Methyl Esters from Jatropha Oil." Journal of Fuels 2014 (October 16, 2014): 1–6. http://dx.doi.org/10.1155/2014/470790.

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Metal catalysts for transesterification of vegetable oils can cause autoxidation side reactions which reduces the fuel quality of the biodiesel. On the other side, oxidation of highly unsaturated oils can open opportunities for the synthesis of other important renewable chemical products. This study reports catalytic oxidation of fatty acids of Jatropha curcas oil (JCO) by Li-CaO/Fe2(SO4)3 catalyst during transesterification at mild reaction conditions. The catalytic oxidation of the triglycerides was shown to be enhanced by the presence of lithium incorporated in the otherwise active catalyst combination of CaO/Fe2(SO4)3 used for high conversion into FAME. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) was used to assess the reaction products.

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Richters, Stefanie, Hartmut Herrmann, and Torsten Berndt. "Different pathways of the formation of highly oxidized multifunctional organic compounds (HOMs) from the gas-phase ozonolysis of <i>β</i>-caryophyllene." Atmospheric Chemistry and Physics 16, no. 15 (August 4, 2016): 9831–45. http://dx.doi.org/10.5194/acp-16-9831-2016.

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Abstract. The gas-phase mechanism of the formation of highly oxidized multifunctional organic compounds (HOMs) from the ozonolysis of β-caryophyllene was investigated in a free-jet flow system at atmospheric pressure and a temperature of 295 ± 2 K. Reaction products, mainly highly oxidized RO2 radicals containing up to 14 oxygen atoms, were detected using chemical ionization – atmospheric pressure interface – time-of-flight mass spectrometry with nitrate and acetate ionization. These highly oxidized RO2 radicals react with NO, NO2, HO2 and other RO2 radicals under atmospheric conditions forming the first-generation HOM closed-shell products. Mechanistic information on the formation of the highly oxidized RO2 radicals is based on results obtained with isotopically labelled ozone (18O3) in the ozonolysis reaction and from hydrogen/deuterium (H/D) exchange experiments of acidic H atoms in the products. The experimental findings indicate that HOM formation in this reaction system is considerably influenced by the presence of a double bond in the RO2 radicals primarily formed from the β-caryophyllene ozonolysis. Three different reaction types for HOM formation can be proposed, allowing for an explanation of the detected main products: (i) the simple autoxidation, corresponding to the repetitive reaction sequence of intramolecular H-abstraction of a RO2 radical, RO2 → QOOH, and subsequent O2 addition, next forming a peroxy radical, QOOH + O2 → R′O2; (ii) an extended autoxidation mechanism additionally involving the internal reaction of a RO2 radical with a double bond forming most likely an endoperoxide and (iii) an extended autoxidation mechanism including CO2 elimination. The individual reaction steps of the reaction types (ii) and (iii) are uncertain at the moment. From the product analysis it can be followed that the simple autoxidation mechanism accounts only for about one-third of the formed HOMs. Time-dependent measurements showed that the HOM formation proceeds at a timescale of 3 s or less under the concentration regime applied here. The new reaction pathways represent an extension of the mechanistic understanding of HOM formation via autoxidation in the atmosphere, as recently discovered from laboratory investigations on monoterpene ozonolysis.

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Millington, Keith R., Michael J. Jones, Siti Farhana Zakaria, and George Maurdev. "Using Chemiluminescence to Study the Photodegradation of Materials." Materials Science Forum 654-656 (June 2010): 2414–17. http://dx.doi.org/10.4028/www.scientific.net/msf.654-656.2414.

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Chemiluminescence (CL) is a straightforward method for studying the free radical degradation of organic and biological materials. A simple modification to a commercial thermal CL instrument and an effective experimental protocol allows the study of photoinduced chemiluminescence (PICL) emission. PICL originates from the reactions of macroperoxy radical intermediates formed during the autoxidation chain reaction. We have applied the PICL technique to study the photooxidation of polymer films and coatings, fibrous webs such as textile fabrics or paper, and powdered samples. Oxygen permeability appears to be a key factor affecting the intensity of PICL emission from polymer films.

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Hassanein, Mahmoud T., Shady S. Gerges, Mohamed A. Abdo, and Sahar H. El-Khalafy. "Studies on the oxidation of 2,6-di-tert-butylphenol by molecular oxygen catalyzed by cobalt(II) tetraarylporphyrins bound to cationic latex." Journal of Porphyrins and Phthalocyanines 09, no. 09 (September 2005): 621–25. http://dx.doi.org/10.1142/s1088424605000721.

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A cationic latex has been prepared by emulsion copolymerization of styrene and divinylbenzene with 2 mol.% of quaternary ammonium ion surfactant monomer. The catalytic activity of cobalt(II) sulfonated tetraarylporphrins 1-5 supported on the cationic latex 6 was investigated in the autoxidation of 2,6-di-tert-butylphenol in water. All colloidal catalysts showed good catalytic activity in the autoxidation of 2,6-di-tert-butylphenol. Reaction products were identified as 2,6-di-tert-butyl-1,4-benzoquinone and the oxidative coupling product as 3,3',5,5'-tetra-tert-butyl-4,4'-diphenoquinone. The rate of autoxidation reaction catalyzed by 5 supported on cationic latex was found to increase with increasing pH in the range 7.0-10.0. At constant concentration of cobalt(II) porphyrin 5 in the reaction mixture, the rate as a function of the weight of the latex showed a maximum. The rate of autoxidation increased with increasing partial pressure of dioxygen in the range between 0.2 and 1.0 atm. 5,10,15,20-tetrakis(2,4,6-trimethyl-3,5-disulfonatopheny)porphyrinatocobalt(II) bound to the cationic latex was found to be the most reactive catalyst and the latex supported 5,10,15,20-tetrakis(2,6-dichloro-3-sulfonatophenyl)porphyrinatocobalt(II) showed the highest stability.

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23

Rissanen, Matti P., Jyri Mikkilä, Siddharth Iyer, and Jani Hakala. "Multi-scheme chemical ionization inlet (MION) for fast switching of reagent ion chemistry in atmospheric pressure chemical ionization mass spectrometry (CIMS) applications." Atmospheric Measurement Techniques 12, no. 12 (December 17, 2019): 6635–46. http://dx.doi.org/10.5194/amt-12-6635-2019.

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Abstract. A novel chemical ionization inlet named the Multi-scheme chemical IONization inlet (MION), Karsa Ltd., Helsinki, Finland) capable of fast switching between multiple reagent ion schemes is presented, and its performance is demonstrated by measuring several known oxidation products from much-studied cyclohexene and α-pinene ozonolysis systems by applying consecutive bromide (Br−) and nitrate (NO3-) chemical ionization. Experiments were performed in flow tube reactors under atmospheric pressure and room temperature (22 ∘C) utilizing an atmospheric pressure interface time-of-flight mass spectrometer (APi-ToF-MS, Tofwerk Ltd., Thun, Switzerland) as the detector. The application of complementary ion modes in probing the same steady-state reaction mixture enabled a far more complete picture of the detailed autoxidation process; the HO2 radical and the least-oxidized reaction products were retrieved with Br− ionization, whereas the highest-oxidized reaction products were detected in the NO3- mode, directly providing information on the first steps and on the ultimate endpoint of oxidation, respectively. While chemical ionization inlets with multiple reagent ion capabilities have been reported previously, an application in which the charging of the sample occurs at atmospheric pressure with practically no sample pretreatment, and with the potential to switch the reagent ion scheme within a second timescale, has not been introduced previously. Also, the ability of bromide ionization to detect highly oxygenated organic molecules (HOM) from atmospheric autoxidation reactions has not been demonstrated prior to this investigation.

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24

Jankovic, Ivana, and Ljubica Josimovic. "Autoxidation of tryptophan in aqueous solutions." Journal of the Serbian Chemical Society 66, no. 9 (2001): 571–80. http://dx.doi.org/10.2298/jsc0109571j.

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Autoxidation of tryptophan was investigated in aqueous solutions by the gamma radiolytic technique. The oxygen uptake and formation of peroxide materials was followed as a function of pH, dose rate and concentration of tryptophan. The results obtained indicate that TrpH(OH)OO. radicals react with tryptophan by adduct formation thus propagating autoxidation. The chain propagation length (CPL) for a 2x10-2 mol dm-3 tryptophan solution at pH 9.5 and a dose rate 0.01Gy s-1 was estimated to be ? 5.8, which shows that the autoxidation of tryptophan is a short chain reaction.

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25

Siddiquee, Muhammad N., and Arno de Klerk. "Heterocyclic Addition Reactions during Low Temperature Autoxidation." Energy & Fuels 29, no. 7 (June 22, 2015): 4236–44. http://dx.doi.org/10.1021/acs.energyfuels.5b00767.

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26

Miller, D. "Transition metals as catalysts of “autoxidation” reactions." Free Radical Biology and Medicine 8, no. 1 (1990): 95–108. http://dx.doi.org/10.1016/0891-5849(90)90148-c.

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27

Rudziński, Krzysztof J., and Rafał Szmigielski. "Aqueous Reactions of Sulfate Radical-Anions with Nitrophenols in Atmospheric Context." Atmosphere 10, no. 12 (December 9, 2019): 795. http://dx.doi.org/10.3390/atmos10120795.

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Nitrophenols, hazardous environmental pollutants, react promptly with atmospheric oxidants such as hydroxyl or nitrate radicals. This work aimed to estimate how fast nitrophenols are removed from the atmosphere by the aqueous-phase reactions with sulfate radical-anions. The reversed-rates method was applied to determine the relative rate constants for reactions of 2-nitrophenol, 3-nitrophenol, 4-nitrophenol, 2,4-dinitrophenol, and 2,4,6-trinitrophenol with sulfate radical-anions generated by the autoxidation of sodium sulfite catalyzed by iron(III) cations at ~298 K. The constants determined were: 9.08 × 108, 1.72 × 109, 6.60 × 108, 2.86 × 108, and 7.10 × 107 M−1 s−1, respectively. These values correlated linearly with the sums of Brown substituent coefficients and with the relative strength of the O–H bond of the respective nitrophenols. Rough estimation showed that the gas-phase reactions of 2-nitrophenol with hydroxyl or nitrate radicals dominated over the aqueous-phase reaction with sulfate radical-anions in deliquescent aerosol and haze water. In clouds, rains, and haze water, the aqueous-phase reaction of 2-nitrophenol with sulfate radical-anions dominated, provided the concentration of the radical-anions was not smaller than that of the hydroxyl or nitrate radicals. The results presented may be also interesting for designers of advanced oxidation processes for the removal of nitrophenol.

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Zhang, Shi-Nan, Zhong-Hua Xue, Xiu Lin, Yun-Xiao Lin, Hui Su, Shin-Ichi Hirano, Xin-Hao Li, and Jie-Sheng Chen. "Autoxidation of polythiophene tethered to carbon cloth boosts its electrocatalytic activity towards durable water oxidation." Journal of Materials Chemistry A 8, no. 38 (2020): 19793–98. http://dx.doi.org/10.1039/d0ta06368a.

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29

Rudziński, K. J., L. Gmachowski, and I. Kuznietsova. "Isoprene, sulphoxy radical-anions and acidity." Atmospheric Chemistry and Physics Discussions 8, no. 6 (December 12, 2008): 20869–900. http://dx.doi.org/10.5194/acpd-8-20869-2008.

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Abstract. Transformation of isoprene coupled with autoxidation of SIV in aqueous solutions was studied experimentally and by chemical-kinetic modelling over broad range of solution acidities (pH=3–9) to complement the research on aqueous-phase and heterogeneous transformation of isoprene reported recently by many laboratories. Isoprene significantly slowed down the autoxidation in acidic and basic solutions, and accelerated it slightly in neutral solutions. Simultaneously, production of sulphate ions and formation of solution acidity were significantly reduced. Formation of sulphite and sulphate derivatives of isoprene – sulphurous acid mono-(2-methyl-4-oxo-but-2-enyl) ester (m/z=162.9), sulphurous acid mono-(4-hydroxy-2-methyl-but-2-enyl) ester (m/z=164.9), sulphuric acid mono-(2-methyl-4-oxo-but-2-enyl) ester (m/z=178.9), sulphuric acid mono-(4-hydroxy-2-methyl-but-2-enyl) ester (m/z=180.9) – was indicated by mass spectroscopic analysis of post-reaction mixtures. The results of experiments were explained by changes in a subtle quantitative balance of three superimposed processes whose rates depended in different manner on the acidity of reacting solutions – the scavenging of sulphoxy radicals by isoprene, the formation of sulphoxy radicals during further reactions of isoprene radicals, and the autoxidation of SIV itself. A chemical mechanism based on this idea was explored numerically to show good agreement with experimental data. Interaction of isoprene with sulphur(IV) species and oxygen can possibly result in formation of new organosulphate components of atmospheric aerosols and waters, and influence distribution of reactive sulphur and oxygen species in isoprene-emitting organisms exposed to SIV pollutants.

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30

Zhang, Qing-An, Xi Wang, Yun Song, Xue-Hui Fan, and Juan Francisco García Martín. "Optimization of Pyrogallol Autoxidation Conditions and Its Application in Evaluation of Superoxide Anion Radical Scavenging Capacity for Four Antioxidants." Journal of AOAC INTERNATIONAL 99, no. 2 (March 1, 2016): 504–11. http://dx.doi.org/10.5740/jaoacint.15-0223.

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Abstract In this study, some factors influencing pyrogallol autoxidation, including EDTA, temperature, and solvent, were systematically investigated to improve its feasibility in the evaluation of antioxidants for the first time. Subsequently, the improved pyrogallol autoxidation conditions were used to assess the superoxide anion scavenging activity (SASA) of four commonly used antioxidants, namely, ascorbic acid, rutin, catechin, and gallic acid, by both the reaction rate method and the terminated method. The results indicate that pyrogallol autoxidation could be successfully used to determine the antioxidant capacity of ascorbic acid and rutin, which correspondingly suggests the feasibility of its use to measure the superoxide anion radical scavenging activity of polysaccharides and flavonols, because these compounds have a similar basic structural unit as ascorbic acid and rutin, respectively. Unexpectedly, however, pyrogallol autoxidation cannot be used to evaluate the SASA of catechin and gallic acid, although their good antioxidant capacity was confirmed by the 1,1-diphenyl-2-picrylhydrazyl assay. Together, these results suggest the importance of noting the conditions used for pyrogallol autoxidation when assessing the SASA of targeted compounds.

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Kazin, Vyacheslav N., Evgenii A. Guzov, Valentina A. Moshareva, and Evgenii M. Pliss. "Influence of a Constant Magnetic Field on the Mechanism of Adrenaline Oxidation." Magnetochemistry 8, no. 7 (July 1, 2022): 70. http://dx.doi.org/10.3390/magnetochemistry8070070.

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In order to establish the role of the magnetic effect in the key stages of the autoxidation and initiated oxidation radical-chain reactions, the experimental data and kinetic analysis of the influence of a magnetic field on the oxidative transformations of adrenaline are presented in this work. In the case of autoxidation, the process is being controlled by the rate of adrenaline consumption in the gross process of quinoid oxidation. The analysis of the obtained results is estimative and is based on the assumption of the leading role of superoxide radical during the autoxidation. Superoxide radical concentration increases with the increase in the applied magnetic field strength, which leads to the decrease in the rate of initiation of the quinoid process. In the case of initiated oxidation, the results obtained are based on the known radical-chain mechanism, and they were interpreted using the theory of radical pairs. The observed magnetic effect is explained by the influence of a constant magnetic field on the mechanism of chain termination of radical-chain oxidation and/or initiation of the autoxidation process.

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32

Nohl, H., L. Gille, and K. Staniek. "The Exogenous NADH Dehydrogenase of Heart Mitochondria Is the Key Enzyme Responsible for Selective Cardiotoxicity of Anthracyclines." Zeitschrift für Naturforschung C 53, no. 3-4 (April 1, 1998): 279–85. http://dx.doi.org/10.1515/znc-1998-3-419.

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Abstract The molecular mechanism of the anthracycline-dependent development of cardiotoxicity is still far from being clear. However, it is generally accepted, that mitochondria play a significant role in triggering this organ specific injury. The results presented in this study demonstrate that, in contrast to liver mitochondria, isolated heart mitochondria shuttle single electrons to adriamycin, giving rise to oxygen radical formation via autoxidation of adriamycin semiquinones. This one electron reduction of anthracyclines is catalyzed by the exogenous NADH dehydrogenase associated with complex I of heart mitochondria, an enzyme which is lacking in liver mitochondria. Upon addition of NADH heart mitochondria generate significant amounts of adriamycin sem iquinones while liver mitochondria were ineffective. Adriamycin semiquinones undergo both autoxidation leading to superoxide radical release and complex reactions under formation of adriamycin aglycone. Due to the high lipophilicity adriamycin aglycones accumulate in the inner mitochondrial membrane where they interfere with electron carriers of the respiratory chain. Adriamycin aglycone sem iquinones emerging from an interaction with complex I were found to trigger homolytic cleavage of H2O2 which results in the formation of hydroxyl radicals. As demonstrated in this study the activation of adriamycin by the exogenous NADH dehydrogenase of cardiac mitochondria initiates a cascade of reaction steps leading to the establishment of oxidative stress. Our experiments sug gest the exogenous NADH dehydrogenase of heart mitochondria to play a key role in the cardiotoxicity of adriamycin. This organ-specific enzyme initiates a sequence of one electron transfer reactions ending up in the establishment of oxidative stress.

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33

Wolff, S. P., and M. J. C. Crabbe. "Low apparent aldose reductase activity produced by monosaccharide autoxidation." Biochemical Journal 226, no. 3 (March 15, 1985): 625–30. http://dx.doi.org/10.1042/bj2260625.

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Low apparent aldose reductase activity, as measured by NADPH oxidation, can be produced by the spontaneous autoxidation of monosaccharides. NADPH is oxidized to metabolically active NADP+ in a solution of autoxidizing DL-glyceraldehyde at rates of up to 15 X 10(-4) A340/min. The close parallelism between the effects of buffer salt type and concentration, monosaccharide structure and temperature activation on autoxidation and NADPH oxidation imply that autoxidation is a prerequisite for the NADPH oxidation, probably via the hydroperoxy radical. Nucleotide-binding proteins enhanced NADPH oxidation induced by DL-glyceraldehyde, up to 10.6-fold with glucose-6-phosphate dehydrogenase. Glutathione reductase-catalysed NADPH oxidation in the presence of autoxidizing monosaccharide showed many characteristics of the aldose reductase reaction. Aldose reductase inhibitors acted as antioxidants in inhibiting this NADPH oxidation. These results indicate that low apparent aldose reductase activities may be due to artifacts of monosaccharide autoxidation, and could provide an explanation for the non-linear steady-state kinetics observed with DL-glyceraldehyde and aldose reductase.

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34

Wang, Yuwei, Archit Mehra, Jordan E. Krechmer, Gan Yang, Xiaoyu Hu, Yiqun Lu, Andrew Lambe, et al. "Oxygenated products formed from OH-initiated reactions of trimethylbenzene: autoxidation and accretion." Atmospheric Chemistry and Physics 20, no. 15 (August 14, 2020): 9563–79. http://dx.doi.org/10.5194/acp-20-9563-2020.

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Abstract. Gas-phase oxidation pathways and products of anthropogenic volatile organic compounds (VOCs), mainly aromatics, are the subject of intensive research, with attention paid to their contributions to secondary organic aerosol (SOA) formation and potentially new particle formation (NPF) in the urban atmosphere. In this study, a series of OH-initiated oxidation experiments of trimethylbenzene (TMB, C9H12) including 1,2,4-TMB, 1,3,5-TMB, 1,2,3-TMB, and 1,2,4-(methyl-D3)-TMBs (C9H9D3) were investigated in an oxidation flow reactor (OFR) in the absence and presence of NOx. Products were measured using a suite of state-of-the-art instruments, i.e. a nitrate-based chemical ionization–atmospheric pressure interface time-of-flight mass spectrometer (nitrate CI-APi-TOF), an iodide-adduct chemical ionization time-of-flight mass spectrometer (iodide CI-TOF) equipped with a Filter Inlet for Gases and AEROsols (FIGAERO), and a Vocus proton-transfer-reaction mass spectrometer (Vocus PTR). A large number of C9 products with 1–11 oxygen atoms and C18 products presumably formed from dimerization of C9 peroxy radicals were observed, hinting at the extensive existence of autoxidation and accretion reaction pathways in the OH-initiated oxidation reactions of TMBs. Oxidation products of 1,2,4-(methyl-D3)-TMBs with deuterium atoms in different methyl substituents were then used as a molecular basis to propose potential autoxidation reaction pathways. Accretion of C9 peroxy radicals is the most significant for aromatics with meta-substituents and the least for aromatics with ortho-substituents if the number and size of substituted groups are identical. The presence of NOx would suppress the formation of highly oxygenated molecules (HOMs) of C18 and enhance the formation of organonitrates and even dinitrate organic compounds. Our results show that the oxidation products of TMB are much more diverse and could be more oxygenated than the current mechanisms predict.

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35

Morishita, Y., S. Murata, and S. Sunada. "Studies On An Aerobic Oxidation Of Dibenzothiophene And Related Compounds Using Ruthenium Catalyst." Archives of Metallurgy and Materials 60, no. 2 (June 1, 2015): 1015–16. http://dx.doi.org/10.1515/amm-2015-0252.

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Abstract An aerobic oxidation of dibenzothiophene and related compounds using a catalytic amount of ruthenium chloride in hydrocarbon solvents at 80°C for 20 h gave the corresponding sulfones in almost quantitative yields. The reaction might proceed via autoxidation of solvents to hydroperoxides and the reaction of sulfur compounds with the resulting hydroperoxides.

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36

Iyer, Jayant, Isha Saraf, Andrew Ray, Michael Brunsteiner, and Amrit Paudel. "Assessment of Diverse Solid−State Accelerated Autoxidation Methods for Droperidol." Pharmaceutics 14, no. 6 (May 24, 2022): 1114. http://dx.doi.org/10.3390/pharmaceutics14061114.

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The present study aimed to investigate methods for accelerating autoxidation of crystalline drugs in the solid-state that can potentially predict real−time stability. Solid droperidol (DPD) was selected as the model drug. A common free−radical initiator, 2,2′−azobisisobutyronitrile (AIBN), was used to induce autoxidation in solutions. AIBN decomposes at elevated temperatures to yield carbon−centred cyano−isopropyl free radicals that can auto−oxidize neighboring drug molecules. Although the reaction of AIBN is relatively straightforward in solution, it is less so in solids. In this study, we used solid AIBN mixed with DPD powder in the presence and absence of pressurized oxygen headspace. Samples were prepared directly in the form of binary mixtures with DPD and additionally in the form of powder compact/pellet with DPD. The main challenge in carrying out the reaction was related to the preservation of AIBN at elevated temperatures due to the disintegration of the pellet containing the latter. A commercially available free−radical coated silica particle (i.e., 2,2,6,6−tetramethyl−1−piperinyloxy (TEMPO) or (SiliaCATTM TEMPO)) was tested as a potential stressor, but with limited success to induce autoxidation. The most valuable results were obtained when a physical mixture of pre−milled PVP K−60 containing free radicals and DPD was exposed to elevated oxygen−temperature conditions, which yielded significant degradation of DPD. The study highlights the practical challenges for conducting accelerated solid−state stress studies to assess the autoxidation susceptibility of drugs using traditional free−radical initiators and presents a proof of application of milled PVP with free−radical as a potential alternative.

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Kamińska, Adrianna, Nikola Maciejewska, Piotr Miądlicki, Karolina Kiełbasa, Joanna Sreńscek-Nazzal, and Beata Michalkiewicz. "Fe-modified activated carbon obtained from biomass as a catalyst for α-pinene autoxidation." Polish Journal of Chemical Technology 23, no. 2 (June 1, 2021): 73–80. http://dx.doi.org/10.2478/pjct-2021-0020.

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Abstract The presented work describes the autoxidation of alpha-pinene for the first time using a catalyst based on activated carbon from biomass with introduced Fe. The raw material for the preparation of the carbon material was waste orange peel, which was activated with a KOH solution. The following instrumental methods characterized the obtained catalyst (Fe/O_AC):N2 adsorption at 77 K, XRD, UV, SEM, TEM, X-ray microanalysis, and catalytic studies. It was shown that the Fe/O_AC catalyst was very active in the autoxidation of alpha-pinene. The main reaction products were: alpha-pinene oxide, verbenone, verbenol, and campholenic aldehyde.

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38

Postlethwait, Edward M., Rafael Cueto, Leonard W. Velsor, and William A. Pryor. "O3-induced formation of bioactive lipids: estimated surface concentrations and lining layer effects." American Journal of Physiology-Lung Cellular and Molecular Physiology 274, no. 6 (June 1, 1998): L1006—L1016. http://dx.doi.org/10.1152/ajplung.1998.274.6.l1006.

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Recent evidence suggests that inhaled ozone (O3) does not induce toxicity via direct epithelial interactions. Reactions with epithelial lining fluid (ELF) constituents limit cellular contact and generate products, including lipid ozonation products, postulated to initiate pathophysiological cascades. To delineate specific aspects of lipid ozonation product formation and to estimate in situ surface concentrations, we studied the O3absorption characteristics of ELF constituent mixtures and measured hexanal, heptanal, and nonanal yields as a function of ascorbic acid (AH2) concentration. Exposures of isolated rat lungs, bronchoalveolar lavage fluid (BALF) and egg phosphatidylcholine (PC) liposomes were conducted. 1) O3 absorption by AH2, uric acid, and albumin exceeded that by egg PC and glutathione. O3 reaction with egg PC occurred when AH2 concentrations were reduced. 2) Aldehydes were produced in low yield during lung and BALF exposures in a time- and O3 concentration-dependent manner. 3) Diminishing BALF AH2 content lowered O3 uptake but increased aldehyde yields. Conversely, AH2 addition to egg PC increased O3 uptake but reduced aldehyde yields. Estimations of bioactive ozonation and autoxidation product accumulation within the ELF suggested possible nanomolar to low micromolar concentrations. The use of reaction products as metrics of O3 exposure may have intrinsic sensitivity and specificity limitations. Moreover, due to the heterogenous nature of O3 reactions within the ELF, dose-response relationships may not be linear with respect to O3 absorption.

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39

DEAN, Roger T., Shanlin FU, Roland STOCKER, and Michael J. DAVIES. "Biochemistry and pathology of radical-mediated protein oxidation." Biochemical Journal 324, no. 1 (May 15, 1997): 1–18. http://dx.doi.org/10.1042/bj3240001.

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Radical-mediated damage to proteins may be initiated by electron leakage, metal-ion-dependent reactions and autoxidation of lipids and sugars. The consequent protein oxidation is O2-dependent, and involves several propagating radicals, notably alkoxyl radicals. Its products include several categories of reactive species, and a range of stable products whose chemistry is currently being elucidated. Among the reactive products, protein hydroperoxides can generate further radical fluxes on reaction with transition-metal ions; protein-bound reductants (notably dopa) can reduce transition-metal ions and thereby facilitate their reaction with hydroperoxides; and aldehydes may participate in Schiff-base formation and other reactions. Cells can detoxify some of the reactive species, e.g. by reducing protein hydroperoxides to unreactive hydroxides. Oxidized proteins are often functionally inactive and their unfolding is associated with enhanced susceptibility to proteinases. Thus cells can generally remove oxidized proteins by proteolysis. However, certain oxidized proteins are poorly handled by cells, and together with possible alterations in the rate of production of oxidized proteins, this may contribute to the observed accumulation and damaging actions of oxidized proteins during aging and in pathologies such as diabetes, atherosclerosis and neurodegenerative diseases. Protein oxidation may also sometimes play controlling roles in cellular remodelling and cell growth. Proteins are also key targets in defensive cytolysis and in inflammatory self-damage. The possibility of selective protection against protein oxidation (antioxidation) is raised.

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40

Peres, Matheus R., Vanessa R. Miranda, Aguinaldo R. Robinson De Souza, Nelson H. Morgon, and Valdecir F. Ximenes. "Autoxidation of melatonin at excited state: mechanism proposal for formation of N1-acetyl-N2-formyl-5-methoxykynuramine." Melatonin Research 5, no. 3 (September 30, 2022): 325–34. http://dx.doi.org/10.32794/mr112500135.

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N1-acetyl-N2-formyl-5-methoxykynuramine (AFMK) is one of the primary oxidation products of melatonin. There is growing evidence of its beneficial biological properties, including antioxidant features and modulators of cytokines and enzymes involved in the inflammatory process. Here, the autoxidation of melatonin mediated by UVC was studied regarding the formation of AFMK and the reaction mechanism. The parameters evaluated were irradiation, pH, dissolved oxygen, superoxide radical anion, and hydroxyl radical. We found that the AFMK yield is directly correlated with UVC irradiation. The AFMK concentration decreased 95% when a 280 nm cutoff filter blocked the irradiation. By removing the dissolved oxygen from the medium, the decrease was 90%. Superoxide dismutase, acting as a scavenger of superoxide radical anion, caused a 64% reduction. At pH 7.0, the AFMK yield was just 14% of those obtained at pH 10. These findings are consistent with a typical autoxidation reaction. In addition, the low yield of AFMK in the absence of UVC irradiation suggested that electronically excited melatonin is the species involved in the initial electron transfer. Density Functional Theory (DFT) calculations were performed to strengthen the proposal. Corroborant with the experimental results, the theoretical analyses revealed that electron transfer from melatonin to molecular oxygen is only energetically feasible in the excited state. In conclusion, the direct autoxidation of melatonin at excited state in alkaline pH is a straightforward approach to producing AFMK.

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Strader, Michael Brad, Rachel Bangle, Claire J. Parker Siburt, Cornelius L. Varnado, Jayashree Soman, Andres S. Benitez Cardenas, Premila P. Samuel, et al. "Engineering oxidative stability in human hemoglobin based on the Hb providence (βK82D) mutation and genetic cross-linking." Biochemical Journal 474, no. 24 (December 11, 2017): 4171–92. http://dx.doi.org/10.1042/bcj20170491.

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Previous work suggested that hemoglobin (Hb) tetramer formation slows autoxidation and hemin loss and that the naturally occurring mutant, Hb Providence (HbProv; βK82D), is much more resistant to degradation by H2O2. We have examined systematically the effects of genetic cross-linking of Hb tetramers with and without the HbProv mutation on autoxidation, hemin loss, and reactions with H2O2, using native HbA and various wild-type recombinant Hbs as controls. Genetically cross-linked Hb Presbyterian (βN108K) was also examined as an example of a low oxygen affinity tetramer. Our conclusions are: (a) at low concentrations, all the cross-linked tetramers show smaller rates of autoxidation and hemin loss than HbA, which can dissociate into much less stable dimers and (b) the HbProv βK82D mutation confers more resistance to degradation by H2O2, by markedly inhibiting oxidation of the β93 cysteine side chain, particularly in cross-linked tetramers and even in the presence of the destabilizing Hb Presbyterian mutation. These results show that cross-linking and the βK82D mutation do enhance the resistance of Hb to oxidative degradation, a critical element in the design of a safe and effective oxygen therapeutic.

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Slavíková, Barbora, Alexander Kasal, and Miloš Buděšínský. "Autoxidation vs Hydrolysis in 16α-Acyloxy Steroids." Collection of Czechoslovak Chemical Communications 64, no. 7 (1999): 1125–34. http://dx.doi.org/10.1135/cccc19991125.

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Some enolizable α-hydroxy ketones are extremely susceptible to oxidation with traces of air in a reaction vessel. Autoxidation can be used in synthesis of oxo acids or diacids and their derivatives. Yet alkaline hydrolysis of the substrate is possible though under strictly air-free conditions.

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Krazinski, J. L., S. P. Vanka, J. A. Pearce, and W. M. Roquemore. "A Computational Fluid Dynamics and Chemistry Model for Jet Fuel Thermal Stability." Journal of Engineering for Gas Turbines and Power 114, no. 1 (January 1, 1992): 104–10. http://dx.doi.org/10.1115/1.2906291.

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This paper describes the development of a model for predicting the thermal decomposition rates of aviation fuels. A thermal deposition model was incorporated into FLANELS-2D, an existing computational fluid dynamics (CFD) code that solves the Reynolds-averaged conservation equations of mass, momentum, and energy. The decomposition chemistry is modeled by three global Arrhenius expressions in which the fuel decomposition was assumed to be due to an autoxidation reaction with dissolved oxygen. The deposition process was modeled by assuming that all deposit-forming species transported to the wall adhered and formed a deposit. Calibration of the model required the determination of the following parameters for a given fuel: (1) the pre-exponential constant and activation energy for the wall reaction, (2) the pre-exponential constant and activation energy for the bulk autoxidation reaction, and (3) the pre-exponential constant and activation energy for the precursor decomposition reaction. Values for these parameters were estimated using experimental data from published heated-tube experiments. Results show that the FLANELS-2D code performed well in estimating the fuel temperatures and that the three-equation chemistry model performed reasonably well in accounting for both the rate of deposition and the amount of dissolved oxygen present in the fuel at the end of the heated tube.

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Barclay, Lawrence Ross Coates, Steven Jeffrey Locke, and Joseph Mark MacNeil. "Autoxidation in micelles. Synergism of vitamin C with lipid-soluble vitamin E and water-soluble Trolox." Canadian Journal of Chemistry 63, no. 2 (February 1, 1985): 366–74. http://dx.doi.org/10.1139/v85-062.

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A study was made of the effect of the inhibitors ascorbic acid (C), α-tocopherol (E), and 6-hydroxy-2,5,7,8-tetramethyl-chroman-2-carboxylate (Trolox, T) on the autoxidation of linoleic acid in 0.50 M sodium dodecyl sulfate (SDS) micelles at pH 7.0 in phosphate buffer. Reactions were thermally initiated at 30 °C in the SDS micelles by a micelle-soluble initiator, di-tert-butylhyponitrite (DBHN). Although water-soluble C alone is an inefficient inhibitor, when combined with micelle-soluble E, it acts synergistically with the latter to extend the efficient antioxidant action of E beyond the sum of the induction periods of C and E acting separately. Similarly C acts synergistically with the water-soluble antioxidant, T. Quantitative studies of these effects under controlled rates of initiation (Ri,) reveal that C functions to regenerate a mole of E (or T) per mole of C used. Kinetic studies show that the rate of autoxidation is first order in micellar linoleic acid and one-half order in micellar DBHN concentrations. Therefore, the classical rate law, −dO2/dt = kp[R—H] (Ri)1/2/(2k1)1/2 is followed. The higher oxidizability (kp/2kt1/2 = 4.48 × 10−2 M−1/2 s−1/2) of linoleate in micelles compared to that in homogeneous solution in chlorobenzene (kp/2kt1/2 = 2.30 × 10−2 M−1/2 s−1/2) is interpreted in terms of the effect of the polar interfacial region of the micelles on a dipolar transition state, R—OŌ: H•R, of the propagation reaction.

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Shahidi, Fereidoon, and Abul Hossain. "Role of Lipids in Food Flavor Generation." Molecules 27, no. 15 (August 6, 2022): 5014. http://dx.doi.org/10.3390/molecules27155014.

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Lipids in food are a source of essential fatty acids and also play a crucial role in flavor and off-flavor development. Lipids contribute to food flavor generation due to their degradation to volatile compounds during food processing, heating/cooking, and storage and/or interactions with other constituents developed from the Maillard reaction and Strecker degradation, among others. The degradation of lipids mainly occurs via autoxidation, photooxidation, and enzymatic oxidation, which produce a myriad of volatile compounds. The oxidation of unsaturated fatty acids generates hydroperoxides that then further break down to odor-active volatile secondary lipid oxidation products including aldehydes, alcohols, and ketones. In this contribution, a summary of the most relevant and recent findings on the production of volatile compounds from lipid degradation and Maillard reactions and their interaction has been compiled and discussed. In particular, the effects of processing such as cooking, drying, and fermentation as well as the storage of lipid-based foods on flavor generation are briefly discussed.

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46

Nivinskas, H., R. L. Koder, Z. Anusevicius, J. Sarlauskas, A. F. Miller, and N. Cenas. "Two-electron reduction of nitroaromatic compounds by Enterobacter cloacae NAD(P)H nitroreductase: description of quantitative structure-activity relationships." Acta Biochimica Polonica 47, no. 4 (December 31, 2000): 941–49. http://dx.doi.org/10.18388/abp.2000_3949.

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Enterobacter cloacae NAD(P)H:nitroreductase catalyzes the reduction of a series of nitroaromatic compounds with steady-state bimolecular rate constants (kcat/Km) ranging from 10(4) M(-1) s(-1) to 10(7) M(-1) s(-1), and oxidizing 2 moles NADH per mole mononitrocompound. Oxidation of excess NADH by polynitrobenzenes including explosives 2,4,6-trinitrotoluene (TNT) and 2,4,6-trinitrophenyl-N-methylnitramine (tetryl), has been observed as a slower secondary process, accompanied by O2 consumption. This type of 'redox cycling' was not related to reactions of nitroaromatic anion-radicals, but was caused by the autoxidation of relatively stable reaction products. The logs kcat/Km of all the compounds examined exhibited parabolic dependence on their enthalpies of single-electron- or two-electron (hydride) reduction, obtained by quantum mechanical calculations. This type of quantitative structure-activity relationships shows that the reactivity of nitroaromatics towards E. cloacae nitroreductase depends mainly on their hydride accepting properties, but not on their particular structure, and does not exclude the possibility of multistep hydride transfer.

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47

Lissel, Manfred. "Reaktionen mit Kaliumsuperoxid 3 [1] Über den Mechanismus der Ketonspaltung durch KO2 / Reactions with Potassium Superoxide 3 [1] On the Mechanism of the Cleavage of Ketones by KO2." Zeitschrift für Naturforschung B 42, no. 1 (January 1, 1987): 12–14. http://dx.doi.org/10.1515/znb-1987-0104.

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Chen, Hauh-Jyun Candy, and Fung-Lung Chung. "Formation of Etheno Adducts in Reactions of Enals via Autoxidation." Chemical Research in Toxicology 7, no. 6 (November 1994): 857–60. http://dx.doi.org/10.1021/tx00042a021.

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49

Siddiquee, Muhammad N., and Arno de Klerk. "Hydrocarbon Addition Reactions during Low-Temperature Autoxidation of Oilsands Bitumen." Energy & Fuels 28, no. 11 (October 16, 2014): 6848–59. http://dx.doi.org/10.1021/ef501694s.

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Tajima, G., and K. Shikama. "Autoxidation of oxymyoglobin. An overall stoichiometry including subsequent side reactions." Journal of Biological Chemistry 262, no. 26 (September 1987): 12603–6. http://dx.doi.org/10.1016/s0021-9258(18)45248-9.

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Journal articles on the topic 'Autoxidative reactions'

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