Autooxidation Reactions Research Articles

α-Hemoglobin Stabilizing Protein (AHSP), a Kinetic Scheme of the Action of a Human Mutant, AHSPV56G

A kinetic analysis has been made of the interaction of alpha-Hb chains with a mutant alpha-hemoglobin stabilizing protein, AHSP(V56G), which is the first case of an AHSP mutation associated with clinical symptoms of mild thalassemia syndrome. The chaperone AHSP is thought to protect nascent alpha chains until final binding to the partner beta-Hb. Rather than protecting alpha chains, the mutant chaperone is partially unfolded but recovers its secondary structure via interaction with alpha-Hb. For both AHSP(WT) and AHSP(V56G), the binding to alpha-Hb is quite rapid relative to the alpha-beta reaction, as expected because the chaperone binding must be quite competitive to complete the alpha chain folding process before alpha-Hb binds irreversibly to beta-Hb. The main kinetic difference is a dissociation rate of AHSP(V56G).alpha-Hb some four times faster relative to AHSP.alpha-Hb. Considering a role of protein folding, the AHSP(V56G) apparently does not bind long enough (0.5 s versus 2 s for the WT) to complete the structural modifications. The overall replacement reaction (AHSP.alpha-Hb + beta-Hb --> AHSP + alphabeta) can be quite long, especially if there is an excess of AHSP relative to beta-Hb monomers.

Oxidation of 2,6-Di-tert-butylphenol by dioxygen catalyzed by tetrasodium phthalocyaninatocobalt(II) tetrasulfonate in aqueous micellar media

The oxidation of 2,6-di-tert-butylphenol by dioxygen has been investigated in aqueous micellar aggregates of cetyltrimethylammonium bromide (CTAB) using tetrasodium phthalocyaninatocobalt(II) tetrasulfonate (CoPcTsNa4) as catalyst. The CTAB/CoPcTsNa4 system showed enhanced catalytic activity in the oxidation of 2,6-di-tert-butylphenol compared to that observed in the oxidation reaction in the absence of CTAB. 2,6-Di-tert-butyl-1,4-benzoquinone and 3,5,3′,5′-tetra-tert-butyl-4,4-diphenoquinone were identified as reaction products. The initial rate constants of auto-oxidation reaction was found to increase with increasing the pH range from 7.0 to 13.0. The rate constants kobs of auto-oxidation reaction showed linear dependence on catalyst concentration. The rate of auto-oxidation reaction was found to fit a Michealis-Menten kinetic model for the saturation of catalyst sites with increasing 2,6-di-tert-butylphenol concentration and dioxygen pressure. Tetrasodium phthalocyaninatocobalt(II) tetrasulfonate in aqueous micellar solution of CTAB was found to be mainly monomeric.

Auto-Oxidation of Human Hemoglobin and the Roles of Distal Heme Pocket Substitutions

This study investigates the auto-oxidation reaction of human normal adult hemoglobin (Hb A) and the effects of distal heme pocket substitutions, P50, and tetramer-dimer dissociation on the rate and mechanism of auto-oxidation. Recombinant hemoglobins (rHbs) with single amino acid substitutions at helical positions E11 and B10 have been expressed in Escherichia coli and purified, as well as di-α linked and octameric rHbs. These rHbs include: rHb (αV62L), rHb (αV62I), rHb (βV67L), rHb (βV67I), rHb(αL29W), rHb(αL29F), rHb(α-Gly-α/β gene di-α/β), rHb(diαL29F), rHb(diαL29W), and rHb(βG83C). Auto-oxidation measurements were conducted with 32μM heme in MES buffer (pH 6.5) for 60 hours at 35 °C. A monophasic nature of auto-oxidation has been observed for Hb A and a biphasic nature for all other rHbs. In comparison to the other mutants, including di-α linked and octameric rHbs, rHb (αL29F) is most resistant to oxidation and rHb (αL29W) is the least resistant to oxidation. Characterization of three novel rHbs; (βL28F, βV67I), (αL29F, βV67I), (αL29F,αV62I) will test whether the fast and slow phases of the observed biphasic nature of auto-oxidation can be attributed to the mutated and wild-type subunits, respectively. Our studies will also provide new insights into the roles of amino acid residues in the distal heme pockets on the structure-function relationship in hemoglobin(Supported by NIH grants HL-024525 and GM-084614, HHMI, and The Arnold and Mabelle Beckman Undergraduate Research Scholars Program).

The use of antioxidants in vegetable oils – A review

The shelf life of vegetable oils in food uses and their applicability in industrial situations is greatly dependent on their oxidative stabilities. Methods of improving oxidative stability values currently available include genetic modifications, compositional changes via chemical means, as well as the inhibition of oxidation by means of substances known as antioxidants. This paper reviews the properties of vegetable oils which predispose them to auto oxidation reactions, explores the nature and mechanisms of the operation of antioxidants in brief, and finally summarizes current research efforts geared towards identifying and evaluating the effectiveness and commercial promise of less toxic new antioxidants derived as natural extracts from various plant species.

The use of antioxidants in vegetable oils – A review

The shelf life of vegetable oils in food uses and their applicability in industrial situations is greatly dependent on their oxidative stabilities. Methods of improving oxidative stability values currently available include genetic modifications, compositional changes via chemical means, as well as the inhibition of oxidation by means of substances known as antioxidants. This paper reviews the properties of vegetable oils which predispose them to auto oxidation reactions, explores the nature and mechanisms of the operation of antioxidants in brief, and finally summarizes current research efforts geared towards identifying and evaluating the effectiveness and commercial promise of less toxic new antioxidants derived as natural extracts from various plant species.

Evaluation of the Self‐Heating Tendency of Vegetable Oils by Differential Scanning Calorimetry

The evaluation of the self-heating propensity of a vegetable (or animal) oil may be of significant importance during the investigation of a fire. Unfortunately, iodine value and gas chromatographic-mass spectrometric analysis do not lead to meaningful results in this regard. To the contrary, differential scanning calorimetry (DSC), which does not measure the chemical composition of the oil, but rather its thermodynamic behavior, produces valuable results. After a thorough literature review on the autooxidation of vegetable oils, several oils with different self-heating tendencies were analyzed using a Mettler-Toledo differential scanning calorimeter DSC 25 between 40 degrees C and 500 degrees C. Analyses were carried out both under air and nitrogen atmosphere to identify the phenomena due to autooxidation reactions. Using DSC, it was possible to observe the induction period of the oil (when available), the three different exothermic events, and the autoignition temperature (relatively independent of the oil type).

Laser microfabrication of long thin holes on biodegradable polymer in vacuum for preventing clogginess and its application to blood collection

The present paper investigates the excimer laser microfabrication of long thin holes on biodegradable polymer material (polylactic acid, referred to herein as PLA). The fabrication was carried out on several kinds of polymers in the atmosphere. In the case of PLA, a phenomenon was observed after fabrication whereby the inside of the hole is clogged at several points by ablated material and residual gas. Analysis of chemical components of the ablated products was performed using a gas chromatography–mass spectrometer (GC/MS). They are proved to be intermediate products of ester compound and lactide, and their oxides, which indicates that the clogging phenomenon is partially caused by the hydrolysis reaction based on the biodegradable characteristics of PLA. The fabrication was carried out in vacuum and nitrogen gas. The clogging tendency was eliminated in vacuum, whereas it was not eliminated in nitrogen gas, which indicates that the ablated residues are evaporated by lowering the ambient pressure below their vapor pressure, proving the effectiveness of the fabrication in vacuum for preventing the clogginess. The effect of existence of oxygen in the ambient atmosphere on the laser fabrication rate was also investigated, proving that auto-oxidation reactions urge the decomposition of polymer. The fabricated long thin hole on PLA was applied to blood collection.

Monitoring Chemical Changes for Stored Sawdust from Pine and Spruce Using Gas Chromatography-Mass Spectrometry and Visible-Near Infrared Spectroscopy

Fuel pellets that are very often made of sawdust represent a renewable energy source for heat production and there is a growing interest in these products in a large part of the world. Raw material production in the sawmills and use of sawdust in the pellet mills are out of phase during a large part of the year and for reasons of logistics there is a need for storage of large quantities of the raw material. Long-term storage changes the sawdust and, therefore, processing parameters have to be adapted, making some knowledge of storage time or maturity necessary. An experiment on the industrial storage of pine and spruce sawdust was carried out over a period of 16 weeks. Samples were taken out every week and all samples were analysed by visible-near infrared (vis-NIR) spectroscopy, while some samples were analysed by GC/MS for their composition of fatty- and resin acids. The resulting data were subjected to multivariate data analysis. GC/MS data showed the difference between pine and spruce sawdust and the influence of maturity. This maturity effect could be associated with the decrease in fatty- and resin acids due to auto-oxidative reactions. The first six weeks of storage had no influence on the concentration of fatty- and resin acids. Most of the changes in the amount of fatty- and resin acids occurred in the fresh pine sawdust during weeks six to 12. Since the spruce sawdust had less initial amounts of fatty- and resin acids, the changes were less in absolute terms but the fractional changes were similar to pine. During weeks 13 to 17 the fatty- and resin acids content had stabilised and changes were marginal. Multivariate analysis of the vis-NIR data showed a major effect due to maturity associated with a colour change and also weaker effects of fatty- and resin acid differences. PLS regression was used to predict the storage time with RMSEP values between 10 and 15 days. However, since weather conditions, precipitation and seasonal variation, have a very strong influence on the rate of maturing of sawdust it will be necessary to monitor the stored sawdust to determine the degree of maturity. Because of the large flow rate human eye assessment should be replaced by frequent vis-NIR measurements. The vis-NIR spectra allow prediction of storage time and therefore maturity.

Study on the cytochrome P450-mediated oxidative metabolism of the terpene alcohol linalool: Indication of biological epoxidation

The cytochrome P450-mediated oxidative metabolism of the terpene alcohol linalool was studied in vitro by enzymatic assays using recombinant human cytochrome P450 enzymes. Three different enzymatic products of allylic hydroxylation and epoxidation were identified by gas chromatography-mass spectrometry. Identified enzymatic products were 8-hydroxylinalool ((R/S)-3,7-dimethyl-1,6-octadiene-3,8-diol) and the cyclic ethers pyranoid-linalool oxide ((R/S)-2,2,6-trimethyl-6-vinyltetrahydro-2H-pyran-3-ol) and furanoid-linalool oxide (R/S)-2-(1,1-dimethylethyl)-5-methyl-5-vinyltetrahydrofuran. The cyclic ethers result most likely from the epoxidation of the 6,7-carbon double carbon bond of (R/S)-linalool, followed by the intramolecular rearrangement of the 6,7-epoxy-linalool. Allylic-hydroxylation of the 8-methyl group of linalool was catalyzed by CYP2C19 and CYP2D6 while the enzymatic epoxidation of linalool was only observed with CYP2D6. The results indicate that the electrophilic oxidation products of linalool such as 6,7-epoxy-linalool which may cause sensitization and irritational skin reactions are not only produced by auto-oxidation reactions in the presence of air-oxygen as published in the past, but also by P450-mediated oxidative biological transformation.

Study on the cytochrome P450-mediated oxidative metabolism of the terpene alcohol linalool: Indication of biological epoxidation

The cytochrome P450-mediated oxidative metabolism of the terpene alcohol linalool was studied in vitro by enzymatic assays using recombinant human cytochrome P450 enzymes. Three different enzymatic products of allylic hydroxylation and epoxidation were identified by gas chromatography-mass spectrometry. Identified enzymatic products were 8-hydroxylinalool ((R/S)-3,7-dimethyl-1,6-octadiene-3,8-diol) and the cyclic ethers pyranoid-linalool oxide ((R/S)-2,2,6-trimethyl-6-vinyltetrahydro-2H-pyran-3-ol) and furanoid-linalool oxide (R/S)-2-(1,1-dimethylethyl)-5-methyl-5-vinyltetrahydrofuran. The cyclic ethers result most likely from the epoxidation of the 6,7-carbon double carbon bond of (R/S)-linalool, followed by the intramolecular rearrangement of the 6,7-epoxy-linalool. Allylic-hydroxylation of the 8-methyl group of linalool was catalyzed by CYP2C19 and CYP2D6 while the enzymatic epoxidation of linalool was only observed with CYP2D6. The results indicate that the electrophilic oxidation products of linalool such as 6,7-epoxy-linalool which may cause sensitization and irritational skin reactions are not only produced by auto-oxidation reactions in the presence of air-oxygen as published in the past, but also by P450-mediated oxidative biological transformation.

Superoxide Reductases

AbstractReactive oxygen species (ROS), when in excess, are among the most deleterious species an organism can deal with. The physiological effects of ROS include amino acid chain cleavage, DNA degradation and lipid oxidation, among others. They can be formed in the cytoplasm in a variety of ways, including autooxidation reactions (FMN‐ and FAD‐containing enzymes) and Fenton reactions as a result of the cytoplasmatic pool of iron ions. The superoxide anion (O2·–), despite its short half‐life in solution, is particularly pernicious as it can form other reactive ROS (such as the strong oxidant peroxynitrite) or oxidize and/or reduce cellular components. For strict anaerobic or microaerophilic bacteria it is of particular importance to be able to dispose of ROS in a controlled manner, especially if these organisms are temporarily exposed to air. This review aims to describe the structural characteristics of superoxide reductases (SORs) and mechanistic aspects of biological superoxide anion reduction. SORs can be considered the main class of enzymes behind the oxygen detoxification pathway of anaerobic and microaerophilic bacteria. The geometry of the active site (three classes have been described), the possible electron donors in vivo and the current hypothesis for the catalytic mechanism will be discussed. Some phylogenetic considerations are presented, regarding the primary structure of SORs currently available in genome databases.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Interrelation between the electrochemical activity of alkyl-and thioalkylphenols and their antioxidant action

The oxidation potentials of alkyl-and thioalkylphenols of various structures and the rate constants for their reactions with styrene peroxide radicals were determined. The overall inhibiting activity of the substances in a model reaction of the thermal autooxidation of lard was studied. The oxidation potential of phenols was found to correlate with the O-H bond energy, the rate constants for phenol reactions with styrene peroxide radicals and phenoxyl radical reactions with Tetralin molecules, and the effectiveness of the overall inhibiting action of these compounds.

Kinetic characteristics of lipids of mammalian tissues in autooxidation reactions

We generalize the results of multiyear studies of the level of antioxidative activity of lipids isolated from tissues of laboratory rodents of different species and lines. A classification of lipids according to their ability to inhibit thermal autooxidation of methyl oleate is proposed. The involvement of lipids in low-temperature autooxidation reactions at the radical initiation and chain propagation stages was proved using the model developed. In addition to antioxidative activity, the initial content of peroxides in lipids, determined by their degree of unsaturation, and the antiperoxide activity of lipids are proposed for quantitative estimation of the kinetic characteristics of lipids of mammalian tissues. The dependence of effects on the rate of radical initiation in the system is shown, which is determined by the influence of the physicochemical properties of lipids on the coordination of relationships and balance of biochemical functions in biological objects differing in the intensity of oxidation processes.

Disruption of thiol homeostasis in plasma of terminal renal failure patients

Background The aim of the present studies was to investigate the changes in concentrations of different forms of thiols in plasma of terminal renal failure patients before and after hemodialysis. Methods Total concentrations of thiols, their free forms and the level of their mixed disulfides with proteins were determined with HPLC. Results In terminal renal failure patients before dialysis, total concentrations of cysteine, homocysteine and cysteinylglycine and their free and protein-bound fractions increased while level of all such forms of glutathione dropped. A single dialysis session caused short-lasting return of concentrations of all forms of thiols to the level equal or close to the control group. The changes observed in non-dialyzed patients were similar to those observed in dialyzed patients before single dialysis procedure. Conclusions The obtained results showed severe disturbance of thiol homeostasis in plasma of terminal renal failure patients. The following changes have to be emphasized: (1) high level of free cysteine (cystine) fraction, (2) strong tendency of homocysteine to form mixed disulfides with proteins, (3) drop of glutathione level. These observations confirm a suggestion that atherogenic action of homocysteine can be a result of S-homocysteinylation and N-homocysteinylation reactions, whereas toxic action of cysteine can result from auto-oxidation reaction.

Catalytic activity and stability of anionic and cationic water soluble cobalt(II) tetraarylporphyrin complexes in the oxidation of 2-mercaptoethanol by molecular oxygen

The catalytic activity and stability of anionic cobalt(II) porphyrin complexes: 5,10,15,20-tetrakis(2,6-dichloro-3-sulfonatophenyl)porphyrinatocobalt(II), 5,10,15,20-tetrakis(2,4,6-trimethyl-3,5disulfonatophenyl)porphyrinatocobalt(II) and the cationic cobalt(II) porphyrin: 5,10,15,20-tetrakis[4-(diethylmethylammonio)phenyl]porphyrinatocobalt(II) tertraiodide have been investigated in the oxidation of 2-mercaptoethanol by dioxygen. All complexes were efficient catalysts for the auto-oxidation of 2-mercaptoethanol. The cationic cobalt(II) porphyrin has been found to be the most reactive catalyst. The rate of auto-oxidation of 2-mercaptoethanol catalysed by 5,10,15,20-tetrakis(2,4,6-trimethyl-3,5disulfonatophenyl)porphyrinatocobalt(II) has been found to increase with increasing the pH from 7 to 9 then decreased at higher pH. The rate constants of auto-oxidation reaction showed linear dependence on catalyst concentration and saturation kinetics in both 2-mercaptoethanol concentrations and dioxygen pressure. Anionic cobalt(II) porphyrin complexes showed higher stability than the cationic catalyst in repeat oxidation reactions. Immobilizing the anionic catalysts on ion exchange resin and supporting the cationic catalyst on clay mineral montmorillonite improved their stabilities towards oxidation.

Synthesis and Antioxidative Activity of N, N-Dialkyl-ω-[4-hydroxy(methoxy)aryl]alkylamines and Their N-Oxides

Aminoalkylphenols of various structures were prepared by reactions of ω-[4-hydroxy(methoxy)aryl]haloalkanes with dialkylamines. The corresponding N-oxides were prepared by oxidation of aminoalkylphenols with hydrogen peroxide and cumene hydroperoxide. The inhibiting activities of these compounds in a model reaction of thermal autooxidation of lard were compared.

Chemiluminescent reaction of sulphite auto-oxidation in the presence of Ni(II)/tetraglycine and ruthenium(II)/bipy complexes: mechanistic considerations

The present work is a mechanistic study of the possible analytical chemiluminescent reaction of sulphite oxidation in the presence of dissolved oxygen, Ni(II)/tetraglycine and [RuII(bipy)3]2+ ions. The Ni(III) complex oxidizes SO32- to SO3-, reacts with oxygen to produce SO5-, initiating a radical chain reaction. The strong oxidants generated oxidize Ni(II) and Ru(II) complexes in one redox cycle, which is related to the balance of SO32- and oxygen concentrations. The emission intensity depends on the concentrations of SO32-, Ni(II) and Ru(II) complexes.

Role of catalyst deactivation and regeneration in the heck reaction involving unactivated aryl bromides

The kinetics of low-temperature autooxidation of methyl oleate for a bimolecular mechanism of the degenerate branched reaction were analyzed taking into account changes in the methyl oleate concentration for different amounts of peroxides formed. This analysis made it possible to explain the experimental data. The role of the initial peroxide concentration in the mechanism and kinetics of the chain degenerate branched reaction of methyl oleate autooxidation was studied in the steady-state approximation and in the course of establishing a steady-state concentration of radicals. A systematic approach to estimating the antioxidant properties of lipids on the basis of the methyl oleate model was proposed.

Redox reactions in seafloor basalts: possible insights into silicic hydrothermal systems

Many features of the magma-hydrothermal interface are directly observable in, near seafloor hydrothermal systems at mid-ocean ridges. A striking aspect observed at that interface is the spontaneous redox reaction that occurs during rapid crystallization of basaltic magma, which results in generation of highly reducing hydrothermal fluids. A consequence of the reaction is that the ferric/ferrous ratio observed in the resulting crystalline basalt is much higher than it was in the basaltic magma, the redox state of the magma inferred from the ferric/ferrous ratio in the crystalline rock is considerably higher than it was in the magma [Earth Planet. Sci. Lett. 79 (1986) 397]. Magnetite-ulvöspinel is the only ferric iron-containing phase observed in the crystalline portion of the basalt. This suggests that the driving force for that reaction is related to the stability of magnetite relative to the FeO component in the basaltic liquid (or glass), resulting in the oxidation of ferrous iron by H 2O dissolved in the melt, yielding magnetite, releasing H 2 from the system. This is an auto-oxidation reaction in which all reactants are present internally in the basalt magma prior to crystallization. H 2O is the limiting reagent for magnetite formation in the case of MORB magma. If a similar auto-oxidation occurs in the more silicic magmas commonly associated with terrestrial hydrothermal ore deposits, it would have important consequences for the interpretation of the redox condition existing at terrestrial magma-hydrothermal interfaces. Glassy I-type dacites extruded on the seafloor in the Manus Basin have ferric/ferrous ratios that are significantly lower than in I-type plutons, terrestrial volcanics. The ferric/ferrous ratios in the Manus Basin dacites yield oxygen fugacities from about one to more than two log units below that of nickel–nickel oxide. Oxidation of ferrous iron in these silicic magmas is predicted to generate an amount of H 2 that is proportional to the amount of ferrous iron present, rather than the amount of H 2O (as in the case of MORB) due to the high ratio of H 2O to ferrous iron in silicic magmas. These relatively reduced dacitic magmas would yield significant quantities of H 2 on crystallization, which would make hydrothermal fluids at the interface strongly reducing, thus affect the speciation in fluids at the magma-hydrothermal interface.

Rapid and Selective Electrochemical Determination of Nitrite in Cured Meat in the Presence of Ascorbic Acid

A simple, fast and selective amperometric procedure for nitrite determination in cured meat based on the use of a carbon paste electrode is presented. Direct interference of ascorbic acid, which interferes with electrochemical detection, was eliminated by applying a cellulose acetate membrane of 100 Da molecular weight cut-off on the electrode. Indirect interference of ascorbic acid due to its auto-oxidation reaction and its reaction with nitrite is discussed. In order to stabilise the ascorbic acid, metaphosphoric acid and EDTA were added. In contrast to the standard spectrophotometric method, which requires careful control of pH and the use of carcinogenic reagents, amperometric deter- mination of nitrite is simple, rapid, and works without reagents. Also, sample preparation is simpler because it requires neither heating to 80 � C nor the centrifuga- tion steps of the official spectrophotometric method. The detection limit achieved was 14 ppb (0.2mM) nitrite in the solution, which corresponds to a detec- tion of 2.8 ppm in meat samples. The method was compared with the standard spectrophotometric pro- cedure and applied to the detection of nitrites in cured meat samples with satisfactory results.