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Autooxidation

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John S Olson – 1st expert on this subject based on the ideXlab platform

  • factors governing Autooxidation of human hemoglobin
    Biophysical Journal, 2017
    Co-Authors: Andres Benitez S Cardenas, John S Olson

    Abstract:

    Determining mechanisms for the Autooxidation of hemoglobin is required for understanding and treating unstable hemoglobinopathies and for developing more stable hemoglobin based O2 carriers. Previous studies suggested significant differences in Autooxidation rates of α and β subunits. We used an azide reaction assay to measure the concentrations of ferric α and β chains at different time points during Autooxidation. Our results showed no differences between the subunits. To obtain more accurate time courses for Autooxidation, we deconvoluted observed spectra into the decay of HbO2, metHb appearance, hemichrome generation, and increases in turbidity due to hemin loss and apoprotein precipitation. The time courses for HbO2 decay at high concentrations (≥ 100µM heme) accelerate implying cooperative Autooxidation, where as at low concentrations (≤ 10uM) the time courses are biphasic. These results suggest that the biphasic time courses at low hemoglobin are due to differences between tetramers and dimers. We have also measured Autooxidation rates for a recombinant hemoglobin, rHb0.1, that contains a genetically crosslinked di-α subunit. This hemoglobin shows a monophasic time course for Autooxidation at both high and low protein concentrations, and the azide binding assay showed equal amounts of ferric α and β subunits. We have also examined recombinant mutant hemoglobins to examine the structural factors that govern Autooxidation. Increased rates of Autooxidation were found for rHb Providence, rHb Bethesda, rHb Presbyterian, and rHb Kirklareli. We have also confirmed that the rate of Autooxidation shows a bell-shaped dependence on oxygen concentration and increases markedly as the pH is decreased.Supported by NIH Grant P01 HL110900 and by Grant C-0612 from the Robert A. Welch Foundation.

  • genetic engineering of myoglobin as a simple prototype for hemoglobin based blood substitutes
    Artificial Cells Blood Substitutes and Biotechnology, 1994
    Co-Authors: John S Olson

    Abstract:

    Site-directed mutagenesis has been used to examine the structural and functional roles of distal pocket residues in regulating O2 affinity, CO binding, rates of association and dissociation, Autooxidation, and hemin loss in mammalian myoglobins and human hemoglobin. In myoglobin, His-E7 inhibits CO binding by requiring displacement of distal pocket water. In the case of O2 binding, this displacement is compensated by a strong hydrogen bond between the bound ligand and the imidazole side chain. The isopropyl side chain Val-E11 also sterically restricts CO binding. The rates of ligand binding are regulated by distal pocket water displacement, steric restrictions near the iron atom, and an outer more global protein barrier. Autooxidation occurs by two mechanisms, direct dissociation of HO2 and bimolecular reaction of external O2 with unliganded heme. Both processes are inhibited markedly by hydrogen bonding interactions with His-E7. Double mutants have been constructed to decrease oxygen affinity, but still …

  • the mechanism of Autooxidation of myoglobin
    Journal of Biological Chemistry, 1993
    Co-Authors: R E Brantley, Stephen J Smerdon, Anthony J Wilkinson, E W Singleton, John S Olson

    Abstract:

    Abstract Time courses for the Autooxidation of native and mutant sperm whale and pig myoglobins were measured at 37 degrees C in the presence of catalase and superoxide dismutase. In sperm whale myoglobin, His64(E7) was replaced with Gln, Gly, Ala, Val, Thr, Leu, and Phe; Val68(E11) was replaced with Ala, Ile, Leu, and Phe; Leu29(B10) was replaced with Ala, Val, and Phe. In pig myoglobin, His64(E7) was replaced with Val; Val68(E11) was replaced with Thr and Ser; Thr67(E10) was replaced with Ala, Val, Glu, and Arg; Lys45(CD3) was replaced with Ser, Glu, His, and Arg. The observed pseudo-first order rate constants varied over 4 orders of magnitude, from 58 h-1 (H64A) to 0.055 h-1 (native) to 0.005 h-1 (L29F) at 37 degrees C, pH 7, in air. The dependences of the observed Autooxidation rate constant on oxygen concentration and pH were measured for native and selected mutant myoglobins. In the native proteins and in most mutants still possessing the distal histidine, Autooxidation occurs through a combination of two mechanisms. At high [O2], direct dissociation of the neutral superoxide radical (HO2) from oxymyoglobin dominates, and this process is accelerated by decreasing pH. At low [O2], Autooxidation occurs by a bimolecular reaction between molecular oxygen and deoxymyoglobin containing a weakly coordinated water molecule. The neutral side chain of the distal histidine (His64) inhibits Autooxidation by hydrogen bonding to bound oxygen, preventing both HO2 dissociation and the oxidative bimolecular reaction with deoxymyoglobin. Replacement of His64 by amino acids incapable of hydrogen bonding to the bound ligand markedly increases the rate of Autooxidation and causes the superoxide mechanism to predominate. Increasing the polarity of the distal pocket by substitution of Val68 with Ser and Thr accelerates Autooxidation, presumably by facilitating protonation of the Fe(II).O2 complex. Increasing the net anionic charge at the protein surface in the vicinity of the heme group also enhances the rate of Autooxidation. Decreasing the volume of the distal pocket by replacing small amino acids with larger aliphatic or aromatic residues at positions 68 (E11) and 29 (B10) inhibits Autooxidation markedly by decreasing the accessibility of the iron atom to solvent water molecules.

N V Khrustova – 2nd expert on this subject based on the ideXlab platform

  • kinetic characteristics of lipids of mammalian tissues in Autooxidation reactions
    Biophysics, 2006
    Co-Authors: L N Shishkina, N V Khrustova

    Abstract:

    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.

  • the kinetic characteristics of lipids of animal tissues in Autooxidation reactions
    Biofizika, 2006
    Co-Authors: L N Shishkina, N V Khrustova

    Abstract:

    : The results of long-time research of antioxidative activity (AOA) of lipids from tissues of different species and lines of laboratory rodents are generalized. The classification of lipids according to their ability to inhibit the thermal Autooxidation of methyl oleate is proposed. The participation of lipids in low-temperature Autooxidation reactions at the initiation and chain propagation stages was proved by means of the model proposed. In addition to the lipid antioxidative activity, the initial quantity of peroxides in lipids due to the extent of their unsaturation and lipid antiperoxide activity are proposed for the estimation of the kinetic characteristics of lipids. The dependence of effects on the rate of radical initiation in the system is shown to be caused by the influence of physicochemical properties of lipids on the interrelation coordination and balance of biochemical functions in biological objects differing in the intensity of oxidation processes.

  • the role of peroxides in the mechanism of low temperature Autooxidation of methyl oleate and its solutions with lipids
    Kinetics and Catalysis, 2004
    Co-Authors: N V Khrustova, L N Shishkina

    Abstract:

    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.

Michelle L Coote – 3rd expert on this subject based on the ideXlab platform

  • revising the mechanism of polymer Autooxidation
    Organic and Biomolecular Chemistry, 2011
    Co-Authors: Ganna Grynova, Jennifer L Hodgson, Michelle L Coote

    Abstract:

    The basic scheme for Autooxidation of polymers, originally developed by Bolland, Gee and co-workers for rubbers and lipids, is now widely applied to all types of polymeric materials. According to their scheme, the reaction that makes this process autocatalytic, referred to as the propagation step, is a hydrogen abstraction from the next substrate by the peroxyl radical (ROO˙ + RH → ROOH + R˙). In this study, using advanced quantum-chemical methods, we have shown that this step is actually characterised by largely positive Gibbs free energy (10–65 kJ mol−1) for most regular polymers with saturated chains (polypropylene, polyethylene, polyvinyl chloride, polyvinyl acetate, polyurethane, poly(methyl methacrylate)etc.) and even some polymers with unsaturated fragments (polystyrene, polyethylene terephthalate). Neither elevated temperature, nor solvation makes this process thermodynamically favourable. Only when the formed radical centre is conjugated with adjacent double bonds (as in polybutadiene) or captodatively stabilised by two suitable functional groups (such as a carbonyl and a lone pair donor such as oxygen or nitrogen), is the propagation step exoergic. Instead, we show that it is the presence of structural defects, such as terminal or internal double bonds, formed either during polymerisation or in the degradation process itself, that is responsible for the Autooxidation of most polyesters and most polyalkenes. Recognition of the real mechanism of Autooxidation in polymers is a key to developing strategies for the prevention of their degradation.