Hydroxyl/hydrogen radicals

Sostaric et al. [67] also found that dissolution of CdS could be achieved through sonochemical reduction of the sulphur by hydroxyl radicals, hydrogen peroxide and superoxide ... 

Colquhoun and Schumacher [98] have shown that y-linolcnic acid and eicosapentaenoic acid, which inhibit Walker tumor growth in vivo, decreased proliferation and apoptotic index in these cells. Development of apoptosis was characterized by the enhancement of the formation of reactive oxygen species and products of lipid peroxidation and was accompanied by a decrease in the activities of mitochondrial complexes I, III, and IV, and the release of cytochrome c and caspase 3-like activation of DNA fragmentation. Earlier, a similar apoptotic mechanism of antitumor activity has been shown for the flavonoid quercetin [99], Kamp et al. [100] suggested that the asbestos-induced apoptosis in alveolar epithelial cells was mediated by iron-derived oxygen species, although authors did not hypothesize about the nature of these species (hydroxyl radicals, hydrogen peroxide, or iron complexes ). 

The absence of substituents with free radical scavenging properties in most of the (3-blockers makes doubtful their efficacy as powerful antioxidants. Arouma et al. [293] tested the antioxidative properties of several 3-blockers in reactions with superoxide, hydroxyl radicals, hydrogen peroxide, and hypochlorous acid. It was demonstrated that most of the compounds tested were inactive in these experiments. Nonetheless, propranolol, verapamil, and flunarizine effectively inhibited iron ascorbate-stimulated microsomal lipid peroxidation and all drugs (excluding flunarizine) were effective scavengers of hydroxyl radicals. Contrary to Janero et al. [292], these authors did not find the inhibition of xanthine oxidase by propranolol. It was concluded that 3-blockers are not the effective in vivo antioxidants. 

For aqueous solutions, Sargent and Gardy (1976) have advocated the use of DMPO, which gives persistent spin adducts with hydroxyl radicals hydrogen-atom adducts arise by electron scavenging and subsequent protonation of DMPCK, but this can be minimized by incorporating N20 in the system, which traps electrons and raises the yield of hydroxyl radicals (28). 

Joshi, AA Locke, BR Arce, P Finney, WC. Formation of hydroxyl radicals, hydrogen peroxide and aqueous electrons by pulsed streamer corona discharge in aqueous solution. Journal of Hazardous Materials, 1995 41,3-30. 

Iron(II) hydroxyl radical, hydrogen peroxide determination, 641... 

Scavenger is a term used for substrates reacting with hydroxyl radicals that do not yield species that propagate the chain reaction. Scavengers can hinder oxidation by consuming hydroxyl radicals, hydrogen peroxide, and UV light. 

In the zeolite, owing to the lack of multimolecular degradation, oxidation of water by [Ru(bpy)3] + becomes possible. The reaction is slow, and hydroxyl radicals, hydrogen peroxide and superoxide are created as intermediates. In plant photosynthesis, an Mn-based water-splitting catalyst system in which the reaction with water only occurs after four electrons have been stored in the water-splitting enzyme... 

OH + e (aq) + n + HzO + H + H2O2 + H2 The first 14 water molecules per nucleotide in the hydration layer surrounding DNA have approximately the same mass as DNA [84] and, therefore, the same number of ionizations are expected to occur in the primary hydration layer as in the DNA strand. However, it is unknown how the water molecules in the primary hydration layer are affected by radiation. One possibility is that water cations and electrons are formed, which transfer their ionic character to the DNA strand (quasi-direct effects). Water cations can also transfer protons to neighboring water molecules resulting in hydroxyl radicals. The products formed in the hydration layer (hydroxyl radicals, hydrogen atoms or aqueous electrons) can subsequently react with DNA (indirect effects). Quasi-direct and indirect effects are expected to yield very different radicals. 

The three intermediates formed by irradiating water, the hydroxyl radicals, hydrogen peroxide and superoxide radicals, react in very different ways. However, because all three are linked and can be formed from each other, they might be considered equally dangerous. Indeed, the three actually work together as part of an insidious catalytic system. We will consider each in turn, in the order that they are produced by radiation on route from water to oxygen. 

During metabolism of oxygen to water in the mitochondria, a small fraction of the oxygen is reductively converted into superoxide as a by-product. Superoxide may be further converted into various ROS, i.e., hydroxyl radical, hydrogen peroxide and others. 

Radiation chemistry of ice, i.e., solid water, is described in two newer book chapters (Kroh 1991 Wypych 1999), but it was also discussed in many former books on radiation chemistry. Here also, as with liquid water fast kinetic spectroscopic techniques were used to identify the early processes. Pulse radiolysis measurements have been carried out mostly with single crystal ice, which is sufficiently transparent. As it is common in solid-state radiation chemistry some of the intermediates remain trapped in the matrix and can be studied by means of standard spectroscopic techniques like optical absorption and EPR spectroscopy using these techniques hydroxyl radicals, hydrogen atoms, and trapped electrons were identified at low temperature. The intermediates disappear upon warming up the soUd sample. The hydrogen atoms formed at —269°C completely disappear when the solid is warmed to —196°C. The hydroxyl radicals produced at the latter temperature decay between -170°G and -140°C. 

Oxidative stress Excess formation of reactive oxygen species (ROS) superoxide hydroxyl radicals hydrogen peroxide Reduced production and disturbances in NO signaling by ROS upregulation of NO synthase disturbance of enzymes mediating antioxidant processes increased activation of NAD(P)H oxidase membrane/lipid peroxidation Dogru et al. (2008), Quintanar-Escorza etal. (2007)... 

In aqueous solution, the indirect action of radiation plays an important role, since the primary radiolysis products (Scheme 5.26) - that is, hydroxyl radicals, hydrogen atoms and hydrated electrons - are highly reactive. They are formed with G (OH ) = 2.7, G(H ) = 0.55, and G(e ) = 2.65. 

The production of numerous active oxidants hydroxyl radicals, hydrogen peroxide, ozone, peroxodisulfate, etc., has been simplified with the use of the BDD anodes. The AOPs use these oxidants to destroy low concentrations of biorefractory organic species. Some of these oxidants are unstable, and thus the innovative BDD anodes allow an easier use of the AOPs in the field of wastewater treatment. 

Since hardly any oxygen is electrogenerated via water oxidation on BDD electrodes, even when an anodic potential of more than 2 V vs. NHE is applied, various forms of active oxygen, such as the hydroxyl radical, hydrogen peroxide and ozone, can therefore be produced. Indeed, the BDD electrode shows a high capability to produce active oxygen, as shown in Table 23.1. 

Just as water can find its way downhill by many different pathways, so there are many chemical pathways by which SO2 and NOx are converted to acid in the atmosphere. The major pathways do not involve oxygen directly, but instead involve more powerful oxidizing agents, including hydroxyl radical, hydrogen peroxide, and ozone, which are ubiquitous in the atmosphere. 

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