Hydroxyl radical initiation

These have already been noted in the context of hydroxyl radical-initiated oxidations, and reference should be made to an extensive review by Worobey (1989) that covers a wider range of abiotic oxidations. Some have attracted interest in the context of the destruction of xenobiotics, and reference has already been made to photochemically induced oxidations. 

Rodenas et al. [77] studied PMN-stimulated lipid peroxidation of arachidonic acid. As MDA formation was inhibited both with L-arginine (supposedly due to the formation of excess NO) and DTPA (an iron ion chelator), it was concluded that about 40% of peroxidation was initiated by hydroxyl radicals formed via the Fenton reaction and about 60% was mediated by peroxynitrite. However, it should be noted that the probability of hydroxyl radical-initiated lipid peroxidation is very small (see above). Phagocyte-mediated LDL oxidation is considered below. 

By a comparison of the calculated values for the OH° concentration according to equation 5-4 and 5-6 in connection with 5-11 it was shown that the initiation term was not negligible and the simplified model not appropriate. Thus, the authors defined a hydroxyl radical initiating rate 8 that includes all possible initiating reactions, calculated by the OH° concentration difference between the experiment and the model. 

Beltran o,. cyuv distilled water with/without scavengers OH, UV HC03-, C032, ferf-butanol B hydroxyl radical initiating term prediction was only possible with B included... 

Because AOPs take advantage of the high reactivity of hydroxyl radicals, initial, propagation, promotion, recombination, and reversible reactions are commonly involved in the degradation of organic pollutants. Table 4.3 lists these major elementary reactions. 

It was also shown that the ratio of oxidized alcohol to oxidized Fe2+ could be greater then one. Baxendale and Wilson (1957) showed that hydroxyl radical initiating the chain polymerization of olefins by hydrogen peroxide was the same process as the rapid oxidation of glycolic acid. Merz and Waters (1947) confirmed that simple water-soluble alcohols are oxidized rapidly by Fenton s reagent. The primary alcohols are oxidized to aldehydes, which are further oxidized at comparable rates by exactly the same mechanism. Merz and Waters proposed a mechanism of chain oxidation of alcohols and aldehydes by sodium persulfate, hydrogen peroxide, and an excess of ferrous salt as follows ... 

The atmospheric chemical kinetics of linear perfluorinated aldehyde hydrates, Cx-F2x+iCH(OH)2, have been measured for x = 1,3, and 4, focusing on formation (from aldehyde, by hydration), dehydration, and chlorine atom- and hydroxyl radical-initiated oxidation.211 The latter reaction is implicated as a significant source of perfluorinated carboxylic acids in the environment. 

The mechanism of the hydroxyl radical-initiated oxidation of /i-pincnc in the presence of NO has been investigated using a discharge-flow system. Propagation of hydroxyl radicals was observed after the addition of O2 and NO, and the measured concentration profiles were compared with simulations based on both the master chemical mechanism and the regional atmospheric chemistry mechanism for /i-pinene oxidation.228... 

Two important factors in initiating graft copolymerization reactions of vinyl monomers with activated cellulose are (1) the lifetime of the free radical sites and (2) the accessibility of the free radical sites to the monomers. For ceric ion initiation or hydroxyl radical initiation the lifetimes of the free radicals on the cellulose molecule were short (5, 19) therefore, the monomer should be present when the free radicals were formed. For ionizing radiation both short lived and long lived (trapped) free radicals were formed (22, 26, 44). Consequently, the activation reaction and the copolymerization reaction could either be conducted... 

Lopez JL, Garcia Einschlag FS, Gonzalez MC, Capparelli AL, Oliveros E, Hashem TM, Braun AM (2000) Hydroxyl Radical Initiated Photodegradation of 4-Chloro-3,5-dinitrobenzoic Acid in Aqueous Solution, J Photochem. Photobiol. A Chem. 137 177-184. 

Figure 3. Mechanism for the hydroxyl radical initiated oxidation of CHCl=CCl2.

Hoigne, J., and H. Bader (1978), "Ozone and Hydroxyl Radical-Initiated Oxidations of Organic and Organometallic Trace Impurities in Water, Organometals and Organomettaloids Occurrence and Fate in the Environment, F. E. Brinckman and J. M. Bellama, Eds. (ACS Symposium Series No. 92), (American Chemical Society), Washington, DC, 292-313. 

Fig 24.7. Free radical-mediated cellular injury. Superoxide and the hydroxyl radical initiate lipid jjeroxidation in the cellular, mitochondrial, nuclear, and endoplasmic reticulum membranes. The increase in cellular permeability results in an influx of Ca, which causes further mitochondrial damage. The cysteine sulfhydryl groups and other amino acid residues on proteins are oxidized and degraded. Nuclear and mitochondrial DNA can be oxidized, resulting in strand breaks and other types of damage. RNOS (NO, NO2, and perox5mitrite) have similar effects. 

Hoigne, J. and Bader, H. (1978) Ozone and hydroxyl radical-initiated oxidations of organic and organometallic trace impurities in water. In Brinckman, F.E. and Bellama, J.M. (eds) Organometallics and Organometalloids Occurrence and Fate in the Environment. American Chemical Society, Washington, DC, pp. 292-313. 

Hydrogen peroxide/Iron (II) (Fenton s Reagent) Initiationo Latexes formed using hydroxyl radical initiation were considerably less, stable than those initiated by PBI, Particle sizes and the corresponding particle concentrations are given in Tables IV and V respectively, A log-log plot of the data in Table V is presented in Figure 7,... 

As you can see, the free radical reaction initiates a slow burning of CH4 in a series of steps that produce carbon dioxide and water and some additional free radicals. The hydroxyl radical initiates similar reactions with other pollutants as weU as undesirable naturally occurring atmospheric gases. Without the hydroxyl free radical— sometimes called the atmospheric vacuum cleaner—our atmosphere would be a much dirtier place. 

Pramanick and Sankar [99] investigated the polymerization of methyl methacrylate polymerization initiated by only ceric ions and found that the mechanism of initiation depends strongly on the acidity of the medium and is independent of the nature of anion associated with the ceric ion. In a moderately acidic medium, the primary reaction is the formation of hydroxyl radical by ceric-ion oxidation of water. When ceric sulfate is used, the hydroxyl radicals initiate the polymerization and appear as end groups in the polymer molecule. If, on the other hand, ceric ammonium sulfate or a mixture of ceric sulfate and ammonium sulfate are used, some of the hydroxyl radicals react with the ammonium ion, producing ammonium radicals, and both radicals act as initiators, giving polymers with both hydroxyl and amino end groups. In the polymerization of acrylamide by ceric salt, the infrared (IR) spectra suggests the formation of monomer-ceric salt complexes in aqueous solution [98]. This coordination bond presumably consists of both... 

Niki, H., P.D. Maker, C.M. Savage, and M.D. Hurley (1987), Fourier transform infrared smdy of the kinetics and mechanisms for the chlorine-atom- and hydroxyl-radical-initiated oxidation of glycolaldehyde, J. Phys. Chem., 91, 2174—2178. 

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