Activation hydroxy radical

Photoactive Additives.—Ferric compounds, in particular, the chloride, continue to attract much interest as photosensitizers for thermoplastics. " From e.s.r. work the mechanism appears to involve a redox reaction resulting in the formation of active hydroxy-radicals. Photodegradable polyethylene film has been developed by doping it with radiation-modified atactic polypropylene and hydroxyethyl-ferrocene. Several workers have studied the dye-sensitized photo-oxidation of polyisoprene and di-n-butyl sulphide embedded in Augustyniak and... 

One of the most used systems involves use of horseradish peroxidase, a 3-diketone (mosl commonly 2,4-pentandione), and hydrogen peroxide." " " Since these enzymes contain iron(II), initiation may involve decomposition of hydrogen peroxide by a redox reaction with formation of hydroxy radicals. However, the proposed initiation mechanism- involves a catalytic cycle with enzyme activation by hydrogen peroxide and oxidation of the [3-diketone to give a species which initiates polymerization. Some influence of the enzyme on tacticity and molecular... 

Cyclic acetals. In combination with iodine, this reagent resembles lead tetraacetate in the ability to generate alkoxy or aminyl radicals (12,243) under thermal or light activation. This radical oxidation can be used to convert p- or y-hydroxy ethers into dioxolanes or dioxanes.4... 

We conclude that oxidative transformations of organic substrates can be readily understood as emanating from either photogenerated surface adsorbed radical cations or from radicals formed by activated oxygen radicals (surface oxides or adsorbed hydroxy, hydroperoxy or peroxy radicals). Photoelectrochemical methods not only generate the reactive species by interfacial electron transfer, but also control the subsequent activity of the surface adsorbed intermediate. 

The latter reaction which has the activation energy about 85 kJ/mol seems to be more probable at higher temperatures at lower temperatures hydroxy radicals may appear in other reaction pathways as in the monomolecular decomposition of hydroperoxides, etc. Hydroxyl which are very mobile and very reactive propagate the reaction site only to a short distance (the rate constant of transfer reaction of HO radicals with CH3 group of ethane is equal 108 dm3 mol-1 s approximately at 20 °C). 

The oxidant can be formulated either as a hydroxy radical bound to Cu(II) or as a hydroxide ligand on Cu(III). In either case, the activated complex is capable of strand scission, and the cleavage pattern suggests that the oxidant is nondiffusible and therefore bound to the metal (17). Cleavage by this reagent involves sugar oxidation, as discussed in subsequent paragraphs. 

Brown DM, Fisher C, Donaldson K. 1998. Free radical activity of s mthetic vitreous fibers Iron chelation inhibits hydroxy radical generation by refractory ceramic fiber. J Toxicol Environ Health 53 545-561. 

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