Hydroperoxy radicals, from hydrogen peroxid

Hydroperoxy radical or HOO-. This is a very reactive free radical that can be generated from hydrogen peroxide, particularly via metal ion-catalyzed decomposition. This radical can generate superoxide. 

The hydroxyl radical is normally present only in low concentrations in the troposphere, as it reacts with further ozone to form the hydroperoxy radical HOO- which in turn gives hydrogen peroxide H202. Ozone, the hydroxyl radical, and hydrogen peroxide are the main oxidizing species in the troposphere, from the standpoint of environmental chemistry. The hydroxyl radical in particular performs an important function as a natural cleansing agent for the atmosphere.26 In elevated concentrations, however,... 

This oxidative process has been successful with ketones,244 esters,245 and lactones.246 Hydrogen peroxide can also be used as the oxidant, in which case the alcohol is formed directly.247 The mechanisms for the oxidation of enolates by oxygen is a radical chain autoxidation in which the propagation step involves electron transfer from the carbanion to a hydroperoxy radical.248... 

When active oxygen species are produced this may lead to a cycle of oxidation and reduction (redox cycle) with electrons being donated to oxygen to yield superoxide. This is the case with paraquat and also a number of cytotoxic quinones. Thus, there is a cyclic process which produces superoxide by adding electrons from paraquat (see Chapter 7) or a semiquinone to oxygen (figure 6.10). The superoxide produced may then be metabolized to hydrogen peroxide by superoxide dismutase, which is further metabolized to water (see below) or protonated to the hydroperoxy radical, HOO ... 

Reactive free radicals extract electrons (usually as hydrogen atoms) from other compounds to complete their own orbitals, thereby initiating free radical chain reactions. The hydroxyl radical is probably the most potent of the ROS. It initiates chain reactions that form lipid peroxides and organic radicals and adds direcdy to compounds. The superoxide anion is also highly reactive, but has limited hpid solubility and cannot diffuse far. However, it can generate the more reactive hydroxyl and hydroperoxy radicals by reacting nonenzymatically with hydrogen peroxide in the Haber-Weiss reaction (Fig 24.4). 

PEO and polymethyl vinyl ether were UV irradiated in hydrogen peroxide solutions. Hydroxy and hydroperoxy radicals accelerate the oxidative degradation of these polymers. Hydroxy and possibly hydroperoxy radicals can abstract hydrogen from methylene groups in both polymers. As a result of further oxidative reactions, different carbonyl, hydroxy and hydroperoxy groups are formed (297). 

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