Production of Free Radicals

Free radicals are produced when chemical bonds are broken by what is termed a homolytic process (13.144), as distinct from a heterolytic process in which ions are obtained (13.145). The former may be effected by thermal or photochemical means (thermolysis or photolysis), by excitation in flames, by electrolysis, by electron impact in mass spectrometers, or during radiochemical breakdown processes. 

Phosphinidene Phosphide Phosphinyl Phosphine Phosphinium Phosphonium Phosphonium Phosphoranyl  

Nitrene Nitride ion Aminyl radical Ammonia Ammonium Ammonium Ammonium  

Phosphite Phosphite Hypophosphite Hypophosphite Phosphonyl HPO molecule Monometaphosphate  

Free radicals have been most studied in connection with carbon chemistry, but a number of the possible phosphorus radicals in Table 13.12 are now well authenticated. 

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Biological Antioxidant Models. Tea extracts, tea polyphenol fractions, and purified catechins have all been shown to be effective antioxidants in biologically-based model systems. A balance between oxidants and antioxidants is critical for maintenance of homeostasis. Imbalances between free radicals and antioxidants may be caused by an increased production of free radicals or decreased effectiveness of the antioxidants within the reaction system. These imbalances can be caused by the radicals overwhelming the antioxidants within the system, or by an excess of antioxidants leading to a prooxidant functionaHty (105—118). When antioxidant defense systems are consistently overwhelmed by oxidative reactions, significant damage can... 

Copper is an essential trace element. It is required in the diet because it is the metal cofactor for a variety of enzymes (see Table 50—5). Copper accepts and donates electrons and is involved in reactions involving dismu-tation, hydroxylation, and oxygenation. However, excess copper can cause problems because it can oxidize proteins and hpids, bind to nucleic acids, and enhance the production of free radicals. It is thus important to have mechanisms that will maintain the amount of copper in the body within normal hmits. The body of the normal adult contains about 100 mg of copper, located mostly in bone, liver, kidney, and muscle. The daily intake of copper is about 2—A mg, with about 50% being absorbed in the stomach and upper small intestine and the remainder excreted in the feces. Copper is carried to the liver bound to albumin, taken up by liver cells, and part of it is excreted in the bile. Copper also leaves the liver attached to ceruloplasmin, which is synthesized in that organ. 

Oliver, C.N., Starke-Reed, P.E., Stadtman, E.R., Liu, G.J., Carney, J.M. and Floyd, R.A. (1990). Oxidative damage to brain proteins, loss of glutamine synthetase activity, and production of free radicals during ischemia/reperfusion-induced injury to gerbil brain. Proc. Natl Acad. Sd. USA 87, 5144-5147. 

Human chronic inflammatory diseases are characterized by populations of cells with altered regulation and function. A large body of evidence suggests that many of these cellular abnormalities may be linked to an increase in the production of free radicals and/or deficiencies of antioxidant defence systems. Oxygen free radicals attack cell structures, altering their function, and are cytotoxic. They have therefore been implicated in the pathogenesis of rheumatoid arthritis as well as many other human diseases (HaUiwell, 1991). 

Direct evidence of increased production of free radicals... 

There is some support for a role for free radicals in the pathogenesis of ischaemic colitis from animal studies. Murthy and Qi (1992) used a spin trap to demonstrate increased production of free radicals up to 60 min after reperfusion, whereas Douglas etal. (1989) demonstrated increases in malondialdehyde and conjugated dienes (presumptive measures of lipid peroxidation) in a rat model of ischaemic colitis. There is no data relating to human ischaemic colitis. 

Direct Evidence of Increased Production of Free Radicals... 

The production of free radicals has been implicated in the mechanism of liver injury due to a number of drugs and toxins. These include adtiamycin (Pritsos et al., 1992), halothane (Neuberger and Williams, 1984), phenobar-bital and thiopental (Kanazawa and Ashida, 1991), carbon tetrachloride (Williams and Burk, 1990), 1,1,2,2-tetrachloroethane (Paolini aal., 1992), and paraquat and related bipyridylium compounds (Togashi a al., 1990 De Gray etal., 1991 Kanazawa and Ashida, 1991 Petty etal., 1992). 

Pyrolysis of more complex molecules proceeds via production of free radicals. Then formula (4.5) fails, because reactions of creation and recombination of radicals in these systems are irreversible. Therefore, the steady-state concentration of active particles in these systems depends on conditions of pyrolysis, determining the first or the second order of recombination of active particles, and is governed by the following equations [8]... 

From the above reasoning it may be concluded that the quantitative theory as it stands today gives the opportunity to provide an exhaustive description of the chemical structure of the products of free-radical copolymerization of any number of monomers m. 

In the model under consideration all macromolecules of fixed length Z have the same composition X(Z). However, owing to the substantial polydispersity of the products of free-radical copolymerization for length (even for polymer specimens obtained under low conversions), their composition distribution ... 

The objective of this chapter is to compile work related to the beginning of sonochemical research and its extension to the aqueous solutions of metal ions. Ultrasound propagation in aqueous salt solutions leads to the hydrolysis, reduction, complexation, decomplexation and crystallization. Such works from different laboratories, along with the effect of dissolved gases on the production of free radicals in water and aqueous solutions upon sonication has been reviewed in this chapter. The generation of turbidity, due to the formation of metal hydroxides and changes in the conductivity of these aqueous solutions, carried out in this laboratory, has also been reported, to give firsthand information of the ultrasound interaction of these solutions. 

Principle The production of free radicals is measured with luminol (5-amino-2,3-dihydrophthalazine-1,4-dione), that is employed to amplify... 

Potent inhibition of PGH synthase-dependent BP oxidation by antioxidants suggests that the quinones are products of free radical reactions (18 ). ... 

J. Kroh, B.C. Green, and J.W.J. Spinks, Electron paramagnetic resonance (EPR) studies on the production of free radicals in hydrogen peroxide at liquid nitrogen temperature. J. Am. Chem. Soc. 83, 2201-2202 (1961). 

Bound rubber in an unvulcanised carbon black-rubber mix. It results from the production of free radicals in the mastication of rubber these radicals attach themselves chemically to the particles of carbon black and form a proportion of carbon gel which is insoluble in the usual rubber solvents. 

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