Site specific free radical generation

The hydroxylation of single- and double-stranded DNA are changes characteristic of free-radical attack (reviewed by Winyard et al., 1992). An important mechanism is site-specific OH generation, catalysed by iron bound to... 

Excessive iron in specific tissue sites is associated with development of infection, neoplasia, cardiomyopathy, arthropathy, and a variety of endocrine and neurological diseases. Chelators, which remove excess iron, while not depriving cells of the essential iron needed for normal metabolism and prevent iron from participating in the generation of harmful free radicals, are potential drugs. We mention a few examples only. 

Radical generation at inappropriate sites may thus lead to protein destruction since they are also critical targets for free radical attack, both intracellularly and extracellularly. Proteins may be directly damaged, by specific interactions of oxidants or free radicals with particularly susceptible amino acids. Several amino acyl constituents crucial for a protein s function are particularly vulnerable to radical damage (Fig. 4) [21,22]. 

The individual specific rate and adsorption equilibrium constants are defined in Table 1. In Equations (4) and (5) [Sitesjrefer to the available concentration of sites for adsorption on the Ti02 film, [O2] to the liquid phase oxygen concentration, [M] to the concentration of water, atomic or free radical species, reactor walls or other surfaces trapping atomic chlorine, and Rg to the superficial rate of electrons and holes generation. 

When a free radical is formed and held tightly within a molecule, reactions of quite high site specificity (regioselectivity) may be observed. The free radical may be generated from another functional group in the molecule, but the result is the substitution at a centre that in a formal sense has the characteristics of a hydrocarbon. Such reactions are observed in the photolysis of nitrite esters (RONO) (the Barton reaction), the... 

Three major classes of photoreactive compounds have been used to label specific sites of proteins nitrenes, carbenes, and free radicals. Carbenes, generated by photolysis of diazo derivatives, are highly reactive and relatively nonselective in their target sites. Nitrenes, formed by photoactivation of azido derivatives, are less reactive than carbenes and more electrophilic, exhibiting a preference... 

---