3] Free radical initiators as source of water- or lipid-soluble peroxyl radicals

Abstract

Publisher Summary This chapter discusses the role of free radical initiators as source of water- or lipid-soluble peroxyl radicals. Free radicals can be generated in either an aqueous or the lipid phase as required by using water-soluble 2,2′-Azo-bis(2-amidinopropane) dihydrochloride (AAPH) or lipid-soluble 2,2′-azobis(2,4-dimethylvaleronitrile) (AMVN). Admittedly, such azo compounds are not present in biological systems, but they are useful tools for studying quantitatively (1) the damage induced by free radicals on biological and related molecules and membranes and (2) the inhibition in model systems. The advantages are that the radicals can be generated at a constant rate at a specific site and that the rate of radical flux can be measured and controlled. Obviously, the most important characteristic of the free radical reaction is that it proceeds by a chain mechanism—that is, the rate of the overall reaction or the extent of damage can be quite significant even if the rate of initial radical formation or the amount of attacking radical is very small. It is, therefore, quite important to know how long the kinetic chain lasts. The chain length can never be known without knowing the rate of chain initiation or the radical flux. In fact, in the in vitro experiment, the kinetic chain length is as long as 100 in the oxidation of erythrocyte membranes induced by AAPH. Another advantage in using azo compounds is that, unlike peroxides, they are not explosive and can be handled easily and safely.