Radiation-Induced Free Radical Reactions

Abstract

The irradiation of aqueous systems gives rise to the formation of both transient radical species (OH^•, e ^¯_aq , H^•, O$\left( {O_2^{\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\cdot}$}}{ - } }} \right)$ etc, Spinks and Woods, 1990) and more persistent products (Czapski et al., 1992) whose chemical reactivity is of great importance within the area of free radical chemistry and biology. Indeed, for thechemical study of free radicals the technique of radiolytic generation such as in pulse radiolysis is probably the method of choice, since the identity and yield of individual radical types formed are extremely well known. Oxygen radicals such as$^.OH$ and O$\left( {O_2^{\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\cdot}$}}{ - } }} \right)$have been intensively studied and both kinetic and thermodynamic aspects of their reactions have been extensively tabulated (Wardman and Ross, 1991). A further aspect of this approach is that a great many relevant organic radicals may also be produced and studied by radiolysis (von Sonntag, 1987) and this provides a basis for the understanding of more complex free radical reactions in biological systems such as DNA strand breakage, lipid peroxidation and protein damage. Indeed, now that the initial reactions of oxygen radicals with biological targets are becoming well characterised, the emphasis is turning to the study of subsequent free radical transformations such as those that allow radical migration in proteins (Prutz et al., 1982), the formation of cross-links between macromolecules such as proteins and DNA (Schuessler and Jung, 1989), the formation of long-lived reductive moieties in proteins (Simpson et al., 1992) and the mechanisms of antioxidant action (Neta et al., 1989).