A brief account on radiation chemical studies of antioxidants : Examples from natural phenols, sulfur and selenium compounds

Reactive oxygen species (ROS) is a collective term used for a group or oxidants, which are either free radicals or molecular species capable of generating free radicals. Excessive production of ROS in living cells is a pathological condition known as oxidative stress. These species, depending on their reactivity and oxidizing ability, participate in a variety of chemical reactions and their reactions often cause irreversible chemical changes In biomolecules. Antioxidants are employed to protect the biomolecules from the damaging effects of such free radicals, primarily by their direct reaction. Although free radical reactions involving ROS with antioxidants are studied by several Indirect methods, their direct monitoring is possible only by employing fast kinetic methods. Radiation chemistry of aqueous solutions and pulse radiolysis technique in particular has been found to be well suited to probe such reactions. Thus in this article, contributions from radiation chemistry section of BARC on the reactions of biologically important free radicals involved in oxidative stress with antioxidants have been discussed. Reactions or such radicals with curcumin, an antioxidant from turmeric, which was studied extensively In this laboratory using pulse radiolysis technique, has also been presented. In the last three decades, the section has contributed significantly to the understanding of sulfur and selenium based antioxidants. A few recent highlights on these systems using pulse radiolysis have also been compared.