Spin trapping as tool for investigating radiation induced free radicals in biologically active molecules

Since from the second half of the last century the spin trapping has found wide applications in chemistry, biology and medicine [1]. Of particular interest are the studied of the free radicals induced in biologically active molecules, such as DNA and proteins, when they are exposed to ionizing radiation. Their characterization allows to investigate the radiation-induced primary processes inside living cells. Indeed, ionizing radiations produce many kinds of free radicals through direct action; radicals can be formed also by indirect actions. However, the direct detection of these radicals is hard to obtain as they have a too short lifetime and this makes difficult to record them by conventional electron spin resonance (ESR) technique. This limitation can be overcome by means of spin-trapping method wherein these short-lived free radicals are converted using a diamagnetic scavenger (the spin trap) to longer-lived radicals (the spin adducts), which can be conveniently investigated by means of ESR. Here, we review a combined method of ESR and spin trapping to identify free radicals induced by direct ionization as well as OH-radical reactions in nucleic-acid related and protein-related compounds. ESR combined with spin trapping remains a useful method for clarifying these processes in a living organism.