National d'Histoire Naturelle, INSERM U201, CNFtS ERA 951, 61 rue Buffon, 75005 PARIS After a long controversy, t h e involvement of f r e e radicals i n some normal or pathological biological processes is now recognized'), mainly through E.S.R. spectroscopy. such as flash photolysis and pulse radiolysis*) have made considerable contributions i n t h e study and i d e n t i f i c a t i o n of these transient species. Radicals absorb at wavelengths different f'rom t h e i r parent molecule and thus f a s t kinetic spectrophotometry i s the main detection technique. and femtoseconds (lo-", 10-15s).
Potent techniques
Time resolution now ranges from seconds t o nanoseconds (10-9s) and recently t o pico-Conductivity, polarography, emission, electron spin resonance, nuclear magnetic resonance and resonance Raman spectroscopies are a l s o used as monitoring techniques a f t e r a pulsed irradiation.
free radicals which can be beneficial as i n photosynthesis of plants or deleterious as i n the damage of nucleic acids and proteins. reactions which a r e not radiation-induced, by selectively generating c e r t a i n types of radicals present i n biological systems. '.butions t o the Chemistry of Biology and Medicine, (1983) Pergamon Press.