EPR STUDY OF WOOL IRRADIATED WITH BLUE LIGHT

Abstract— Wool fibres were exposed to visible light in the blue range. The free radicals created by the illumination were studied using electron paramagnetic resonance. It is shown that by control of the light intensity and frequency it is possible to get considerable insight into the mechanism of the creation and the decay of the free radicals. The radical population under the above conditions appears to consist of an initial stable radical insensitive to radiation, and three other radicals, two of which follow decay kinetics considerably different from that of the remaining free radical. All the latter three radicals are probably caused by N–H or C–H bond scission.
The kinetics of radicals in irradiated proteins is discussed. It is shown that the mechanisms previously suggested in the literature are inadequate to account for the form of the experimental curve describing the number of radicals vs. time in irradiated protein. A new mechanism is suggested in which the decayed radicals form sites immune to further irradiation. Such a mechanism is shown to be consistent with the experimental curves. The kinetics of the decay of radicals after the cessation of illumination is examined in detail. It is found that in the case of irradiated keratin the mechanisms assuming first order decay are inconsistent with the experimental results, while the assumption of second order decay for two different species of radicals yields results consistent with the experimental evidence.