Intermolecular Transfer of Radiation Energy at 77°K: An ESR Study of Irradiated Mixtures of Macromolecules and Oxidized Penicillamine

Electron spin resonance studies have been carried out on dry molecular mixtures containing the disulfide, oxidized penicillamine, and a macromolecule (Sephadex, DEAE-Sephadex, CM-Sephadex, Thiogel, or DNA). The samples were irradiated in vacuum with x-rays at 77°K and measurements were carried out immediately after irradiation and after heating of the samples for 10 minutes at 333°K. All electron spin resonance spectra were recorded at 77°K. The radical yields after irradiation at 77°K were in all the mixtures higher than expected from the composition. The "excess radicals" were in most cases localized on the penicillamine molecules and the number of macromolecule radicals was close to that expected. In the mixtures of CM-Sephadex and oxidized penicillamine, however, the excess radicals were localized on the macromolecules. Heat-treatment of the samples resulted in a considerable increase in the number of penicillamine radicals while the majority of the unpaired spins on the macromolecules disappeared. On the basis of the results it is suggested that in certain cases up to 60% of the total transfer of radiation energy from the macromolecules to the disulfide observed after heating had actually occurred during irradiation at 77°K. To account for the transfer of unpaired spins taking place during the heating, 40-100% of the macromolecule radicals which disappeared had to interact with the disulfide.