Radioprotective Effects of Dimethyl Sulfoxide in Golden Hamster Embryo Cells Exposed to γ Rays at 77 K: I. Radical Formation as Studied by Electron Spin Resonance

Formation of free radicals in golden hamster embryo (GHE) cells in the frozen living state by γ irradiation has been studied by electron spin resonance spectroscopy at 4.2 and 77 K. The relative yields of H atoms, OH radicals, and organic radicals trapped in the irradiated GHE cells are 12, 72, and 16%, respectively, of total radical yields. When dimethylsulfoxide (DMSO) is added to GHE cells at 77 K, a large quantity of ${}^{\bullet}{\rm CH}{}_{2}{\rm SOCH}_{3}$ radicals (DMSO radicals) are formed after γ irradiation. The yields of OH radicals are not affected by the addition of DMSO. When the GHE cell-DMSO mixtures are irradiated with γ rays at 77 K and then warmed to 111 K, the OH radicals decay, whereas the DMSO radicals do not increase complementarily. Moreover, the decay rates of the OH radicals at 111 K do not depend upon the concentration of DMSO. Thus OH radicals do not react with DMSO during warming of the irradiated sample. When H atoms are produced by γ irradiation of acid ice at 60 K, the dec...