The reaction of hydrogen atoms with thymine and DNA.

Electron spin resonance (ESR) spectra of radiation-damaged DNA and its constituent bases have been described in several recent studies.1-5 Distinct ESR signals were found in these compounds after they had been subjected to either highenergy or ultraviolet radiation. Through a detailed correlation of the spectra of UV-irradiated DNA and thymine, Pershan et al.3 have recently established that the same radical is present in irradiated DNA and irradiated thymine. Ehrenberg et al.2 and Gordy et al.5 have reached similar conclusions on y-irradiated thymine, thymidine, and DNA. This main radical is believed to be formed through a secondary process in which a hydrogen atom adds to carbon (6) of the pyrimidine ring: 0 0