Neutron-induced Free Radicals in Oriented DNA

Summary Samples of oriented DNA containing 30 per cent water were irradiated with neutrons at 77 K. The electron spin resonance (e.s.r.) spectra obtained from these irradiated DNA samples show that the formation of radicals is different when the incident neutrons are parallel or perpendicular to the DNA helix. When the incident neutrons are perpendicular to the DNA helix the e.s.r. spectra of thymine and guanine ionic radicals (T−·, G+·) are observed. An additional e.s.r. spectrum corresponding to the hydrogen addition radical on thymine (TH·) is observed when the incident neutrons are parallel to DNA helix. The TH· radical appears to be formed by protonation of T−·.