Radicals in irradiated monocrystals of the base-pair complex 9-ethyl adenine: 1-methyl uracil.

SummaryRadical formation in monocrystals of equimolar complexes of 9-ethyl adenine: 1-methyl uracil by irradiation with X-rays was investigated at 77 K and 300 K using e.s.r.-spectroscopy at 9·5 GHz and 35 GHz. Five different types of spectrum were identified, which corresponded to spectra of the irradiated components. A hydrogen abstraction radical (I and III) and a hydrogen addition radical (II and IV) were assigned to each of the two constituents. The fifth species, with an unidentified singlet after irradiation at 77 K, has also been found in irradiated single crystals of 9-ethyl adenine. By bleaching with U.V.-light or heating to about 150 K, it is decomposed irreversibly. After a crystal irradiated at 77 K is warmed to room temperature only pyrimidine radicals I and II are left. At 77 K the two types of radical (I and II) in 1-methyl uracil are present in addition to the singlet line; at 300 K the addition radicals (II and IV) predominate in comparable proportions, but the abstraction radicals (I an...