ESR of nitroxide radical and radical pair species in irradiated 3-hydroxyxanthine single crystals
Single crystal samples of the carcinogenic purine-N-oxide, 3-hydroxyxanthine hydrochloride, have been irradited with ultraviolet (uv) light and studied by ESR techniques at room temperature. One radical species was detected with g-factor principal values of 2.0105, 2.0010, and 2.0050 and nitrogen hyperfine tensor elements of 14.2, 1.2, and 2.9 G. These date are consistent with the interpretation that a hydrogen atom has been abstracted from the hydroxyl group in the molecule and a nitrogen-centered radical is formed. The unpaired spin density in N(3) was found to be 0.24. This radical was also formed when the sample was uv-irradiated at 77 K. Pairwise trapped radical species have been observed in single-crystal samples of 3-hydroxyxanthine hydrochloride when they are irradiated by X rays or high-energy electrons. Two radical pair species, I and II, have been studied at 300 K. The ESR data of radical pairs I and II were characteristic of the interaction between two identical nitrogen-centered radicals. The dipole-dipole splitting constant, Δ(11) of radical pairs I and II, was respectively, 256.3 and 256.3 G, and the r(eff) distance was 6.02 Å for both pairs.
Jahan, M., & Alexander, C. (1978). ESR of nitroxide radical and radical pair species in irradiated 3-hydroxyxanthine single crystals. Radiation Research, 74 (2), 251-264. https://doi.org/10.2307/3574886