Identification of a monoradical species from the EPR study of its radical pair in irradiated 3-hydroxyxanthine single crystals


A model for a monoradical species formed in 77-K X-irradiated 3-hydroxyxanthine has been determined from a study of its radical pair EPR spectra. The monoradical and radical pairs were stable at room temperature and were studied at that temperature. The radical was found to be a π-type nitrogen-centered species with hyperfine values of A∥ = 9.7 ± 1 G and A⊥ approximately 1 G and g-tensor principal values of 2.0093, 2.0081., and 2.0029. The spin density on the nitrogen atom was calculated to be between 0.15 and 0.21, and this was compared to theoretical values from Hückel molecular orbital calculations. A radical model that is consistent with these data is hydrogen abstraction from N(1). The average distance between radicals forming the pair is 6.75 Å and the crystalline interplane spacing is approximately 3.7 Å. © 1981.

Publication Title

Journal of Magnetic Resonance (1969)