ESR study of irradiated 1:1 co-crystals of 9-ethyladenine:5,5-diethylbarbituric acid (barbital) at 295 K

Crystals of the 1:1 complex of 9-ethyladenine:5,5-diethylbarbituric acid have been irradiated with 4.0 MeV electrons at 295 K and examined using electron spin resonance spectroscopy. Three radical species were observed. One of these was identified to be the barbital ethyl-abstraction radical (I) with the main part of the unpaired spin density at C5 interacting with two β protons. A second species is the H adduct at the C2 position of 9-ethyladenine (II). The third radical is tentatively assigned to the corresponding C8 H adduct (III). The relative contribution of each of these radicals to the total resonance is discussed and compared to that for the isolated compounds. It is concluded that the present data give no evidence for horizontal or vertical charge transfer between the bases