FREE-RADICAL FORMATION IN SINGLE-CRYSTALS OF 9-METHYLADENINE X-IRRADIATED AT 10 K - AN ELECTRON-PARAMAGNETIC-RESONANCE AND ELECTRON-NUCLEAR DOUBLE-RESONANCE STUDY

Single crystals of 9-methyladenine were X-irradiated at 10 K and at 65 K and were studied using K-band EPR, ENDOR and field-swept ENDOR (FSE) techniques in the temperature range 10 K to 290 K, Three major radicals are stabilized in 9-methyl-adenine at 10 K, These are: MAI, the adenine anion, probably protonated at N3; MA2, the species formed by net hydrogen abstraction from the 9-methyl group; and MA3, the radical formed by net hydrogen addition to C8 of the adenine moiety. Radical MA1 decayed at about 80 K, possibly into the C2 H adduct (MA4), The other two species (MA2, MA3) were stable at room temperature, A fifth radical species was clearly present in the EPR spectra at 10 K but was not detectable by ENDOR, This species, which decayed above 200 K (possibly into MA3), remains unidentified. The radical population at room temperature is as described by previous authors, The mechanisms for radical formation in 9-methyladenine are discussed in light of the hydrogen bonding scheme and molecular stacking interactions. (C) 1995 by Radiation Research Society