Free Radical Formation in Single Crystals of 9-Methyladenine X-Irradiated at 10 K. An Electron Paramagnetic Resonance and Electron Nuclear Double Resonance Study

• Published in: Radiation research 1995-12, Vol.144 (3), p.258-265
• Main Authors: Hole, Eli O., Sagstuen, Einar, Nelson, William H., Close, David M.
• Format: Article
• Language: English
• Subjects: Adenine - analogs & derivatives; Adenine - chemistry; Adenine - radiation effects; Amino radical; Anions; Biological and medical sciences; Crystallization; Crystals; Electron Spin Resonance Spectroscopy - methods; Electrons; Free Radicals; Fundamental and applied biological sciences. Psychology; Hydrogen; Irradiation; Magnetic Resonance Spectroscopy - methods; Miscellaneous; Models, Molecular; Molecular and cellular biology; Molecular genetics; Molecular Structure; Protons; Single crystals; Space life sciences; Temperature; Tensors; Thermodynamics; X-Rays
• ISSN: 0033-7587; 1938-5404
• DOI: 10.2307/3578944

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-methyladenine at 10 K. These are: MA1, 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.