Hole E O, Sagstuen E, Nelson W H, Close D M
Department of Physics, University of Oslo, Blindern, Norway.
Radiat Res. 1995 Dec;144(3):258-65.
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.
9-甲基腺嘌呤的单晶在10 K和65 K下进行X射线辐照，并在10 K至290 K的温度范围内使用K波段电子顺磁共振（EPR）、电子核双共振（ENDOR）和场扫电子核双共振（FSE）技术进行研究。在10 K时，9-甲基腺嘌呤中稳定存在三种主要自由基。它们分别是：MA1，腺嘌呤阴离子，可能在N3处质子化；MA2，通过从9-甲基净提取氢形成的物种；以及MA3，通过向腺嘌呤部分的C8净加氢形成的自由基。自由基MA1在约80 K时衰变，可能转化为C2 H加合物（MA4）。另外两个物种（MA2、MA3）在室温下稳定。在10 K时的EPR谱中明显存在第五种自由基物种，但ENDOR无法检测到。该物种在200 K以上衰变（可能转化为MA3），仍未鉴定出来。室温下的自由基数量如先前作者所述。根据氢键方案和分子堆积相互作用讨论了9-甲基腺嘌呤中自由基形成的机制。
