Hole E O, Nelson W H, Sagstuen E, Close D M
Department of Physics, University of Oslo, Norway.
Radiat Res. 1998 Feb;149(2):109-19.
Anhydrous single crystals of cytosine hydrochloride (protonated at N3) have been X-irradiated at 10 K and studied using K-band EPR, ENDOR and FSE spectroscopy. At least seven radicals were present at 10 K after X irradiation with a dose of about 150 kGy. Two different protonation states of the one-electron reduced cytosine cation were observed: an amino-protonated species (R1) and the pristine one-electron reduced species (R2) with zero net charge. Apparently three deprotonated versions of the one-electron oxidized cytosine cation were formed: the amino-deprotonated cation (R3), an N3-deprotonated cation (R4) and an N1-deprotonated cation (R5). Finally, two products formed by net hydrogen addition to the cytosine base were observed: a C5 hydrogen-addition radical (R6) and a C6 hydrogen-addition radical (R7). The crystalline lattice of cytosine hydrochloride is characterized in part by a cytosine base initially protonated at the N3-position, thus forming a cytosine base cation, and in part by an extended network of hydrogen bonding involving the chlorine anions. Proton transfer properties of pristine one-electron oxidation and reduction base products in this lattice are discussed and are suggested as explanations of the unusual multitude of positions for deprotonation of the one-electron oxidized species as well as for the two protonation states of the reduction product observed. The magnetic parameters for the amino-protonated species R1 agree well with those extracted from previous studies of cytosine derivatives in frozen solutions and in various glasses.
已在10 K下对无水盐酸胞嘧啶单晶（N3质子化）进行X射线辐照，并使用K波段电子顺磁共振（EPR）、电子核双共振（ENDOR）和场扫电子自旋共振（FSE）光谱进行研究。在用约150 kGy剂量的X射线辐照后，在10 K时至少存在七种自由基。观察到单电子还原胞嘧啶阳离子的两种不同质子化状态：氨基质子化物种（R1）和净电荷为零的原始单电子还原物种（R2）。显然形成了单电子氧化胞嘧啶阳离子的三种去质子化形式：氨基去质子化阳离子（R3）、N3去质子化阳离子（R4）和N1去质子化阳离子（R5）。最后，观察到通过向胞嘧啶碱基净加氢形成的两种产物：C5加氢自由基（R6）和C6加氢自由基（R7）。盐酸胞嘧啶的晶格部分特征在于最初在N3位置质子化的胞嘧啶碱基，从而形成胞嘧啶碱基阳离子，部分特征在于涉及氯阴离子的扩展氢键网络。讨论了该晶格中原始单电子氧化和还原碱基产物的质子转移性质，并将其作为对单电子氧化物种去质子化异常多位置以及观察到的还原产物两种质子化状态的解释。氨基质子化物种R1的磁参数与先前在冷冻溶液和各种玻璃中对胞嘧啶衍生物研究中提取的参数非常吻合。
