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首页> 外文期刊>Chemistry - A European Journal >Hydroxyl Radical Reactions with Adenine: Reactant Complexes, Transition States, and Product Complexes
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Hydroxyl Radical Reactions with Adenine: Reactant Complexes, Transition States, and Product Complexes

机译：腺嘌呤的羟基自由基反应：反应物配合物，过渡态和产物配合物

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摘要

In order to address problems such as aging, cell death, and cancer, it is important to understand the mechanisms behind reactions causing DNA damage. One specific reaction implicated in DNA oxidative damage is hydroxyl free-radical attack on adenine (A) and other nucleic acid bases. The adenine reaction has been studied experimentally, but there are few theoretical results. In the present study, adenine dehydrogenation at various sites, and the potential-energy surfaces for these reactions, are investigated theoretically. Four reactant complexes [AOH]. have been found, with binding energies relative to A+OH. of 32.8, 11.4, 10.7, and 10.1 kcal mol−1. These four reactant complexes lead to six transition states, which in turn lie +4.3, −5.4, (−3.7 and +0.8), and (−2.3 and +0.8) kcal mol−1 below A+OH., respectively. Thus the lowest lying [AOH]. complex faces the highest local barrier to formation of the product (AH).+H2O. Between the transition states and the products lie six product complexes. Adopting the same order as the reactant complexes, the product complexes [(AH)H2O]. lie at −10.9, −22.4, (−24.2 and −18.7), and (−20.5 and −17.5) kcal mol−1, respectively, again relative to separated A+OH.. All six A+OH. → (AH).+H2O pathways are exothermic, by −0.3, −14.7, (−17.4 and −7.8), and (−13.7 and −7.8) kcal mol−1, respectively. The transition state for dehydrogenation at N6 lies at the lowest energy (−5.4 kcal mol−1 relative to A+OH.), and thus reaction is likely to occur at this site. This theoretical prediction dovetails with the observed high reactivity of OH radicals with the NH2 group of aromatic amines. However, the high barrier (37.1 kcal mol−1) for reaction at the C8 site makes C8 dehydrogenation unlikely. This last result is consistent with experimental observation of the imidazole ring opening upon OH radical addition to C8. In addition, TD-DFT computed electronic transitions of the N6 product around 420 nm confirm that this is the most likely site for hydrogen abstraction by hydroxyl radical.
机译：为了解决衰老，细胞死亡和癌症等问题，重要的是要理解引起DNA损伤的反应背后的机制。涉及DNA氧化损伤的一种特定反应是对腺嘌呤（A）和其他核酸碱基的羟基自由基攻击。已经通过实验研究了腺嘌呤反应，但是理论上的结果很少。在本研究中，理论上研究了在各个位置的腺嘌呤脱氢以及这些反应的势能表面。已发现四种反应物配合物[AOH] 。，其结合能相对于A + OH 。为32.8、11.4、10.7和10.1 cal mol -1 。这四个反应物络合物导致六个过渡态，它们依次位于A +以下+ 4.3，-5.4，（-3.7和+0.8）和（-2.3和+0.8）kcal mol -1 OH 。。因此，最低价的[AOH] 。络合物面临形成产物（AH）。 + H 2 O的最高局部障碍。在过渡状态和产品之间存在六个产品复合体。产物络合物[（AH）H 2 O] 采用与反应物相同的顺序。位于-10.9，-22.4，（-24.2和-18.7） ，和（-20.5和-17.5）kcal mol -1 分别相对于分离的A + OH 。。所有六个A + OH 。→（AH）。 + H 2 O路径都放热-0.3，-14.7（（-17.4和-7.8）和（-13.7和-7.8）kcal mol -1 。 N 6 处的脱氢过渡态处于最低能量（相对于A + OH 。。-5.4 kcal mol -1 ），并且因此，很可能在该位置发生反应。这一理论预测与观察到的OH自由基与芳族胺的NH 2 基的高反应性相吻合。然而，在C 8 位点反应的高势垒（37.1 kcal mol -1 ）使C 8 脱氢的可能性很小。最后的结果与在OH自由基加成到C 8 时咪唑开环的实验观察一致。此外，TD-DFT计算得出的N 6 产物在420nm附近的电子跃迁证实了这是最有可能被羟基自由基夺氢的位置。

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