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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Effect of Proton Transfer on the Anionic and Cationic Pathways of Pyrimidine Photodimer Cleavage. A Computational Study
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Effect of Proton Transfer on the Anionic and Cationic Pathways of Pyrimidine Photodimer Cleavage. A Computational Study

机译：质子转移对嘧啶光二聚体裂解的阴离子和阳离子途径的影响。计算研究

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摘要

Proton exchange between pyrimidine photodimers and their environment may have a profound impact on DNA photorepair. On the basis of B3L YP/6-31G~* and AM1 calculations, we present the first computational study of the influence of protonation and deprotonation on the splitting reactions of pyrimidine dimer ion radicals. While proton transfer from a complementary adenine to a Pyr~(<>) Pyr anion is calculated to be endothermic and, therefore, is unlikely in DNA, protonation of the dimer anion is feasible in polar solution. Cleavage of both nonprotonated and protonated dimer anions is a two-step reaction where C5-C5' bond splitting is followed by cleavage of the C6-C6' bond. However, the calculated activation barriers for the splitting of the protonated species are considerably higher than those for the corresponding nonprotonated anion. Proton transfer from a pyrimidine dimer cation to adenine is found to be energetically favorable. The opening of the cyclobutane ring in the dimer cation and its deprotonated state proceeds in reverse order: the C6-C6' bond is broken first, followed by splitting of the C5-C5' bond. Although the splitting of the dimer cation is activationless, rather high activation barriers are predicted for the cleavage of its deprotonated form in the gas phase. However, this barrier decreases substantially in a polar medium and, therefore, deprotonation of the dimer cation does not prevent its splitting in DNA nor in polar solution.
机译：嘧啶光二聚体与其环境之间的质子交换可能会对DNA光修复产生重大影响。在B3L YP / 6-31G〜*和AM1计算的基础上，我们首次进行了质子化和去质子化对嘧啶二聚体离子自由基分裂反应影响的计算研究。尽管质子从互补的腺嘌呤转移至Pyr_（Pyr）阴离子是吸热的，因此在DNA中不太可能发生，但二聚阴离子的质子化在极性溶液中是可行的。非质子化和质子化的二聚体阴离子的裂解是两步反应，其中C5-C5'键分裂，随后裂解C6-C6'键。但是，计算出的用于质子化物质分裂的活化势垒比相应的非质子化阴离子要高得多。发现从嘧啶二聚阳离子到腺嘌呤的质子转移在能量上是有利的。环丁烷环在二聚阳离子中的打开及其去质子化状态的顺序相反：首先破坏C6-C6'键，然后裂解C5-C5'键。尽管二聚阳离子的分裂是无活化的，但是对于气相中其去质子化形式的裂解，预计会有较高的活化势垒。然而，该屏障在极性介质中显着降低，因此，二聚阳离子的去质子化不能阻止其在DNA或极性溶液中分裂。

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