Proton transfer induced SOMO-to-HOMO level switching in one-electron oxidized A-T and G-C base pairs: a density functional theory study.
Proton transfer induced SOMO-to-HOMO level switching in one-electron oxidized A-T and G-C base pairs: a density functional theory study.
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DOI：
10.1021/jp5028004
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发表时间：
2014-05-22
期刊：
影响因子：
--
通讯作者：
Sevilla MD
中科院分区：
文献类型：
--
作者：
Kumar A;Sevilla MD
在本研究中，我们表明，对于单电子氧化的A-T或G-C碱基对，单占据分子轨道（SOMO）位于A或G上，并且能量低于双占据最高占据分子轨道（HOMO）位于嘧啶、T或C上。这将导致嘧啶碱基的第二次电离，产生三重态双自由基双阳离子（A·+-T·+）和（G·+-C·+）。在碱基间质子转移时，SOMO和HOMO能级切换，第二次氧化被重定向到G和A。对于G-C，双氧化单线态G（-H）+-C（H+）比三重态（G·+-C·+）稳定，而对于A-T，三重态（A·+-T·+）能量最低。研究表明，A-T碱基对的双电离产生的三重态二价双自由基比质子转移的三重态或单重态更稳定;而G-C碱基对的双电离产生的质子转移的双氧化单重态G（-H）+-C（H+）更稳定，在鸟嘌呤上具有两种氧化作用。在DNA中，A-T和G-C都存在，多重氧化将转移到鸟嘌呤碱基上。
In the present study, we show that for one-electron oxidized A-T or G-C base pairs the singly occupied molecular orbital (SOMO) is located on A or G and is lower in energy than the doubly occupied highest-occupied molecular orbital (HOMO) localized to the pyrimidines, T or C. This directs second ionizations to the pyrimidine bases resulting in triplet state diradical dications, (A•+-T•+) and (G•+-C•+). On interbase proton transfer, the SOMO and HOMO levels switch and the second oxidation is redirected to G and A. For G-C, the doubly oxidized singlet G(-H)+-C(H+) is more stable than its triplet (G•+-C•+); however, for A-T, the triplet (A•+-T•+) lies lowest in energy. The study demonstrates that double ionization of the A-T base pair results in a triplet dication diradical, which is more stable than the proton-transferred triplet or singlet species; whereas, double ionization of the G-C base pair, the proton transferred doubly oxidized singlet, G(-H)+-C(H+), is more stable and has both oxidations on guanine. In DNA, with both A-T and G-C, multiple oxidations would transfer to the guanine base alone.
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