Density Functional Theory Studies of the Extent of Hole Delocalization in One-Electron Oxidized Adenine and Guanine Base Stacks
Density Functional Theory Studies of the Extent of Hole Delocalization in One-Electron Oxidized Adenine and Guanine Base Stacks
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DOI：
10.1021/jp200537t
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发表时间：
2011-05-05
影响因子：
3.3
通讯作者：
Sevilla, Michael D.
中科院分区：
文献类型：
--
作者：
Kumar, Anil;Sevilla, Michael D.
本研究研究了单电子氧化腺嘌呤(A)和鸟嘌呤(G)堆叠中空穴离域的程度，并表明预测了A-堆叠中具有空穴离域特征的新红外振动带。A-堆的几何形状(A(i)；采用M06-2X/6-31G*方法对中性态和单电子氧化态的g -stack （GG和GGG）和B-DNA构象进行了优化。最高已占据分子轨道（HOMO）定位于a -叠的单个腺嘌呤上，GG和GGG叠的单个鸟嘌呤上，位于叠的5'位点。单电子氧化（从中性的A和g层HOMO中去除一个电子）会产生一个“空穴”。Mulliken电荷分析表明，这些“空穴”在A-stack中的两到三个腺嘌呤碱基上离域。计算出的A(i)（中心点+）（i = 2-8）的自旋密度分布也显示出空穴主要在两个腺嘌呤碱基上离域，在邻近的碱基上也有一些离域。对于GG和GGG自由基阳离子，发现空穴定位在堆栈中的单个G上。GG和GGG的氢氟碳含量计算值与实验值吻合较好。此外，从振动频率分析中发现，中性和相应的单电子氧化腺嘌呤堆叠的红外光谱有很大的不同。A(2)（中心点+）的红外光谱在900和1500 cm（-1）之间有强烈的红外峰，这在中性A2堆栈中不存在。腺嘌呤层中A(2)（中心点+）的存在在1100 cm（-1）处有一个特征性的强峰。因此，红外光谱和拉曼光谱具有监测A叠中空穴离域程度的潜力。
This study investigates the extent of hole delocalization in one-electron oxidized adenine (A) and guanine (G) stacks and shows that new IR vibrational bands are predicted that are characteristic of hole delocalization within A-stacks. The geometries of A-stacks (A(i); i = 2-8) and G-stacks (GG and GGG) in their neutral and one-electron oxidized states were optimized with the bases in a B-DNA conformation using the M06-2X/6-31G* method. The highest occupied molecular orbital (HOMO) is localized on a single adenine in A-stacks and on a single guanine in GG and GGG stacks located at the 5'-site of the stack. On one-electron oxidation (removal of an electron from the HOMO of the neutral A- and G-stacks) a "hole" is created. Mulliken charge analysis shows that these "holes" are delocalized over two to three adenine bases in the A-stack. The calculated spin density distribution of A(i)(center dot+) (i = 2-8) also showed delocalization of the hole predominantly on two adenine bases, with some delocalization on a neighboring base. For GG and GGG radical cations, the hole was found to be localized on a single G in the stack. The calculated HFCCs of GG and GGG are in good agreement with the experiment. Further, from the vibrational frequency analysis, it was found that IR spectra of neutral and the corresponding one-electron oxidized adenine stacks are quite different. The IR spectra of A(2)(center dot+) has intense IR peaks between 900 and 1500 cm(-1) that are not present in the neutral A2 stack. The presence of A(2)(center dot+) in the adenine stack has a characteristic intense peak at similar to 1100 cm(-1). Thus, IR and Raman spectroscopy has potential for monitoring the extent of hole delocalization in A stacks.