School of Chemistry and Chemical Engineering, Shandong University , Jinan, 250100, People's Republic of China.
J Phys Chem B. 2013 Sep 19;117(37):10698-710. doi: 10.1021/jp4042149. Epub 2013 Sep 6.
We present here a theoretical investigation of the structural and electronic properties of di-ionized GG base pairs (G(•+)G(•+),G(-H1)(•)G(•+), and G(-H1)(•)G(-H1)(•)) consisting of the guanine cation radical (G(•+)) and/or dehydrogenated guanine radical (G(-H1)(•)) using density functional theory calculations. Different coupling modes (Watson-Crick/WC, Hoogsteen/Hoog, and minor groove/min hydrogen bonding, and π-π stacking modes) are considered. We infer that a series of G(•+)G(•+) complexes can be formed by the high-energy radiation. On the basis of density functional theory and complete active space self-consistent (CASSCF) calculations, we reveal that in the H-bonded and N-N cross-linked modes, (G(•+)G(•+))WC, (G(-H1)(•)G(-H1)(•))WC, (G(-H1)(•)G(-H1)(•))minI, and (G(-H1)(•)G(-H1)(•))minIII have the triplet ground states; (G(•+)G(•+))HoogI, (G(-H1)(•)G(•+))WC, (G(-H1)(•)G(•+))HoogI, (G(-H1)(•)G(•+))minI, (G(-H1)(•)G(•+))minII, and (G(-H1)(•)G(-H1)(•))minII possess open-shell broken-symmetry diradical-characterized singlet ground states; and (G(•+)G(•+))HoogII, (G(•+)G(•+))minI, (G(•+)G(•+))minII, (G(•+)G(•+))minIII, (G(•+)G(•+))HoHo, (G(-H1)(•)G(•+))minIII, (G(-H1)(•)G(•+))HoHo, and (G(-H1)(•)G(-H1)(•))HoHo are the closed-shell systems. For these H-bonded diradical complexes, the magnetic interactions are weak, especially in the diradical G(•+)G(•+) series and G(-H1)(•)G(-H1)(•) series. The magnetic coupling interactions of the diradical systems are controlled by intermolecular interactions (H-bond, electrostatic repulsion, and radical coupling). The radical-radical interaction in the π-π stacked di-ionized GG base pairs ((G(•+)G(•+))ππ, (G(-H1)(•)G(•+))ππ, and (G(-H1)(•)G(-H1)(•))ππ) are also considered, and the magnetic coupling interactions in these π-π stacked base pairs are large. This is the first theoretical prediction that some di-ionized GG base pairs possess diradical characters with variable degrees of ferromagnetic and antiferromagnetic characteristics, depending on the dehydrogenation characters of the bases and their interaction modes. Hopefully, this work provides some helpful information for the understanding of different structures and properties of the di-ionized GG base pairs.
我们在这里提出了一种理论研究，即使用密度泛函理论计算，研究由鸟嘌呤阳离子自由基（G(•+)）和/或去氢鸟嘌呤自由基（G(-H1)(•)）组成的二离子 GG 碱基对（G(•+)G(•+)、G(-H1)(•)G(•+)和 G(-H1)(•)G(-H1)(•)）的结构和电子性质。考虑了不同的耦合模式（沃森-克里克/WC、霍金斯/ Hoogsteen 和小沟/小氢键和 π-π 堆积模式）。我们推断一系列 G(•+)G(•+) 配合物可以通过高能辐射形成。基于密度泛函理论和完全活性空间自洽（CASSCF）计算，我们揭示了在氢键和 N-N 交联模式下，（G(•+)G(•+)）WC、（G(-H1)(•)G(-H1)(•))WC、（G(-H1)(•)G(-H1)(•))minI 和（G(-H1)(•)G(-H1)(•))minIII 具有三重态基态；（G(•+)G(•+)）HoogI、（G(-H1)(•)G(•+))WC、（G(-H1)(•)G(•+))HoogI、（G(-H1)(•)G(•+))minI、（G(-H1)(•)G(•+))minII 和（G(-H1)(•)G(-H1)(•))minII 具有开壳破对称双自由基特征的单重态基态；和（G(•+)G(•+)）HoogII、（G(•+)G(•+)）minI、（G(•+)G(•+)）minII、（G(•+)G(•+)）minIII、（G(•+)G(•+)）HoHo、（G(-H1)(•)G(•+))minIII、（G(-H1)(•)G(•+))HoHo 和（G(-H1)(•)G(-H1)(•))HoHo 是闭壳系统。对于这些氢键双自由基配合物，磁相互作用较弱，特别是在双自由基 G(•+)G(•+) 系列和 G(-H1)(•)G(-H1)(•) 系列中。双自由基体系的磁偶合相互作用受分子间相互作用（氢键、静电排斥和自由基偶合）的控制。还考虑了 π-π 堆积的二离子 GG 碱基对（（G(•+)G(•+))ππ、（G(-H1)(•)G(•+))ππ和（G(-H1)(•)G(-H1)(•))ππ）中自由基-自由基相互作用，这些 π-π 堆积碱基对中的磁偶合相互作用较大。这是第一个理论预测，一些二离子 GG 碱基对具有可变程度的铁磁和反铁磁特性的双自由基特征，这取决于碱基的去氢性质及其相互作用模式。希望这项工作能为理解二离子 GG 碱基对的不同结构和性质提供一些有帮助的信息。
