Radical鈥揜adical Interactions among Oxidized Guanine Bases Including Guanine Radical Cation and Dehydrogenated Guanine Radicals

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• 作者：Jing Zhao ; Mei Wang ; Hongfang Yang ; Meng Zhang ; Ping Liu ; Yuxiang Bu
• 刊名：Journal of Physical Chemistry B
• 出版年：2013
• 出版时间：September 19, 2013
• 年：2013
• 卷：117
• 期：37
• 页码：10698-10710
• 全文大小：691K
• 年卷期：v.117,no.37(September 19, 2013)
• ISSN：1520-5207

文摘

We present here a theoretical investigation of the structural and electronic properties of di-ionized GG base pairs (G^鈥?G^鈥?,G(-H1)^{鈥?/sup>G鈥?, and G(-H1)鈥?/sup>G(-H1)鈥?/sup>) consisting of the guanine cation radical (G鈥?) and/or dehydrogenated guanine radical (G(-H1)鈥?/sup>) using density functional theory calculations. Different coupling modes (Watson鈥揅rick/WC, Hoogsteen/Hoog, and minor groove/min hydrogen bonding, and 蟺鈥撓€ stacking modes) are considered. We infer that a series of G鈥?G鈥? 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鈥揘 cross-linked modes, (G鈥?G鈥?)_WC, (G(-H1)鈥?/sup>G(-H1)鈥?/sup>)_WC, (G(-H1)鈥?/sup>G(-H1)鈥?/sup>)_minI, and (G(-H1)鈥?/sup>G(-H1)鈥?/sup>)_minIII have the triplet ground states; (G鈥?G鈥?)_HoogI, (G(-H1)鈥?/sup>G鈥?)_WC, (G(-H1)鈥?/sup>G鈥?)_HoogI, (G(-H1)鈥?/sup>G鈥?)_minI, (G(-H1)鈥?/sup>G鈥?)_minII, and (G(-H1)鈥?/sup>G(-H1)鈥?/sup>)_minII possess open-shell broken-symmetry diradical-characterized singlet ground states; and (G鈥?G鈥?)_HoogII, (G鈥?G鈥?)_minI, (G鈥?G鈥?)_minII, (G鈥?G鈥?)_minIII, (G鈥?G鈥?)_HoHo, (G(-H1)鈥?/sup>G鈥?)_minIII, (G(-H1)鈥?/sup>G鈥?)_HoHo, and (G(-H1)鈥?/sup>G(-H1)鈥?/sup>)_HoHo are the closed-shell systems. For these H-bonded diradical complexes, the magnetic interactions are weak, especially in the diradical G鈥?G鈥? series and G(-H1)鈥?/sup>G(-H1)鈥?/sup> series. The magnetic coupling interactions of the diradical systems are controlled by intermolecular interactions (H-bond, electrostatic repulsion, and radical coupling). The radical鈥搑adical interaction in the 蟺鈥撓€ stacked di-ionized GG base pairs ((G鈥?G鈥?)_蟺蟺, (G(-H1)鈥?/sup>G鈥?)_蟺蟺, and (G(-H1)鈥?/sup>G(-H1)鈥?/sup>)_蟺蟺) are also considered, and the magnetic coupling interactions in these 蟺鈥撓€ 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.}