Electron Attachment to the Guanine鈥揅ytosine Nucleic Acid Base Pair and the Effects of Monohydration and Proton Transfer

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• 作者：Ashutosh Gupta ; Heather M. Jaeger ; Katherine R. Compaan ; Henry F. Schaefer ; III
• 刊名：The Journal of Physical Chemistry B
• 出版年：2012
• 出版时间：May 17, 2012
• 年：2012
• 卷：116
• 期：19
• 页码：5579-5587
• 全文大小：455K
• 年卷期：v.116,no.19(May 17, 2012)
• ISSN：1520-5207

文摘

The guanine鈥揷ytosine (GC) radical anion and its interaction with a single water molecule is studied using ab initio and density functional methods. Z-averaged second-order perturbation theory (ZAPT2) was applied to GC radical anion for the first time. Predicted spin densities show that the radical character is localized on cytosine. The Watson鈥揅rick monohydrated GC anion is compared to neutral GC路H₂O, as well as to the proton-transferred analogue on the basis of structural and energetic properties. In all three systems, local minima are identified that correspond to water positioned in the major and minor grooves of macromolecular DNA. On the anionic surface, two novel structures have water positioned above or below the GC plane. On the neutral and anionic surfaces, the global minimum can be described as water interacting with the minor groove. These structures are predicted to have hydration energies of 9.7 and 11.8 kcal mol^鈥?, respectively. Upon interbase proton-transfer (PT), the anionic global minimum has water positioned in the major groove, and the hydration energy increases to 13.4 kcal mol^鈥?. PT GC路H₂O^{鈥⑩€?/sup> has distonic character; the radical character resides on cytosine, while the negative charge is localized on guanine. The effects of proton transfer are further investigated through the computed adiabatic electron affinities (AEA) of GC and monohydrated GC, and the vertical detachment energies (VDE) of the corresponding anions. Monohydration increases the AEAs and VDEs by only 0.1 eV, while proton-transfer increases the VDEs substantially (0.8 eV). The molecular charge distribution of monohydrated guanine鈥揷ytosine radical anion depends heavily on interbase proton transfer.}