The Center for Modeling and Simulation Chemistry, Institute of Theoretical Chemistry, Shandong University, Jinan 250100, People's Republic of China.
J Comput Chem. 2011 Apr 30;32(6):1159-69. doi: 10.1002/jcc.21699. Epub 2010 Nov 29.
Internucleotide (2h)J(NN) spin-spin couplings and chemical shifts (δ((1)H) and Δδ((15)N)) of N-H···N H-bond units in the natural and radiation-damaged G-C base pairs were predicted using the appropriate density functional theory calculations with a large basis set. Four possible series of the damaged G-C pairs (viz., dehydrogenated and deprotonated G-C pairs, GC(•-) and GC(•+) radicals) were discussed carefully in this work. Computational NMR results show that radicalization and anionization of the base pairs can yield strong effect on their (2h)J(NN) spin scalar coupling constants and the corresponding chemical shifts. Thus, variations of the NMR parameters associated with the N-H···N H-bonds may be taken as an important criterion for prejudging whether the natural G-C pair is radiation-damaged or not. Analysis shows that (2h)J(NN) couplings are strongly interrelated with the energy gaps (ΔE(LP→σ*)) and the second-order interaction energies (E(2)) between the donor N lone-pair (LP(N)) and the acceptor σ*(N-H) localized NBO orbitals, and also are sensitive to the electron density distributions over the σ*(N-H) orbital, indicating that (2h)J(NN) couplings across the N-H···N H-bonds are charge-transfer-controlled. This is well supported by variation of the electrostatic potential surfaces and corresponding charge transfer amount between G and C moieties. It should be noted that although the NMR spectra for the damaged G-C pair radicals are unavailable now and the states of the radicals are usually detected by the electron spin resonance, this study provides a correlation of the properties of the damaged DNA species with some of the electronic parameters associated with the NMR spectra for the understanding of the different state character of the damaged DNA bases.
使用适当的密度泛函理论计算和大基组，预测了天然和辐射损伤的 G-C 碱基对中 N-H···N H 键单元的核苷酸间（2h）J（NN）自旋-自旋偶合常数和化学位移（δ（1）H 和Δδ（15）N）。在这项工作中，我们仔细讨论了四个可能的损伤 G-C 对系列（即脱氢和去质子化的 G-C 对、GC（•-）和 GC（•+）自由基）。计算 NMR 结果表明，碱基对的自由基化和阴离子化会对其（2h）J（NN）自旋标量耦合常数和相应的化学位移产生强烈影响。因此，与 N-H···N H 键相关的 NMR 参数的变化可以作为判断天然 G-C 对是否受到辐射损伤的重要标准。分析表明，（2h）J（NN）偶合与能量间隙（ΔE（LP→σ*））和供体 N 孤对（LP（N））与受体 σ*（N-H）局域 NBO 轨道之间的二阶相互作用能（E（2））密切相关，也对 σ*（N-H）轨道上的电子密度分布敏感，表明 N-H···N H 键之间的（2h）J（NN）偶合是电荷转移控制的。这很好地支持了 G 和 C 部分之间的静电势表面和相应的电荷转移量的变化。值得注意的是，尽管目前还无法获得损伤 G-C 对自由基的 NMR 谱，并且自由基的状态通常通过电子自旋共振来检测，但这项研究提供了损伤 DNA 物种的性质与一些与 NMR 谱相关的电子参数之间的相关性，有助于理解损伤 DNA 碱基的不同状态特征。
