Environmental Chemistry Modeling Laboratory, EPFL, 1015 Lausanne, Switzerland.
J Phys Chem A. 2010 Sep 16;114(36):9606-16. doi: 10.1021/jp908941u.
π-π interactions in heteroaromatic systems are ubiquitous in biological systems. In the present study, stabilization energies of stacked and hydrogen-bonded dimers of N-heteroaromatic systems (pyridine, pyrazine, sym-triazine, and sym-tetrazine) have been computed using a benchmark quality coupled cluster through the perturbative triples (CCSD(T)) method at the estimated complete basis set (CBS) limit. In the case of stacking, monomer units are found to be stacked in parallel planes with displaced geometries. The stabilization energies for the most stable stacked geometry of pyridine, pyrazine, sym-triazine, and sym-tetrazine dimers are found to be -3.39, -4.14, -4.02, and -3.90 kcal/mol, respectively at the est. CCSD(T)/CBS level of theory, which is clearly larger than the stabilization energy for the most stable geometry of the benzene dimer. In the case of spreading, hydrogen bonded dimers and trimers are stabilized by weak C-H···N interactions. The stabilization energies for the stacked and the spread out complexes are found to be comparable. The stabilization energy for the trimers is computed using the MP2, MP3, and B3LYP-D methods. The present study is aimed at unraveling the basis of preferred conformations of N-heteroaromatic dimers. These model systems explain partly the stability of double helical DNA and RNA structures that are formed by stacking and hydrogen bonding between nucleic acid bases.
杂芳环体系中的π-π 相互作用在生物体系中普遍存在。在本研究中，使用基准质量耦合簇通过微扰三（CCSD(T)）方法在估计的完整基组（CBS）极限下计算了 N-杂芳环体系（吡啶、吡嗪、对称三嗪和对称四嗪）的堆叠和氢键二聚体的稳定能。在堆叠的情况下，单体单元被发现以平移的几何形状平行堆叠在平面上。在估计的 CCSD(T)/CBS 理论水平下，吡啶、吡嗪、对称三嗪和对称四嗪二聚体最稳定堆叠构型的稳定能分别为-3.39、-4.14、-4.02 和-3.90 kcal/mol，明显大于苯二聚体最稳定构型的稳定能。在展开的情况下，氢键二聚体和三聚体通过弱 C-H···N 相互作用稳定。堆叠和展开复合物的稳定能相当。使用 MP2、MP3 和 B3LYP-D 方法计算了三聚体的稳定能。本研究旨在揭示 N-杂芳环二聚体优先构象的基础。这些模型体系部分解释了由核酸碱基之间的堆叠和氢键形成的双链螺旋 DNA 和 RNA 结构的稳定性。
