Kongsted Jacob, Mennucci Benedetta
Department of Theoretical Chemistry, Chemical Center, University of Lund, P.O. Box 124, S-221 00 Lund, Sweden.
J Phys Chem A. 2007 Oct 4;111(39):9890-900. doi: 10.1021/jp074343w. Epub 2007 Sep 11.
We present a comparative study of solvent effects on the 15N NMR shielding constants and the lowest electronic excitation energy (n --> pi*) in the three diazines (pyrazine, pyrimidine, and pyridazine) in aqueous solution. This solvent is modeled using either a polarizable continuum model (PCM) or a discrete polarizable model (DPM). We analyze the results obtained with the two models in terms of differences/similarities in the reaction field produced at the solute. The PCM reaction field is found to be quite sensitive to the dimension of the cavity and so are the molecular properties. However, constructing the cavity so that the DPM and PCM reaction fields become similar in magnitude leads to quite similar results for the studied molecular properties modeling the solvent using either the PCM or the DPM. Compared to experimental data, the most accurate predicted results are obtained by describing the closest water molecules at the same level of sophistication as that of the solute, whereas the bulk solvent may be described using either PCM or MM. Finally, a comparison with geometry-optimized clusters seems to show that it is important to check potential deficiencies in the force field in order for this to treat hydrogen bonding in a consistent manner.
我们展示了一项关于溶剂对水溶液中三种二嗪（吡嗪、嘧啶和哒嗪）的(^{15}N)核磁共振屏蔽常数和最低电子激发能（(n\to\pi^*)）影响的比较研究。该溶剂使用可极化连续介质模型（PCM）或离散可极化模型（DPM）进行建模。我们根据溶质处产生的反应场的差异/相似性来分析用这两种模型获得的结果。发现PCM反应场对腔的尺寸相当敏感，分子性质也是如此。然而，构建腔使得DPM和PCM反应场在大小上变得相似，对于使用PCM或DPM对溶剂进行建模的所研究分子性质会得到相当相似的结果。与实验数据相比，通过以与溶质相同的精细程度描述最接近的水分子可获得最准确的预测结果，而本体溶剂可以使用PCM或MM来描述。最后，与几何优化簇的比较似乎表明，为了以一致的方式处理氢键，检查力场中潜在的缺陷很重要。
