Cation-pi interactions in simple aromatics: Electrostatics provide a predictive tool
Cation-pi interactions in simple aromatics: Electrostatics provide a predictive tool
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DOI：
10.1021/ja9539608
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发表时间：
1996-03-06
影响因子：
15
通讯作者：
Dougherty, DA
中科院分区：
文献类型：
--
作者：
Mecozzi, S;West, AP;Dougherty, DA
近年来，阳离子-π相互作用被认为是一种重要的非共价结合力。1在气相中的研究，2在水介质中使用合成受体的研究，3以及在生物背景下与一些蛋白质系统1、4、5的研究已经确定了这种相互作用的广泛范围和意义。一个完整的、定量的阳离子-π相互作用的描述将涉及许多分子间力，如电荷-四极、电荷-偶极、电荷诱导的偶极、电荷转移、色散力，在某些情况下，还包括疏水成分。然而，我们已经论证了1，3a，4，阳离子-π相互作用的主要方面是性质上的静电，涉及阳离子与芳香族的大的永久四极矩的相互作用。6在本工作中，我们描述了静电模型在多大程度上能够合理地解释不同芳香族体系之间阳离子结合能力的变化。我们发现，实际上，静电模型提供了对一系列典型芳香体系的趋势的定量理解。我们对钠离子(Na+)与结构1-11的π面的结合进行了一系列从头计算研究(图1)。我们认为这种络合物为阳离子-π相互作用中预期的定量趋势提供了一个很好的模型。例如，我们以前已经证明，用NH4+代替Na+不会改变这些数据中的任何趋势，因此这些更简单的模型计算与真实的实验系统有关。结合能在6-31G**//6-31G**水平上用Gaussian928程序计算。对于这样的研究来说，这种理论水平是相当足够的。9为了估计静电对结合的贡献，我们用虚拟探针原子取代了优化的络合物的Na+，并计算了该点的静电势(EPopt)。我们还使用未络合的芳香族分子的几何构型进行了相同的计算，并对
In recent years, the cation-π interaction has come to be appreciated as an important noncovalent binding force. 1 Studies in the gas phase, 2 in aqueous media using synthetic receptors, 3 and in a biological context with a number of protein systems1, 4, 5 have established the broad scope and significance of this interaction. A complete, quantitative description of the cation-π interaction would involve a number of intermolecular forces, such as charge-quadrupole, charge-dipole, chargeinduced dipole, charge transfer, dispersion forces, and, in some cases, a hydrophobic component. However, we have argued1, 3a, 4 that, to first order, the major aspect of the cation-π interaction is electrostatic in nature, involving the interaction of the cation with the large, permanent quadrupole moment of the aromatic. 6 In the present work we describe an evaluation of the extent to which the electrostatic model can rationalize Variations in cation binding abilities among various aromatic systems. We find that, indeed, the electrostatic model provides a quantitative understanding of the trend seen across a series of prototypical aromatic systems.We have performed a series of ab initio computational studies on the binding of the sodium cation (Na+) to the π face of structures 1-11 (Chart 1). We consider such complexes to provide a good model for the quantitative trends expected in the cation-π interaction. For example, we have previously shown3b that using NH4+ in place of Na+ does not alter any trends in such data, and so these simpler model calculations are relevant to real experimental systems. Binding energies were evaluated at the 6-31G**//6-31G** level, 7 using the Gaussian 928 package. This level of theory is quite adequate for such a study. 9 To estimate the electrostatic contribution to binding, we replaced the Na+ of the optimized complex with a dummy probe atom and evaluated the electrostatic potential (EPopt) at that point. We also performed the same calculation using the geometry of the uncomplexed aromatic molecule and evaluating