Experimental dissection of dispersion energies from electrostatic contributions and solvent effects in face-to-face pi-stacking complexes

面对面 π 堆积复合物中静电贡献和溶剂效应的色散能的实验剖析

• 批准号: 397985541
• 负责人: Dr. Frank Biedermann
• 金额: --
• 依托单位: Institut für Nanotechnologie (INT)
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2018
• 资助国家: 德国
• 起止时间: 2017-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/397985541?language=en
• 关键词: Experimental; dissection; dispersion; energies; electrostatic

We propose a novel experimental toolbox for evaluating the binding energies of face-to-face “stacking” aromatic systems, which will be of help to separate electrostatic from dispersive contributions for typical pi-pi complexes. Our approach is complementary to existing experimental approaches, e.g. studies with association complexes of small molecules, the molecular balance technique or the double mutant cycle analysis, which have to date not been fully conclusive in scrutinizing competing theoretical models about pi-pi stacking interactions.Stable and geometrically well-defined rotaxanated complexes of the large macrocycle cucurbit[8]uril and a suitable aromatic component will serve as the receptor moiety for binding a second aromatic guest. In this design, both aromatic compounds, i.e. the rotaxanated one, and the incoming second aromatic guest, are hold in a face-to-face orientation (=> high geometric control) and are each almost completely shielded from contact with solvent molecules (=> minimization of solvation effects on the overall pi-pi stacking energy). We also propose a path how the desolvation energy cost of the binding partners can be experimentally accounted for without the need for computational treatments. Both the high geometric control and the subtraction of solvation effects are important advantages over other association-complex-based studies. Furthermore, it will be straightforward to generate a data library, because the second aromatic binding partner can be readily mixed in and does not need to be covalently tethered, as is the case for molecular-balances. In fact, our supramolecular approach also avoids probing a “non-optimal” binding geometry, which can be a shortcoming for covalent molecular-balance setups.In the proposed line of research, we will first prepare the rotaxanated complexes and will then measure by isothermal titration calorimetry (ITC) the binding enthalpies and free enthalpies of their pi-pi-complex formation with aromatic second guests. Having direct access to binding enthalpies will facilitate the comparison to computed pi-pi interaction energies, as the computationally difficult to treat entropic component can be disregarded. Having access to free energies (and thus entropies) will provide a valuable data sets to test future improved theoretical models.Information about the pi-pi stacking geometry will be obtained by structure-based methods such as NMR spectroscopy in solution and X-ray diffraction structure analysis of crystallized complexes. By systematically varying both the aromatic binding partners, including systems with typical “polar” substituents or with “dispersion donors”, we will aim towards an experimental separation of electrostatic and dispersive effects for the face-to-face pi-pi interaction motif. This study will complement the emerging picture of the importance of dispersive interactions for molecular recognition and self-assembly.

我们提出了一个新的工具箱，用于评估面对面“堆叠”芳族系统的结合能，该系统将从典型的PI-PI复合物的分散贡献中有助于TE静电。在审查有关PI-PI堆叠相互作用的理论模型时，技术或双重突变周期分析是完全结论性的。为了结合芳香的gn，两种芳族化合物，即旋转式的，以及传入的第二芳族客人，都保持在面对面的方向（=>高几何控制） LVITION对PI-PI堆叠能量的影响。因为可以很容易地混合第二种芳香结合，因此我们的超分子也避免探测“非最佳”结合几何形状，这可能是通过等温滴定钙仪（ITC）的共价分子 - 平衡设置的缺点。可以忽略TS，可以通过结构 - PI-PI堆栈来测试，以忽略了TS，可以通过结构 - 基于溶液和X射线衍射结构的频谱结构。面对面的PI-PI相互作用基序。