Department of Theoretical Chemistry and Amsterdam Center for Multiscale Modeling , Vrije Universiteit Amsterdam , De Boelelaan 1083 , 1081 HV Amsterdam , The Netherlands.
Leiden Institute of Chemistry, Gorlaeus Laboratories , Leiden University , Einsteinweg 55 , 2333 CC Leiden , The Netherlands.
J Am Chem Soc. 2019 Mar 27;141(12):4878-4885. doi: 10.1021/jacs.8b13358. Epub 2019 Mar 7.
The secondary electrostatic interaction (SEI) model is often used to predict and explain relative hydrogen bond strengths of self-assembled systems. The SEI model oversimplifies the hydrogen-bonding mechanisms by viewing them as interacting point charges, but nevertheless experimental binding strengths are often in line with the model's predictions. To understand how this rudimentary model can be predictive, we computationally studied two tautomeric quadruple hydrogen-bonded systems, DDAA-AADD and DADA-ADAD. Our results reveal that when the proton donors D (which are electron-donating) and the proton acceptors A (which are electron-withdrawing) are grouped together as in DDAA, there is a larger accumulation of charge around the frontier atoms than when the proton donor and acceptor groups are alternating as in DADA. This accumulation of charge makes the proton donors more positive and the proton acceptors more negative, which enhances both the electrostatic and covalent interactions in the DDAA dimer. The SEI model is thus predictive because it provides a measure for the charge accumulation in hydrogen-bonded monomers. Our findings can be understood from simple physical organic chemistry principles and provide supramolecular chemists with meaningful understanding for tuning hydrogen bond strengths and thus for controlling the properties of self-assembled systems.
二次静电相互作用 (SEI) 模型常用于预测和解释自组装体系中相对氢键强度。SEI 模型通过将氢键视为相互作用的点电荷来简化氢键机制，但实验结合强度通常与模型的预测相符。为了理解这个基本模型为何具有预测性，我们通过计算研究了两种互变异构的四重氢键体系，DDAA-AADD 和 DADA-ADAD。我们的结果表明，当质子供体 D（电子供体）和质子受体 A（电子受体）像在 DDAA 中那样聚集在一起时，前沿原子周围的电荷积累比质子供体和受体基团交替出现时（如 DADA）更大。这种电荷积累使质子供体带更多正电荷，质子受体带更多负电荷，从而增强了 DDAA 二聚体中的静电和共价相互作用。因此，SEI 模型具有预测性，因为它提供了衡量氢键单体中电荷积累的方法。我们的发现可以用简单的物理有机化学原理来理解，为超分子化学家提供了有意义的理解，有助于调节氢键强度，从而控制自组装体系的性质。
