Issue 5, 2019

Supramolecular cage encapsulation as a versatile tool for the experimental quantification of aromatic stacking interactions

Abstract

The widespread presence of aromatic stacking interactions in chemical and biological systems, combined with their relatively small energetic contribution, have led to a plethora of theoretical and experimental studies for their quantification and rationalization. Typically, π–π aromatic interactions are studied as a function of substituents to gather information about the interaction mechanism. While experiments suggest that aromatic interactions are dominated by local electrostatic contacts between π-electron density and CH groups, theoretical work has raised the possibility that direct electrostatic interactions between local dipoles of the substituents may play a role. We describe a supramolecular cage that binds two aromatic carboxylates in a stacked geometry such that the aromatic substituents are remote in space. Chemical Double Mutant Cycles (DMCs) were used to measure fifteen different aromatic stacking interactions as a function of substituent (NMe2, OMe, Me, Cl and NO2). When both aromatic rings have electron-withdrawing nitro substituents, the interaction is attractive (−2.8 kJ mol−1) due to reduced π-electron repulsion. When both aromatic rings have electron-donating di-methylamino substituents, the interaction is repulsive (+2.0 kJ mol−1) due to increased π-electron repulsion. The results show that aromatic stacking interactions are dominated by short range electrostatic contacts rather than substituent dipole interactions.

Graphical abstract: Supramolecular cage encapsulation as a versatile tool for the experimental quantification of aromatic stacking interactions

Supplementary files

Article information

Article type
Edge Article
Submitted
04 Oct 2018
Accepted
22 Nov 2018
First published
22 Nov 2018
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY-NC license

Chem. Sci., 2019,10, 1466-1471

Supramolecular cage encapsulation as a versatile tool for the experimental quantification of aromatic stacking interactions

C. Bravin, G. Licini, C. A. Hunter and C. Zonta, Chem. Sci., 2019, 10, 1466 DOI: 10.1039/C8SC04406F

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