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Issue 5, 2019
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Supramolecular cage encapsulation as a versatile tool for the experimental quantification of aromatic stacking interactions

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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

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Publication details

The article was received on 04 Oct 2018, accepted on 22 Nov 2018 and first published on 22 Nov 2018


Article type: Edge Article
DOI: 10.1039/C8SC04406F
Chem. Sci., 2019,10, 1466-1471
  • Open access: Creative Commons BY-NC license
    All publication charges for this article have been paid for by the Royal Society of Chemistry

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    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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