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Modulating the binding of polycyclic aromatic hydrocarbons inside a hexacationic cage by anion-π interactions.

Authors
  • Hafezi, Nema
  • Holcroft, James M
  • Hartlieb, Karel J
  • Dale, Edward J
  • Vermeulen, Nicolaas A
  • Stern, Charlotte L
  • Sarjeant, Amy A
  • Stoddart, J Fraser
Type
Published Article
Journal
Angewandte Chemie International Edition in English
Publisher
Wiley (John Wiley & Sons)
Publication Date
Jan 07, 2015
Volume
54
Issue
2
Pages
456–461
Identifiers
DOI: 10.1002/anie.201408400
PMID: 25410825
Source
Medline
Keywords
License
Unknown

Abstract

We report the template-directed synthesis of BlueCage(6+), a macrobicyclic cyclophane composed of six pyridinium rings fused with two central triazines and bridged by three paraxylylene units. These moieties endow the cage with a remarkably electron-poor cavity, which makes it a powerful receptor for polycyclic aromatic hydrocarbons (PAHs). Upon forming a 1:1 complex with pyrene in acetonitrile, however, BlueCage⋅6 PF6 exhibits a lower association constant Ka than its progenitor ExCage⋅6 PF6. A close inspection reveals that the six PF6(-) counterions of BlueCage(6+) occupy the cavity in a fleeting manner as a consequence of anion-π interactions and, as a result, compete with the PAH guests. This conclusion is supported by a one order of magnitude increase in the Ka value for pyrene in BlueCage(6+) when the PF6(-) counterions are replaced by much bulkier anions. The presence of anion-π interactions is supported by X-ray crystallography, and confirms the presence of a PF6(-) counterion inside its cavity.

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