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Internet Electronic Journal of Molecular Design - IEJMD, ISSN 1538-6414, CODEN IEJMAT
| ABSTRACT - Internet Electron. J. Mol. Des. April 2005, Volume 4, Number 4, 264-269 |
Unexpected Binding Affinity of [2.2]Paracyclophane to Cations
Antonio Frontera, Carolina Garau, David Quiñonero, Pablo Ballester, Antoni Costa, and Pere M. Deyà
Internet Electron. J. Mol. Des. 2005, 4, 264-269
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Abstract:
The interaction of a cation with an aromatic ring, namely cation-π
interaction is a strong noncovalent force of great importance in
many systems, including cation receptors and biomolecules.
Cyclophanes and especially calixarenes are widely used cation
receptors based on this interaction. [2.2]Paracyclophanes are not
used for building cation receptors; however its binding capability
toward cations is superior to benzene. HF and B3LYP calculations
have been used to carry out the geometry optimizations of
[2.2]paracyclophane (1) complexes with lithium and sodium
cation. Benzene complexes are also studied for comparison
purposes. Comparative AIM and NICS analyses of the complexes
have been performed. Several cation-π complexes have been
optimized and compared. Complexes of 1 are considerably more
stable (~10 kcal/mol) than benzene complexes. This unexpected
difference is explained by the reduction of the repulsive interaction
of the π-systems in 1 due to the close proximity of the two benzene
rings upon complexation. The AIM analysis is in agreement with
this explanation. From the results presented here, derived from the
higher binding affinity of 1 in comparison to benzene toward
cations, the following conclusion arises: [2.2]paracyclophane is an
excellent binding unit for the construction of cation receptors.
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