Cation-π interactions between ammonium ion and aromatic rings:: an energy decomposition study

The nature of the cation-pi interaction between ammonium ion and a series of aromatic groups has been revisited through standard supermolecular energy decomposition schemes such as the Kitaura-Morokuma and the reduced variational space self-consistent field approaches. The emerged picture describes the ammonium-aromatics interaction as basically governed by electrostatics with significant contributions from the polarization, dispersion, and at a minor extent from, even from the aromatic-ammonium charge transfer. The role of molecular properties of the aromatic partners such as their mutipole moments, first and second order polarizability as well as the electronic properties of the frontier orbitals have been investigated in the light of the decomposed components. A final comment on the implications of our results on the reliability of the force fields currently employed for classical simulations and drug design investigations, has also been addressed. (C) 2002 Elsevier Science B.V. All rights reserved.