Combined application of pair potentials and the MM2 force field for the modeling of ionophores

Complexes of alkali and alkaline earth cations with organic compounds are modeled by describing ionligand interaction energies with pair potentials and intraligand as well as interligand energies with the MM2 potential. New pair potentials for the interaction of Li⁺, Na⁺, K⁺, Mg²⁺, and Ca²⁺ ions are derived on the basis of 30,000 ab initio interaction energy values with 70 selected model ligand molecules. Various problems of the combination of these two basically different potentials are discussed. An application for the K⁺ complex of 18-crown-6 is presented. For more flexible ligands the introduction of three-body correction terms of the pair potentials seems necessary.