Organic Ligand-Receptor Interactions between Cucurbituril and Alkylammonium Ions

摘要

Experimental binding energies for 24 substituted ammonium ion ligands for the synthetic receptor cucurbituril are adjusted for ligand solvation and then are factored by regression analysis into contributions from various fragments of the ligands in their inclusion complexes. This allows quantitative estimation of noncovalent forces occurring in the interaction of ligand with receptor. It is concluded that the center of cucurbituril constitutes a lipophilic region but that the entrances to the interior (ammonium ion binding site) are countervailingly lipophobic. Enhanced dispersion forces involving the thioether functional group may exist in the receptor complexes of such ligands, but they make no extra contribution to the hydrophobic effect generally. The specificity of cucurbituril as a molecular receptor is explained in terms of ion dipole attractions and shape complementarity with ligands. Reprints. (MJM)