Ab initio study of p-tert-butylcalix[4]crown-6-ether complexed with alkyl ammonium cations

The conformations and energies of p-tert-butylcalix[4]crown-6-ether (1) and its alkyl ammonium complexes have been calculated by ab initio HF/6-31G qu antum mechanics method. The cone conformation was found to be most stable f or free host 1. We have determined the binding site of these host-guest com plexes focusing on the crown-6-ether or p-tert-butylcalix[4]arene pocket of the cone conformation of host molecule 1. The primary binding site of host 1 for the recognition of alkyl ammonium guests was confirmed to be the cen tral part of the crown moiety of cone conformation. The complexation energy calculations revealed that the ammonium cation without alkyl group showed the highest complexation efficiency when combined with host 1, that is in s atisfactory agreement with the experimental results.