Ab initio study of the complexation behavior of calix[5]arene derivative toward alkyl ammonium cations

Abstract

The structures and complexation energies of penta-O-alkylated 1b and penta-O-tert-butyl ester le of p-tert-butylcalix[5]arene and their simplified structures (2b and 2e) toward a series of alkyl ammonium guests have been calculated by a semi-empirical AM I method. For AM I calculations, complexation efficiencies of the simplified host 2e are very similar to the values of host le. The complexes of simplified host;2e with alkyl ammonium ions also have been optimized by ab initio HF/6-31G method. The calculated complexation efficiencies for 2e by ab initio method have been found to be bigger in magnitude than the values obtained by AMI calculations for linear alkyl ammonium guests. Calculation results show that all of the calix[5]aryl derivatives investigated in this study have much better complexation ability toward ammonium cation without alkyl group compared with other alkyl ammonium guests. Ab initio calculations also well duplicate the molecular discriminating behaviors of calix[5]arene derivative 2e between butyl ammonium ions: n-BuNH3+ > iso-BuNH3+ > sec-BuNH3+> tert-BuNH3+.