NMR investigation of the complexation of neutral guests by cucurbituril

Abstract

The effect of acidity on the stability of the complexes of neutral guests with cucurbituril (CB), a synthetic receptor, in aqueous Na2SO4 solutions is investigated by Xe-129, F-19 and H-1 NMR spectroscopy. The apparent affinity constants of THF and xenon for CB were measured and found to be independent of the pH of the solution. It was also observed that small acids, such as TFA, in their undissociated form can be encapsulated inside the CB cavity. The apparent association constants of THF, Xe and TFA for CB are estimated to be around 1700 M-1 210 M-1 and 11 M-1. respectively.