Resorcin[4]arene-Based Molecular Baskets and Water-Soluble Container Molecules: Synthesis and 1H NMR Host-Guest Complexation Studies

Resorcin[4]arene-based molecular baskets, with four free or methylene-bridged HO groups, and water-soluble container molecules bearing poly(ethylene glycol) chains of different lengths on the lower rim and cap have been synthesized. These cavitands, topped with p-xylylene bridges, feature well-defined cavities capable of encapsulating heteroalicyclic guests. Association constants (K-a) were determined by H-1 NMR spectroscopy for the organic-soluble molecular baskets in CDCl3 and for the water-soluble container molecules in D2O/CD3CN (2:1). Opposite guest selectivities were observed in the two environments. Upon complexation, the water-soluble hosts show changes in their H-1 NMR spectra. In the absence of guests, the p-xylylene bridge rotates rapidly on the H-1 NMR timescale, revealing a time-averaged achiral C-2v structure, whereas this rotation is hindered by guest inclusion, resulting in spectra showing a racemic C-2-symmetric host, indicative of planar chirality.