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

• Published in: European journal of organic chemistry Vol. 2014; no. 17; pp. 3575 - 3583
• Main Authors: Fankhauser, Daniel, Kolarski, Dušan, Grüning, Wolfram R., Diederich, François
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01.06.2014; WILEY‐VCH Verlag; Wiley Subscription Services, Inc
• Subjects: Host-guest systems; Molecular recognition; NMR; Nuclear magnetic resonance; Spectrum analysis; Supramolecular chemistry
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/ejoc.201402140

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 (Ka) were determined by 1H 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 1H NMR spectra. In the absence of guests, the p‐xylylene bridge rotates rapidly on the 1H NMR timescale, revealing a time‐averaged achiral C2v structure, whereas this rotation is hindered by guest inclusion, resulting in spectra showing a racemic C2‐symmetric host, indicative of planar chirality. 1H NMR binding studies of novel resorcin[4]arene‐based molecular baskets and water‐soluble container molecules have been performed with small molecular guests. Sequences of complexation strength for structurally similar heteroalicyclic guests differ in organic and aqueous media. Guest inclusion rigidifies the water‐soluble hosts and rotation of the capping bridge slows, revealing planar chirality.