Heteroditopic Bis-Urea and Bis-Thiourea Receptors on Merrifield and Wang Resins: Solid-Phase Synthesis and Ion-Pair Recognition.

Abstract

A library of twelve heteroditopic bis-urea and bis-thiourea receptors supported on Merrifield and Wang resins was prepared by solid-phase synthesis. The receptors incorporate dual hydrogen-bond-donor units for anion binding and a polyether spacer that simultaneously functions as a cation-binding site, enabling ion-pair recognition at the solid-liquid interface. Molecular recognition studies were performed using several inorganic and tetraalkylammonium salts, and fluorescence changes were monitored by microplate measurements in DMSO and DMSO/H₂O (95:5, <i>v</i>/<i>v</i>). Univariate and factorial statistical analyses revealed statistically significant fluorescence changes and identified the structural variables governing guest recognition in each medium. Under the conditions examined, several systems exhibited reproducible ion-pair-induced fluorescence responses, highlighting the influence of receptor type and spacer architecture. These findings provide a basis for the rational optimization of supported receptors for sensing and extraction applications.