N-Alkyl Ammonium Resorcinarene Chloride Receptors for Guest Binding in Aqueous Environment

Host systems with guest binding ability in water and/or biological fluids are a current challenge in supramolecular host-guest chemistry. Here we present the first syntheses of water-soluble N-ethanol ammonium resorcinarene chlorides (NARCls) with terminal hydroxyl groups at the upper rim. The NARCls possess deep cavities and are shown to bind a variety of guest molecules such as linear and cyclic alkanes, linear halogenated alkanes, and aromatic fluorophores (naphthalene, p-(phenylazo)phenol) in water through hydrophobic interactions, as well as 1,4-dioxane (a water soluble guest) via hydrogen bonds. The receptors are monomeric in aqueous media and form 1:1 host-guest complexes with binding constants of up to 559m^-1 in D₂O/MeOD (9:1, v/v) at 298K. Solid-state analysis in purely organic media, reveals a dimeric 2:2 capsule and a self-included dimer of nanometer dimensions. The host-guest complexes are analyzed in solid state by single-crystal X-ray diffraction and in solution by ¹HNMR and diffusion-ordered NMR spectroscopy.