A macrobicyclic receptor with versatile recognition properties: Simultaneous binding of an ion pair and selective complexation of dimethylsulfoxide

A bicyclic receptor was synthesized and evaluated for its ability to bind a lkali halide salts and polar neutral molecules in organic solvents. The rec eptor design is relatively straightforward in the sense that it is a combin ation of a dibenzo-18-crown-6 and a bridging 1,3-phenyldicarboxamide. In th e presence of 1 mol equiv of metal cation, chloride affinities are enhanced in the order: K+ (9-fold enhancement) > Na+ (8-fold enhancement) much grea ter than Cs+ (no enhancement). An X-ray crystal structure shows that the re ceptor binds sodium chloride as a solvent-shared ion pair. The receptor has very weak affinity for acetonitrile, nitromethane, or acetone in chlorofor m solvent, whereas the association constant for dimethylsulfoxide is 160 M- 1 at 295 K. An X-ray crystal structure shows that the dimethylsulfoxide is bound deeply in the receptor cavity and forms hydrogens bonds to the recept or via a bridging water molecule. There is also evidence for CH-O interacti ons. Solid-liquid extraction studies show that the receptor can dissolve an d associate with urea, primary amides, and primary sulfonamides in CDCl3 bu t does not dissolve amino acids.