Hydrophilic and hydrophobic carboxamide pincers as anion hosts.

Hydrophobic and hydrophilic, monotopic and ditopic carboxamide pincer hosts containing ethyl, hexyl, 2-hydroxyethyl and 2-hydroxyethyl ethyl ether pendant arms were synthesized. Solubility trends indicated that solubilities in water or hydrocarbon solvents varied depending on the nature of the pendant arms. Binding constants for hydrophilic pincers were larger in general than their hydrophobic analogs.

Exploiting the Hydrogen Bond Donor/Acceptor Properties of PN-Heterocycles: Selective Anion Receptors for Hydrogen Sulfate.

We describe two novel hybrid receptors combining a phosphorus-/nitrogen-containing (PN) phosphonamidate heterocycle with urea recognition units in an arylethynyl backbone. Structural, spectroscopic and computational studies reveal that the origin of superior binding for hydrogen sulfate (HSO ) anion is correlated with the formation of strong hetero-complementary hydrogen bonds with the phosphonamidate motif. We further demonstrate that the hybrid host system is capable of capturing/transporting the HSO anion from an aqueous, biphasic system.

Methanesulfonyl-polarized halogen bonding enables strong halide recognition in an arylethynyl anion receptor.

A 3,5-bis((2-iodophenyl)ethynyl)pyridinium scaffold was synthesized which introduces the use of methanesulfonyl withdrawing groups to polarize iodine halogen bonding units for anion binding. We investigate the capability of this receptor to bind halides in polar media, while further probing the structure-property relationship of this well-polarized yet under-explored halogen bonding system.

Convergent Ditopic Receptors Enhance Anion Binding upon Alkali Metal Complexation for Catalyzing the Ritter Reaction.

A supramolecular approach to catalyzing the Ritter reaction by utilizing enhanced anion-binding affinity in the presence of alkali metal cations was developed with ditopic hydrogen-bonded amide macrocycles. With prebound cations in the macrocycle, particularly Li ion, their metal complexes exhibit greatly enhanced catalytic activities. The catalysis is switchable by removal or addition of the bound cation.

Conformationally flexible arylethynyl bis-urea receptors bind disparate oxoanions with similar, high affinities.

Conformationally flexible hosts with relatively small binding pockets are seldom shown to bind oxoanions preferentially over other guests. Herein, we disclose the binding of diprotic, monoprotic, and aprotic tetrahedral oxoanions with three different pyridylethynyl bis-urea scaffolds. In less polar solvent, the trend in association constants appears to be heavily influenced by solvation and entropic effects.