The road to aryl CHanion binding was paved with good intentions: fundamental studies, host design, and historical perspectives in CH hydrogen bonding.

Throughout the design and development of supramolecular receptors for anion binding, many different non-covalent anion-binding motifs have been employed. One motif seen in many host-guest systems is the sometimes weaker, 'non-traditional' aryl CH hydrogen bond. From June Sutor's discovery of the interaction and its subsequent dismissal by the field in the 1960s to today's use of the aryl CH hydrogen bond in synthetic anion receptors, the path our lab took to begin studying this interaction has been influenced by many other researchers in the field. This feature article highlights the history and properties of the CH hydrogen bond, with a particular focus on aryl CH hydrogen bonds in anion recognition. We highlight select recent developments in the field of anion receptors utilizing aryl CH hydrogen bonds, with an emphasis on how this has influenced the evolution of our approach in designing fundamental studies on CH hydrogen bonding and exploiting this interaction in efforts aimed toward preferential anion binding.

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. However, in a more polar solvent, the trend in association constants matches that of the pKa of the conjugate acid of the anionic guest, as expected for H-bond donating hosts.

Do CH-Anion and Anion-π Interactions Alter the Mechanism of 2:1 Host-Guest Complexation in Arylethynyl Monourea Anion Receptors?

Selective tuning of arylethynyl urea scaffolds for anionic guests requires an understanding of preferred binding motifs of the host-guest interaction. To investigate the binding preference of receptors without a pre-organized binding pocket, two electron-deficient phenylacetylene receptors with a single urea moiety have been prepared and were found to bind halides as 2:1 host-guest complexes that feature key CH-anion or anion-π interactions. These supporting interactions also appear to influence the mechanism of the 2:1 binding event.