Anion recognition plays a fundamental role in life, and as a result, the devising of artificial systems for anion complexation has figured prominently in supramolecular chemistry. The most prevalent strategies for anion binding have relied on electrostatic interactions and/or hydrogen bonding to overcome the frequently strong solvation of highly hydrated anions. In Nature however, not all anion interactions involve Coulombic or hydrogen bonding interactions; some involve much weaker – often inappropriately named non-specific – interactions with non-polar groups. Indeed, there is a growing consensus that anion-non-polar group interactions are important in the Hofmeister effect, for example in the ability of salts to increase or decrease the solubility of solutes in water. In order to study anion recognition in aqueous media using non-polar recognition sites, we have studied the affinity that anions have for four water-soluble hosts: Octa Acid(OA), Tetra-endo-methyl Octa Acid (TEMOA), α-cyclodextrin (α-CD) and permethylated α-cyclodextrin (PM-α-CD) by 1H-NMR and Isothermal Titration Calorimetry. The results of these thermodynamic studies indicate that not only does each host have its own anion selectivity profiles, but that the association constants (Ka) that some anions have for the hosts can range over almost four orders of magnitude. We will discuss these results.

Hydrated anions binding within the water-soluble hosts

254th National Meeting (2017)

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