Deep-cavity cavitands have been shown to be a receptor for anions in both the deep-cavity and the crown of trimethylammoniums at the base of the cavitand. In an effort to better understand this crown binding—specifically as it relates to the reverse Hofmeister effect—we have synthesized several novel methylene bridged cavitands including four water-soluble cavitands bearing different functionalities to impart host solubility. Moreover, these novel systems, containing an analogous crown of ammoniums allow for the attenuation of anion affinity and host solubility. These hosts contain varying degrees of hydrophobicity ultimately affecting their water-solubility and recognition properties. The crown-binding (figure 1) of the anions from a series of monovalent sodium salts spans the entire spectrum of the Hofmeister series, where the “salting-in” salts have the stronger affinity for the crown, whilst also demonstrating an inverse Hofmeister effect where these same salts result in host precipitation at increased equivalence of anion. The critical precipitation concentration (CPC) correlates with the affinity (figure 2a) as well as the aqueous entropy of the anions (figure 2b) whilst the affinity itself displays a direct Hofmeister trend (figure 2c). The binding affinity and reverse Hofmeister effect were investigated by <sup>1</sup>H NMR titration, Isothermal Titration Calorimetry (ITC), and Dynamic Light Scattering (DLS). Ultimately, these results suggest modes of addressing the specific needs of supramolecular chemists by addressing the water-solubilizing groups of the host molecule to bring about specific solubility, affinity, and selectivity.

Getting specific about non-specific interactions: Functional group dependence for the inverse Hofmeister series

255th National Meeting (2018)

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