Driving forces of anion binding in water in contrast to nonpolar environments are of high interest because of their relevance to biology and medicine. Here we report a neutral bambusuril macrocycle (1), soluble in both water and nonpolar solvents due to decoration with 12 polyethylene glycol-based substituents. The new bambusuril has the highest affinity for I in pure water ever reported for a synthetic macrocycle relying on hydrogen bonding interactions rather than metal coordination or Coulombic forces. Isothermal titration calorimetry (ITC) experiments in nine different solvents, ranging from polar water to nonpolar carbon tetrachloride, provided insight into the forces responsible for halide binding by bambusurils. The different importance of anion solvation and solvent expulsion from the cavity of the macrocycle in various solvents is illustrated by the fact that halide binding in water and chloroform is exclusively driven by favorable enthalpy with an entropic penalty, while in alcohols and nonpolar solvents, both favorable enthalpy and entropy contribute to anion encapsulation. DFT calculations and correlation of thermodynamic data with the solvent Swain acity parameter further underscore the importance of solvent effects on anion binding by bambusurils.

A sulphonamidic moiety was utilized as an electron‐withdrawing group for enhancement of anion complexation features of urea‐based receptors. A series of receptors varying in acidity of sulphonamidic and urea NH groups was synthesized and thoroughly tested. The individual complexation properties reflect deprotonation/complexation equilibrium in a given molecule as a function of the substitution. The receptors containing electron‐donating groups in conjugation to the sulphonamidic moiety showed higher association constants towards H2PO4− and carboxylate anions, while those containing electron‐withdrawing groups inclined to deprotonation of sulphonamidic NH. The deprotonation issue can be avoided by alkylation at the early step of receptor synthesis or it can be utilized for insertion of suitable groups that enable its anchoring on various substrates to form more elaborated receptor structures.

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