Exploiting the Dimerization Characteristic of HPO to Promote Its Selective Recognition by a Tetra-Amido Macrocycle.

Creating a confined cavity that matches the size and binding site of the substrate is a prevalent strategy to achieve selective recognition of specific anions. However, this not only requires sophisticated receptor design but also leads to challenging receptor synthesis. In this contribution, by utilizing the dimerization characteristic of HPO, we demonstrate that selective recognition of HPO can also be achieved in DMSO by a synthetically simple tetra-amido macrocycle (). By reaction condition optimization, the yield of the final cyclization reaction was improved. Through H NMR titration studies, we exhibit a sharp contrast in the binding affinity between HPO and other anions, as well as the exclusive recognition of HPO from competitive environments containing various anions. Through Job's plot, nonlinear fitting, single-crystal X-ray diffraction, computational study, variable temperature NMR, and DOSY NMR, the binding mechanism of +HPO was extensively studied, including binding stoichiometry (1:2 host-guest), stability constant (β = 1.4 × 10 M), recognition sites, possible binding structure, and the corresponding hydrodynamic radius (). Binding studies in DCM and 50% methanol/chloroform further support the proposed binding mechanism. This study therefore explores a new approach to achieve selective recognition by taking advantage of the self-assembly characteristics of substrates.