Programmable Ammonium Sequestration and Release via a Kinetically Gated Supramolecular Host ^†

Comprehensive Summary Biological ion channels regulate ion flux through gating and blockade, yet translating such precise kinetic control into discrete synthetic containers remains a fundamental challenge in supramolecular chemistry. Here we report a bioinspired calix[4]trap ion container engineered with a crown ether binding site at its aperture to implement ion controlled gating. Specifically, K + and NH 4 + occupy a deeply buried pocket, whereas Cs + preferentially and exclusively binds at the entrance, acting as a removable gatekeeping ion that restricts access to the cavity. Consequently, Cs + bound at the entrance hinders both ion encapsulation and release, enabling direct observation of otherwise rapid uptake processes and providing a quantitative handle to decelerate release. Importantly, the release kinetics are strictly decoupled from the thermodynamic driving force. The release rate is governed by the concentration of the gatekeeping Cs + rather than the stoichiometric amount of the chemical trigger (DBU). This allows for sustained and programmable ion release over hours through a simple stoichiometric input. This minimal noncovalent gatekeeping strategy offers a general blueprint for designing tunable ion carrier containers and programmable biomimetic transport systems.