Engineering Hierarchy to Porous Organic Cages for Biomimetic Catalytic Applications

Abstract

In nature, hierarchy is a core organizational principle intricately woven into biological systems, facilitating the compartmentalization of enzymes within living cells. This spatial arrangement enables multistep metabolic reactions to occur simultaneously with remarkable efficiency and precision. Inspired by this, significant progress has been made in artificial biomimetic heterogeneous catalytic systems using porous materials like metal–organic frameworks, porous organic polymers, and zeolites. Among these, molecular cages, with their well-defined cavities, stand out as synthetic models for enzyme-mimic catalysis. They not only provide biomimetic microenvironments for substrate binding, mimicking the highly specific and efficient interactions observed in natural enzymatic systems, but also integrate active centers within confined nanoscale spaces, enabling synergistic functionality. However, research in cage-based biomimetic catalysts has largely focused on tailoring the cavity environment─such as optimizing cavity size, pore geometry, and functional groups on the pore walls─to regulate catalytic processes, while comparatively less attention has been given to the catalytic role of metal centers, akin to the critical function in natural metalloenzymes. While metal nodes in metal–organic cages can act as active sites, their catalytic efficiency may be hindered by coordination saturation. Moreover, the restricted (sub)nanoscale space of molecular cage reactors limits their capacity to host larger active sites or accommodate bulky substrates. Thus, rationally engineering the confined spaces and optimizing the spatial arrangement of active sites within molecular cage-based catalytic systems is essential for advancing the field and unlocking their full potential.