Three-Dimensional COF with “the” Topology as Enzyme Host: Comparative Insights into Activity, Stability, and Reusability in Surface versus Pore Immobilization Strategies

Three-dimensional (3D) covalent organic frameworks (COFs) with high connectivity provide an intricate yet robust scaffold for precise enzyme immobilization—striking a balance between substrate accessibility and enzyme protection, both critical for efficient biocatalysis. In this work, we investigate the effects of enzyme localization—surface anchoring versus pore entrapment—on catalytic performance by employing two structurally distinct 3D COFs, TUS-39 and TUS-64, as host matrices. We herein report the designed synthesis of TUS-39, a new (8,3)-connected COF featuring the topology and microporous structure (0.9 nm) through dynamic imine condensation between a D2h-symmetric tetragonal prism node and a D3h-symmetric planar triangular linker. This architecture enabled efficient surface anchoring of amano lipase PS, resulting in remarkably high catalytic activity and reusability in the kinetic resolution of racemic (R,S)-1-phenylethanol via transesterification. In contrast, the mesoporous (4.7 nm) COF TUS-64 facilitated encapsulation of the enzyme within its pore channels, affording enhanced stability under harsh chemical and thermal environments. The comparative study reveals that surface immobilization on the tightly connected microporous network of TUS-39 enhances substrate accessibility and catalytic conversion rate, while the internal confinement within the larger mesopores of TUS-64 protects the biocatalyst from denaturation and degradation, albeit with a modest trade-off in catalytic efficiency. These findings underscore the critical interplay between surface characteristics, pore metrics, and enzyme localization in dictating the overall efficiency, resilience, and recyclability of COF-supported biocatalysts.