Control of Structure Topology and Spatial Distribution of Biomacromolecules in Protein@ZIF-8 Biocomposites

The protective capacity and applications of biomimetically mineralized biomacromolecule zeolitic imidazolate framework (ZIF) composites are likely dependent on the localization of the biomolecule and the topology of the mineralized ZIF coating. Herein, we identify reaction conditions to reliably yield the porous ZIF-8 sodalite topology (high ZIF-8 precursor concentrations; high 2-methylimidazole:Zn2+ ratios) in preference to other more dense phases. Furthermore, protocols to universally prepare biocomposites with a range of biomacromolecules are canvassed. Through the use of fluorophore-tagged proteins and confocal laser scanning microscopy (CLSM), we further establish the positioning of biomolecules within ZIF-8 crystals. CLSM reveals subsurface localization with fluorescein-tagged bovine serum albumin (BSA) or full encapsulation with rhodamine B-tagged BSA. These observations allowed us to demonstrate that core-shell ZIF-8 growth strategies afford complete encapsulation with varying thicknesses of potentially active biocomposite or protective ZIF-8. The demonstrated control over ZIF topology (enabling mass transport) and biomacromolecule localization is critical for applications of MOF biocomposites in catalysis.