Cavity Formation in Protein@Metal-Organic Frameworks Through Late-Stage Crystal Dissolution

Area of Science:

• Materials Science
• Biomaterials Engineering
• Nanotechnology

Background:

• Proteins are used to template metal-organic frameworks (MOFs), creating protein@MOFs (p@MOFs) with tunable porosity.
• Understanding protein influence on MOF crystallization mechanisms is crucial for biohybrid material development.

Purpose of the Study:

• To elucidate the crystallization pathway of ferritin@ZIF-8 (Fn@ZIF-8) using distributed electron microscopy.
• To investigate the role of proteins in MOF nucleation, growth, and defect formation.

Main Methods:

• Utilized a combination of cryogenic transmission electron microscopy (cryo-TEM), cryogenic electron tomography (cryo-ET), and liquid-phase TEM (LP-TEM).
• Employed the ferritin iron oxide core as an intrinsic nanoscale tracer to monitor structural transformations.

Main Results:

• Visualized the transformation from amorphous precursors to crystalline Fn@ZIF-8 particles, including ripening and aggregation.
• Observed the emergence of large, surface-accessible cavities through localized dissolution and recrystallization during later growth stages.
• Documented protein enrichment at crystal peripheries and depletion from cavity-rich regions, linking protein behavior to framework restructuring and defect formation.

Conclusions:

• Protein organization and dissolution-driven restructuring are key contributors to defect formation in p@MOFs.
• Established a mechanistic framework for hierarchical porosity development in p@MOFs.
• Demonstrated the utility of distributed electron microscopy for studying biohybrid crystallization pathways.