Combined In Situ Synchrotron X-Ray and Electron Microscopy Studies of Metal-Organic Framework Crystallization

Protein-metal-organic frameworks (p-MOFs) offer a diverse platform for immobilization of biomolecules to enhance their stability and enzymatic activity. In a process analogous to biomineralization, biomolecules can induce the formation of p-MOF structures. However, the nucleation and growth mechanisms of these biomimetic crystallizations have not been well investigated. By gaining a better understanding of the parameters that govern nucleation and growth of MOF systems, a connection can be drawn between the structure formation and p-MOF function that can aid in the development of new MOFs for specific purposes. In this work we studied the formation of a model zeolitic imidazole framework (ZIF-8) and the factors that lead to the formation of different polymorphs such as ligand to metal ratio, the introduction of a biomolecule, and solution pH. To understand the mechanism and factors that affect ZIF-8 formation of sodalite (SOD) and diamondoid (DIA) polymorph formation, studies were performed using time resolved in-situ small and wide X-ray scattering (SAXS/WAXS), Liquid Phase Electron Microscopy (LP-EM), Cryo-Electron Microscopy (Cryo-EM), micro-electron diffraction (microED) and electrospray ionization MS (ESI-MS). These data allow us to determine the influence of prenucleation clusters on final polymorph formation and the effect that a biomolecule has on changing the prenucleation clusters leading to a different polymorph. Understanding polymorph control in p-MOF systems will lead to a better understanding of the structure function relationship and tighter control in the development of new MOFs.