Enzyme Immobilization in Mesoporous Metal-Organic Frameworks by SANS*

Metal-organic frameworks (MOFs) are an emerging class of solid supports for enzyme immobilization owing to their high accessible pores and tunable pore size and surface for increasing affinity between enzymes and supports. Although the immobilization of enzymes by MOFs has shown improved catalytic efficiency, enzymes’ location in the hierarchical solid matrix, the relationship between enzyme dimension and pore size, and conformations of encapsulated enzymes remain elusive. In this work, we present a small-angle neutron scattering (SANS) characterization of cytochrome C (CyT. C) adsorbed into Tb-TATB under in-situ conditions. The scattering curve of unloaded Tb-TATB showed mass fractal feature arising from the network structure and a shoulder at ~0.03Å presumably corresponding to disordered building blocks or defects in the crystals. The correlation peaks located between 0.07 and 0.4 Å^-1 were attributed to ordered arrangement of two nanopores, 39 Å and 47 Å, respectively. Upon loading of the CyT. C, substantial decreasing intensities of Bragg peaks proved the entry of enzyme molecules into the MOF’s cages with entry windows that are smaller than the enzyme.