Water-Soluble Ionic Metal-Organic Polyhedra as a Versatile Platform for Enzyme Bio-immobilization.

Metal-organic polyhedra (MOPs) can act as elementary structural units for the design of modular porous materials; however, their association with biological systems remains greatly restricted by their typically low stabilities and solubilities in water. Herein, we describe the preparation of novel MOPs bearing either anionic or cationic groups and exhibiting a high affinity for proteins. Simple mixing of the protein bovine serum albumin (BSA) and ionic MOP aqueous solutions resulted in the spontaneous formation of MOP-protein assemblies, in a colloidal state or as solid precipitates depending on the initial mixing ratio. The versatility of the method was further illustrated using two enzymes, catalase and cytochrome c, with different sizes and isoelectric points (pI's) below and above 7. This mode of assembly led to the high retention of catalytic activity and enabled recyclability. Furthermore, the co-immobilization of cytochrome c with highly charged MOPs resulted in a substantial 44-fold increase of its catalytic activity.

Crystalline assembly of metal-organic polyhedra driven by ionic interactions with polyoxometalates.

Charge-driven self-assembly of cationic zirconium-based metal-organic polyhedra (MOPs) with polyoxometalates (POMs) leads to a series of porous crystalline salts, prepared by simple mixing of soluble precursors. The reactivity of immobilized POMs was greatly increased, as demonstrated by their fast reduction by hydrazine vapors, without loss of structural integrity.