MOF-templated rough, ultrathin inorganic microcapsules for enzyme immobilization

Abstract

Ultrathin titania microcapsules with rough surfaces were prepared by using a metal-organic framework (ZIF-8) as one kind of hard template to mediate the structures of the microcapsule shell. Specifically, CaCO 3 particles were first coated with tannic acid (TA) followed by the deposition of hydrophobic ZIF-8 and another TA layer, the obtained particles were then assembled with protamine/TiO 2 bilayers through biomimetic mineralization. Finally, the microcapsules (Z-TiO 2 ) were obtained after simultaneously removing CaCO 3 and ZIF-8 templates using ethylenediaminetetraacetic acid (EDTA). The coordination interaction between TA and ZIF-8 ensured the robust templating which endowed the microcapsules with a rough surface and an ultrathin microcapsules shell (100 nm) with 4.4 nm pore size. Moreover, the surface roughness of microcapsules can be regulated by changing the size of ZIF-8 crystals. The microcapsules were then utilized to immobilize penicillin G acylase (PGA). And PGA@Z-TiO 2 retained 69% activity of equivalent free PGA with a loading capacity of 160 mg g À1 . The PGA@Z-TiO 2 microcapsules exhibited superior reusability: after recycling 8 times, the conversion of the enzymatic reaction remained 36.0%, which was twice higher than that of PGA@TiO 2 (14.7%). Moreover, compared with free PGA and PGA@TiO 2 microcapsules, PGA@Z-TiO 2 microcapsules exhibited higher thermal and storage stability. After storing for 60 days, the relative activity of PGA@Z-TiO 2 remained 89.6%, which was higher than that of free PGA (34.5%) and PGA@TiO 2 (73.6%). ZIF-8 can be envisioned to be a novel class of hard template for preparing a broad variety of microcapsules with different hierarchical structures. † Electronic supplementary information (ESI) available: SEM and TEM images of ZIF-8 particles, nitrogen adsorption-desorption isotherms of ZIF-8 particles, and UV-vis spectra of the assembled multilayer film. See Fig. 12 Recycling stability of PGA@Z-TiO 2 and PGA@TiO 2 (a), temperature stability (b), pH stability (c), and storage stability (d) of free PGA, PGA@Z-TiO 2 and PGA@TiO 2 MCs.

Biocompatibility characteristics of the metal organic framework ZIF-8 for therapeutical applications

“…We used 50 mM Ethylenediaminetetraacetic acid (EDTA) as a chelating agent for our positive control. [33] Furthermore two phosphate-citrate buffers at pH 5 and 6 were used and finally the cell medium DMEM at pH 7.4. After 5 days on a shaker at 150 rpm, the tubes were centrifuged and the supernatant was transferred into a new tube for further preparation steps.…”

Structural Insight into Stabilization of Pickering Emulsions with Fe3O4@SiO2 Nanoparticles for Enzyme Catalysis in Organic Media

“…It is known that the Michaelis–Menten equation is related to the rate of an enzyme‐catalyzed reaction to the concentration of substrateswhere R si (×10 −3 m s −1 ) is the initial enzyme‐catalyzed reaction rate in Pickering emulsion system, C si (×10 −3 m ) is the initial substrate concentration at the W/O interfaces, K m (×10 −3 m ) is the Michaelis–Menten constant, and r max (×10 −3 m s −1 ) is the maximum reaction rate in this system. Within the Pickering emulsion systems (which catalyze the oil‐soluble substrates at the W/O interfaces of emulsion droplets by enzymes in the aqueous system), the enzymatic reaction rate is also crucially depended on the diffusion of substrates from oil phase to the W/O interfaces . The diffusion rate equation is as followingwhere R sd (×10 −3 m s −1 ) is the diffusion rate of substrates from oil phase to the W/O interfaces, k G (g s −1 m −2 ) is the mass transfer coefficient, and S g (m 2 g −1 ) is the specific surface area of the total Pickering emulsion droplets.…”

Metal–Organic Framework-Based Enzyme Biocomposites

“…Subsequently, full removal of the CaCO3/ZIF-8 core could be achieved by treating the biocomposite with EDTA. 65 After the dissolution of the MOF template, PGA encapsulated in TiO2 retained activity, furthermore, the composite was reused eight times and showed higher activity than the same enzyme immobilized into silica-based monoliths. Alternatively, Chen and co-workers 66 encapsulated bovine serum albumin (BSA) and catalase (CAT) in ZIF-90 or ZPF-10 2 (constructed from Zn 2+ and 2-hydroxy-5-fluoropyrimidine; ZPF = zeolitic pyrimidine framework), which allowed a covalent-organic framework (COF) shell to be grown on the surface of the composites via condensation of 1,3,5-triformylbenzene (or 1,3,5-tris(pformylphenyl)benzene) and 2,5-bis(ethoxy)terephthalohydrazide (COF-42-B or COF-43-B).…”