Xizhen Lian

Stable metal-organic frameworks containing single-molecule traps for enzyme encapsulation

Enzymatic catalytic processes possess great potential in chemical manufacturing, including pharmaceuticals, fuel production and food processing. However, the engineering of enzymes is severely hampered due to their low operational stability and difficulty of reuse. Here, we develop a series of stable metal-organic frameworks with rationally designed ultra-large mesoporous cages as single-molecule traps (SMTs) for enzyme encapsulation. With a high concentration of mesoporous cages as SMTs, PCN-333(Al) encapsulates three enzymes with record-high loadings and recyclability. Immobilized enzymes that most likely undergo single-enzyme encapsulation (SEE) show smaller Km than free enzymes while maintaining comparable catalytic efficiency. Under harsh conditions, the enzyme in SEE exhibits better performance than free enzyme, showing the effectiveness of SEE in preventing enzyme aggregation or denaturation. With extraordinarily large pore size and excellent chemical stability, PCN-333 may be of interest not only for enzyme encapsulation, but also for entrapment of other nanoscaled functional moieties.

Cooperative Cluster Metalation and Ligand Migration in Zirconium Metal–Organic Frameworks

Cooperative cluster metalation and ligand migration were performed on a Zr-MOF, leading to the isolation of unique bimetallic MOFs based on decanuclear Zr6M4 (M = Ni, Co) clusters. The M(2+) reacts with the μ3-OH and terminal H2O ligands on an 8-connected [Zr6O4(OH)8(H2O)4] cluster to form a bimetallic [Zr6M4O8(OH)8(H2O)8] cluster. Along with the metalation of Zr6 cluster, ligand migration is observed in which a Zr-carboxylate bond dissociates to form a M-carboxylate bond. Single-crystal to single-crystal transformation is realized so that snapshots for cooperative cluster metalation and ligand migration processes are captured by successive single-crystal X-ray structures. In(3+) was metalated into the same Zr-MOF which showed excellent catalytic activity in the acetaldehyde cyclotrimerization reaction. This work not only provides a powerful tool to functionalize Zr-MOFs with other metals, but also structurally elucidates the formation mechanism of the resulting heterometallic MOFs.

Derivation and Decoration of Nets with Trigonal-Prismatic Nodes: A Unique Route to Reticular Synthesis of Metal–Organic Frameworks

Quests for advanced functionalities in metal-organic frameworks (MOFs) inevitably encounter increasing complexity in their tailored framework architectures, accompanied by heightened challenges with their geometric design. In this paper, we demonstrate the feasibility of rationally exploiting topological prediction as a blueprint for predesigned MOFs. A new triangular frusta secondary building unit (SBU), {Zn4(tz)3}, was bridged by three TDC(2-) fragments to initially form a trigonal prismatic node, {Zn8(tz)6(TDC)3} (Htz = 1H-1,2,3-triazole and H2TDC = 2,5-thiophenedicarboxylic acid). Furthermore, the trigonal prism unit can be considered as a double SBU derived from triply bound triangular frusta. By considering theoretical derived nets for linking this trigonal-prismatic node with ditopic, tritopic, and tetratopic linkers, we have synthesized and characterized a new family of MOFs that adopt the decorated lon, jea, and xai nets, respectively. Pore sizes have also been successively increased within TPMOF-n family, which facilitates heterogeneous biomimetic catalysis with Fe-porphyrin-based TPMOF-7 as a catalyst.

High efficiency and long-term intracellular activity of an enzymatic nanofactory based on metal-organic frameworks

Enhancing or restoring enzymatic function in cells is highly desirable in applications ranging from ex vivo cellular manipulations to enzyme replacement therapies in humans. However, because enzymes degrade in biological milieus, achieving long-term enzymatic activities can be challenging. Herein we report on the in cellulo properties of nanofactories that consist of antioxidative enzymes encapsulated in metal–organic frameworks (MOFs). We demonstrate that, while free enzymes display weak activities for only a short duration, these efficient nanofactories protect human cells from toxic reactive oxygen species for up to a week. Remarkably, these results are obtained in spite of the nanofactories being localized in lysosomes, acidic organelles that contain a variety of proteases. The long-term persistence of the nanofactories is attributed to the chemical stability of MOF in low pH environment and to the protease resistance provided by the protective cage formed by the MOF around the encapsulated enzymes.Cellular delivery of proteins is currently limited by inefficient release from their carrier or by altering the protein structure after chemical modification. Here the authors use metal-organic frameworks which act as nanofactories and show a supported enzymatic activity for an extended period of time.

Enzyme‐MOF Nanoreactor Activates Nontoxic Paracetamol for Cancer Therapy

Prodrug activation, by exogenously administered enzymes, for cancer therapy is an approach to achieve better selectivity and less systemic toxicity than conventional chemotherapy. However, the short half-lives of the activating enzymes in the bloodstream has limited its success. Demonstrated here is that a tyrosinase-MOF nanoreactor activates the prodrug paracetamol in cancer cells in a long-lasting manner. By generating reactive oxygen species (ROS) and depleting glutathione (GSH), the product of the enzymatic conversion of paracetamol is toxic to drug-resistant cancer cells. Tyrosinase-MOF nanoreactors cause significant cell death in the presence of paracetamol for up to three days after being internalized by cells, while free enzymes totally lose activity in a few hours. Thus, enzyme-MOF nanocomposites are envisioned to be novel persistent platforms for various biomedical applications.

Delivery of nanoparticles inside the cytosol of live cells for the monitoring of cellular processes (Conference Presentation)

The delivery of MOF-enzyme nanofactories (50-100 nm in diameter) into the cytosol of cells will be presented. Delivery is achieved by co-incubation with the peptide dfTAT, a dimeric construct of the HIV TAT peptide. Cytosolic targeting is highly efficient and dfTAT circumvents the endosomal entrapment of macromolecular cargos. The delivery protocol does not require interactions between dfTAT and nanoparticles, thereby eliminating complex labeling steps. Cytosolic access is rapid and cells recover from the delivery process in a matter of minutes. Overall, this approach should facilitate the monitoring of intracellular processes by nanoparticle probes.