Zr(IV)-based metal-organic frameworks (MOFs) such as the Zr(IV) trimesate MOF-808 are promising materials for catalytic applications. In this work, we report an aqueous solution-based room temperature strategy to produce well-defined monodispersed MOF-808 nanocrystals down to 35 nm with a high space-time yield, up to 2516 g/ m 3 / day, and an excellent crystallinity and porosity. The resulting nanocrystals show remarkable colloidal dispersion during one day in a wide range of nanoparticles concentrations. As a result, 35 nm MOF-808 colloidal-level nanocrystals exhibit the highest rate of selective peptide bond and protein hydrolysis among reported Zr(IV)-based MOFs. This result may open new opportunities for highly efficient peptide or protein hydrolysis using scalable nano-catalyst.
The discovery of nanozymes for selective fragmentation of proteins would boost the emerging areas of modern proteomics, however, the development of efficient and reusable artificial catalysts for peptide bond hydrolysis is challenging. Here we report the catalytic properties of a zirconium metal-organic framework, MIP-201, in promoting peptide bond hydrolysis in a simple dipeptide, as well as in horse-heart myoglobin (Mb) protein that consists of 153 amino acids. We demonstrate that MIP-201 features excellent catalytic activity and selectivity, good tolerance toward reaction conditions covering a wide range of pH values, and importantly, exceptional recycling ability associated with easy regeneration process. Taking into account the catalytic performance of MIP-201 and its other advantages such as 6-connected Zr6 cluster active sites, the green, scalable and cost-effective synthesis, and good chemical and architectural stability, our findings suggest that MIP-201 may be a promising and practical alternative to commercially available catalysts for peptide bond hydrolysis.
The catalytic activity of metal−organic frameworks (MOFs) toward peptides and proteins provides an attractive route for the development of nanozymes for applications in biotechnology and proteomics, particularly in the field of protein identification using mass spectrometry. Here, we report that carefully tuning the Ce/Zr metal ratio is a promising strategy to overcome structural limitations that originate from the high connectivity of the Zr 6 node and also increase the peptidase activity of the MOF while preserving the material's nano-topology and stability. A series of bimetallic Ce/Zr-UiO-66 MOFs, in which the amount of Ce was systematically varied from 28 to 87 mol%, have been shown to efficiently catalyze peptide bond hydrolysis in a large variety of peptides with different functional groups, demonstrating their nanozyme potential. Detailed kinetic analysis of the hydrolysis of peptide bonds with a range of Ce/Zr MOFs suggests that among the different metallic clusters present in UiO-66, the Ce 6 clusters have superior reactivity compared to the CeZr 5 sites. In addition to increasing the catalytic potency of the MOF toward peptide bond hydrolysis, the introduction of Ce(IV) also broadens the reaction scope of MOF catalysts. Selective oxidation of the thiol sidechains and the formation of disulfide bridges have been observed at physiological pH both in cysteine and in glutathione tripeptide as substrates. The rate of oxidation is directly proportional to the amount of Ce present in the MOF, demonstrating that the introduction of Ce into these nanomaterials is a promising strategy to introduce oxidase activity toward biologically relevant substrates. In addition to this, adsorption of dipeptides onto MOF nanomaterials has been studied for the first time. These studies revealed a close link between the nature of peptide side chains and the extent of their adsorption, which has a direct influence on their ability to act as substrates in MOF-catalyzed reactions.
The performance of MOFs in catalysis is largely derived from structural features, and much work has focused on introducing structural changes such as defects or ligand functionalisation to boost the reactivity of the MOF. However, the effects of different parameters chosen for the synthesis on the catalytic reactivity of the resulting MOF remains poorly understood. Here, we evaluate the role of metal precursor on the reactivity of Zr-based MOF-808 towards hydrolysis of the peptide bond in the glycylglycine model substrate. In addition, the effect of synthesis temperature and duration has been investigated. Surprisingly, the metal precursor was found to have a large influence on the reactivity of the MOF, surpassing the effect of particle size or number of defects. Additionally, we show that by careful selection of the Zr-salt precursor and temperature used in MOF syntheses, equally active MOF catalysts could be obtained after a 20 minute synthesis compared to 24 h synthesis.
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