Nanoproteases: Alternatives to Natural Protease for Biotechnological Applications.

Some nanomaterials with intrinsic protease-like activity have the advantages of good stability, biosafety, low price, large-scale preparation and unique property of nanomaterials, which are promising alternatives for natural proteases in various applications. An especial term, "nanoprotease", has been coined to stress the intrinsic proteolytic property of these nanomaterials. As a new generation of artificial proteases, they have become a burgeoning field, attracting many researchers to design and synthesize high performance nanoproteases. In this review, we summarize recent progress on all types of nanoproteases with regard of their activity, mechanism and application and introduce a new and effective strategy for engineering high-performance nanoproteases. In addition, we discuss the challenges and opportunities of nanoprotease research in the future.

Supramolecular Self-Assembly of Proteins Promoted by Hybrid Polyoxometalates.

Controlling the formation of supramolecular protein assemblies and endowing them with new properties that can lead to novel functional materials is an important but challenging task. In this work, a new hybrid polyoxometalate is designed to induce controlled intermolecular bridging between biotin-binding proteins. Such bridging interactions lead to the formation of supramolecular protein assemblies incorporating metal-oxo clusters that go from several nanometers in diameter up to the micron range. Insights into the self-assembly process and the nature of the resulting biohybrid materials are obtained by a combination of Small Angle X-ray Scattering (SAXS), Transmission Electron Microscopy (TEM), and Dynamic Light Scattering (DLS), along with fluorescence, UV-vis, and Circular Dichroism (CD) spectroscopy. The formation of hybrid supramolecular assemblies is determined to be driven by biotin binding to the protein and electrostatic interactions between the anionic metal-oxo cluster and the protein, both of which also influence the stability of the resulting assemblies. As a result, the rate of formation, size, and stability of the supramolecular assemblies can be tuned by controlling the electrostatic interactions between the cluster and the protein (e.g., through varying the ionic strength of the solution), thereby paving the way toward biomaterials with tunable assembly and disassembly properties.

Embedding Multiple Magnetic Components in Carbon Nanostructures via Metal-Oxo Cluster Precursor for High-Efficiency Low-/Middle-Frequency Electromagnetic Wave Absorption.

With the advent of wireless technology, magnetic-carbon composites with strong electromagnetic wave (EMW) absorption capability in low-/middle-frequency range are highly desirable. However, it remains challenging for rational construction of such absorbers bearing multiple magnetic components that show uniform distribution and favorable magnetic loss. Herein, a facile metal-oxo cluster (MOC) precursor strategy is presented to produce high-efficiency magnetic carbon composites. Nanosized MOC Fe15 shelled with organic ligands is employed as a novel magnetic precursor, thus allowing in situ formation and uniform deposition of multicomponent magnetic Fe/Fe3O4@Fe3C and Fe/Fe3O4 nanoparticles on graphene oxides (GOs) and carbon nanotubes (CNTs), respectively. Owing to the good dispersity and efficient magnetic-dielectric synergy, quaternary Fe/Fe3O4@Fe3C-GO exhibits strong low-frequency absorption with RLmin of -53.5 dB at C-band and absorption bandwidth covering 3.44 GHz, while ultrahigh RLmin of -73.2 dB is achieved at X-band for ternary Fe/Fe3O4-CNT. The high performance for quaternary and ternary composites is further supported by the optimal specific EMW absorption performance (-15.7 dB mm-1 and -31.8 dB mm-1) and radar cross-section reduction (21.72 dB m2 and 34.37 dB m2). This work provides a new avenue for developing lightweight low-/middle-frequency EMW absorbers, and will inspire the investigation of more advanced EMW absorbers with multiple magnetic components and regulated microstructures.

Sub-second pair distribution function using a broad bandwidth monochromator.

Here the use of a broad energy bandwidth monochromator, i.e. a pair of B4C/W multilayer mirrors (MLMs), is demonstrated for X-ray total scattering (TS) measurements and pair distribution function (PDF) analysis. Data are collected both on powder samples and from metal oxo clusters in aqueous solution at various concentrations. A comparison between the MLM PDFs and those obtained using a standard Si(111) double-crystal monochromator shows that the measurements yield MLM PDFs of high quality which are suitable for structure refinement. Moreover, the effects of time resolution and concentration on the quality of the resulting PDFs of the metal oxo clusters are investigated. PDFs of heptamolybdate clusters and tungsten α-Keggin clusters from X-ray TS data were obtained with a time resolution down to 3 ms and still showed a similar level of Fourier ripples to PDFs obtained from 1 s measurements. This type of measurement could thus open up faster time-resolved TS and PDF studies.

High-Valence Metal-Organic Framework Materials Constructed from Metal-Oxo Clusters: Opportunities and Challenges.

Metal-organic framework (MOF), which possesses stable framework structure constructed by highly connected metal-oxo cluster nodes and organic linkers, has shown great promise in gas storage, adsorption, and separation, owing to the high surface areas, tunable pore aperture, and rich functional groups. In this review article, we summarized recent progress made in synthesizing high-valence MOF (e. g., UiO-66, MIL-125, PCN-22, and MIP-207) with metal-oxo cluster as metal source. Of particular note, recent breakthroughs in the preparation of UiO-66 and MIL-125 membranes with the corresponding Zr6 -oxo and Ti8 -oxo cluster sources (e. g., Zr6 O4 (OH)4 (OAc)12 and Ti8 O8 (OOCR)16 clusters) possessing superior separation performance were highlighted. In the end, an outlook on the preparation of versatile high-valence MOF membranes with the corresponding metal-oxo clusters as metal sources was highlighted.

Protection of Ag Clusters by Metal-Oxo Modules.

Monodisperse and atomically precise Ag nanoclusters have attracted considerable recent research interest. A conventional silver cluster usually consists of a silver metallic kernel and an organic peripheral ligand shell. Nevertheless, the present inevitable problem is the unsatisfied stability of such nanoclusters. In this concept, we will give an introduction to Ag clusters protected by metal-oxo modules, which exhibit enhanced stability and unique properties. Accordingly, three different types of clusters are summarized: (1) Ag clusters protected by mononuclear oxometallates; (2) Ag clusters protected by block-like metal-oxo clusters; (3) Ag clusters protected by hollow-like metal-oxo clusters. The aim of this concept is to offer possible general guidance and insight into future rational design of more metal-oxo clusters protected silver clusters or even other coinage metal nanoclusters.

Discrete Hf18 Metal-oxo Cluster as a Heterogeneous Nanozyme for Site-Specific Proteolysis.

The selective hydrolysis of proteins by non-enzymatic catalysis is difficult to achieve, yet it is crucial for applications in biotechnology and proteomics. Herein, we report that discrete hafnium metal-oxo cluster [Hf18 O10 (OH)26 (SO4 )13 ⋅(H2 O)33 ] (Hf18 ), which is centred by the same hexamer motif found in many MOFs, acts as a heterogeneous catalyst for the efficient hydrolysis of horse heart myoglobin (HHM) in low buffer concentrations. Among 154 amino acids present in the sequence of HHM, strictly selective cleavage at only 6 solvent accessible aspartate residues was observed. Mechanistic experiments suggest that the hydrolytic activity is likely derived from the actuation of HfIV Lewis acidic sites and the Brønsted acidic surface of Hf18 . X-ray scattering and ESI-MS revealed that Hf18 is completely insoluble in these conditions, confirming the HHM hydrolysis is caused by a heterogeneous reaction of the solid Hf18 cluster, and not from smaller, soluble Hf species that could leach into solution.

Insights into Catalytic Gas-Phase Hydrolysis of Organophosphate Chemical Warfare Agents by MOF-Supported Bimetallic Metal-Oxo Clusters.

Zirconium-based metal-organic frameworks (Zr-MOFs) have been reported to be efficient catalysts for the hydrolysis of organophosphate chemical warfare agents (CWAs) in buffered solutions. However, for the gas-phase reaction, which is more relevant to the situation in a battlefield gas mask application, the kinetics of Zr-MOF catalysts may be severely hindered by strong product inhibition. To improve the catalytic performance, we computationally screened a series of synthetically accessible Zr-MOF-supported bimetallic metal-oxo clusters in which the metal-oxygen-metal active motif is preserved, aiming to find catalysts that have lower binding affinities to the hydrolysis product. For the promising catalyst Al2O2(OH)2@NU-1000 identified from the screening using density functional theory, we mapped out the full reaction pathway of gas-phase dimethyl p-nitrophenolphosphate (DMNP) hydrolysis and analyzed the free energy profile as well as the turnover frequency (TOF). We found that the catalytic mechanism on the new catalyst is slightly different from the one on NU-1000, which also led to a different TOF-limiting step. Additional factors that can affect the overall catalytic performance in practical application, such as the amount of ambient moisture and the existence of acid gases that may poison the catalyst, have also been evaluated.

Antibacterial Activity of Polyoxometalates Against Moraxella catarrhalis.

The antibacterial activity of 29 different polyoxometalates (POMs) against Moraxella catarrhalis was investigated by determination of the minimum inhibitory concentration (MIC). The Preyssler type polyoxotungstate (POT) [NaP5W30O110]14- demonstrates the highest activity against M. catarrhalis (MIC = 1 µg/ml) among all tested POMs. Moreover, we show that the Dawson type based anions, [P2W18O62]6-, [(P2O7)Mo18O54]4-, [As2Mo18O62]6-, [H3P2W15V3O62]6-, and [AsW18O60]7- are selective on M. catarrhalis (MIC range of 2-8 µg/ml). Among the six tested Keggin type based POTs ([PW12O40]3-, [H2PCoW11O40]5-, [H2CoTiW11O40]6-, [SiW10O36]8-, [SbW9O33]9-, [AsW9O33]9-), only the mono-substituted [H2CoTiW11O40]6- showed MIC value comparable to those of the Dawson type group. Polyoxovanadates (POVs) and Anderson type POMs were inactive against M. catarrhalis within the tested concentration range (1-256 µg/ml). Four Dawson type POMs [P2W18O62]6-, [(P2O7)Mo18O54]4-, [As2Mo18O62]6-, [H3P2W15V3O62]6- and the Preyssler POT [NaP5W30O110]14- showed promising antibacterial activity against M. catarrhalis (MICs < 8 µg/ml) and were therefore tested against three additional bacteria, namely S. aureus, E. faecalis, and E. coli. The most potent antibacterial agent was [NaP5W30O110]14-, exhibiting the lowest MIC values of 16 µg/ml against S. aureus and 8 µg/ml against E. faecalis. The three most active compounds ([NaP5W30O110]14-, [P2W18O62]6-, and [H3P2W15V3O62]6-) show bacteriostatic effects in killing kinetics study against M. catarrhalis. We demonstrate, that POM activity is mainly depending on composition, shape, and size, but in the case of medium-size POTs (charge is more than -12 and number of addenda atoms is not being higher than 22) its activity correlates with the total net charge.

Thorium Oxo-Clusters as Building Blocks for Open Frameworks.

Fundamental understanding of tetravalent actinide chemistry is essential to optimize many steps of the nuclear fuel cycle, as well as to predict actinide speciation in the environment. Herein, we report synthesis and structure of three open inorganic frameworks composed of Th4+ -oligomers and sulfate anions. The compounds [Th10 O4 (OH)8 (SO4 )12 (H2 O)18 ]⋅28 H2 O (1), [Th9 O4 (OH)5 (SO4 )12 (H2 O)18 ]⋅ 1 TMA⋅18 H2 O (2), and [Th8.5 O4 (OH)4 (SO4 )12 (H2 O)18 ]⋅2 TMA⋅n H2 O (3) were obtained by slow evaporation of aqueous Th4+ -SO42- solutions, with variable SO42- :Th4+ ratios (SO42- :Th4+ =1:1, 1.5:1 and 2:1 for 1, 2, and 3; TMA=tetramethylammonium). The structure of 1 features a neutral open framework architecture with two interpenetrating networks, built from Th6 O4 (OH)412+ hexamers and Th2 (OH)26+ dimers, linked by sulfate anions. The complex anionic framework of 2 is built from hexamers, dimers, and monomers, with charge-balancing TMA cations. Compound 3 is very similar to 2, but it is constructed only from hexamers and monomers. Small angle X-ray scattering (SAXS) of the reaction solutions reveals pre-assembled hexamer building units in the presence of sulfate, and underlines the key role of the sulfate-oxoanion ligand on thorium polymerization processes.

The Role of Bi3+ in Promoting and Stabilizing Iron Oxo Clusters in Strong Acid.

Metal oxo clusters and metal oxides assemble and precipitate from water in processes that depend on pH, temperature, and concentration. Other parameters that influence the structure, composition, and nuclearity of "molecular" and bulk metal oxides are poorly understood, and have thus not been exploited. Herein, we show that Bi3+ drives the formation of aqueous Fe3+ clusters, usurping the role of pH. We isolated and structurally characterized a Bi/Fe cluster, Fe3 BiO2 (CCl3 COO)8 (THF)(H2 O)2 , and demonstrated its conversion into an iron Keggin ion capped by six Bi3+ irons (Bi6 Fe13 ). The reaction pathway was documented by X-ray scattering and mass spectrometry. Opposing the expected trend, increased cluster nuclearity required a pH decrease instead of a pH increase. We attribute this anomalous behavior of Bi/Fe(aq) solutions to Bi3+ , which drives hydrolysis and condensation. Likewise, Bi3+ stabilizes metal oxo clusters and metal oxides in strongly acidic conditions, which is important in applications such as water oxidation for energy storage.

Aqueous Bismuth Titanium-Oxo Sulfate Cluster Speciation and Crystallization.

Inorganic aqueous metal-oxo clusters are both functional "molecular metal oxides" and intermediates to understand metal oxide growth from water. There has been a recent surge in discovery of aqueous Ti-oxo clusters but without extensive solution characterization. We use small-angle and total X-ray scattering, dynamic light scattering, transmission electron microscopy, and a single-crystal X-ray structure to show that heterometals such as bismuth stabilize labile Ti-oxo sulfate clusters in aqueous solution.[Ti22 Bi7 O41 (OH)(OH2 )30 (SO4 )12 ]2+ features edge-sharing between the Ti and Bi polyhedra, in contrast to the dominant corner-linking of Ti-oxo clusters. Bi stabilizes the Ti-polyhedra, which are synergistically stabilized by the bidentate sulfates. Gained stability and potential functionality from heterometals is an incentive to develop more broadly the landscape of heterometallic Ti-oxo clusters.

Lead-rich carboxylate-substituted titanium-lead oxo clusters.

ABSTRACT: The carboxylate-substituted mixed-metal oxo clusters Pb6Ti6O9(acetate)(methacrylate)17 and Pb4Ti8O10(OiPr)18(acetate)2 contain a higher number of lead atoms in the cluster core than previously reported compounds. The metal atoms in both clusters are arranged in three layers of different composition, which are connected through oxygen, propionate and/or carboxylate bridges.

A heterobimetallic copper-titanium oxo cluster with a new structural motif.

ABSTRACT: Mixed-metal oxo clusters Cu4Ti5O6(OOCR)16 (OOCR = methacrylate, propionate) were obtained by reaction of titanium alkoxides and copper carboxylates with propionic or methacrylic acid.

Crown-ether-like structures derived from a Ti(8)O(8) (carboxylate)(16) metallacycle.

Mixed-metal clusters have been obtained from the reaction of titanium alkoxides with either strontium or lead acetate and methacrylic acid. The structures of the clusters are derived from the metallacycle Ti8 O8 (methacrylate)16 . The Sr and Pb atoms in Sr2 Ti8 O8 X2 (OOCMe)2 (methacrylate)16 (X: acetate or OiPr) and Pb2 Ti8 O8 (OBu)2 X2 (methacrylate)16 (BuOH)2 (X: acetate or methacrylate) occupy the central cavity of the Ti8 O8 ring. In addition to the crown-ether-like coordination of the ring oxygen atoms to the Sr or Pb atoms, bridging carboxylate ligands support the coordination of the latter atoms. In the compound Pb2 Ti6 O5 (OiPr)3 X(methacrylate)14 (X: OiPr or methacrylate), the lead atoms are coordinated by a fragment of the Ti8 O8 (methacrylate)16 metallacycle.