Dynamics of Linkers in Metal-Organic Framework Glasses.

Metal-organic framework (MOF) glasses have emerged as a new class of organic-inorganic hybrid glass materials. Considerable efforts have been devoted to unraveling the macroscopic dynamics of MOF glasses by studying their rheological behavior; however, their microscopic dynamics remain unclear. In this work, we studied the effect of vitrification on linker dynamics in ZIF-62 by solid-state 2H nuclear magnetic resonance (NMR) spectroscopy. 2H NMR relaxation analysis provided a detailed picture of the mobility of the ZIF-62 linkers, including local restricted librations and a large-amplitude twist; these details were verified by molecular dynamics. A comparison of ZIF-62 crystals and glasses revealed that vitrification does not drastically affect the fast individual flipping motions with large-amplitude twists, whereas it facilitates slow cooperative large-amplitude twist motions with a decrease in the activation barrier. These observations support the findings of previous studies, indicating that glassy ZIF-62 retains permanent porosity and that short-range disorder exists in the alignment of ligands because of distortion of the coordination angle.

Isolation of phase edges using off-axis q-plate filters.

Edge-enhanced microscopes with a q-plate have attracted more attention to enhance the edges of phase-amplitude objects in biological samples due to their capacity for all-directional edge enhancement, while differential interference-contrast microscopy enhances edges in only one-direction. However, the edge-enhanced microscopes cannot distinguish the edges of phase and amplitude objects, as both edges are equally enhanced. This study introduces a novel method for isolating the edge of a phase object from an amplitude object using an off-axis q-plate filter in a 4f system. Herein, we combined off-axis q-plates with four different displacements to isolate the phase object edge from the amplitude object. To demonstrate the proposed method, we conducted experiments using two distinct samples. The first sample comprised a phase test target surrounded by an aperture, and the second sample involved an overlap between the phase test target and a white hair with non-zero transmittance. In the samples, the isolated phase object edge is in good agreement with the theoretical expectations, and the amplitude object edge was reduced by approximately 93%. The proposed method is a novel and effective approach for isolating the edge of a phase object from an amplitude object and can be useful in various biological imaging applications.

Edge-enhanced microscopy of complex objects using scalar and vectorial vortex filtering.

Recently, a 4f system containing a q-plate has been used to perform edge detection and enhancement of amplitude or phase objects. However, only a few studies have concentrated on edge enhancement of complex phase-amplitude objects. Here we experimentally verified the functional difference between scalar and vectorial vortex filtering with the q-plate using an onion cell as a complex object and the vectorial vortex filtering successfully enhanced the edges of phase and amplitude objects in the phase-amplitude object. One problem, however, is indistinguishability of the equally-enhanced edges of the phase and amplitude objects. To address this issue, we propose a method to isolate the edge of the phase object from the edge of the amplitude object using off-axis beam illumination. We theoretically calculated the isolation of the edge of the phase object from the amplitude object, and verified via numerical simulations.

Induction of plant disease resistance by mixed oligosaccharide elicitors prepared from plant cell wall and crustacean shells.

Basal plant immune responses are activated by the recognition of conserved microbe-associated molecular patterns (MAMPs), or breakdown molecules released from the plants after damage by pathogen penetration, so-called damage-associated molecular patterns (DAMPs). While chitin-oligosaccharide (CHOS), a primary component of fungal cell walls, is most known as MAMP, plant cell wall-derived oligosaccharides, cello-oligosaccharides (COS) from cellulose, and xylo-oligosaccharide (XOS) from hemicellulose are representative DAMPs. In this study, elicitor activities of COS prepared from cotton linters, XOS prepared from corn cobs, and chitin-oligosaccharide (CHOS) from crustacean shells were comparatively investigated. In Arabidopsis, COS, XOS, or CHOS treatment triggered typical defense responses such as reactive oxygen species (ROS) production, phosphorylation of MAP kinases, callose deposition, and activation of the defense-related transcription factor WRKY33 promoter. When COS, XOS, and CHOS were used at concentrations with similar activity in inducing ROS production and callose depositions, CHOS was particularly potent in activating the MAPK kinases and WRKY33 promoters. Among the COS and XOS with different degrees of polymerization, cellotriose and xylotetraose showed the highest activity for the activation of WRKY33 promoter. Gene ontology enrichment analysis of RNAseq data revealed that simultaneous treatment of COS, XOS, and CHOS (oligo-mix) effectively activates plant disease resistance. In practice, treatment with the oligo-mix enhanced the resistance of tomato to powdery mildew, but plant growth was not inhibited but rather tended to be promoted, providing evidence that treatment with the oligo-mix has beneficial effects on improving disease resistance in plants, making them a promising class of compounds for practical application.

Selective Synthesis of Oligosaccharides by Mechanochemical Hydrolysis of Chitin over a Carbon-Based Catalyst.

Oligosaccharides possess fascinating functions that are applicable in a variety of fields, such as agriculture. However, the selective synthesis of oligosaccharides, especially chitin-oligosaccharides, has remained a challenge. Chitin-oligosaccharides activate the plant immune system, enabling crops to withstand pathogens without harmful agrichemicals. Here, we demonstrate the conversion of chitin to chitin-oligosaccharides using a carbon catalyst with weak acid sites and mechanical milling. The catalyst produces chitin-oligosaccharides with up to 94 % selectivity in good yields. Monte-Carlo simulations indicate that our system preferentially hydrolyzes larger chitin molecules over oligomers, thus providing the desired high selectivity. This unique kinetics is in contrast to the fact that typical catalytic systems rapidly hydrolyze oligomers to monomers. Unlike other materials carbons more strongly adsorb large polysaccharides than small oligomers, which is suitable for the selective synthesis of small oligosaccharides.

Vanishing and Nonvanishing Persistent Currents of Various Conserved Quantities.

For every conserved quantity written as a sum of local terms, there exists a corresponding current operator that satisfies the continuity equation. The expectation values of current operators at equilibrium define the persistent currents that characterize spontaneous flows in the system. In this Letter, we consider quantum many-body systems on a finite one-dimensional lattice and discuss the scaling of the persistent currents as a function of the system size. We show that, when the conserved quantities are given as the Noether charges associated with internal symmetries or the Hamiltonian itself, the corresponding persistent currents can be bounded by a correlation function of two operators at a distance proportional to the system size, implying that they decay at least algebraically as the system size increases. In contrast, the persistent currents of accidentally conserved quantities can be nonzero even in the thermodynamic limit and even in the presence of the time-reversal symmetry. We discuss "the current of energy current" in S=1/2 XXZ spin chain as an example and obtain an analytic expression of the persistent current.

Decision tree-based identification of Staphylococcus aureus via infrared spectral analysis of ambient gas.

In this study, eight types of bacteria were cultivated, including Staphylococcus aureus. The infrared absorption spectra of the gas surrounding cultured bacteria were recorded at a resolution of 0.5 cm-1 over the wavenumber range of 7500-500 cm-1. From these spectra, we searched for the infrared wavenumbers at which characteristic absorptions of the gas surrounding Staphylococcus aureus could be measured. This paper reports two wavenumber regions, 6516-6506 cm-1 and 2166-2158 cm-1. A decision tree-based machine learning algorithm was used to search for these wavenumber regions. The peak intensity or the absorbance difference was calculated for each region, and the ratio between them was obtained. When these ratios were used as training data, decision trees were created to classify the gas surrounding Staphylococcus aureus and the gas surrounding other bacteria into different groups. These decision trees show the potential effectiveness of using absorbance measurement at two wavenumber regions in finding Staphylococcus aureus.

Direct measurement of ultrafast temporal wavefunctions.

The large capacity and robustness of information encoding in the temporal mode of photons is important in quantum information processing, in which characterizing temporal quantum states with high usability and time resolution is essential. We propose and demonstrate a direct measurement method of temporal complex wavefunctions for weak light at a single-photon level with subpicosecond time resolution. Our direct measurement is realized by ultrafast metrology of the interference between the light under test and self-generated monochromatic reference light; no external reference light or complicated post-processing algorithms are required. Hence, this method is versatile and potentially widely applicable for temporal state characterization.

Impact of tensile and compressive forces on the hydrolysis of cellulose and chitin.

Mechanochemistry enables unique reaction pathways in comparison to conventional thermal reactions. Notably, it can achieve selective hydrolysis of cellulose and chitin, a set of abundant and recalcitrant biomass, by solvent-free ball-milling in the presence of acid catalysts. Although the merits of mechanochemistry for this reaction are known, the reaction mechanism is still unclear. Here, we show how the mechanical forces produced by ball-milling activate the glycosidic bonds of carbohydrate molecules towards hydrolysis. This work uses experimental and theoretical evaluations to clarify the mechanism. The experimental results reveal that the ball-mill accelerates the hydrolysis by mechanical forces rather than local heat. Meanwhile, the classical and quantum mechanics calculations indicate the subnano to nano Newton order of tensile and compressive forces that activate polysaccharide molecules in the ball-milling process. Although previous studies have taken into account only the stretching of the molecules, our results show that compressive forces are stronger and effective for the activation of glycosidic bonds. Accordingly, in addition to stretching, compression is crucial for the mechanocatalytic reaction. Our work connects the classical physics of ball-milling on a macro scale with molecular activation at a quantum level, which would help to understand and control mechanochemical reactions.

On the Electronic Structure Origin of Mechanochemically Induced Selectivity in Acid-Catalyzed Chitin Hydrolysis.

Recently, mechanical ball milling was applied to chitin depolymerization. The mechanical activation afforded higher selectivity toward glycosidic bond cleavage over amide bond breakage. Hence, the bioactive N-acetylglucosamine (GlcNAc) monomer was preferentially produced over glucosamine. In this regard, the force-dependent mechanochemical activation-deactivation process in the relaxed and pulled GlcNAc dimer undergoing deacetylation and depolymerization reactions was studied. For the relaxed case, the activation energies of the rate-determining steps (RDS) proved that the two reactions could occur simultaneously. Mechanical forces associated with ball milling were approximated with linear pulling and were introduced explicitly in the RDS of both reactions through force-modified potential energy surface (FMPES) formalism. In general, as the applied pulling force increases, the activation energy of the RDS of deacetylation shows no meaningful change, while that of depolymerization decreases. This result is consistent with the selectivity exhibited in the experiment. Energy and structural analyses for the depolymerization showed that the activation can be attributed to a significant change in the glycosidic dihedral at the reactant state. A lone pair of the neighboring pyranose ring O adopts a syn-periplanar conformation relative to the glycosidic bond. This promotes electron donation to the σ*-orbital of the glycosidic bond, leading to activation. Consequently, the Brønsted-Lowry basicity of the glycosidic oxygen also increases, which can facilitate acid catalysis.

Ligand-Functionalization-Controlled Activity of Metal-Organic Framework-Encapsulated Pt Nanocatalyst toward Activation of Water.

We first report the systematic control of the reactivity of H2O vapor in metal-organic frameworks (MOFs) with Pt nanocrystals (NCs) through ligand functionalization. We successfully synthesized Pt NCs covered with a water-stable MOF, UiO-66 (Pt@UiO-66), having different metal ions or functionalized ligands. The ligand functionalization of UiO-66 significantly affected the catalytic performance of the water-gas shift reaction, and the replacement of Zr4+ ions with Hf4+ ions in UiO-66 had no impact on the catalytic activity. The introduction of a -Br group lowered the reactivity of Pt@UiO-66 by nearly half, whereas the substitution of -Br with a -Me2 group triply enhanced the activity. The origin of the enhanced catalytic activity was found to be the change in H2O activity in the UiO-66 pores by the ligand functionalization, which was investigated using H2O sorption, solid-state NMR, X-ray photoelectron spectroscopy, and in situ IR measurements. This work opens a new prospect to develop MOFs as a platform to activate H2O.

Fabrication of Integrated Copper-Based Nanoparticles/Amorphous Metal-Organic Framework by a Facile Spray-Drying Method: Highly Enhanced CO2 Hydrogenation Activity for Methanol Synthesis.

We report on Cu/amUiO-66, a composite made of Cu nanoparticles (NPs) and amorphous [Zr6 O4 (OH)4 (BDC)6 ] (amUiO-66, BDC=1,4-benzenedicarboxylate), and Cu-ZnO/amUiO-66 made of Cu-ZnO nanocomposites and amUiO-66. Both structures were obtained via a spray-drying method and characterized using high-resolution transmission electron microscopy, energy dispersive spectra, powder X-ray diffraction and extended X-ray absorption fine structure. The catalytic activity of Cu/amUiO-66 for CO2 hydrogenation to methanol was 3-fold that of Cu/crystalline UiO-66. Moreover, Cu-ZnO/amUiO-66 enhanced the methanol production rate by 1.5-fold compared with Cu/amUiO-66 and 2.5-fold compared with γ-Al2 O3 -supported Cu-ZnO nanocomposites (Cu-ZnO/γ-Al2 O3 ) as the representative hydrogenation catalyst. The high catalytic performance was investigated using in situ Fourier transform IR spectra. This is a first report of a catalyst comprising metal NPs and an amorphous metal-organic framework in a gas-phase reaction.

Significant Enhancement of Hydrogen Evolution Reaction Activity by Negatively Charged Pt through Light Doping of W.

We report novel PtW solid-solution nanoparticles (NPs) produced through electrochemical cleaning of core/shell PtW@WO3 NPs. The resulting PtW NPs achieved a record hydrogen evolution reaction (HER) performance as a class of Pt-based solid-solution alloys. A current density of 10 mA cm-2 was reached with an overpotential of 19.4 mV, which is significantly lower than that of a commercial Pt catalyst (26.3 mV). The PtW NPs also exhibited long-term stability. Theoretical calculations revealed that negatively charged Pt atoms adjacent to a W atom provide favorable hydrogen adsorption energies for the HER, realizing significantly enhanced HER activity.

Lettuce-derived secretory IgA specifically neutralizes the Shiga toxin 1 activity.

MAIN CONCLUSION: An edible plant was tested as a host for the production of secretory monoclonal IgA against Shiga toxin 1 (Stx1). The lettuce-derived IgA completely protected Vero cells from Stx1. Secretory immunoglobulin A (SIgA) is thought to control mucosal infections and thus it may be applicable to oral passive immunotherapy. Edible plants are candidate hosts for producing oral formulations with SIgA against pathogenic agents. We previously established a recombinant IgA specific for the B subunit of Shiga toxin 1 (Stx1B) consisting of the Fab fragment of Stx1B-specific monoclonal IgG and the Fc region of IgA (hyIgA). Here, we developed transgenic lettuce (Lactuca sativa) that produces hyIgA in a secretory form (S-hyIgA). An Arabidopsis-derived light-harvesting complex II (LHCB) promoter was used for the expression of all four transgenes (hyIgA heavy, light and j chains, and secretory component). Agrobacterium-mediated transformation was carried out to introduce genes into lettuce leaf discs by means of a single vector harboring all four transgenes. Consistent with the tissue specificity of the LHCB promoter, the expression of hyIgA transgenes was observed in leaf and stem tissues, which contain chloroplasts, at the mRNA and protein levels. The leaves produced hyIgA in a more than tenfold higher yield as compared with stems. The lettuce-derived S-hyIgA was found to bind to Stx1B in a dose-dependent manner by means of ELISA. A leaf extract of the transgenic lettuce completely neutralized the cytotoxicity of Stx1 against Vero cells, which are highly susceptible to Stx1. In conclusion, we established a transgenic lettuce producing a secretory form of hyIgA that can bind bacterial toxin. The results indicate that edible practical plants containing S-hyIgA will provide a possible means for immunotherapy for food poisoning.

Cellulose Depolymerization over Heterogeneous Catalysts.

Cellulosic biomass is the largest source of renewable organic carbon on our planet. Cellulose accounts for 40-50 wt % of this lignocellulose, and it is a feedstock for industrially important chemicals and fuels. The first step in cellulose conversion involves its depolymerization to glucose or to its hydrogenated product sorbitol. The hydrolysis of cellulose to glucose by homogeneous mineral acids was the subject of research for almost a century. However, homogeneous acids have significant drawbacks and are neither economical nor environmentally friendly. In 2006, our group reported for the first time the ability of heterogeneous catalysts to depolymerize cellulose through hydrolytic hydrogenation to produce sorbitol. Later, we reported the hydrolysis of cellulose to glucose using carbon catalyst containing weakly acidic functional groups. Understanding the reaction between cellulose and heterogeneous catalyst is a challenge as the reaction occurs between a solid substrate and a solid catalyst. In this Account, we describe our efforts for the conversion of cellulose to sorbitol and glucose using heterogeneous catalysts. Sorbitol is produced by sequential hydrolysis and hydrogenation of cellulose in one pot. We reported sorbitol synthesis from cellulose in the presence of supported metal catalysts and H2 gas. The reducing environment of the reaction prevents byproduct formation, and harsh reaction conditions can be used to achieve sorbitol yield of up to 90%. Glucose is produced by acid catalyzed hydrolysis of cellulose, a more challenging reaction owing to the tendency of glucose to rapidly decompose in hot water. Sulfonated carbons were first reported as active catalysts for cellulose hydrolysis, but they were hydrothermally unstable under the reaction conditions. We found that carbon catalysts bearing weakly acidic functional groups such as hydroxyl and carboxylic acids are also active. Weakly acidic functional groups are hydrothermally stable, and a soluble sugar yield of 90% was achieved in a 20 min reaction. We clarified that the polycyclic aromatic surface of the carbon adsorbs cellulose molecules on its surface by CH-π and hydrophobic interactions driven by a positive change in entropy of the system. The adsorbed molecules are rapidly hydrolyzed by active sites containing vicinal functional groups that recognize the hydroxyl groups on cellulose to achieve a high frequency factor. This phenomenon is analogous to the hydrolysis of cellulose by enzymes that use CH-π and hydrophobic interactions along with weakly acidic carboxylic acid and carboxylate pair to catalyze the reaction. However, in comparison with enzymes, carbon catalyst is functional over a wide range of pH and temperatures. We also developed a continuous flow slurry process to demonstrate the feasibility for commercial application of carbon-catalyzed cellulose hydrolysis to glucose using inexpensive catalyst prepared by air oxidation. We believe that further efforts in this field should be directed toward eliminating roadblocks for the commercialization of cellulose conversion reactions.

Surface Modification of a Supported Pt Catalyst Using Ionic Liquids for Selective Hydrodeoxygenation of Phenols into Arenes under Mild Conditions.

The selective and efficient removal of oxygenated groups from lignin-derived phenols is a critical challenge to utilize lignin as a source for renewable aromatic chemicals. This report describes how surface modification of a zeolite-supported Pt catalyst using ionic liquids (ILs) remarkably increases selectivity for the hydrodeoxygenation (HDO) of phenols into arenes under mild reaction conditions using atmospheric pressure H2 . Unmodified Pt/H-ZSM-5 converts phenols into aliphatic species as the major products along with a slight amount of arenes (10 % selectivity). In contrast, the catalyst modified with an IL, 1-butyl-3-methylimidazolium triflate, keeps up to 76 % selectivity for arenes even at a nearly complete conversion of phenols. The IL on the surface of Pt catalyst may offer the adsorption of phenols in an edge-to-face manner onto the surface, thus accelerating the HDO without the ring hydrogenation.

Hydrogen in Palladium and Storage Properties of Related Nanomaterials: Size, Shape, Alloying, and Metal-Organic Framework Coating Effects.

One of the key issues for an upcoming hydrogen energy-based society is to develop highly efficient hydrogen-storage materials. Among the many hydrogen-storage materials reported, transition-metal hydrides can reversibly absorb and desorb hydrogen, and have thus attracted much interest from fundamental science to applications. In particular, the Pd-H system is a simple and classical metal-hydrogen system, providing a platform suitable for a thorough understanding of ways of controlling the hydrogen-storage properties of materials. By contrast, metal nanoparticles have been recently studied for hydrogen storage because of their unique properties and the degrees of freedom which cannot be observed in bulk, i. e., the size, shape, alloying, and surface coating. In this review, we overview the effects of such degrees of freedom on the hydrogen-storage properties of Pd-related nanomaterials, based on the fundamental science of bulk Pd-H. We shall show that sufficiently understanding the nature of the interaction between hydrogen and host materials enables us to control the hydrogen-storage properties though the electronic-structure control of materials.

Plant-derived secretory component forms secretory IgA with shiga toxin 1-specific dimeric IgA produced by mouse cells and whole plants.

KEY MESSAGE: A key module, secretory component (SC), was efficiently expressed in Arabidopsis thaliana. The plant-based SC and immunoglobulin A of animal or plant origin formed secretory IgA that maintains antigen-binding activity. Plant expression systems are suitable for scalable and cost-effective production of biologics. Secretory immunoglobulin A (SIgA) will be useful as a therapeutic antibody against mucosal pathogens. SIgA is equipped with a secretory component (SC), which assists the performance of SIgA on the mucosal surface. Here we produced SC using a plant expression system and formed SIgA with dimeric IgAs produced by mouse cells as well as by whole plants. To increase the expression level, an endoplasmic reticulum retention signal peptide, KDEL (Lys-Asp-Glu-Leu), was added to mouse SC (SC-KDEL). The SC-KDEL cDNA was inserted into a binary vector with a translational enhancer and an efficient terminator. The SC-KDEL transgenic Arabidopsis thaliana produced SC-KDEL at the level of 2.7% of total leaf proteins. In vitro reaction of the plant-derived SC-KDEL with mouse dimeric monoclonal IgAs resulted in the formation of SIgA. When reacted with Shiga toxin 1 (Stx1)-specific ones, the antigen-binding activity was maintained. When an A. thaliana plant expressing SC-KDEL was crossed with one expressing dimeric IgA specific for Stx1, the plant-based SIgA exhibited antigen-binding activity. Leaf extracts of the crossbred transgenic plants neutralized Stx1 cytotoxicity against Stx1-sensitive cells. These results suggest that transgenic plants expressing SC-KDEL will provide a versatile means of SIgA production.

The First Study on the Reactivity of Water Vapor in Metal-Organic Frameworks with Platinum Nanocrystals.

We first studied the reactivity of H2 O vapor in metal-organic frameworks (MOFs) with Pt nanocrystals (NCs) through the water-gas shift (WGS) reaction. A water-stable MOF, UiO-66, serves as a highly effective support material for the WGS reaction compared with ZrO2 . The origin of the high catalytic performance was investigated using in situ IR spectroscopy. In addition, from a comparison of the catalytic activities of Pt on UiO-66, where Pt NCs are located on the surface of UiO-66 and Pt@UiO-66, where Pt NCs are coated with UiO-66, we found that the competitive effects of H2 O condensation and diffusion in the UiO-66 play important roles in the catalytic activity of Pt NCs. A thinner UiO-66 coating further enhanced the WGS reaction activity of Pt NCs by minimizing the negative effect of slow H2 O diffusion in UiO-66.

A CO Adsorption Site Change Induced by Copper Substitution in a Ruthenium Catalyst for Enhanced CO Oxidation Activity.

Ru is an important catalyst in many types of reactions. Specifically, Ru is well known as the best monometallic catalyst for oxidation of carbon monoxide (CO) and has been practically used in residential fuel cell systems. However, Ru is a minor metal, and the supply risk often causes violent fluctuations in the price of Ru. Performance-improved and cost-reduced solid-solution alloy nanoparticles of the Cu-Ru system for CO oxidation are now presented. Over the whole composition range, all of the Cux Ru1-x nanoparticles exhibit significantly enhanced CO oxidation activities, even at 70 at % of inexpensive Cu, compared to Ru nanoparticles. Only 5 at % replacement of Ru with Cu provided much better CO oxidation activity, and the maximum activity was achieved by 20 at % replacement of Ru by Cu. The origin of the high catalytic performance was found as CO site change by Cu substitution, which was investigated using in situ Fourier transform infrared spectra and theoretical calculations.