Rigaku (Japan)

Microcrystal electron diffraction（MicroED）is a technique that provides researchers with three-dimensional molecular structures from submicron-order crystals because the interaction between electrons and material is thousands of times stronger than that of X-rays. Additional advantage of this strong interaction is multiple scattering. Multiple scattering is highly sensitive to the three-dimensional arrangement of atoms, therefore by employing structural refinement based on dynamical diffraction theory, it becomes possible to determine the absolute structure of crystals. In this paper, we introduce characteristics of MicroED, some critical points for measurement and structure analysis, and examples of structure determination using an instrument dedicated to MicroED.

In their Research Article (e202510889), Berkowitz, Wilson, Grubmueller and co-workers describe the malleable structure of CaADH (Clostridium acetobutylicum alcohol dehydrogenase) and its panoply of loop conformers (top). They deploy CaADH for a dynamic reductive kinetic resolution (DYRKR) entry into new side chains for the Taxotere family of chemotherapeutics. The middle image shows an X-ray crystal structure of a key enzymatic product and Taxotere building block with the proper stereochemistry. Artistic Credit: Ewa Kijowska-Stroes.

The Cover Feature highlights the self-assembly of alkyne-protected silver nanoclusters networked through silver⋯pyridyl coordination in the crystalline lattice. In their Research Article (DOI: 10.1002/ceur.202500069), Y. Domoto and co-workers demonstrate that cooperative acetylene coordination, which is provided by a simple bifunctional ligand equipped with both a terminal alkyne and a pyridyl group, is applicable to the spatial organization of photoluminescent atomically precise clusters into the 3D coordination nanomaterials.

These studies reveal the first structure of Clostridiumacetobutylicum alcohol dehydrogenase (CaADH), a protein exhibiting remarkable substrate promiscuity and stereochemical fidelity. The CaADH enzyme is utilized here for synthesizing 20 potential aryl isoserine side chains for the Taxotère family of tubulin‐binding chemotherapeutics. The approach involves dynamic reductive kinetic resolution (DYRKR) upon the corresponding α‐chloro‐β‐keto esters, showing high D‐syn stereoselectivity, including those leading to the clinically relevant Milataxel (Ar = 2‐furyl) and Simotaxel (Ar = 2‐thienyl) side chains. Furthermore, various cross‐coupling chemistries performed on the p‐bromophenyl isoserine side chain significantly enhance the structural diversity of the taxoid side chain library obtained (16 additional taxoid side chains). The CaADH structure is notable: (i) the nicotinamide cofactor is bound in an anti‐conformation, with the amide carbonyl occupying the ketone binding pocket, and (ii) a flexible loop near the active site, likely contributes to the remarkable substrate promiscuity observed in CaADH. We present our perspective on the dynamic nature of the CaADH active site through molecular dynamics simulation, proposing a halogen bonding model as a potential mechanism for the remarkable selectivity for an (S)‐configured C‐Cl bond, in addition to the D‐facial selectivity, demonstrated across twenty diverse substrates by this remarkable short‐chain dehydrogenase enzyme.

Abstract The spatial distribution of electron density in the ionosphere exhibits notable variability and undergoes considerable changes during storms and substorms driven by solar wind disturbances. Electron density variations and irregularities can cause total signal blackouts during strong scintillation periods and enhance satellite positioning errors. We analyzed Global Navigation Satellite System (GNSS) - total electron content (TEC) and Arase satellite observation data to elucidate the characteristics of the electron density variation in the plasmasphere and ionosphere during the May 2024 super storm. To identify the electron density variation in the ionosphere, we calculated the ratio of the TEC difference (rTEC), which is defined as the difference from the 10-quiet-day average TEC normalized by the average value. Additionally, we estimated the electron density in the plasmasphere and inner magnetosphere from the upper frequency limit of the upper hybrid resonance (UHR) waves observed by the Arase satellite. Consequently, an L-t plot of the electron density showed that the plasmasphere contracted from L = 7.0 to L = 1.5 within 9 h after a sudden commencement. During the storm recovery phase, the plasmapause gradually shifted to a higher L-shell. The electron density in the plasmasphere recovered the geomagnetically quiet-time level on a 4-day scale. The timescale of the plasmaspheric refilling was much longer than that of other coronal mass ejection (CME)-driven storms during the Arase era. The rTEC in the Northern Hemisphere showed that an enhancement in the rTEC value occurred at high latitudes (60°–70° in magnetic latitude (MLAT)) in the daytime (10–14 in magnetic local time (MLT)), approximately 1 h after the storm onset. Subsequently, a tongue of ionization (TOI) formed in the polar cap owing to the enhancement of two-cell convection in the high-latitude ionosphere. The rTEC was globally depleted during the storm recovery phase. The depletion indicates the occurrence of a negative storm owing to a neutral composition (O/N 2 ) change driven by the energy input from the magnetosphere in the high-latitude thermosphere. The coincidence of the long refilling timescale of the plasmasphere and the depletion of the rTEC suggests that a strong negative storm impedes plasmaspheric refilling.

Abstract Transition‐metal‐catalyzed selective and efficient activation of an inert C−H bond in an organic substrate is of importance for the development of streamlined synthetic methodologies. An attractive approach is the design of a metal catalyst capable of recognizing an organic substrate through noncovalent interactions to control reactivity and selectivity. We report here a spirobipyridine ligand that bears a hydroxy group which recognizes pyridine and quinoline substrates through hydrogen bonding, and in combination with an iridium catalyst enables site‐selective C−H borylation. The site selectivity can be switched by simply changing the position of the hydroxy group on the ligand. The catalyst also accelerates the reactions, overrides steric bias, and selectively recognizes a pyridine substrate in the presence of other hydrogen bond acceptors. These features are reminiscent of enzymatic catalysis and suggest that judicious design of the recognition group on the ligand can become a general strategy to selectively and efficiently functionalize organic substrates.

An increase in the number of drug-resistant microbes is a major threat to human health. Bacterial drug resistance is mostly mediated by biofilm formation. In this study, the culture filtrate from the edible mushroom, Pleurotus ostreatus, was fractionated to isolate compounds that inhibit the biofilm formation of six pathogenic bacteria. Notably, we isolated compounds 1-6 using bioassay-guided chromatographic separations. Spectroscopic and X-ray diffraction analyses identified 1 as a novel fused bicyclic pyrone-furan, named pleuropyronine, whereas 2-6 were known polyketides. Pleuropyronine inhibited biofilm formation in four Gram-negative bacteria, with IC50 values ranging from 5.4 to 8.7µg/mL, whereas 2-6 exhibited IC50 values between 1.0 and 5.3µg/mL against five bacteria. Additionally, pleuropyronine bioactivity was confirmed by the inhibition of exopolysaccharide and biofilm formation induced by C6-homoserine lactone. Thus, this may serve as a pioneering study on the pharmacological potential of isolated compounds, offering valuable insights for future research.

Abstract Technologies for evaluating the creep damage of Ni-base superalloys of Directionally Solidified (DS) materials or single crystal materials, used as gas turbine blades, have been recently developed. One notable inspection technique is the electron back-scatter diffraction (EBSD) method which uses the misorientation analysis within grains of the Ni-base superalloy. However, this is a destructive technique. Another notable inspection technique is the rocking curve method, which uses the relationship between the full width at half maximum (FWHM) of a rocking curve by X-ray diffractometry and the creep damage of the Ni-base superalloy. It requires rotating the sample. Hence, these techniques have problems in practical applications. We have proposed an exclusive technique by applying the transmission Laue method to Ni-base superalloys, to address the problems with the above techniques. All of these techniques utilize a master curve, made by evaluating test pieces damaged at several stages and used as a standard for sample evaluation, however how to evaluate the creep damage of sample by each method is different as described above. There are four advantages to the new technique (patent pending), as follows; Creep damage of a sample is evaluated 1. without moving the sample. 2. non-destructively. 3. regardless of the thickness. 4. in a conventional laboratory. The first advantage uses the Laue method with polychromatic X-rays, which allows the sample to be measured without moving it. Second, the high energy X-ray microbeam probes the sample below any surface coatings by transmission. Thrird, our measurement technique probes the grains within the sample crystal regardless of their depth. Fourth, our new apparatus for generating high energy X-rays allows the samples measured in a conventional laboratory. We are calling this technique “the crystallite orientation deviation method”. In this study, the new technique is primally verified through the theoretical examination for applying the Laue method to the DS or the single crystal material by considering elastic and inelastic crystallite orientation deviations. Then, results of creep tests for test pieces of a Ni-base superalloy of DS material were compared with experimental results obtained from making two master curves by COD using the same test pieces cut out into two sets, respectively one set without thermal barrier coating (TBC) and the other set with TBC. As results, it was found that tendances between the results of COD and the results of creep tests had a good agreement with each other. That is, it validates that COD can successfully evaluate the creep damage of the Ni-base superalloy. Furthermore, it was also found that the results of test pieces without TBC had a good agreement with those with TBC. It shows that the TBC coating on the surface of Ni-base superalloy was correctly penetrated by the polychromatic X-rays based on COD. We expect that this technique COD also can be applied to polycrystalline materials in addition to the single crystals, especially the materials having coarse grains. It suggests that many aircraft parts may be evaluated by COD.

Unsaturated cyclic terpenes often exhibit instability due to the proximation of C=C bonds in the cyclic skeleton, leading to nonenzymatic degradation. In this study, the crystalline sponge (CS) method was employed for the X-ray conformational analysis of a minute amount of oily and cyclic terpene compound, (+)-germacrene D-4-ol, which was produced by a terpene synthase OILTS under in vitro conditions. The CS method revealed a reactive conformation of the cyclic terpene with proximal double bonds. Under weakly acidic in vivo conditions, OILTS gave four pseudo-natural products or artifacts. The CS method also elucidated the structures of these degraded compounds, proposing a degradation mechanism triggered by the transannular reactions.

Two-dimensional (2D) metal–organic frameworks (MOFs) are a class of materials exhibiting various functionalities based on anisotropic layered structures constructed through strong in-plane connectivity and weak van der Waals interlayer interaction. However, their anisotropic mechanical properties and modulation of 2D-MOF crystals have been rarely investigated. Herein, we report the compression and elastic properties of two 2D-MOFs, [Mn(salen)]2[Pt(CN)4]·H2O (1) and [Mn(salen)]2[PtI2(CN)4]·H2O (2), composed of undulating layers. These layers were highly compressive due to the undulation changes whose compressibility were much larger than those of other crystalline 2D materials. 1 and 2 incorporated structural differences involving the zigzag angles of undulating layers, leading to opposite trends in anisotropic compressibility caused by compression-induced structural transformation between flattening and rippling of the layers. In addition, by conducting high-pressure experiments for 1 using two different pressure-transmitting media (oils or alcohols), we found that ethanol molecules were introduced into the interlayer spaces, unlike oils. This hyperfilling phenomenon resulted in an anisotropic structural transformation involving an expansion along the layer-stacking direction under high pressures. Furthermore, these compression behaviors were impacted by the crystal morphology, such as single crystals and powder forms. Moreover, the Young’s moduli in (110) and (001) directions of 1 and 2 were evaluated by nanoindentation experiments, demonstrating the mechanical flexibility of the wavy cyanido-bridged chains.