High‐Resolution Electrochemical Mapping of the Hydrogen Evolution Reaction on Transition‐Metal Dichalcogenide Nanosheets

High‐resolution scanning electrochemical cell microscopy (SECCM) is used to image and quantitatively analyze the hydrogen evolution reaction (HER) catalytically active sites of 1H‐MoS₂ nanosheets, MoS₂, and WS₂ heteronanosheets. Using a 20 nm radius nanopipette and hopping mode scanning, the resolution of SECCM was beyond the optical microscopy limit and visualized a small triangular MoS₂ nanosheet with a side length of ca. 130 nm. The electrochemical cell provides local cyclic voltammograms with a nanoscale spatial resolution for visualizing HER active sites as electrochemical images. The HER activity difference of edge, terrace, and heterojunction of MoS₂ and WS₂ were revealed. The SECCM imaging directly visualized the relationship of HER activity and number of MoS₂ nanosheet layers and unveiled the heterogeneous aging state of MoS₂ nanosheets. SECCM can be used for improving local HER activities by producing sulfur vacancies using electrochemical reaction at the selected region.     

Potent platelet-derived growth factor-beta receptor (PDGF-betaR) inhibitors: Synthesis and structure-activity relationships of 7-[3-(cyclohexylmethyl)ureido]-3-{1-methyl-1H-pyrrolo[2,3-b]pyridin-3-yl}quinoxalin-2(1H)-one derivatives

We found previously that 7-[3-(cyclohexylmethyl)ureido]-3-{1-methyl-1H-pyrrolo[2,3-b]pyridin-3-yl}quinoxalin-2(1H)-one (7d-6) has considerable potency as a PDGF inhibitor. This compound showed potent inhibitory activity in a PDGF-induced CPA (Cell Proliferation Assay) and APA (Auto-Phosphorylation Assay) (IC50 = 0.05 micromol/l in CPA, 0.03 micromol/l in APA). Therefore, we tried to develop a novel and effective PDGF-betaR inhibitor by optimizing a series of its derivatives. We found that trifluoroacetic acid (TFA)-catalyzed coupling of pyrrolo[2,3-b]pyridines with quinoxalin-2-ones proceeded efficiently under mild oxidation condition with manganese(IV) oxide (MnO2) in situ, so this method was applied to prepare a series of derivatives. Results of in vitro screening of newly synthesized derivatives identified compound 7d-9 as having potent (IC50 = 0.014 micromol/l in CPA, 0.007 micromol/l in APA) and selective [IC50 values against vascular endothelial growth factor receptor 2 (VEGFR2, kinase domain region, KDR), epidermal growth factor receptor (EGFR), c-Met (hepatocyte growth factor receptor) and insulin growth factor I receptor (IGF-IR)/IC50 against PDGFR were each >1000] inhibitory activity. Moreover, in this series of derivatives, 7b-2 showed potent inhibitory activity toward both PDGF- and VEGF-induced signaling (PDGFR: IC50 = 0.004 micromol/l in CPA, 0.0008 micromol/l in APA, KDR: IC50 = 0.008 micromol/l in APA). Herein we report a new and convenient synthetic method for this series of derivatives and its SAR study.     

Revised structure of kasarin, an antibacterial pyrazinone compound from the marine microorganism Hyphomycetes sp.

Kasarin is an antibacterial marine alkaloid that was isolated from the microorganism Hyphomycetes sp. Its structure was previously reported to be an azetinone compound 1. However, detailed spectroscopic analysis of the natural compound and its related synthetic analogs revealed that the structure of kasarin should be revised to be a novel 5-malonyloxy-1-methoxy-pyrazin-2(1H)-one derivative 2.     

A Pseudo-rigid model for the inverse dynamics of an Euler beam

Inversion technique has been very successful in the tracking control of nonlinear dynamical systems. However, when applied to manipulators constructed with elastic links, inverse dynamics through direct integration in temporal space causes unbounded controller command. It has been suggested that seeking an inverse dynamics solution for a given tip trajectory with given initial conditions is an ill-posed problem. It has also been suggested that increasing model accuracy by including more terms in a truncated beam model worsens the controller’s ability to stabilize the system dynamics. In this paper, we seek to understand the nature of the inverse dynamics instability and to find an alternative solution. We appeal to the notion of a pseudo-rigid model which describes the beam deflection by a homogeneous displacement field. Particularly, we derive the mode shape in order to yield a bounded inverse dynamics solution. Different from most of the existing solutions where solution stability was achieved through modifying the output function, we modified the inverse dynamics model. A bounded inverse solution and model simplicity provide much needed ease in the design and implementation of an inversion controller. Numerical simulations and experiments have both been conducted to prove the validity of the proposed method.     

A Practical Synthesis of 4′-Methylbiphenyl-2-carbonitrile as a Key Intermediate of Angiotensin II Antagonists

A new and practical synthesis of 4′-methylbiphenyl-2-carbonitrile, a key intermediate of angiotensin II antagonists is described. The key step is Pdcatalyzed dehydrogenation of the compound 6, which proceeds selectively by utilizing hydrogen acceptor such as maleic diester or oxygen.     

Gambieroxide,a novel epoxy polyether compound from the dinoflagellate Gambierdiscus toxicus GTP2 strain

A novel epoxy polyether compound named gambieroxide was isolated from the benthic dinoflagellate Gambierdiscus toxicus (GTP2 strain) collected at Papeete, Tahiti, French Polynesia and its structure comprising of a ladder-frame polyether with twelve contiguous trans-fused ether rings (6/7/6/6/6/7/6/8/6/6/6/6), a sulfate ester group, an epoxide, and two olefines in side chains was elucidated by detailed NMR and MS analysis. It is interesting that the structure strikingly resembles yessotoxin, one of lipophilic toxins in shellfish originating from the dinoflagellate Protoceratium reticulatum.     

Syntheses of all-methylated ellagitannin, isorugosin B and rugosin B

Ellagitannins possess a wide range of biological activities and remarkable structural diversity, which commonly include an axially chiral biaryl unit. This paper describes syntheses of all-methylated versions of isorugosin B and rugosin B, which are regioisomeric, ellagitannin-related compounds. The key features of these syntheses involve the construction of an axially chiral biaryl function on a sugar moiety through a Pd-catalyzed intramolecular biaryl coupling reaction, Bringmann’s atroposelective lactone opening reaction, and a two-step ester formation. This is the first synthetic approach for generating ellagitannins featuring a valoneoyl group.     

Visible-light-derived photocatalyst based on TiO(2-δ)Nδ with a tubular structure

We succeeded in achieving visible-light responsiveness on a tubular TiO(2) sample through the treatment of a tubular TiO(2) that has a large surface area with an aqueous solution of ammonia or triethylamine at room temperature and subsequent calcination at 623 K, which produced a nitrided tubular TiO(2) sample. It was found that the ease of nitridation is dependent on the surface states; washing the tubular TiO(2) sample with an aqueous acidic solution is very effective and indispensable. This treatment causes the appearance of acidic sites on the tubular TiO(2), which was proved by the following experiments: NH(3) temperature-programmed desorption and two types of organic reactions exploiting the acid properties. The prepared samples, TiO(2-δ)N(δ), efficiently absorb light in the visible region, and they exhibit a prominent feature for the decomposition of methylene blue in an aqueous solution at 300 K under irradiation with visible light, indicating the achievement of visible-light responsiveness on the tubular TiO(2) sample. This type of tubular TiO(2-δ)N(δ) sample has merit in the sense that it has a large surface area and a characteristic high transparency for enabling photocatalytic reactions because it has a tubular structure and is composed of thin walls.     

Sliding behavior of water droplets on line-patterned hydrophobic surfaces

We prepared line-patterned hydrophobic surfaces using fluoroalkylsilane (FAS) and octadecyltrimethoxysilane (ODS) then investigated the effect of line direction on sliding behavior of water droplets by direct observation of the actual droplet motion during sliding. Water droplets slide down with a periodic large deformation of the contact line and sliding velocity fluctuation that occurred when they crossed over the 500-μm ODS line regions in FAS regions on a Si surface tilted at 35°. These behaviors are less marked for motion on a 100-μm line surface, or on lines oriented parallel to the slope direction. Smaller droplets slide down with greater displacement in the line direction on 500-μm line patterning when the lines were rotated at 13° in-plane for the slope direction. This sliding behavior depended on the droplet size and rotation angle, and is accountable by the balance between gravitational and retentive forces.     

Right handed or left handed? Forbidden x-ray diffraction reveals chirality

Enantiomers, or stereoisomers, have crystal structures that are mirror images of each other and are thus handed, like our right and left hands. The physical properties of enantiomers are identical except for optical activity, which rotates linearly polarized light by equal amounts but in opposite directions. While conventional x-ray Bragg diffraction can determine crystal structures, it does not distinguish between right- and left-handed crystals. We show resonant Bragg diffraction using circularly polarized x rays reveals the handedness of crystals by coupling x-ray helicity to a crystal screw axis. The intensity of resonantly allowed reflection of alpha-quartz is well described by an admixture of a parity-even and a parity-odd process. Our results are of general importance and demonstrate a new method to directly study chiral motifs in structures that include biomaterials, liquid crystals, magnets, multiferroics, etc.