Surface morphology and crystalline structure of high-stable polycrystalline transparent conductive zinc oxide films

Surface morphology and crystalline structure of high-stable zinc oxide films were evaluated by atomic force microscopy, scanning electron microscopy and X-ray diffraction (XRD) measurements. AFM measurement revealed that the higher stable samples have smaller roughness (average roughness and root mean square) parameters than the lower stable samples. Furthermore, in-plane XRD measurement showed that the crystallite size of high stable samples is smaller than that of the low stable samples. These results indicate that the larger surface area and lower film density deteriorates the stability of zinc oxide films through the adsorption and reaction of water or oxygen molecules. They also suggest that we can prepare the high stable zinc oxide transparent electrode films by controlling the surface morphology.     

Optical emission spectroscopy by Ar ion sputtering of Ti surface under O2 environment

Visible light emission from atoms and ions sputtered on a polycrystalline Ti surface was observed under irradiation of 30 keV Ar³⁺ ions. A number of atomic lines of Ti I and II were observed in the wavelength of 250-850 nm. The intensity of Ti II emission increased 1.3-5.6 times by introducing oxygen molecules at a pressure of 5.8 × 10⁻⁵ Pa, whereas that of Ti I decreased 0.5-0.8 times. Factors enhancing or reducing photon intensities were plotted as a function of energy of the corresponding electrons in the excited states for Ti atoms and Ti⁺ ions.     

Two‐Dimensional Perovskite Oxynitride K2LaTa2O6N with an H+/K+ Exchangeability in Aqueous Solution Forming a Stable Photocatalyst for Visible‐Light H2 Evolution

Undoped layered oxynitrides have not been considered as promising H₂‐evolution photocatalysts because of the low chemical stability of oxynitrides in aqueous solution. Here, we demonstrate the synthesis of a new layered perovskite oxynitride, K₂LaTa₂O₆N, as an exceptional example of a water‐tolerant photocatalyst for H₂ evolution under visible light. The material underwent in‐situ H⁺/K⁺ exchange in aqueous solution while keeping its visible‐light‐absorption capability. Protonated K₂LaTa₂O₆N, modified with an Ir cocatalyst, exhibited excellent catalytic activity toward H₂ evolution in the presence of I^? as an electron donor and under visible light; the activity was six times higher than Pt/ZrO₂/TaON, one of the best‐performing oxynitride photocatalysts for H₂ evolution. Overall water splitting was also achieved using the Ir‐loaded, protonated K₂LaTa₂O₆N in combination with Cs‐modified Pt/WO₃ as an O₂ evolution photocatalyst in the presence of an I₃^?/I^? shuttle redox couple.     

Asymmetric Dearomative Fluorination of 2‐Naphthols with a Dicarboxylate Phase‐Transfer Catalyst

A linked dicarboxylate phase‐transfer catalyst enables smooth asymmetric dearomative fluorination of 2‐naphthols with Selectfluor under mild conditions to give the corresponding 1‐fluoronaphthalenone derivatives in a highly enantioselective manner. This reaction, which is compatible with a range of functional groups, is the first example of catalytic asymmetric fluorination of 2‐naphthols, and is expected to be useful in the synthesis of bioactive molecules.     

Stereospecific Cyclic Poly(methyl methacrylate) and Its Topology‐Guided Hierarchically Controlled Supramolecular Assemblies

In this study, the stereocomplexation between a novel stereospecific cyclic vinyl polymer, that is, cyclic syndiotactic poly(methyl methacrylate) (st‐PMMA), with the complementary linear isotactic (it‐) PMMA was investigated. Surprising new insight into the effects of the topology (i.e., end groups), size, and tacticity of the assembling components on stereocomplex formation was obtained. Characterization of the stereocomplexes revealed that the self‐assembly of cyclic st‐PMMAs and linear it‐PMMAs resulted in the formation of an unprecedented “polypseudorotaxane‐type” supramolecular assembly. This stereocomplex exhibited remarkably different physical properties as compared to the conventional PMMA triple‐helix stereocomplex as a result of the restricted topology imposed by the cyclic st‐PMMA assembling component.     

Elucidation of Pseurotin Biosynthetic Pathway Points to Trans‐Acting C‐Methyltransferase: Generation of Chemical Diversity

Pseurotins comprise a family of structurally related Aspergillal natural products having interesting bioactivity. However, little is known about the biosynthetic steps involved in the formation of their complex chemical features. Systematic deletion of the pseurotin biosynthetic genes in A. fumigatus and in vivo and in vitro characterization of the tailoring enzymes to determine the biosynthetic intermediates, and the gene products responsible for the formation of each intermediate, are described. Thus, the main biosynthetic steps leading to the formation of pseurotin A from the predominant precursor, azaspirene, were elucidated. The study revealed the combinatorial nature of the biosynthesis of the pseurotin family of compounds and the intermediates. Most interestingly, we report the first identification of an epoxidase C‐methyltransferase bifunctional fusion protein PsoF which appears to methylate the nascent polyketide backbone carbon atom in trans.     

Persistent Antimony‐ and Bismuth‐Centered Radicals in Solution

Stibinyl and bismuthinyl radicals are recognized as representative intermediates of antimony and bismuth compounds, but still elusive in the condensed phase. We successfully synthesized persistent stibinyl and bismuthinyl radicals in solution by facile dissociation of the corresponding dimers with bulky substituents. We characterized the radicals by NMR and UV/Vis spectroscopy and estimated the thermodynamic parameters for the dissociation equilibria. The radicals show n→p (HOMO→SOMO) transition bands at 497 nm (stibinyl) and 543 nm (bismuthinyl) in 3‐methylpentane and react with a stable nitroxyl radical to give the cross‐radical coupling products in good yields.     

High‐Throughput Development of a Hybrid‐Type Fluorescent Glutamate Sensor for Analysis of Synaptic Transmission

Fluorescent sensors are powerful tools for visualizing cellular molecular dynamics. We present a high‐throughput screening system, designated hybrid‐type fluorescence indicator development (HyFInD), to identify optimal position‐specific fluorophore labeling in hybrid‐type sensors consisting of combinations of ligand‐binding protein mutants with small molecular fluorophores. We screened sensors for glutamate among hybrid molecules obtained by the reaction of four cysteine‐reactive fluorescence probes with a set of cysteine‐scanning mutants of the 274 amino acid S1S2 domain of AMPA‐type glutamate receptor GluA2 subunit. HyFInD identified a glutamate‐responsive probe (enhanced glutamate optical sensor: eEOS) with a dynamic range >2400 %, good photostability, and high selectivity. When eEOS was specifically tethered to neuronal surfaces, it reliably visualized the spatiotemporal dynamics of glutamate release at single synapses, revealing synapse‐to‐synapse heterogeneity of short‐term plasticity.     

Two‐step Synthesis of Multi‐Substituted Amines by Using an N‐Methoxy Group as a Reactivity Control Element

The development of a two‐step synthesis of multi‐substituted N‐methoxyamines from N‐methoxyamides is reported. Utilization of the N‐methoxy group as a reactivity control element was the key to success in this two‐step synthesis. The first reaction involves a N‐methoxyamide/aldehyde coupling reaction. Whereas ordinary amides cannot condense with aldehydes intermolecularly due to the poor nucleophilicity of the amide nitrogen, the N‐methoxy group enhances the nucleophilicity of the nitrogen, enabling the direct coupling reaction. The second reaction in the two‐step process was nucleophilic addition to the N‐methoxyamides. Incorporation of the N‐methoxy group into the amides increased the electrophilicity of the amide carbonyls and promoted the chelation effect. This nucleophilic addition enabled quick diversification of the products derived from the first step. The developed strategy was applicable to a variety of substrates, resulting in the elaboration of multi‐substituted piperidines and acyclic amines, as well as a substructure of a complex natural alkaloid.