Boundaries between square-shaped,nitrogen-adsorbed islands on Cu(001): Two relief mechanisms of the stress induced by atomic adsorbates

We have performed a scanning tunneling microscopy study on a grid-like mesoscopic pattern formed by nitrogen adsorption on a Cu(001) surface. Two types of boundaries are present between square-shaped N-adsorbed islands: a fine straight line of monoatomic width (“monoatomic line”) and a bare Cu(001) belt of several atoms wide (“multiatomic belt”). The boundary type depends on whether c(2 × 2) protrusions in neighboring islands are aligned in-phase or out-of-phase across the boundary. Considering that an adsorbed N atom prefers to be coordinated by four Cu atoms on a plane and that the topmost Cu layer is expanded by 2–3% by N adsorption, we propose the missing-Cu-atom model for a monoatomic line where a single Cu row is ejected by a compressive stress exerted from neighboring N-islands. The reconstruction maintains the planar 4-fold coordination of Cu atoms to an N atom in the case of in-phase alignment, and relieves the N-induced compressive stress very efficiently. Whereas, the Cu row ejection would destroy the stable local structure in the out-of-phase case. The N-induced compressive stress is relieved in the other mechanism where it is compensated with a tensile stress in a bare Cu(001) region. The region is imaged as a multiatomic belt. The above models for a monoatomic line and a multiatomic belt explain well various features observed in the grid pattern. Moreover, the missing-Cu-atom model rationalizes the attractive interaction between N-islands which was difficult to understand in a traditional, elasticity-based view on the self-organization.     

Photochemical fine-tuning of luminescent color of cadmium selenide nanoparticles: fabricating a single-source multicolor luminophore

Size-selective photoetching was applied to silica-coated cadmium selenide (SiO2/CdSe) nanoparticles to precisely control their photoluminescence properties. The absorption spectra of CdSe was blue-shifted by irradiation of monochromatic light, and finally, the absorption onset agreed with the wavelength of irradiation light, indicating that CdSe particles were photoetched to smaller ones until the irradiated photons were not absorbed by the photoetched particles and that the SiO2 shell layer surrounding the CdSe core prevented coalescence between the photoetched particles. Although as-prepared SiO2/CdSe did not exhibit photoluminescence, the application of size-selective photoetching to SiO2/CdSe resulted in the development of the band gap emission, with the degree being enhanced with progress of the photoetching. The peak wavelength of photoluminescence decreased with a decrease in the wavelength used for the photoetching, so that the luminescence color could be tuned between red and blue. Partial photoetching of SiO2/CdSe nanoparticle films produced intense band gap emission of CdSe at the photoetched area, while the remainder of the SiO2/CdSe films did not exhibit detectable photoluminescence, resulting in the formation of a clear photoluminescence image under UV irradiation. This technique makes it possible to produce a multicolored photoluminescence image by irradiation with monochromatic lights having various wavelengths using a single source material.     

A Water-Gated Organic Thin-Film Transistor for Glyphosate Detection: A Comparative Study with Fluorescence Sensing

This work reports the design of a highly sensitive solid-state sensor device based on a water-gated organic thin-film transistor (WG-OTFT) for the selective detection of herbicide glyphosate (GlyP) in water. A competitive assay among carboxylate-functionalized polythiophene, Cu²⁺, and GlyP was employed as a sensing mechanism. Molecular recognition phenomena and electrical double layer (EDL) (at the polymer/water interface) originated from the field-effect worked cooperatively to amplify the sensitivity for GlyP. The limit of detection of WG-OTFT (0.26 ppm) was lower than that of a fluorescence sensor chip (0.95 ppm) which is the conventional sensing method. In contrast to the previously reported insulated molecular wires to block interchain interactions, molecular aggregates under the field-effect has shown to be effective for amplification of sensitivity through “intra”- and “inter”-molecular wire effects. The opposite strategy in this study could pave the way for fully utilizing the sensing properties of polymer-based solid-state sensor devices.     

Reducing Capsule Based on Electron Programming: Versatile Synthesizer for Size‐Controlled Ultra‐Small Metal Clusters

Controlled reducing capsules with a specific number of reducing electrons were achieved by appropriately placed BH₃ units in the dendritic polyphenylazomethines (DPAs). Using the 1:1 coordination fashion on their basic branches with radius affinity gradient, the 4th generation DPA (DPAG4) possessing four BH₃ units in the central positions was prepared as a template synthesizer for size‐controlled ultra‐small metal clusters. This was well‐demonstrated by reduction of Ag, Pt, and other metal ions resulting in monodispersed ultra‐small clusters.     

High-efficiency tris(8-hydroxyquinoline)aluminum (Alq3) complexes for organic white-light-emitting diodes and solid-state lighting

Combinations of electron-withdrawing and -donating substituents on the 8-hydroxyquinoline ligand of the tris(8-hydroxyquinoline)aluminum (Alq(3)) complexes allow for control of the HOMO and LUMO energies and the HOMO-LUMO gap responsible for emission from the complexes. Here, we present a systematic study on tuning the emission and electroluminescence (EL) from Alq(3) complexes from the green to blue region. In this study, we explored the combination of electron-donating substituents on C4 and C6. Compounds 1-6 displayed the emission tuning between 478 and 526 nm, and fluorescence quantum yield between 0.15 and 0.57. The compounds 2-6 were used as emitters and hosts in organic light-emitting diodes (OLEDs). The highest OLED external quantum efficiency (EQE) observed was 4.6%, which is among the highest observed for Alq(3) complexes. Also, the compounds 3-5 were used as hosts for red phosphorescent dopants to obtain white light-emitting diodes (WOLED). The WOLEDs displayed high efficiency (EQE up to 19%) and high white color purity (color rendering index (CRI≈85).     

Total synthesis of spiruchostatin B aided by an automated synthesizer

The total synthesis of a natural product HDAC inhibitor, spiruchostatin B, was successfully achieved. A 5-step synthesis that included an asymmetric aldol reaction was carried out in an automated synthesizer to provide an (E)-(S)-3-hydroxy-7-thio-4-heptenoic acid segment that is the crucial structure of cysteine-containing, depsipeptidic natural products such as spiruchostatins, FK228, FR901375, and largazole for their inhibitory activity against HDACs.     

Efficient topical delivery of chlorogenic acid by an oil-in-water microemulsion to protect skin against UV-induced damage

We examined the intradermal delivery of a hydrophilic polyphenol chlorogenic acid by in vitro study using excised guinea pig dorsal skin and Yucatan micropig skin. Skin accumulation as well as the solubility of chlorogenic acid in aqueous vehicles was much greater than for other polyphenols such as quercetin and genistein. However, since enhancement of skin delivery seemed to be necessary to exhibit its protective effects against oxidative damage of skin, we examined the effects of microemulsions as vehicles. Using microemulsions consisting of 150 mM NaCl solution, isopropyl myristate, polyoxyethylene sorbitan monooleate (Tween 80) and ethanol, skin accumulation as well as solubility of chlorogenic acid further increased. Enhancement effect of an oil-in-water (o/w-type) microemulsion was greater than that of a water-in-oil (w/o-type) microemulsion possibly due to the greater increase in solubility. This finding was quite different from previous findings on relatively hydrophobic polyphenols such as quercetin and genistein. Pretreatment of guinea pig dorsal skin with chlorogenic acid containing microemulsion gel prevented erythema formation induced by UV irradiation. These findings indicate the potential use of hydrophilic chlorogenic acid with o/w-type microemulsion as a vehicle to protect skin against UV-induced oxidative damage.     

Deposition of gallium oxide nanodots prepared from metal‐assembling dendrimer molecules isolated by the spacing of the nonmetal‐assembling dendrimer molecules in the two‐dendrimers mixture monolayer

Phenylazomethine dendrimers (DPA) can precisely incorporate metal chlorides onto the imine sites in a stepwise fashion. Such precise dendrimer–metal complexes allow the preparation of size‐controlled subnanometer metal particles. We now propose a novel approach for the fabrication of size‐controlled subnanometer metal oxide dots isolated on a substrate using two different‐type dendrimers. One is a fourth‐generation phenylazomethine dendrimer (DPAG4) and the other is a benzylether dendrimer (BzEG3) with a zinc porphyrin core. Even though the diameter of BzEG3 corresponds to that of DPAG4, BzEG3 has no metal‐complexing site. Upon dip coating on a highly oriented pyrolytic graphite substrate by the mixed solution of the metal chloride‐assembling DPAG4 molecules and BzEG3 molecules, the dendrimer monolayer was immobilized on the substrate. The concentration of the dendrimer mixture was determined in order to separate each DPAG4–metal chloride complex molecule by BzEG3. Monodispersed metaloxide nanodot arrays could be obtained from the dendrimer monolayer in which DPAG4–metal chloride complex molecule is well isolated by the BzEG3 as a spacer after the hydrolysis of metal chlorides followed by the complete removal of dendrimers. Copyright © 2013 John Wiley & Sons, Ltd.     

Low-Temperature H2 Reduction of Copper Oxide Subnanoparticles

Subnanoparticles (SNPs) with sizes of approximately 1 nm are attractive for enhancing the catalytic performance of transition metals and their oxides. Such SNPs are of particular interest as redox-active catalysts in selective oxidation reactions. However, the electronic states and oxophilicity of copper oxide SNPs are still a subject of debate in terms of their redox properties during oxidation reactions for hydrocarbons. In this work, in situ X-ray absorption fine structure (XAFS) measurements of Cu₂₈O_x SNPs, which were prepared by using a dendritic phenylazomethine template, during temperature-programmed reduction (TPR) with H₂ achieved lowering of the temperature (T₅₀=138 °C) reported thus far for the Cu^II→Cu^I reduction reaction because of Cu−O bond elongation in the ultrasmall copper oxide particles.