Femtosecond Diffuse-Reflectance Spectroscopy of Various Commercially Available TiO2 Powders

The transient absorption properties of several commercially available TiO₂ photocatalysts were investigated by femtosecond diffuse-reflectance spectroscopy. Using femtosecond diffuse-reflectance spectroscopy, the quantities and rates of the initial trapping processes of holes and electrons generated by the photoexcitation of TiO₂ photocatalysts were investigated. It was found that the total amounts of trapped electrons for the pure-anatase and pure-rutile TiO₂ became smaller with increasing particle size, but increased again when the particles’ diameters were larger than 50 nm. The anatase–rutile mixed TiO₂ photocatalysts were found to have smaller amounts of trapped electrons compared with pure-anatase and pure-rutile TiO₂ photocatalysts. The lifetimes of trapped holes of various TiO₂ photocatalysts were also investigated, and it was found that the lifetimes were proportional to the anatase–rutile mixed ratios.     

Carbon Monoxide Oxidation by Polyoxometalate‐Supported Gold Nanoparticulate Catalysts: Activity,Stability, and Temperature‐ Dependent Activation Properties

Nanoparticulate gold supported on a Keggin‐type polyoxometalate (POM), Cs₄[α‐SiW₁₂O₄₀]?n H₂O, was prepared by the sol immobilization method. The size of the gold nanoparticles (NPs) was approximately 2 nm, which was almost the same as the size of the gold colloid precursor. Deposition of gold NPs smaller than 2 nm onto POM (Au/POM) was essential for a high catalytic activity for CO oxidation. The temperature for 50 % CO conversion was ?67 °C. The catalyst showed extremely high stability for at least one month at 0 °C with full conversion. The catalytic activity and the reaction mechanism drastically changed at temperatures higher than 40 °C, showing a unique behavior called a U‐shaped curve. It was revealed by IR measurement that Au^δ+ was a CO adsorption site and that adsorbed water promoted CO oxidation for the Au/POM catalyst. This is the first report on CO oxidation utilizing Au/POMs catalysts, and there is a potential for expansion to various gas‐phase reactions.     

Multiple-scattering approach to Sn L3-edge X-ray absorption near-edge structure (XANES) analyses for organic tin compounds

We apply multiple-scattering calculations to the analyses of Sn L₃-edge X-ray absorption near-edge structure (XANES) spectra for environmental organotin compounds such as SnCl_4−nMe_n, SnCl_4−nBt_n, and SnCl_4−nPh_n (n = 0–4) where Me = CH₃, Bt = C₄H₉, and Ph = C₆H₅. The XANES peak at 3960 eV has rich information on the local structure. Referring to the optimized structures by density functional theory (DFT) calculations, multiple-scattering calculations well explain the observed spectral changes for different “organic extents”. The present study also supports the widely-used semiempirical rule called ‘Natoli’s rule’ for these environmental compounds, which will be useful to use XANES spectra for the practical analytical tools.     

Synthesis and micromechanical properties of flexible, self-supporting polymer-SiO2 nanofilms

Large-scale, self-supporting ultrathin films composed of an elastomeric polyacrylate network interpenetrated by a silica (SiO2) network were synthesized and characterized. The organic network was first photopolymerized and the silica structure was subsequently developed in situ in the preformed organic gel. Composition and morphology of the hybrid interpenetrated network (IPN) nanofilms were characterized by infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy and compared with the case of zirconia (ZrO2) hybrid IPN reported earlier. Young modulus, ultimate tensile strength, and ultimate tensile elongation were determined for different organic/inorganic molar ratios and give some insights on how the composition of the nanofilms influence their robustness and self-supporting properties.     

Total synthesis of (−)-funebrine via Au-catalyzed regio- and stereoselective γ-butyrolactonization of allenylsilane

The stereoselective total synthesis of (−)-funebrine from 2-butyn-1-ol was described. The crucial steps in the synthesis involved the stereoselective enolate Claisen rearrangement of the (S)-α-acyloxy-α-alkynylsilane 8, the Au-catalyzed regio- and stereoselective lactonization of the allenylsilane 7, and the Paal-Knorr pyrrole condensation using an unsymmetrical 1,4-diketone 4b.     

Enantioselective total synthesis of anti HIV-1 active (+)-calanolide A through a quinine-catalyzed asymmetric intramolecular oxo-Michael addition

Enantioselective total synthesis of anti HIV-1 active (+)-calanolide A was achieved by a quinine-catalyzed asymmetric intramolecular oxo-Michael addition as a key step.     

Mesoscopic nanomaterials generated by interfering femtosecond laser processing

Mesoscopic nanomaterials with a size ranging from a few nanometers to hundreds of nanometers were generated on a metallic thin film by interfering femtosecond (fs) laser processing. Because the nanomaterials seemed to demonstrate liquid behavior, we named their structure nano water drop. The structure is considerably similar to that of a real water drop observed with a high-speed camera. Using the phase shift between interfering beams, a duplicate structure was generated. This is a new surface modification technique, using a top-down approach.     

Axially chiral dicarboxylic acid catalyzed asymmetric semipinacol rearrangement of cyclic β-hydroxy-α-diazo esters

The development of axially chiral dicarboxylic acid catalyzed desymmetrizing asymmetric semipinacol rearrangement of symmetrically substituted six-membered cyclic β-hydroxy-α-diazo esters is reported as a means to give chiral cycloheptanones with good enantioselectivities.     

Landau levels in a novel two-dimensional electron system interacting with charged quantum dots

Landau levels have been theoretically investigated in a two-dimensional electron gas near a quantum dot (QD) layer. By a diagrammatical method, we have formulated the self-energy for the Landau level and deduced its relation to the AC conductivity σ_loc(ω) in the QD layer. As an example, we have examined the density of states in the case where σ_loc(ω) is described by Aω^S(S=0.8). It is found that the Landau levels are broadened due to the interaction with the localized electrons in the QDs.