Synthesis, structural characterization, and catalytic performance of dititanium-substituted gamma-Keggin silicotungstate

A novel titanium-substituted silicotungstate cluster of [{gamma-SiTi2W10O36(OH)2}2(mu-O)2]8- (1) is synthesized by the introduction of titanium(IV) ions into a divacant lacunary gamma-Keggin-type silicotungstate of [gamma-SiW10O36]8-. This titanium-substituted polyoxometalate, 1, exhibits a dimeric structure. One half of the gamma-Keggin fragment of 1 contains a dinuclear titanium center bridged by two hydroxo groups, and the resulting Ti2(mu-OH)2 core connects to the other Ti2(mu-OH)2 core of the paired gamma-Keggin subunit through Ti-O-Ti linkages. The Ti2(mu-OH)2 core of 1 reacts with MeOH to form the corresponding alkoxo derivative, [{gamma-SiTi2W10O36(OH)(OMe)}2(mu-O)2]8- (2). Two of four hydroxo groups of the Ti2(mu-OH)2 cores in 1 are replaced by methoxo groups to give the Ti2(mu-OH)(mu-OMe) core, and the Ti-O-Ti linkages connecting two gamma-Keggin subunits are maintained in 2. The gamma-Keggin dititanium-substituted silicotungstate 1 catalyzes mono-oxygenation reactions, such as the epoxidation of olefins and sulfoxidation of sulfides with hydrogen peroxide under mild conditions, while the monotitanium-substituted silicotungstate, [alpha-SiTiW11O39]4- (3), and the fully occupied silicododecatungstate, [gamma-SiW12O40]4-, are inactive. The epoxidation with 1 is stereospecific; the configurations around the C=C double bonds of the cis- and trans-olefins are completely retained in the corresponding epoxides. For the competitive epoxidation of cis- and trans-2-octenes, the ratio of the formation rate of cis-2,3-epoxyoctane to that of the trans isomer (R(cis)/R(trans)) is relatively high (21.3) in comparison with those observed for the tungstate catalysts, including [gamma-SiW10O34(H2O)2]4-. The epoxidation of 3-methyl-1-cyclohexene is highly diastereoselective and gives the corresponding epoxide with an anti configuration. The molecular structure of 1 is preserved during the catalysis because the 29Si and 183W NMR spectra of the catalyst recovered after completion of the oxidation are consistent with those of as-prepared compound 1. All these facts suggest the contribution of rigid nonradical oxidants generated on the multinuclear titanium center of 1.     

Influence of Gravitational Settling on Turbulent Droplet Clustering and Radar Reflectivity Factor

This study investigates the influence of gravitational settling of droplets on turbulent clustering and the radar reflectivity factor. A three-dimensional direct numerical simulation (DNS) of particle-laden isotropic turbulence is performed to obtain turbulent droplet clustering data. The turbulent clustering data are then used to calculate the power spectrum of droplet number density fluctuations. The results show that the gravitational settling modulates the power spectrum more significantly as the settling becomes larger. The gravitational settling weakens the intensity of clustering at large wavenumbers for St≤1, whereas it significantly enlarges the intensity for St>1. The dependence on the Taylor-microscale-based Reynolds number is also investigated to discuss the contribution of large-scale eddies to the settling influence. The results show that large-scale eddies modulate the small scale clustering structure of large St droplets. The increment of radar reflectivity factor due to turbulent clustering is estimated from the power spectrum for the case of St=1.0. The result shows that the influence of gravitational settling on the radar reflectivity factor can be significant for the case of large settling velocity droplets.     

Detailed Cloud Microphysics Simulation for Investigation into the Impact of Sea Spray on Air-Sea Heat Flux

This paper reports on the development of a numerical weather simulation model combined with a detailed spectral-bin cloud microphysics model that can explicitly consider the droplet motion and droplet-atmosphere interactions of sea spray. Sea spray is composed of liquid droplets ejected from the sea surface into the evaporation layer, where it enhances heat as well as momentum exchanges between the atmosphere and the sea. In our study, we analyzed the results of idealized 3D simulations to investigate the impact of sea spray on latent heat exchanges and their consequent impact on boundary layer cloud development. The results show that sea spray enhances the latent heat flux by up to 62 % for the surveyed 10m-height velocities, which ranged from 12 to 42 m/s. They also show that sea spray moistening significantly enhances boundary layer cloud development.     

Structural and dynamical aspects of alkylammonium salts of a silicodecatungstate as heterogeneous epoxidation catalysts

The structural and dynamical aspects of alkylammonium salts of a silicodecatungstate [(CH(3))(4)N](4)[γ-SiW(10)O(34)(H(2)O)(2)] [C1], [(n-C(3)H(7))(4)N](4)[γ-SiW(10)O(34)(H(2)O)(2)] [C3], [(n-C(4)H(9))(4)N](4)[γ-SiW(10)O(34)(H(2)O)(2)] [C4], and [(n-C(5)H(11))(4)N](4)[γ-SiW(10)O(34)(H(2)O)(2)] [C5] were investigated. The results of sorption isotherms, XRD analyses, and solid-state NMR spectroscopy show that facile sorption of solvent molecules, flexibility of structures, and high mobility of alkylammonium cations are crucial to the uniform distribution of reactant and oxidant molecules throughout the bulk solid, which are related to the high catalytic activities for epoxidation of alkenes.     

Specific Cell Surface Protein Imaging by Extended Self-Assembling Fluorescent Turn-on Nanoprobes

Visualization of tumor-specific protein biomarkers on cell membranes has the potential to contribute greatly to basic biological research and therapeutic applications. We recently reported a unique supramolecular strategy for specific protein detection using self-assembling fluorescent nanoprobes consisting of a hydrophilic protein ligand and a hydrophobic BODIPY fluorophore in test tube settings. This method is based on recognition-driven disassembly of the nanoprobes, which induces a clear turn-on fluorescent signal. In the present study, we have successfully extended the range of applicable fluorophores to the more hydrophilic ones such as fluorescein or rhodamine by introducing a hydrophobic module near the fluorophore. Increasing the range of available fluorophores allowed selective imaging of membrane-bound proteins under live cell conditions. That is, overexpressed folate receptor (FR) or hypoxia-inducible membrane-bound carbonic anhydrases (CA) on live cell surfaces as cancer-specific biomarkers were fluorescently visualized using the designed supramolecular nanoprobes in the turn-on manner. Moreover, a cell-based inhibitor-assay platform for CA on a live cell surface was constructed, highlighting the potential applicability of the self-assembling turn-on probes.     

Complete removal of paint from metal surface by ablation with a TEA CO2 laser

For high-speed metal surface cleaning, we applied TEA CO₂ laser pulses to ablate painted materials on metal surfaces and examined the efficiency of removal under different surface and irradiation conditions. Surfaces treated with a line-focused laser beam were analyzed with an energy dispersive X-ray analyzer and inspected with optical microscopic observation. Although paints were selectively ablated from the metal surface, the cleaning efficiency was found to depend on surface conditions of substrates. An application of a small amount of dimethyl formamide was effective for completely removing of resin without scorching the surface.     

Pd(O) promoted transformation of N-tosyl-2-(1,3-butadienyl)-aziridine into N-tosyl-2-vinyl-3-pyrroline

1,3-Butadienylaziridines activated by N-tosyl group smoothly rearrange to vinylpyrrolidine derivatives in the presence of a catalytic amount of Pd(PPh₃)₄. Transformation of dienylazetidines into vinylpiperidine derivatives is also described.