Stereodivergent catalytic doubly diastereoselective nitroaldol reactions using heterobimetallic complexes

Stereodivergent construction of three contiguous stereocenters in catalytic doubly diastereoselective nitroaldol reactions of alpha-chiral aldehydes with nitroacetaldehyde dimethyl acetal using two types of heterobimetallic catalysts is described. A La-Li-BINOL (LLB) catalyst afforded anti,syn-nitroaldol products in >20:1-14:1 selectivity, and a Pd/La/Schiff base catalyst afforded complimentary syn,syn-nitroaldol products in 10:1-5:1 selectivity.     

Self-assembly of polyoxometalate macroanion-capped pd0 nanoparticles in aqueous solution

The self-assembly behavior of polyoxometalate (POM) macroanion-capped 3-nm-radius Pd (0) nanoparticles in aqueous solution is reported. Pd(0) nanoparticles are synthesized from reducing K(2)PdCl(4) by using Dawson-type V-substituted POM K(9)[H(4)PV (IV)W(17)O(62)] (HPV(IV)) clusters as the reductant and stabilizer simultaneously in acidic aqueous solutions. The starting molar ratio of K(2)PdCl(4) to HPV(IV) (R value) in solution is important to the formation of Pd nanoparticles. When R < 0.6, approximately 20-nm-radius Pd(0) colloidal nanocrystals are formed. When R > or = 0.6, HPV-capped (and therefore negatively charged) 3-nm-radius Pd(0) nanoparticles are formed, which can further self-assemble into stable, hollow, spherical, 30-50-nm-radius supramolecular structures in solution without precipitation, as confirmed by light scattering and transmission electron microscopy studies. This structure resembles the unique supramolecular structure formed by hydrophilic POM macroanions in polar solvents, which we refer to as "blackberry" structures. It is the first evidence that the blackberry formation can occur in hydrophobic nanoparticle systems when the surface of nanoparticles is modified to be partially hydrophilic. Counterions play an important role in the self-assembly of Pd nanoparticles, possibly providing an attractive force for blackberry formation, which is the case for blackberry formation in POM macroanionic solutions. Our results suggest that the blackberry formation is not a specific property of POM macroions but most likely a general phenomenon for nanoparticles with relatively hydrophilic surfaces and suitable sizes and charges in a polar solvent.     

Transition modes in stratified compressible fluids

Normal modes which exist in stratified compressible fluids are investigated. For the analysis, the conservation of the number of zeros in an eigenfunction is used. It is generally shown that the condition for transition modes such as Lamb-wave modes to exist is determined only by boundary conditions. This mathematical result is physically explained by boundary waves, and this explanation crucially depends on which is larger, gravity acceleration g or the product of Brunt–Väisälä frequency and sound speed Nc_s. This theory gives a guide to choose boundary conditions free of spurious boundary waves. It also explains why a distinct Lamb wave is not found in the ocean unlike in the atmosphere: it is simply because the ocean is not deep enough, but if the ocean were stratified a little more strongly than it is, the Lamb wave would not exist in the ocean however deep it might be.     

Two-dimensional gel permeation chromatography (2D GPC) correlation studies of the aggregate-aggregate interactions in acid-catalyzed triethoxysilyl-terminated polystyrene systems. The effect of specific catalysts on growth process

A set of time resolved gel-permeation chromatography (GPC) profiles, for the reaction mixture of a well-defined polymeric silane coupling agent, triethoxysilyl-terminated polystyrene with molecular weight equal to 8000 (TESi-PS (8000)), catalyzed by HCl (0.1 mol/kg) in tetrahydrofuran (THF), was measured over a long time scale (1–768 h). The GPC profiles were then converted to two-dimensional (2D) correlation spectra. The 2D GPC correlation spectra were compared with those for the CH₃SO₃H (0.1 mol/kg)-catalyzed TESi-PS (8000)-THF system. It has been demonstrated that predominant production of less-reactive oligomers in the HCl-catalyzed system hinders further growth of the oligomer, while formation of reactive oligomers leads to further growth of polymeric precursors in the CH₃SO₃H-catalyzed system.     

Asymmetrically modified silica particles: a simple particulate surfactant for stabilization of oil droplets in water

Spherical silica particles that are able to assemble at a phase boundary of a dual-phase mixture of water and an immiscible organic solvent were prepared by a partial modification of their surface hydroxyl groups with an alkylsilylation agent. Scanning electron microscopic observation of these particles in which their remaining surface hydroxyl groups had been selectively modified with colloidal gold particles revealed that each particle has an asymmetric surface structure: one side of the surface is hydrophilic and the other is hydrophobic. We found that these particles could form a micellar structure in water in the presence of an organic solution of a toluene/polystyrene mixture. The micellar structure was evidenced by formation of golf-ball-like polystyrene particles with dimples imprinting morphologies of the hydrophobic part of modified silica particles.     

Platinum‐Containing Polyoxometalates: syn‐ and anti‐[PtII2(α‐PW11O39)2]10− and Formation of the Metal–Metal‐Bonded di‐PtIII Derivatives

The first examples of dimeric, di‐Pt^II‐containing heteropolytungstates are reported. The two isomeric di‐platinum(II)‐containing 22‐tungsto‐2‐phosphates [anti‐Pt^II₂(α‐PW₁₁O₃₉)₂]^10? ( 1 a ) and [syn‐Pt^II₂(α‐PW₁₁O₃₉)₂]^10? ( 2 a ) were synthesized in aqueous pH 3.5 medium using one‐pot procedures. Polyanions 1 a and 2 a contain a core comprising two face‐on PtO₄ units, with a Pt???Pt distance of 2.9–3 Å. Both polyanions were investigated by single‐crystal XRD, IR, TGA, UV/Vis, ³¹P NMR, ESI‐MS, CID‐MS/MS, electrochemistry, and DFT. On the basis of DFT and electrochemistry, we demonstrated that the {Pt₂^II} moiety in 1 a and 2 a can undergo fully reversible two‐electron oxidation to {Pt₂^III}, accompanied by formation of a single Pt?Pt bond. Hence we have discovered the novel subclass of Pt^III‐containing heteropolytungstates.     

Visible‐Light‐Driven CO2 Reduction with Carbon Nitride: Enhancing the Activity of Ruthenium Catalysts

A heterogeneous photocatalyst system that consists of a ruthenium complex and carbon nitride (C₃N₄), which act as the catalytic and light‐harvesting units, respectively, was developed for the reduction of CO₂ into formic acid. Promoting the injection of electrons from C₃N₄ into the ruthenium unit as well as strengthening the electronic interactions between the two units enhanced its activity. The use of a suitable solvent further improved the performance, resulting in a turnover number of greater than 1000 and an apparent quantum yield of 5.7 % at 400 nm. These are the best values that have been reported for heterogeneous photocatalysts for CO₂ reduction under visible‐light irradiation to date.     

Emission and transient absorption measurements of substitution effects of C–C triple bonds on relaxation processes of the fluorescent state of naphthalenes

Photophysical and photochemical properties of naphthalenes substituted with trimethylsilylethynyl, tert-butylethynyl, and trimethylsilylbutadiynyl groups were investigated by measurement of fluorescence yields, lifetimes, and triplet absorption. Introducing trimethylsilylethynyl and tert-butylethynyl groups to the 1-position of the naphthalene skeleton substantially enhanced fluorescence and intersystem crossing (ISC). The rates of fluorescence of 2-substituted naphthalenes were low. The effect of ethynyl groups on the 1-substituted naphthalenes was rationalized in terms of an increase of the transition moment along the short axis of the naphthalene skeleton. Substitution of the trimethylsilylbutadiynyl group at the 1 or 2-position of the naphthalene skeleton caused a considerable decrease in the fluorescence yield (approximately 0.01) and an increase in the ISC yield (0.99).