Photoinduced desorption of sulfur from gold nanoparticles loaded on metal oxide surfaces

We now report photoinduced sulfur desorption from the surfaces of Au nanoparticles loaded on metal oxides. This reaction occurs in water at ordinary temperature and pressure. Nanometer-sized Au particles have been formed on the surfaces of various metal oxides by deposition-precipitation (Au/oxides). Elemental sulfur (S8) is selectively adsorbed on the Au nanoparticle surfaces of Au/oxides in an atomic state at a coverage of (theta) 1/3. Irradiation (lambdaex > 300 nm) of the sulfur adsorbed Au/anatase TiO2 in water has led to reductive desorption of the sulfurs at room temperature. Electrochemical measurements using Au/oxides indicate that the driving force for this reaction is the photoinduced upward shift of Fermi energy of the metal oxide-supported Au nanoprticles. This study will open up a novel and wide application of heterogeneous photocatalysis for thermal catalysts.     

Synthesis of functionalized hydroquinones via [Cp*RuCl2]2-catalyzed cocyclization of alkynes, alpha,beta-unsaturated carbonyl compounds, and carbon monoxide

[reaction: see text] Catalytic [2 + 2 + 1 + 1] cocyclization reaction of an alkyne, an alkene, and two molecules of carbon monoxide, leading to functionalized hydroquinones, was studied. Using [Cp*RuCl2]2 as a catalyst, we found that a variety of electron-deficient alkenes, such as alpha,beta-unsaturated ketones, esters, amides, and nitriles, can be employed as an alkene coupling partner to give the corresponding hydroquinones.     

Creation of novel chiral synthons with enzymes and applications to natural product synthesis. 15. Efficient introduction of chiral centers into cyclohexane ring

The chiral half-ester 2 obtained by asymmetric hydrolysis of the symmetric diester 1 with pig liver esterase has been shown to be a versatile synthon for various chiral cyclohexane derivatives.     

220-MHz NMR spectra of acrylic monomer–2-substituted 1,3-diolefin alternating copolymers

An investigation by 220-MHz NMR spectroscopy was carried out on the alternating copolymers of acrylic monomer with 2-substituted 1,3-diolefin. The chain structures were determined. The acrylic monomers used were methyl methacrylate (MMA), acrylonitrile (AN), and methacrylonitrile (MAN); isoprene (IP) and chloroprene (CLP) were the 1,3-diolefins. In the MAN–IP alternating copolymer, the 1-position methylene protons of IP showed an AB quartet peak, confirming the α-1 linkage structure. Similarly, in the MMA–CLP and AN–CLP copolymers, the 1-position methylene protons of CLP showed and AB quartet and an ABX pattern, respectively, confirming the α-1 linkage structure in both these cases also. The α-1 linkage structure was also revealed by the decoupling technique in the MAN–CLP alternating copolymer. The AN–IP and MMA–IP alternating copolymers also possess a bond between the α-position of the acrylic monomer and the 1-position of IP. The monomeric units in the alternating copolymers of acrylic monomers with 2-substituted 1,3-diolefins were generally linked at the α-position of acrylic monomer and the 1-position of 1,3-diolefin. On the other hand, in the Diels-Alder adducts of acrylic monomer with 2-substituted 1,3-diolefin, the reaction takes place between the α-position of acrylic monomer and the 4-position of 1,3-diolefin. The regioselectivity of the alternating copolymers and the Diels-Alder adducts is quite compatible with the expectations from molecular orbital theory.     

Influence of amino acid side chain packing on Fe-methionine coordination in thermostable cytochrome C

Paramagnetic NMR and optical studies of the oxidized forms of mesophile Pseudomonas aeruginosa cytochrome c(551) and its quintuple mutant (F7A/V13M/F34Y/E43Y/V78I), and thermophile Hydrogenobacter thermophilus cytochrome c(552) demonstrated that the amino acid side chain packings in the protein interior influence the coordination bond between the heme iron and the axial methionine in the proteins. The strength of heme axial coordinations was found to correlate with the overall protein thermostability.     

Installation of carbon chain onto 2-cyclohexene-1,4-diol monoacetate

Alkylation of cyclohexenyl monoacetate 1 with R₂Cu(CN)(MgCl)₂ or RMgBr/CuCN (cat.) in Et₂O produced trans 1,2-isomers 4, while arylation and alkenylation of 1 was accomplished with lithium borates 5 and a nickel cat. to afford trans 1,4-isomers 3 selectively. Furthermore, several transformations of the products were carried out to demonstrate synthetic advantages of the present reactions.     

Ultra-slow Relaxation Dynamics in Triglycine Sulfate and D-Sorbitol Studied by Time-resolved Spectroscopy

The ultra-slow modes with a relaxation time much longer than 1 ns are discovered by a time-resolved spectroscopy in uniaxial ferroelectric (NH₂CH₂COOH)₃H₂SO₄ (TGS) and in glass-former HOCH₂(CHOH)₄CH₂OH (D-sorbitol). A mode discovered in TGS is a thermal relaxational mode and is proved to be the physical origin of the central peak found by Brillouin scattering. Two modes are discovered in D-sorbitol. One is a thermal relaxational mode. The other is a mode characterized by the Kohlraush-Williams-Watts function with a relaxation time _R. A remarkable result is that _R indicates a critical behavior not at the liquid-glass transition temperature T_g =–7°C but at the ergodic to nonergodic transition temperature T_c=33°C.This revised version was published online in November 2005 with corrections to the Cover Date.     

Effects of type and physical properties of oil phase on oil-in-water emulsion droplet formation in straight-through microchannel emulsification, experimental and CFD studies

Straight-through microchannel (MC) emulsification is a novel technique for formulating monodisperse emulsions using an array of micrometer-sized channels vertical to the surface of a silicon plate (a straight-through MC). We studied the effects of the type and physical properties of the dispersed oil phase and of the surfactant concentration on droplet formation from a straight-through MC by experiments and computational fluid dynamics (CFD) simulations. Monodisperse oil-in-water emulsions with coefficients of variation below 4% were formulated from an oblong straight-through MC using silicone oils, tetradecane, medium-chain triglyceride, soybean oil, and liquid paraffin as the oil phase. At oil viscosities (eta(d)) lower than a threshold value of 100 mPa s, the values of the resultant droplet diameter (d(ex)) gradually decreased with increasing eta(d), whereas they were not affected by the surfactant concentration. Conversely, at eta(d) higher than the threshold value, the d(ex) values significantly increased with increasing eta(d), and they were affected by the surfactant concentration. An analysis on the basis of droplet formation time and interfacial tension clarified that the trends in d(ex) at eta(d) above the threshold value would be caused by the significant decrease in the dynamic interfacial tension during droplet formation. We thus discovered that the dynamic interfacial tension is also a parameter affecting the d(ex) along with eta(d) in straight-through MC emulsification. CFD simulations using a three-dimensional (3D) model including a straight-through MC confirmed successful formation of micrometer-sized droplets for the above-mentioned oils. The experimental and CFD results for the resultant droplet size were compared using the dimensionless droplet diameter (d, droplet diameter/channel equivalent diameter). The d(CFD) values agreed well with the d(ex) values at eta(d) below the threshold value of 100 mPa s for all the experiment systems and at eta(d) above the threshold value for the experiment systems that did not contain a surfactant.     

Novel asymmetric through-hole array microfabricated on a silicon plate for formulating monodisperse emulsions

We have proposed a novel microchannel (MC) structure for formulating monodisperse emulsions. The emulsification device is a silicon array of microfabricated, asymmetric through-holes with a slit and a circular channel (an asymmetric straight-through MC). The asymmetric through-holes of a uniform size stably yielded monodisperse emulsions with average droplet diameters of 35-41 mum and coefficients of variation of less than 2% by forcing the to-be-dispersed phase into the continuous phase via the through-holes. Their asymmetry enabled the stable formation of monodisperse emulsion droplets by spontaneous transformation, even using a to-be-dispersed phase with a very low viscosity below 1 mPa s. Additionally, the asymmetric straight-through MC with a high-density through-hole layout has the potential for high-throughput formulation of monodisperse emulsions.     

DNA topology on an increase in positive writhing number of DNA: conformation changes in the time course of cis-diamminedichloroplatinum(II)-DNA adducts

We show that the topological significance of the gel mobility of cis-diamminedichloroplatinum(II) (DDP)-closed circular DNA (ccDNA) adducts decreases with reaction time, until a point at which it joins relaxed DNA, and that the mobility of the adducts increases again. There is no relationship between the relative length of the adducts and the gel mobility. Although the significance of the decrease of gel mobility is due to the unwinding of cis-DDP-DNA (or trans-DDP-DNA) adducts, the conformational significance of the subsequent increase in mobility is unclear. To elucidate the conformational significance for unwinding of the adducts, we measured the writhing number (Wk) of the adducts using electron microscopy and analyzed the topological states of cis-DDP (or trans-DDP) adducts based on the White rule, Lk=Wk+Tk. Where, Lk and Tk represent the linking and twisting number in the ring, respectively. From the data, we found that the Wk of cis-DDP-ccDNA adducts in comparison with trans-DDP-ccDNA adducts increases from a negative to a positive number with time. This suggests that cis-DDP plays a role in the change of the topological state of ccDNA. In the abstraction of platinum from the adducts with CN- ion, the differences in both topological states may explain why Pt in trans-DDP is abstracted more easily than in cis-DDP. To explain the abstraction of Pt ion, we also discuss the findings based on the thermodynamic cycle in a intermolecular crosslink model Pt(NH3)2(guanine)2(2+)-->Pt(CN)4(2-) using the Pt parametrized PM3 method.