Isobutane alkylation over solid acid catalysts under supercritical conditions

Solid catalyzed isobutane alkylation has been investigated for decades, but it has not yet been applied in any commercial uses because of the rapid deactivation of the catalyst. Here, the alkylation reaction has been studied under supercritical conditions using metal-promoted and unpromoted sulfated zirconia as catalysts. The catalytic activity at the supercritical condition of 5.0 MPa, 423K was significantly higher than at lower reaction pressure conditions and the deactivation rate was clearly reduced, independent on the catalyst. Iron- and manganese-promoted sulfated zirconia (SFMZ) showed higher activities under all conditions than unpromoted sulfated zirconia (SZ).     

A problem in the spectrophotometric determination of dissolved total phosphorus in brackish anoxic waters

When dissolved total phosphorus in anoxic brackish waters was determined spectrophotometrically by the heteropoly molybdenum blue method after oxidation with potassium peroxodisulfate, negative dissolved organic phosphorus contents were obtained from the differences between the total phosphorus and inorganic phosphorus contents. A major cause of this inconsistency is coprecipitation of phosphate with the colloidal hydrated iron(III) oxide produced fro miron in these waters, or the formation of iron(III) phosphate during the oxidation process. The problem can be avoided by oxidation with nitric and perchloric acids.     

Imaginary-time path integral for a relativistic spinless particle in an electromagnetic field

A rigorous path integral representation of the solution of the Cauchy problem for the pure-imaginary-time Schrödinger equation _t (t, x)=–[H–mc ²](t,x) is established.H is the quantum Hamiltonian associated, via the Weyl correspondence, with the classical Hamiltonian [(cp–eA(x))²+m ² c ⁴]^1/2+e(x) of a relativistic spinless particle in an electromagnetic field. The problem is connected with a time homogeneous Lévy process.     

Actinorhodin Biosynthesis Terminates with an Unprecedented Biaryl Coupling Reaction

A plethora of dimeric natural products exist with diverse chemical structures and biological activities. A major strategy for dimerization is aryl coupling catalyzed by cytochrome P450 or laccase. Actinorhodin (ACT) from Streptomyces coelicolor A3(2) has a dimeric pyranonaphthoquinone structure connected by a C−C bond. In this study, we identified an NmrA-family dimerizing enzyme, ActVA-ORF4, and a cofactor-independent oxidase, ActVA-ORF3, both involved in the last step of ACT biosynthesis. ActVA-ORF4 is a unique NAD(P)H-dependent enzyme that catalyzes the intermolecular C−C bond formation using 8-hydroxydihydrokalafungin (DHK-OH) as the sole substrate. On the other hand, ActVA-ORF3 was found to be a quinone-forming enzyme that produces the coupling substrate, DHK-OH and the final product, ACT. Consequently, the functional assignment of all essential enzymes in the biosynthesis of ACT, one of the best-known model natural products, has been completed.     

A validated HPLC‐fluorescence method with a semi‐micro column for routine determination of homocysteine,cysteine and cysteamine,and the relation between the thiol derivatives in normal human plasma

A semi‐micro column HPLC‐fluorescence method for routine determination of thiol derivatives such as homocysteine (Hcy), cysteine (Cys) and cysteamine (CA) is described. The thiol derivatives labeled with ammonium‐7‐fluorobenzo‐2‐oxa‐1,3‐diazole‐4‐sulfonate (SBD‐F) were isocratically separated within 12 min on a semi‐micro ODS column (Daisopak‐SP‐120‐5‐ODS‐BP) with a mixture of 25 mm acetate buffer (pH 2.00) and CH₃CN as a mobile phase. The purity and similarity of SBD‐thiols by a multi‐wavelength fluorescence detector were more than 92.3 and 96.7%. The detection limits of Hcy, Cys and CA at a signal‐to‐noise ratio of 3 were 0.16, 0.47 and 0.03 µm , respectively. Furthermore validation parameters such as accuracy, precision and robustness of the proposed method showed satisfactory results. Almost 850 plasma sample injections (range 572–1076, n = 3) for a column could be performed without differences in retention time and peak heights of labels. As an application of the proposed method, the determination of thiol derivatives in normal human plasma (n = 103) was demonstrated. The correlation coefficients between Hcy vs Cys and Hcy vs CA were 0.38 and −0.35, respectively. Copyright © 2009 John Wiley & Sons, Ltd.     

Control of ridge shape for the formation of nanometer-scale GaAs ridge quantum wires by molecular beam epitaxy

We have investigated the molecular beam epitaxial (MBE) growth mechanisms of nanometer scale GaAs ridge structures formed on patterned substrates and studied the way to control the widths of ridges and those of quantum wires grown on them. It is found that the width of the ridge structure decreases, as the growth temperature is reduced, reaching about 20 nm when grown below 580°C. The width of an AlAs ridge (10 nm at 570°C) is always found to be narrower than that of GaAs. A Monte Carlo simulation is performed to investigate the diffusion process of atoms in these ridge structures and indicates the important role of thermodynamical stability on the shape of a nanometer structure.     

Tight-binding calculations of the {211} Σ=3 boundary in diamond

The atomic and electronic structure of the {211} =3 boundary in diamond has been calculated by using the transferable tight-binding method. Several atomic models with symmetry consistent with the electron microscopy observation have been dealt with. The four-fold coordinated model is the most stable, although its interfacial energy is fairly high as compared with four-fold coordinated configurations in Si and other boundaries in diamond. Thus the models with three-fold coordinated sites may exist partially as defects. The electron energy-loss spectra of this boundary have been calculated by the tight-binding method for the first time. The K-edge spectra of the models with three-fold coordinated sites have small peaks below the bulk conduction-band peak caused by unoccupied gap states. These can explain the increases at the position of the * peak below the * peak in the observed spectra of this boundary.     

Studies on the extraction and determination of metals-I Extraction of hafnium into methyl isobutyl ketone and tributyl phosphate

The effect of various factors on the distribution of hafnium ( 5.60 × 10⁻⁴M) between different acids and methyl isobutyl ketone (MIBK) or tributyl phosphate (TBP) was studied by using ^{176 + 181} Hf as a tracer, when the extraction is made from 7.5–11M hydrochloric acid with an equal volume of IM TBP in benzene, hafnium is extracted quantitatively (>99%). The hafnium can be stripped with 1–3M hydrochloric acid.     

Effects of indium doping on the superconducting properties of YBa2Cu3Oy sintered compounds and thin films

We investigated the effects of indium doping on the superconducting properties of YBCO sintered samples and thin films. In₂O₃-doped YBCO and YBa₂Cu_3−xIn_xO_y sintered samples showed a gradual decrease in the critical temperature (T_c) with increasing indium content; however, a T_c value above 80 K was maintained even up to 30 vol.% addition and x = 0.4, respectively. Ba₃Cu₃In₄O₁₂ was detected by X-ray diffractometry and energy-dispersive X-ray spectroscopy as a reaction product for both sintered samples. The normalized J_c under a magnetic field of 0.1 T showed a maximum at x = 0.3. Indium-doped YBCO films prepared by pulsed laser deposition showed a similar dependence of T_c on indium content as the sintered samples.