Self-extraction of negatively charged carriers from anodic vacuumarcs

Measurement and magnetic analysis of self-extracted negatively charged carriers (NCCs) from anodic vacuum arcs are presented. They flow to charge collectors made of stainless steel, which are electrically connected to a cathode. When a 60-Hz sinusoidal arc current of 40 kA is burned on 20-mm-diameter copper electrodes spaced 4 mm apart, a negative current of approximately 900 A flows to a cylindrical collector surrounding the arc. The floating collector potential relative to the cathode is measured, and the mean energy of the NCCs is estimated to be greater than 40 eV. It is difficult for the NCCs to flow from anodic vacuum arcs when an anode is made of zinc or cadmium, the atoms of which have electron affinities of less than 0 eV. A magnetic filter of about 500 G, which is placed between the arc and a 30-mm-diameter circular collector, does not affect the NCC's flow from a 4-kA arc burned on copper electrodes. It is possible to extract a large amount of negative copper ions from the anodic copper vacuum arcs     

Diplatinum(ii)-coordinated polyoxotungstate: synthesis, molecular structure, and photocatalytic performance for hydrogen evolution from water under visible-light irradiation

The synthesis and molecular structure of a monomeric diplatinum(ii) complex composed of mono-lacunary α-Keggin polyoxometalate is described. The polyoxometalate, Cs(3)[α-PW(11)O(39){cis-Pt(NH(3))(2)}(2)]·8H(2)O (Cs-1), afforded by a stoichiometric reaction of mono-lacunary Keggin polyoxotungstate with cis-diamminedichloroplatinum(ii) in water, followed by crystallization from water, was obtained as analytically pure, homogeneous, yellow crystals. The compound Cs-1 was characterized by elemental analysis, thermogravimetric/differential thermal analysis (TG/DTA), Fourier transform infrared (FTIR) and UV-visible spectroscopy, solution (1)H and (31)P nuclear magnetic resonance (NMR), and X-ray crystallography. The single-crystal X-ray structure analysis revealed that the two cis-platinum(ii) moieties, [cis-Pt(NH(3))(2)](2+), were coordinated each to two oxygen atoms in a mono-vacant site of [α-PW(11)O(39)](7-) with asymmetric configuration, resulting in an overall C(1) symmetry. Furthermore, hydrogen evolution from an EDTA·2Na (ethylenediamine tetraacetic acid disodium salt) aqueous solution under visible-light irradiation (≥400 nm) was achieved by using polyoxoanion 1 and titanium dioxide.     

Investigation of ion behavior associated with anode-spot modetransition in vacuum arcs

The ion behavior phenomenon associated with transitions of the anode discharge mode to the anode-spot mode is studied by measuring the wall ion current and by spectroscopic observation in vacuum arcs. The anode mode transfers when the wall ion current attains a certain magnitude that is independent of the cathode, but dependent on the anode. The ion-current function to the arc current increases when the arc current increases in the diffuse arc. Spectral-line intensity of Cu III emitted from the plasma in the anode region increases with an instantaneous arc current of a 5-kA peak (kAp) sinusoidal half-wave. These findings suggest an idea for the mode transition, that an ion generation region appears, and that an increase in the ion density produces a positive potential hump near the anode, which results in the negative anode voltage drop triggering the mode transition. After the mode transition, an arc current is found to reduce the ion current near the crest of a sinusoidal current in a copper arc. This appears to be significant for the arc on a small anode. The decrease in the ion current is attributed to the recombination of ions decelerated by anode vapor with electrons emitted from the hot spot on the anode     

Photoluminescence of strained-layer superlattices

The strained-layer superlattices (SLS's) of In_xGa_1?xAsGaAs and the single hetero-structure of In_xGa_1?xAs on GaAs were grown by MBE method. The samples obtained have a perfect surface morphology. The alloy composition of In_xGa_1?xAs layer and the growth rate were determined with high accuracy by in situ observation of the intensity oscillation of RHEED pattern. Photoluminescence peak energies of SLS's are in agreement with the calculated value by the Kronig-Penny analysis.     

Copper-catalyzed gamma-selective and stereospecific substitution reaction of allylic carbonates with diboron: efficient route to chiral allylboron compounds

A copper-catalyzed gamma-selective and stereospecific substitution reaction of allylic carbonates with a diboron reagent affording allylboron compounds is described. Boryl group was selectively introduced at the gamma-position of the leaving carbonate group. Functionalized allylboronates that have an acetal, ester, or isolated alkene were prepared. The reaction of optically active allylic carbonates underwent complete alpha-to-gamma chirality transfer with anti-stereochemistry to produce optically active allylboronates having a boron-substituted stereogenic center.     

Synthesis,characterization, and catalytic performance of single-site iron(III) centers on the surface of SBA-15 silica

A new molecular precursor strategy has been used to prepare a series of single-site catalysts that possess isolated iron centers supported on mesoporous SBA-15 silica. The iron centers were introduced via grafting reactions of the tris(tert-butoxy)siloxy iron(III) complex Fe[OSi(O(t)Bu)(3)](3)(THF) with SBA-15 in dry hexane. This complex reacts cleanly with the hydroxyl groups of SBA-15 to eliminate HOSi(O(t)Bu)(3) (as monitored by (1)H NMR spectroscopy) with formation of isolated surface species of the type identical with SiO-Fe-[OSi(O(t)Bu)(3)](2)(THF). In this way, up to 21% of the hydroxyl sites on SBA-15 were derivatized (0.23 Fe nm(-)(2)), and iron loadings in the range of 0.0-1.90% were achieved. The structure of the surface-bound iron species, as determined by spectroscopic methods (electron paramagnetic resonance (EPR), nuclear magnetic resonance (NMR), UV-vis, and in situ infrared measurements) and by elemental analyses, contains a pseudotetrahedral iron(III) center. The THF ligand of this surface-bound complex was quantitatively displaced by acetonitrile (by (1)H NMR spectroscopy). Calcination of these materials at 300 degrees C for 2 h under oxygen resulted in removal of all organic matter and site-isolated iron surface species that are stable to condensation to iron oxide clusters. Spectroscopic data (UV-vis and EPR) suggest that the iron centers retain a mononuclear, pseudotetrahedral iron(III) structure after calcination. The calcinated, iron-grafted SBA-15 materials exhibit high selectivities as catalysts for oxidations of alkanes, alkenes, and arenes, with hydrogen peroxide as the oxidant.     

Determination of ofloxacin in tablets by room-temperature phosphorimetry on a poly(vinyl alcohol) solid substrate

An easy and sensitive method for the quantitative determination of ofloxacin (OFLX), a new fluoroquinolone antimicrobial agent, in a pharmaceutical formulation, tablet, was developed by using solid-substrate room-temperature phosphorimetry (RTP) on a poly(vinyl alcohol) substrate. The method did not require a dry gas flush during the measurement of phosphorescence. The influence of different conditions such as solution pH and concentrations of heavy atoms, used as the enhancer, were studied. The phosphorescence intensity of OFLX was enhanced using NaOH and KI as enhancers. A linear relationship between concentration and RTP intensity for each standard solution was obtained in the concentration range of 4-18000 ng/ml, and the determination limit was 4 ng/ml. The proposed method was applied to a determination of OFLX in a commercial tablet, and the results were compared with those of fluorescence and UV methods. It was proven that OFLX in a commercial tablet can be accurately measured by this method with a very small amount of sample solution.     

Determination of diazepam and its metabolites in human urine by liquid chromatography/tandem mass spectrometry using a hydrophilic polymer column

Diazepam and its major metabolites, nordazepam, temazepam and oxazepam, in human urine samples, were analyzed by liquid chromatography (LC)/tandem mass spectrometry (MS/MS) using a hydrophilic polymer column (MSpak GF-310 4B), which enables direct injection of crude biological samples. Matrix compounds in urine were eluted first from the column, while the target compounds were retained on the polymer stationary phase. The analytes retained on the column were then eluted into an acetonitrile-rich mobile phase using a gradient separation technique. All compounds showed base-peak ions due to [M+H]+ ions on LC/MS with positive ion electrospray ionization, and product ions were produced from each [M+H]+ ion by LC/MS/MS. Quantification was performed by selected reaction monitoring. All compounds spiked into urine showed method recoveries of 50.1-82.0%. The regression equations for all compounds showed excellent linearity in the range of 0.5-500 ng/mL of urine. The limits of detection and quantification for each compound were 0.1 and 0.5 ng/mL of urine, respectively. The intra- and inter-day coefficients of variation for all compounds in urine were not greater than 9.6%. The data obtained from actual determination of diazepam and its three metabolites, oxazepam, nordazepam and temazepam, in human urine after oral administration of diazepam, are also presented.