Simplified method for the Re-Os dating of molybdenite using acid digestion and isotope dilution ICP-MS

An analytical method was developed for Os-Re dating of molybdenite. The method is based on determination of Os and Re concentrations in molybdenite by isotope dilution inductively-coupled plasma mass spectrometry (ID-ICP-MS). Sample digestion and sample/spike equilibration were achieved by a two-stage autoclave-based procedure using a mixture of nitric and sulphuric acids. Os was separated from the sample digest by modified single-stage distillation of osmium tetraoxide (OsO₄) using elevated temperature and on-line addition of hydrogen peroxide. OsO₄(g) was trapped in a mixture of 0.05% thiourea in 0.05 M sodium hydroxide. An anion-exchange column was used to separate Re from excess Mo in the solution remaining after distillation. Os and Re isotope ratio measurements were performed by single-collector, double focusing inductively-coupled plasma mass spectrometry (ICP-MS) with on-line mass-bias correction. Typical instrumental precision was in the range 0.02-0.2% relative standard deviation (R.S.D.) depending on the analyte concentrations. Notorious Os memory effects in the ICP-MS introduction system were eliminated using 5% ammonia solution, both as matrix for final dilution of the trap mixture as well as for washing between the samples. The reproducibility of the entire analytical procedure was accessed by replicate dating of two molybdenite standards and three molybdenite separates, and was found to be in the range 0.87-1.52% R.S.D. Though accuracy of the method is limited by difficulties in evaluating exact concentration of Os in spike solution, ages obtained in the course of these work agrees well with previously published data.     

Advanced oxidation processes for decolorization of aqueous solution containing acid red G azo dye

Some investigations concerning the decolorization of Acid Red G azo dye by photooxidation with hydrogen peroxide were performed. The influences of pH, oxidant concentration, and the presence of Fe²⁺ or other metal ions (Co²⁺, Cu²⁺, Ni²⁺, Mn²⁺) as potential catalysts, were investigated. The best results were obtained in the presence of ferrous ions in acid and neutral media. The other ions are not as effective as Fe²⁺ for dye decolorization. Co²⁺ and Cu²⁺ ions have a catalytic action, at low concentration, within a wide range of pH. Ni²⁺ and Mn²⁺ ions have no catalytic effect in photooxidation with hydrogen peroxide at acid Ni²⁺ and Mn²⁺ ions have no catalytic effect in photooxidation with hydrogen peroxide at acid pH values, but show a weak action in alkaline media.     

Solid-phase synthetic method for (±)-α-amino acids via phase-transfer catalytic alkylation

A solid supported glycineimine t-butyl ester was designed and successfully applied to the synthesis of (±)-α-amino acids. The phase-transfer catalytic alkylation, followed by acidic hydrolysis and benzoylation gave N-benzoyl-α-amino acid tert-butyl esters in high yields (up to 92%).     

Diastereoselective synthesis of unsaturated 1,2-amino alcohols from α-hydroxy allyl ethers using chlorosulfonyl isocyanate

Diastereoselective synthesis of 1,2-amino alcohols was achieved from a highly diastereoselective allylic amination reaction of α-hydroxy allyl ethers using chlorosulfonyl isocyanate. Diastereoselectivities varied depending on the stereochemistry of the ethers used and the stability of the carbocation intermediate obtained during the reaction. We propose that this CSI reaction is the results of either a S_Ni or S_N1 mechanism, according to the stability of the carbocation intermediate.     

Fluorometric determination of urea in alcoholic beverages by using an acid urease column-FIA system

An acid urease column was applied to a fluorometric flow-injection analysis (FIA) system as a recognition element for determination of urea in rice wines.

The acid urease has specific properties of showing its catalytic activity in low pH range and tolerance to ethanol in comparison to those of a urease from jack-beans. The enzymes were covalently immobilized onto porous glass beads with controlled pore size and then, packed into a small polymer column. The flow-type of the biosensing system was assembled with a sample injection valve, the immobilized enzyme column, and a flow-through quartz cell attached to a fluorescent spectrophotometer. Citrate buffer (50 mM, pH 5.0) as the carrier solution was continuously pumped through the system. Sample solutions were introduced into the system via a rotary injection valve. A standard urea solution was measured through monitoring variations in fluorescent intensity attributable to fluorescent isoindole derivatives formed by coupling with ammonia molecules released in the enzymatic hydrolysis of urea and orthophthalaldehyde reagents. The fluorescent intensity was measured under the conditions of λ_ex = 415 nm and λ_em = 485 nm. A wide, linear relationship was obtained between the concentration of urea (1.0–100 μM) and the variation in fluorescent intensity. The monitoring did not suffer from ethanol and various amino acids contained in rice wines. Real samples pretreated with ion exchange resins for removal of endogenous ammonia were introduced into the FIA system and urea in the samples was determined. These results were compared with those obtained with use of an F-kit method. The proposed FIA system should present sensitive, selective and convenient analysis of urea in alcoholic beverages.     

A stereoselective synthesis of (2R,3S)-2-amino-3,4-dihydroxybutyric acid using an ether directed aza-Claisen rearrangement

A new approach for the stereoselective synthesis of (2R,3S)-2-amino-3,4-dihydroxybutyric acid, an α-amino acid from Lyophyllum ulmarium, has been accomplished using an ether directed aza-Claisen rearrangement. On investigation of optimal conditions for this key step it was shown for the first time that Au(I) can be used to catalyse this transformation.     

非晶态Co-B的局域电子结构的Xα原子簇计算

In the research on metallic glass, there are arguments against the "rigid band charge transfer", model which assumes a charge transfer from metalloid atoms to transition metal atoms to explain the experimental evidence of linear reduction of average atomic magnetic moment with the increasing concentration of metalloid atoms, but they could not explain the experimental relation of the reduction. In the present work, spin-polarized SCC-DV-X_a calculation for atomic clusters for metallic glass Co-B has been empoloyed to investigate the local electronic structure and magnetic property of the metallic glass. As opposed to the "rigid band charge transfer" model, calculation in the present work indicates that charge transfers from Co4s to both B and Co3d. It is found that there is Co3d4s-B2p hybird bonding in Co-B, which leads to the linear reduction of average atomic magnetic moment. Thus the explanation removes the above controversy.