Usage of Empore™ membrane in alcoholic media for copper(II) distribution studies

The sorption of copper(II) on a solid, iminodiacetic based, chelating material, the Empore™ membrane, in alcoholic solutions is considered. Determination of the acid-base properties, kinetic of metal sorption and complexing properties, in solutions with different percentages of ethanol, ranging from 0 to 40% is undertaken. The results are compared with those obtained using the classical iminodiacetic resin Chelex 100 in beads. No significant differences are found in the thermodynamic properties, but the kinetics of the metal sorption on the membrane is slower and a dependence of the process rate with the alcoholic content is observed. In the present investigation, the detection of copper(II) species both in alcoholic Italian distillate “grappa” and in its intermediate product (“flemma”), is carried out by the Resin Titration (RT) method using, as competitive reagent, the Empore™ membrane. To validate the procedure, synthetic solutions containing different percentages of ethanol are analysed.     

Microwave assisted fluorination: an improved method for side chain fluorination of substituted 1-arylethanones

A two-step, one-pot microwave (MW) assisted fluorination of 1-arylethanones to their corresponding 1-aryl-2-fluoroethanones has been developed. The first step utilises Selectfluor™ as a fluorinating agent in methanol forming 1-aryl-2-fluoroethanones and their corresponding dimethyl acetals. In the second step, water is added and Selectfluor™ acts as a Lewis acid in the hydrolytic cleavage of the dimethyl acetals. Compared to the thermal synthesis, the MW assisted method leads to a reduction in reaction time both in the fluorination and for the dimethyl acetal cleavage. Moreover, the one-pot procedure reduces reagent and solvent consumption. The method is best suited for the preparation of 1-aryl-2-fluoroethanones containing substituents that deactivates electrophilic aromatic substitution, however highly electron deficient ketones such as 1-(3,5-dinitrophenyl)ethanone reacts more slowly. Reactions using electron rich aromatic ketones had a low regioselectivity, and also produced fluoroaromatic products.     

Microcalorimetric study on expression of foreign genes in Bacillus thuringiensis

The thermogenic curves of the aerobic metabolism of the three strains of Bacillus thuringiensis B.t. A, B.t. B and B.t. C have been determined by using an LKB-2277 BioActivity Monitor. B.t. A was the host bacterium without foreign gene. B.t. B and B.t. C were constructed by transforming different foreign genes into the host B.t. A, respectively. B.t. B expressed erythromycin resistant gene, while B.t. C expressed both erythromycin resistant gene and tyrosinase gene. The heat flow rate of these strains is B.t. A> B.t. B >B.t. C. These results indicated that there is obvious interrelation between expression of foreign genes and heat flow rate of B.t. strains. This revised version was published online in August 2006 with corrections to the Cover Date.     

Magtrieve™ (CrO2) and MnO2 mediated oxidation of aldoximes: studying the reaction course

Magtrieve™ (CrO₂) and MnO₂ mediated oxidation of aldoximes to nitrile oxides were studied in details. In presence of external radical source, TEMPO, these reagents did not furnish nitrile oxides, instead favoured deoximation to aldehydes. A common trend of deoximation was established from electronically tuned aldoximes, which is: aliphatic>aromatic>aldoximes with strong electron-withdrawing group, though the extent of deoximation was less in case of CrO₂. Above effects were not observed with chloramine-T and diacetoxyiodobenzene, reagents known to produce nitrile oxides via hydroximoyl halide or equivalent ionic intermediates. A putative reaction mechanism is proposed for MO₂ (M=Cr, Mn) mediated oxidation of aldoximes through formation of a nitroso-oxime tautomeric pair. Formation of nitrile oxide is possibly occurred from the oxime tautomer via a σ-type iminoxy radical intermediate. The deoximation process, dominating in presence of external radical environment, is explained following decomposition of the nitroso tautomer.     

The influence of fluorine on the asymmetric reduction of fluoromethyl ketones

A comparative study of the asymmetric reduction of representative aryl and alkyl α-fluoro- and α-chloromethyl ketones using (−)-diisopinocampheylchloroborane [(−)-DIP-Chloride™] and (−)-B-isopinocampheyl-9-borabicyclo[3.3.1]nonane [R-Alpine-Borane^®] has been made. It was observed that DIP-Chloride™ is superior in terms of the rate and enantioselectivity for both classes of halo-ketones. While the reduction of monofluoroacetone and trifluoroacetone with DIP-Chloride™ provided the product alcohols in 61% ee and 96% ee, respectively, the reduction of difluoroacetone yielded only 5% ee. The influence of a lone halogen atom was not observed for monochloroacetone, all of which point towards a chelating effect of monofluoroacetone on the Lewis acidic chloroborane.     

外汇储备规模与多元变量弹性系数的实证研究

中国外汇储备近几年的迅速增长引发了关于中国外汇储备规模是否适度的广泛讨论。本文从需求的角度,运用计量经济学的多元线性回归的方法,建立中国外汇储备与平均进口倾向、进口和国际收支三变量的双对数模型,通过计算并通过相关检验得到外汇储备与相关变量的弹性系数。为预测和制定相关政策提供依据。     

A recursive linear programming analysis of the future of the pulp and paper industry in the United States: Changes in supplies and demands,and the effects of recycling

The impacts of increased paper recycling on the U.S. pulp and paper sector are investigated, using the North American Pulp And Paper (NAPAP) model. This dynamic spatial equilibrium model forecasts the amount of pulp, paper and paperboard exchanged in a multi-region market, and the corresponding prices. The core of the model is a recursive price-endogenous linear programming system that simulates the behavior of a competitive industry. The model has been used to make forecasts of key variables describing the sector from 1986 to 2012, demand for paper would have the greatest impact on the amount of wood used. But the minimum recycled content policies envisaged currently would have no more effect than what will come about due to unregulated market forces.     

Optimization of spiroimidazolidinone derivatives synthesis on solid phase using SynPhase™ Lanterns

We report the synthesis of 1,4,8-triazaspiro[4.5]decan-2-one derivatives from N-benzyl-4-piperidone and N-protected amino acid amides on solid support. We have translated the chemistry from solution to solid phase using a backbone amide linker (BAL) mimic. Using a parallel combinatorial approach, we performed the optimization of the synthesis on SynPhase™ Lanterns.     

Regiocontrolled fluorination of 2-hydroxyalkyl dihydropyrans and carbonyl derivatives

Reaction of polysubstituted 2-hydroxyalkyldihydropyrans with DAST led regiospecifically to fluorination at the exocyclic position, except for primary alcohols. Difluorination of carbonylated analogues with deoxo-fluor™ occurred also regioselectively. The unexpected stability and synthetic potential of these new allylic fluorides are discussed.     

信息技术在美国大学物理课程中的应用——以美国俄亥俄州立大学为例

随着信息时代的来临,信息技术作为新型的教学工具逐步走进了校园,进入了课堂,成为现代化教学不可缺少的手段和教学改革的利器.文章根据作者在美国访学一年的经历,以美国俄亥俄州立大学为例,详细介绍信息技术在美国大学工科物理主要教学环节中的应用,并对中美大学在信息化建设方面的差异进行总结;通过比较可以看到,国内在信息技术常态化以及将信息技术深入融合到教学的具体环节方面和美国还存在有一定差距,需要进一步加强.