一种双锂引发剂及一步法合成SBS

<正> 目前合成SBS的一般方法是以单锂烷基化合物,按二步法、三步法或偶合法进行,更简便的方法是用双锂引发剂一步法合成SBS。该方法基于苯乙烯、丁二烯彼此间竞聚率差别很大,将两种单体混在一起亦可进行嵌段共聚,与三步法或偶合法的差异是:在聚丁二烯嵌段两端存在着丁苯无规成份,文献称之为“tapered”SBS共聚物。     

Gold/monolayer graphitic carbon nitride plasmonic photocatalyst for ultrafast electron transfer in solar-to-hydrogen energy conversion

Gold (Au) plasmonic nanoparticles were grown evenly on monolayer graphitic carbon nitride (g-C₃N₄) nanosheets via a facile oil-bath method. The photocatalytic activity of the Au/monolayer g-C₃N₄ composites under visible light was evaluated by photocatalytic hydrogen evolution and environmental treatment. All of the Au/monolayer g-C₃N₄ composites showed better photocatalytic performance than that of monolayer g-C₃N₄ and the 1% Au/monolayer g-C₃N₄ composite displayed the highest photocatalytic hydrogen evolution rate of the samples. The remarkable photocatalytic activity was attributed largely to the successful introduction of Au plasmonic nanoparticles, which led to the surface plasmon resonance (SPR) effect. The SPR effect enhanced the efficiency of light harvesting and induced an efficient hot electron transfer process. The hot electrons were injected from the Au plasmonic nanoparticles into the conduction band of monolayer g-C₃N₄. Thus, the Au/monolayer g-C₃N₄ composites possessed higher migration and separation efficiencies and lower recombination probability of photogenerated electron-hole pairs than those of monolayer g-C₃N₄. A photocatalytic mechanism for the composites was also proposed.     

Collisional broadening of Ba I line (553.5 nm) by He or Ar

The Doppler-free line shape of the 6s ^{2 1} S ₀ – 6s ¹6p ^{1 1} P ₁ transition at 553.5 nm in natural Ba in the presence of an argon or helium buffer gas has been measured at 744 K for gas pressures from 0.2 to 100 Torr. Using the measured data for pressures above 5 Torr, the broadening rate coefficients for the half width at half maximum (HWHM) are determined to be (4.9±0.5)10^–9 and (5.0±0.5)10^–9 s^–1 cm^–3 for helium and argon respectively.     

甲烷无氧脱氢芳构化催化剂Mo/HZSM-5的研究

催化剂Ｍｏ／ＨＺＳＭ－５在甲烷地氧脱氢芳构化反应中表现出很高的活性，用ＸＲＤ，ＢＥＴ经表面，ＮＨ３－ＴＰＤ及ＴＰＲ等手段，对不抽提前后催化剂上的活性ｏ的种进行了研究，ＸＲＤ结果表明，Ｍｏ物种高度分散于筛表面，随着Ｍｏ担载量的提高，ＢＥＴ比表面积有所下降；但氨水抽提后，比表面积有很大程度的恢复，ＮＨ３－ＴＰＤ结果表明，Ｍｏ物种优先占据分子筛中的强酸位。ＴＰＲ结果显示出有ＭｏＯ３晶相存在的催化剂较易被     

Highly diastereoselective formation of 1,2,3-trisubstituted cyclopropane derivatives

A highly diastereoselective formation of cyclopropane derivatives was reported. When the chiral phenylvinyl epoxide reacted with lithiated 2-alkyl-1,3-dithiane or lithiated alkyl carbonanion in the presence of HMPA, cyclopropanes bearing stereochemistry at all three positions on the ring were readily obtained in high yields of 80-97% and high dr values of 68:32-99:1. This reaction was supposed to be a tandem conjugation addition-epoxide opening sequence. [reaction: see text]     

新型高硅Y(NHSY)沸石的研究:Ⅱ.NHSY沸石的结构特点

用ＩＲ，ＸＰＳ，ＴＥＭ，低温氮吸附和化学分析等手段表征了ＮＨＳＹ沸石的结构特点，结果表明，ＮＨＳＹ具有Ａｌ分布均匀，骨架Ａｌ空位少、含非骨架Ａｌ少而适量和二次孔体系发达等显著特点，这些特点使ＮＨＳＹ具有很好的结构稳定性和很高的催化活性及选择性。     

切花泥主成分的色谱—质谱联用分析

本文通过切花泥的高温裂解，利用色谱－质谱联用方法对其成分进行了结构分析。     

Designing new chiral ketone catalysts. Asymmetric epoxidation of cis-olefins and terminal olefins

This paper describes a new class of chiral oxazolidinone ketone catalyst for asymmetric epoxidation. High ee values have been obtained for a number of cyclic and acyclic cis-olefins. The epoxidation was stereospecific with no isomerization observed in the epoxidation of acyclic systems. Encouragingly high ee values have also been obtained for a number of terminal olefins. Mechanistic studies show that electronic interactions play an important role in stereodifferentiation.     

Lidar-observed temperature structures and gravity-wave perturbations of the mesopause region in the springs of 1990–1992 over Fort Collins,CO

The Na temperature lidar data taken during the nine nights in springs 1990 and 1991 at Fort Collins, CO, have been re-analyzed by a refined procedure, which takes into account the effects of (i) the more accurately determined lidar operational frequencies, (ii) the proper inclusion of extinction in the Na layer and (iii) additional temporal and spatial smoothing. Depending on altitudes, the new lidar frequencies and the effect of Na extinction combined to lower the calculated temperature values by 2–8 K. Although the occasionally noted large rapid change (in 15 min) in the centroid temperature is reduced from 40 K to 20 K due to the added smoothing first employed by Bills and Gardner, the general conclusion presented in the recently published paper [1] remains valid. In this paper, we also present the analysis of new data (a total of 17 nights) taken during spring 1992 which further substantiates the fact that the averaged mesopause in spring rises from a lower altitude before midnight to a higher altitude after midnight. In addition, parameters depicting atmospheric gravity-wave perturbations have been derived from the measured temperature profiles. Using the data collected in 26 spring nights, we have determined the averaged relative density (temperature) perturbation, Brunt Vaisala period and Richardson number to be, respectively, 5.1±1.1%, 5.1±0.3 min, and 1.8±1.0.