Highly Enantioselective Cross‐Aldol Reactions of Acetaldehyde Mediated by a Dual Catalytic System Operating under Site Isolation

Polystyrene‐supported (PS) diarylprolinol catalysts 1 a (Ar=phenyl) and 1 b (Ar=3,5‐bis(trifluoromethyl)phenyl) have been developed. Operating under site‐isolation conditions, PS‐ 1 a / 1 b worked compatibly with PS‐bound sulfonic acid catalyst 2 to promote deoligomerization of paraldehyde and subsequent cross‐aldol reactions of the resulting acetaldehyde in one pot, affording aldol products in high yields with excellent enantioselectivities. The effect of water on the performance of the catalytic system has been studied and its optimal amount (0.5 equiv) has been determined. The dual catalytic system ( 1 / 2 ) allows repeated recycling and reuse (10 cycles). The potential of this methodology is demonstrated by a two‐step synthesis of a phenoperidine analogue (68 % overall yield; 98 % ee) and by the preparation of highly enantioenriched 1,3‐diols 4 and 3‐methylamino‐1‐arylpropanols 5 , key intermediates in the synthesis of a variety of druglike structures.     

脱质子化1,3环加成石墨烯外在固定位上的贵金属纳米线(英文)

为研究纳米线的形成机理,通过密度泛函理论(DFT)研究了贵金属(铂)在脱质子化1,3-环加成石墨烯上的吸附.研究发现:(1)吸附在1,3-环加成石墨烯上的铂原子引起该结构的脱质子化过程并形成脱质子化1,3-环加成石墨烯;(2)贵金属在脱质子化1,3-环加成石墨烯上的锚定位是氮原子邻位的碳原子,这在邻位碳原子的平均巴德电荷分析(高达1.0e)中得到进一步的证实;(3)铂原子在相邻的脱质子化吡啶炔单元上形成金属纳米线,并且该纳米线比相应的铂团簇稳定得多;(4)电子结构分析表明,铂的吸附并没有从根本上改变脱质子化1,3-环加成石墨烯的电子性质.铂金属的掺杂使得Pt6团簇吸附形成的复合物呈现金属性,而Pt6纳米线形成的复合物则为半金属性.     

31P MAS NMR固体核磁共振研究稀土改性Y分子筛的酸性

以三甲基磷氧（TMPO）和三丁基磷氧（TBPO）为探针分子,用³¹P魔角旋转核磁共振（³¹P MAS NMR）法对稀土改性Y型分子筛的酸性进行了定性和定量分析. 结果表明,以TMPO为探针分子的³¹P MAS NMR谱分别在δ = 78,70,65,62,58,55和53处存在与酸中心相关的吸收峰,其中δ = 78和70处吸收峰与分子筛内部和外部酸性有关,δ = 65,62,58和53处吸收峰归属于TMPO在分子筛内部Brönsted酸中心上的贡献,δ = 55处吸收峰归属于TMPO在分子筛内部Lewis酸中心上的贡献. 随着稀土含量的增加,中等强度Brönsted酸中心（δ = 62和58）数量显著增加,而强Brönsted酸中心（δ = 65）和较弱Lewis酸中心（δ = 55）数量显著降低. 结合分子筛骨架铝和非骨架铝对分子筛酸性的影响进一步探讨了稀土改型Y分子筛的酸性.     

Effect of Chain Topology of Polyethylenimine on Physisorption and Chemisorption of Carbon Dioxide

Polyethylenimine (PEI) is a promising candidate for CO₂ capture. In this work, the physisorption and chemisorption of CO₂ on various low‐molecular‐weight PEIs are investigated to identify the effect of chain architecture on sorption. The reliability of theoretical calculations are partially supported by our experimental measurements. Physisorption is calculated independently by the reference interaction‐site model integral equation theory; chemisorption is distinguished from the total sorption given by the quantum density functional theory. It is shown that, as the chain length increases, both chemisorption and physisorption drop off nonlinearly, but the decay amplitude of chemisorption is more apparent. Conversely, as the amine group approaches the central triamine unit of each oligomer, the sorption capacity decreases, affecting the sorption equilibrium in a complex way. This arises from the cooperative contribution of an increased steric effect and renormalized electronic distribution.     

Evaluation of a multi‐fiber exchange solid‐phase microextraction system and its application to on‐site sampling

Until recently, multiple solid‐phase microextraction fibers could not be automatically desorbed in a single gas chromatographic sequence without manual intervention from an operator. This drawback had been a critical issue, particularly during the analysis of numerous on‐site samples taken with various fiber assemblies. Recently, a Multi‐Fiber Exchange system, designed to overcome this flaw found in other commercially available autosamplers, was released. In the current research, a critical evaluation of the Multi‐Fiber Exchange system performance in terms of storage stability and long‐term operation is presented. It was established in the course of our research that the Multi‐Fiber Exchange system can operate continuously and precisely for multiple extraction/injection cycles. However, when the effect of residence time of commercial fibers on the Multi‐Fiber Exchange tray was evaluated, results showed that among the evaluated fiber coatings, Carboxen/polydimethylsiloxane was the only coating capable of efficient storage on the tray for up to 24 h after field sampling without suffering significant loss of analytes (≤10% for benzene, toluene, ethylbenzene, o‐xylene, decane, and limonene). Additionally, the system capability for high‐throughput analysis was demonstrated by the unattended desorption of multiple fibers after on‐site sampling of toluene, indoor air levels, in a polymer synthesis lab.     

V2O5-CeO2/TiO2-ZrO2催化剂表征及NH3还原NOx性能

商业选择性催化还原(SCR)催化剂V2O5-WO3(MoO3)/TiO2存在反应温度窗口窄(300–400 oC)和SO3转化率高等缺点,同时占催化剂总质量80%以上的载体TiO2比表面积小,热稳定性差.已有研究发现TiO2-ZrO2固溶体具有较大的比表面积和较强的表面酸性, TiO2与ZrO2的摩尔比为1：1时其比表面积达到最大. CeO2作为SCR催化剂的组成部分,由于其优良的储氧和放氧能力受到广泛关注.研究表明, CeO2-CuO, Ce/Ti-Si-Al和Mo2O3(Co2O3)/Ce-Zr等催化剂具有优良的SCR脱硝活性,同时对V2O5-WO3/TiO2催化剂进行CeO2改性,可提高催化剂的抗SO2中毒能力.实际烟气组分中同时存在SO2和H2O,必定会导致催化剂硫酸盐中毒,而目前对含Ce催化剂的硫酸盐中毒情况研究较少,因此开发新型高效脱硝催化剂十分必要.前期我们研究了xCeO2-3%V2O5/TiO2-ZrO2催化剂,发现CeO2可以显著拓宽脱硝温度窗口,同时增强催化剂酸性位点,但是V2O5含量较高时对环境及人体健康均有较大危害.本文采用共沉淀法制备摩尔比为1：1的TiO2-ZrO2固溶体,用浸渍法负载不同摩尔比的CeO2和1%的V2O5,得到一系列V-xCe/Ti-Zr催化剂,结合X射线衍射(XRD)、比表面积测试(BET)、高分辨透射电镜(HRTEM)、程序升温还原(H2-TPR)、原位漫反射红外光谱(in situ DRIFTS)和程序升温脱附(NH3-TPD)等手段分析催化剂的晶相、活性物质分散程度、氧化还原性质及表面酸性,在200–450 oC范围内考察Ce掺杂催化剂选择性催化还原NOx的脱硝活性,并在250 oC测试催化剂在NH3+NO+O2+SO2+H2O气氛中的脱硝活性,研究催化剂抗硫酸盐中毒能力.研究发现,CeO2掺杂可以拓宽脱硝反应活性窗口, V-0.2Ce/Ti-Zr (摩尔比Ce：Ti =0.2)表现出最优的脱硝性能,在250–350oC范围内脱硝效率均在92%以上,同时与前期研究结果对比发现CeO2含量较高时会导致高温段NOx转化率下降. XRD和HRTEM结果表明,ZrO2的添加可以显著降低载体TiO2的结晶度,复合氧化物TiO2-ZrO2呈无定形态, CeO2高度分散于载体之上,并且催化剂以单晶形式存在. H2-TPR结果表明,CeO2能显著提高催化剂的还原能力,主要的还原反应发生在CeO2的α(200–430oC)和β(430–600 oC)还原峰上,总体而言, V-0.2Ce/Ti-Zr表现出最大的氢气消耗量,即其还原性最强.低V2O5负载有利于较低温度SCR反应, V-0.3Ce/Ti-Zr的钒氧化物还原峰强度最大,其次是V-0.2Ce/Ti-Zr. NH3-TPD测试发现V2O5/TiO2主要存在中强酸及强酸,而V2O5/TiO2-ZrO2主要是弱酸, CeO2负载后随着其含量提高,弱酸强度增加.结合氨气原位漫反射红外光谱发现, CeO2可以增加催化剂Br?nsted和Lewis酸位数量,同时出现反应中间物–NH2, V2O5的负载量较高会抑制1660 cm–1处Br?nsted酸吸收峰的出现. BET结果发现, TiO2-ZrO2和V2O5/Ti-ZrO2比表面积分别可达255.73和143.77 m2/g, V2O5/TiO2仅为66.1 m2/g,表明ZrO2的添加可以显著增大催化剂比表面积,进而有利于SCR反应进行,沉积的氧化物进入载体孔道导致催化剂比表面积降低. V2O5-xCeO2/TiO2-ZrO2表现出较强的抗SO2中毒能力,但是在H2O存在条件下脱硝活性较差,可能是生成的硫酸铵盐及亚硫酸盐阻塞催化剂孔道所致. SO2和H2O停止通入后, V2O5-0.3CeO2/TiO2-ZrO2活性恢复至原有水平, V2O5-0.2CeO2/TiO2-ZrO2恢复至最初的84%.对中毒催化剂进行不同反应温度下的活性测试,发现V2O5-0.2CeO2/TiO2-ZrO2在中温段反应活性显著降低,可能是由于Ce(SO4)2的形成所致,由于V2O5-0.3CeO2/TiO2-ZrO2的Ce含量较高,其在此温度范围内活性依旧较高.两者在高温段NOx转化率均较高,推测是V2O5开始发挥活性组分作用的缘故.     

Field-portable X-ray fluorescence spectrometry as rapid measurement tool for landfill mining operations: comparison of field data vs. laboratory analysis

Landfill mining applied in reclamation at the territories of old dump sites and landfills is a known approach tended to global economic and environmental benefits as recovery of metals and energy is an important challenge. The aim of this study was to analyse the concentration of several metallic elements (Ca, Cu, Cr, Fe, K, Mn, Pb, Zn) in the fine fraction of waste derived in the landfill and to compare the results of measurements obtained by field-portable equipment with the data gained by advanced analytical tools. Atomic absorption spectrometry (AAS) and inductively coupled plasma mass spectrometry (ICP-MS) were used for the quantitative detection of metallic elements at the laboratory; whereas field-portable X-ray fluorescence spectrometry (FPXRF) was applied for rapid sample characterisation in the field (on-site). Wet digestion of samples (fine fraction of waste at landfill) was done prior analytical procedures at the laboratory conditions, but FPXRF analysis was performed using raw solid samples of waste fine fraction derived in the Kudjape Landfill in Estonia. Although the use of AAS and ICP-MS for the measurements of metals achieves more precise results, it was concluded that precision and accuracy of the measurements obtained by FPXRF is acceptable for fast approximate evaluation of quantities of metallic elements in fine fraction samples excavated from the waste at landfills. Precision and accuracy of the results provided by express method is acceptable for quick analysis or screening of the concentration of major and trace metallic elements in field projects; however, data correction can be applied by calculating moisture and organic matter content dependent on sample matrix as well as special attention must be paid on sample selection and homogenisation and number of analysed samples.     

噻吩并嘧啶类FLT3抑制剂结合模式预测与分析

FLT3(FMS样酪氨酸酶III)是酪氨酸激酶受体(RTKIII)成员之一,其异常超表达或突变与急性髓细胞白血病(AML)呈现非常大的相关性,成为治疗AML的重要靶位点。本文采用不同的方法对FLT3活性位点进行了预测,利用分子对接、分子动力学以及药效团分析研究了新型嘧啶类化合物与FLT3的相互作用与结合模式。分子对接得到的结合模式与分子动力学模拟得到的结果一致,结合药效团分析表明该嘧啶类化合物主要通过疏水相互作用和氢键与FLT3激活位点结合,从而起到抑制作用。本研究对以FLT3为靶点的嘧啶类抑制剂的开发提供了理论和实验依据。     

Transfert du trichloréthylène en milieu poreux à partir d'un panache de vapeursMass transfer of trichloroethylene in a porous medium from a vapor plume

A large scale experiment has been carried out on an experimental facility to study the mass transfer of trichloroethylene (TCE) in a partially saturated porous medium. 5 liters of TCE have been infiltrated in the vadose zone of the site. The mass transfer of TCE from the vapor plume in the unsaturated zone towards the top of groundwater was quantified based on an analytical and a numerical approach. The mass of the pollutant measured at the exit of the model is well represented by the two mathematical approaches. It is found that the transfer of TCE towards the groundwater from the vapor plume is weak, which corresponds to 285 g of TCE, approximately 4% of the initial mass. To cite this article: H. Benremita, G. Schäfer, C. R. Mecanique 331 (2003).