A new heterogeneous chiral (salen)manganese(III) system for enantioselective epoxidation of non‐functionalized olefins

This communication describes the design and application of a novel catalytic epoxidation system derived from the initial immobilization of a homogeneous sulfonato (salen)Mn(III) complex on two solid carriers (silica gel and siliceous earth) and subsequent dispersion of the supported manganese complexes into ionic liquid 1‐butyl‐3‐methylimidazolium hexafluorophosphate (BMImPF₆) and 1‐butyl‐3‐methylimidazolium tetrafluoroborate (BMImBF₄) for recycling. The performance of chiral (salen)Mn(III) system in enantioselective epoxidation of olefins was investigated systematically. Even higher enantioselectivity than that of the homogeneous counterpart was obtained with similar catalytic activity. In particular, the best catalytic result is that the combination of the silica gel‐supported (salen)Mn(III) catalyst and BMImPF₆ affords 97–100% ee for epoxidation of α‐methylstyrene, and high ee values were retained even after three cycles. Copyright © 2010 John Wiley & Sons, Ltd.     

Suppression of Chemotactic Explosion by Mixing

Chemotaxis plays a crucial role in a variety of processes in biology and ecology. In many instances, processes involving chemical attraction take place in fluids. One of the most studied PDE models of chemotaxis is given by the Keller–Segel equation, which describes a population density of bacteria or mold which is attracted chemically to substance they secrete. Solutions of the Keller–Segel equation can exhibit dramatic collapsing behavior, where density concentrates positive mass in a measure zero region. A natural question is whether the presence of fluid flow can affect singularity formation by mixing the bacteria thus making concentration harder to achieve. In this paper, we consider the parabolic-elliptic Keller–Segel equation in two and three dimensions with an additional advection term modeling ambient fluid flow. We prove that for any initial data, there exist incompressible fluid flows such that the solution to the equation stays globally regular. On the other hand, it is well known that when the fluid flow is absent, there exists initial data leading to finite time blow up. Thus the presence of fluid flow can prevent the singularity formation. We discuss two classes of flows that have the explosion arresting property. Both classes are known as very efficient mixers. The first class are the relaxation enhancing (RE) flows of (Ann Math:643–674, 2008). These flows are stationary. The second class of flows are the Yao–Zlatos near-optimal mixing flows (Mixing and un-mixing by incompressible flows. arXiv:1407.4163, 2014), which are time dependent. The proof is based on the nonlinear version of the relaxation enhancement construction of (Ann Math:643–674, 2008), and on some variations of the global regularity estimate for the Keller–Segel model.     

QuEChERS净化-液相色谱-串联质谱法测定茶叶中氯噻啉

建立了茶叶中农药氯噻啉残留的液相色谱-串联质谱检测方法。茶叶样品用乙腈提取,提取液经QuEChERS法净化,利用PSA(N-丙基乙二胺)、C₁₈、GCB(石墨化炭黑)等吸附剂材料进一步去除杂质,净化液经过离心后取上清液以水等体积稀释。以乙腈-0.1%(v/v)甲酸水溶液为流动相,在0.30 mL/min流速下梯度洗脱,用C₁₈色谱柱进行液相色谱分离,电喷雾正离子模式电离(ESI⁺),选择反应监测(SRM)模式检测,外标法定量。结果表明:氯噻啉在1~500 μ g/L范围内线性关系良好(相关系数r为0.9999),定量限为0.01 mg/kg(S/N≥10),在乌龙茶和绿茶中3个添加水平(0.01、0.3和3 mg/kg)的平均回收率为87.0%~101.0%,相对标准偏差(RSD, n=7)在2.1%~13.1%之间。对多种茶叶的测定结果表明,该方法操作简便、成本低、准确性高、特异性好、分析速度快,可以对茶叶中氯噻啉残留进行定性和定量检测。     

Kinetics and Mechanism of Oxidation of Sarcosine by Diperiodatocuprate(III) Complex in Alkaline Medium

The kinetics of oxidation of sarcosine by diperiodatocuprate(III) (DPC) was studied with spectrophotometry in a temperature range of 292.2–304.2 K. The reaction between diperiodatocuprate(III) and sarcosine in alkaline medium exhibits 1:1 stoichiometry (DPC:sarcosine). The reaction was found to be first order with respect to both DPC and sarcosine. The observed rate constant (k_obs) decreased with the increase of the [IO^?₄], decreased with the increase of the [OH^?], and then increased with the increase of the [OH^?] after a turning point. There was no salt effect, and free radicals were detected. Based on the experimental results, a mechanism involving the diperiodatocuprate(III) (DPC) as the reactive species of the oxidant has been proposed. The activation parameters, as well as the rate constants of the rate‐determining step, have been calculated.     

Transport evidence of 3D topological nodal-line semimetal phase in ZrSiS

Topological nodal-line semimetal is a new emerging material, which is viewed as a three-dimensional (3D) analog of graphene with the conduction and valence bands crossing at Dirac nodes, resulting in a range of exotic transport properties. Herein, we report on the direct quantum transport evidence of the 3D topological nodal-line semimetal phase of ZrSiS with angular-dependent magnetoresistance (MR) and the combined de Hass-van Alphen (dHvA) and Shubnikov-de Hass (SdH) oscillations. Through fitting by a two-band model, the MR results demonstrate high topological nodal-line fermion densities of approximately 6×10²¹ cm⁻³ and a perfect electron/hole compensation ratio of 0.94, which is consistent with the semi-classical expression fitting of Hall conductance Gxy and the theoretical calculation. Both the SdH and dHvA oscillations provide clear evidence of 3D topological nodal-line semimetal characteristic.     

Iterative weighted partial spline least squares estimation in semiparametric modeling of longitudinal data

In this paper we consider the estimating problem of a semiparametric regression modelling whenthe data are longitudinal.An iterative weighted partial spline least squares estimator(IWPSLSE)for the para-metric component is proposed which is more efficient than the weighted partial spline least squares estimator(WPSLSE)with weights constructed by using the within-group partial spline least squares residuals in the sense     

吡啶二羧酸修饰的稀土嵌入碲钨酸盐的合成及电化学生物识别性质

在乙酸钠水溶液中, 采用微波加热一步自组装策略合成了一系列罕见的2,6-吡啶二羧酸修饰的稀土嵌入Keggin型碲钨酸盐(PTEA)₇H₃K[RE₂(B-α-TeW₉O₃₃)₃W₃O₅(H₂O)₃(HDPA)]·22H₂O[RE=Ce³⁺(1), Pr³⁺(2), Nd³⁺(3), Sm³⁺(4); H₂DPA=2,6-吡啶二羧酸; PTEA=质子化的三乙醇胺]. 化合物1~4的聚阴离子由3个三缺位Keggin型 [B-α-TeW₉O₃₃]^8-构筑块通过1个{RE₂W₃O₅(H₂O)₃(HDPA)}¹³⁺异金属簇连接而成. 该异金属簇中, 2,6-吡啶二羧酸作为四齿配体与2个稀土离子(RE1和RE2)配位形成平面三杂环结构, 且RE1和RE2所在平面与W2, W2A, W16形成的平面互相垂直. 此外, 化合物1可与羧基化多壁碳纳米管(CMWCNT)复合形成1-CMWCNT复合材料. 该复合材料可以作为电极材料构建电化学生物传感器, 用于检测特定的DNA序列.     

Supramolecular Enantiodifferentiating Photocyclodimerization of 2-Anthracenecarboxylic Acid Mediated by Bridged β-Cyclodextrins: Critical Effects of the Host Structure,pH and Co-Solvents

Several sulfoxide- and sulfone-bridged β-cyclodextrin (CD) dimers were synthesized for mediating the enantiodifferentiating [4+4] photocyclodimerization of 2-anthracenecarboxylic acid (AC). The complexation behavior of these chiral hosts with AC was investigated by UV-vis, circular dichroism, fluorescence, and NMR spectroscopies and certified the formation of 1 : 1 and 1 : 2 host-guest complexes. The product distribution and enantioselectivity of the photoreaction turned out to be a critical function of the chemical structure of bridged CDs. Comparing to the sulfur-bridged 2A_X−3G_X β-CD dimer 7 , the conversion of the photolyzes with sulfoxide-bridged was significantly improved, and the ee of cyclodimer 2 was remarkably increased from −82.8% with 7 to −96.7% with the sulfoxide-bridged 2A_X−3G_X β-CD dimer 8 . The relative yields and ee values of the slipped cyclodimers 5 and 6 were greatly enhanced in the presence of 6 M CsCl. The reaction selectivity is susceptible to the pH variation of the aqueous buffer solution, demonstrating that the supramolecular photochirogenesis is controlled by multidimensional factors, including the chemical structure of the chiral host, solvent, and pH conditions.     

硫促进改性MgAl水滑石催化剂的制备及Aldol缩合反应性能

利用镁铝水滑石的记忆效应,以过硫酸铵为改性剂,经过浸渍焙烧复原过程,制得一系列硫促改性镁铝水滑石催化剂.利用XRD,BET,SEM和FT-IR等手段对催化剂的物理化学性质进行了表征.结果显示,改性后催化剂仍保有原水滑石层状晶体结构,催化剂表面具有碱中心与酸中心.随着硫含量增加,催化剂碱中心逐渐减少,酸中心增加,酸性增强.以对硝基苯甲醛与丙酮的羟醛缩合为探针反应,考察了催化剂的催化性能.     

Solid-phase impregnation promotes Ce doping in TiO2 for boosted denitration of CeO2/TiO2 catalysts

CeO₂/TiO₂（denoted as Ce Ti） catalysts obtained by solid-phase impregnation behaved better in lowtemperature selective catalytic reduction of NO_xwith NH₃（NH₃-SCR） than that by conventional wet impregnation.To explore the main factors for activity distinction,the texture property,CeO₂dispersion and structure changes of TiO₂were comprehensively analyzed.It was found that surface changes of TiO₂had a significant ...