S(N)2 ring opening of beta-lactones: an alternative to catalytic asymmetric conjugate additions

Merging catalytic asymmetric acyl halide-aldehyde cyclocondensation (AAC) reactions with ensuing Grignard-mediated ring opening of the derived enantiomerically enriched beta-lactones is presented as a generally useful asymmetric synthesis of beta-disubstituted carboxylic acids. Enantiomerically enriched beta-lactones are subject to efficient S(N)2 ring opening with a variety of copper-modified alkyl Grignard reagents, including highly branched nucleophiles. Considerable structural variation in the lactone electrophile is also tolerated. Phenyl- and vinyl-derived organometallics are not efficient nucleophiles for the ring-opening reactions.     

μ-邻苯二甲酸希土与5-硝基-1,10-菲咯啉双核配合物的合成、光谱、磁性

本文合成了四个以邻苯二甲酸阴离子为桥联配体的新型希土双核配合物［Ｌｎ２（Ｐｈｔｈ）（ＮＯ２－ｐｈｅｎ）４］（ＣｌＯ４）４．ｘＨ２Ｏ［Ｌｎ＝Ｇｄ，Ｈｏ，Ｅｒ，ＮＯ２－Ｐｈｅｎ＝５－硝基－１，１０－菲咯啉，Ｐｈｔｈ－邻苯二甲酸阴离子）。经元素分析，ＩＲ，电导，电子吸收光谱，表征了配合物，测定了［Ｇｄ２（ｐｈｔｈ）（ＮＯ２－ｐｈｅｎ）４］（ＣｌＯ４）４．４Ｈ２Ｏ的变温磁化率（４－３００Ｋ），其数值用最小     

Practical method for transforming alkynes into alpha-diketones

[reaction: see text] Oxidation of alkynes to alpha-dicarbonyl derivatives through a convenient one-pot procedure via a Br?nsted acid-promoted "hydration" and a DMSO-based oxidation sequence has been achieved in high yields. The scope and limitations of the reaction have also been investigated.     

硝基呋喃亚甲基哌啶类化合物的合成与抗结核活性

结核是由结核分枝杆菌引起的一种慢性呼吸道传染病,对人类的健康构成严重威胁。 本文利用药效团拼接原理,将片段硝基呋喃和苯基噻唑组合,得到了19个2-(1-((5-硝基呋喃-2-基)甲基)哌啶-4-基)噻唑(5)和2-(1-((5-硝基呋喃-2-基)甲基)哌啶-4-基)-4-苯噻唑(6)系列化合物,测试了所有化合物在1和0.1 μmol/L浓度下对结核分枝杆菌H37Ra的抑制率。 构效关系分析表明,苯环上有取代基有利于活性,且苯环上对位取代普遍优于间位和邻位取代,对位吸电子基团取代活性优于对位供电子基团取代活性。在苯环对位吸电子基团取代中,—CF₃取代的化合物2-(1-((5-硝基呋喃-2-基)甲基)哌啶-4-基)-4-(4-三氟甲基)苯基)噻唑(6f)活性最高,在1和0.1 μmol/L浓度下,抑制率分别为99.6%和93.4%。 鉴于新化合物具有抗结核高活性,化合物6f可作为抗结核候选化合物进一步研究。     

Uricase-Based Highly Sensitive and Selective Spectrophotometric Determination of Uric Acid Using BSA-Stabilized Au Nanoclusters as Artificial Enzyme

ABSTRACT

The enzymatic spectrophotometric analysis of uric acid based on BSA-stabilized Au nanoclusters (Au NCs) as peroxidase mimetics was first developed. Compared with natural enzyme horseradish peroxidase (HRP), which was used widely to detect H₂O₂ generated by uric acid, the BSA-stabilized Au NCs as peroxidase mimetics are easy to prepare, low cost, and stable. Kinetic analysis indicates that the BSA-stabilized Au NCs have even higher catalytic activity than HRP. Under the optimum conditions, the detection limit for uric acid is 3.6 × 10^?7 mol L^?1. The feasibility of the developed method for uric acid analysis in human serum was confirmed.     

Spin polarization direction switch based on an asymmetrical quantum wire

A scheme for a spin polarization direction switch is investigated by studying the spin-dependent electron transport of an asymmetrical quantum wire with Rashba spin–orbit coupling. It is found that the spin polarization direction can be switched by changing the direction of the external current. The physical mechanism of this device arises from the fact that the symmetries in the longitudinal and transverse directions are all broken but _C2$C_2$-rotation and time-reversal symmetries are still preserved. Further studies show that the spin polarization is robust against disorder, displaying the feasibility of the proposed structure for a potential application.     

Modification-Free Fluorescent Biosensor for CEA Based on Polydopamine-Coated Upconversion Nanoparticles

Journal of Fluorescence - Upconversion nanoparticles (UCNPs) have achieved considerable success in protein sensing in vitro. And aptamer is one of the most frequently used biomolecules to modify...     

Rational Construction of 2D Fe3O4@Carbon Core–Shell Nanosheets as Advanced Anode Materials for High-Performance Lithium-Ion Half/Full Cells

Transition metal oxides have vastly limited practical application as electrode materials for lithium-ion batteries (LIBs) due to their rapid capacity decay. Here, a versatile strategy to mitigate the volume expansion and low conductivity of Fe₃O₄ by coating a thin carbon layer on the surface of Fe₃O₄ nanosheets (NSs) was employed. Owing to the 2D core–shell structure, the Fe₃O₄@C NSs exhibit significantly improved rate performance and cycle capability compared with bare Fe₃O₄ NSs. After 200 cycles, the discharge capacity at 0.5 A g⁻¹ was 963 mA h g⁻¹ (93 % retained). Moreover, the reaction mechanism of lithium storage was studied in detail by ex situ XRD and HRTEM. When coupled with a commercial LiFePO₄ cathode, the resulting full cell retains a capacity of 133 mA h g⁻¹ after 100 cycles at 0.1 A g⁻¹, which demonstrates its superior energy storage performance. This work provides guidance for constructing 2D metal oxide/carbon composites with high performance and low cost for the field of energy storage.     

凸可行问题的平行近似次梯度投影算法

对凸可行问题提出了包括上松弛的平行近似次梯度投影算法和加速平行近似次梯度投影算法．与序列近似次梯度投影算法相比, 平行近似次梯度投影算法(每次迭代同时运用多个凸集的近似次梯度超平面上的投影)能够保证迭代序列收敛到离各个凸集最近的点． 上松弛的迭代技术和含有外推因子的加速技术的应用, 减少了数据存储量, 提高了收 敛速度. 最后在较弱的条件下证明了算法的收敛性, 数值实验结果验证了算法的有效性和优越性.     

What Role Does the Incident Light Intensity Play in Photocatalytic Conversion of CO2: Attenuation or Intensification?

Artificial photoreduction of CO₂ is vital for the sustainable development of human beings via solar energy storage in stable chemicals. This process involves intricate light-matter interactions, but the role of incident light intensity in photocatalysis remains obscure. Herein, the influence of excitation intensity on charge kinetics and photocatalytic activity is investigated. Model photocatalysts include the pure graphitic carbon nitride (g-C₃N₄) and g-C₃N₄ loaded with noble/non-noble-metal cocatalysts (Ag, TiN, and CuO). It is found that the increase of light intensity does not always improve the electron utilization. Overly high excitation intensities cause charge carrier congestion and changes the recombination mechanism, which is called the light congestion effect. The electron transport channels can be established to mitigate the light-induced effect via the addition of cocatalyst, leading to a nonlinear growth in the reaction rate with increasing light intensity. From experiments and simulations, it is found that the light intensity and active site density should be collectively optimized for increasing the energy conversion efficiency. This work elucidates the effect of light intensity on photocatalytic CO₂ reduction and emphasizes the synergistic relationship of matching the light intensity and the photocatalyst category. The study provides guidance for the design of efficient photocatalysts and the operation of photocatalytic systems.