Recent advances in annulations enabled by nucleophilic Lewis base/metal dual catalysis

Metal/nucleophilic Lewis base dual catalysis has been recognized as a reliable and promising strategy for finishing ideal organic synthesis over the past decades. The new strategy can usually achieve some chemical reactions that cannot be realized by the traditionally mono-catalytic system, dramatically expanding the synthetic utility of chemical transformations by leveraging additional activation modes. Thus considerable progress has been made in the synthesis of a wide range of heterocyclic and biologically active compounds by using the combination of diversely metal/nucleophilic Lewis base dual catalysts, including metal/phosphine, metal/N-heterocyclic carbene (NHC) and metal/tertiary amine dual catalysis systems. In this review, we describe a comprehensive and updated advance of metal/nucleophilic Lewis base dual catalytic annualtion reactions, meanwhile, the related mechanism and the application of these annulation strategies in natural product total synthesis will be highlighted in detail.     

Enhanced Li+ migration in solid polymer electrolyte driven by anion-containing polymer-chains

Li-ion batteries with solid polymer electrolytes (SPEs) are safer than conventional liquid electrolytes due to the absence of highly flammable liquid electrolytes. However, their performance is limited by the poor Li⁺ transport in SPEs at room temperature. Anion-containing polymer-chains incorporated SPEs (ASPEs) are therefore developed to enhance Li⁺ diffusion kinetics. Herein, we propose a novel and feasible strategy to incorporate the anion-containing polymer-chains, such as lithiated perfluorinated sulfonic acid (PFSA), into polyvinylidene fluoride (PVDF) polymer-based SPEs. The immobile anion groups from the PFSA-chains impede the migration of mobile anion groups dissociated from the Li salt. The transference number is thus raised from ∼0.3 to 0.52 with the introduction of anion-containing polymer-chains into SPEs. The electrostatic repulsion among anion-containing chains also reduces the close chain stacking and brings 159% increase in the ionic conductivity to 0.83 × 10⁻³ S/cm at 30 °C in contrast with the pure PVDF-based SPE. In addition, LiFeO₄/Li batteries with ASPEs exhibit 55% capacity boost at 0.5 C in contrast to the capacity of batteries with pure-PVDF SPEs, and also offer more than 1000 charge/discharge cycles. Our research findings potentially offer a facile strategy to design thermal stable SPEs with superior Li⁺ transport behaviors towards developing high-performance SPEs-based batteries.     

Identification of the Active Sites on Metallic MoO2−x Nano-Sea-Urchin for Atmospheric CO2 Photoreduction Under UV,Visible, and Near-Infrared Light Illumination

We report an oxygen vacancy (V_o)-rich metallic MoO_2−x nano-sea-urchin with partially occupied band, which exhibits super CO₂ (even directly from the air) photoreduction performance under UV, visible and near-infrared (NIR) light illumination. The V_o-rich MoO_2−x nano-sea-urchin displays a CH₄ evolution rate of 12.2 and 5.8 μmol g_catalyst⁻¹ h⁻¹ under full spectrum and NIR light illumination in concentrated CO₂, which is ca. 7- and 10-fold higher than the V_o-poor MoO_2−x, respectively. More interestingly, the as-developed V_o-rich MoO_2−x nano-sea-urchin can even reduce CO₂ directly from the air with a CO evolution rate of 6.5 μmol g_catalyst⁻¹ h⁻¹ under NIR light illumination. Experiments together with theoretical calculations demonstrate that the oxygen vacancy in MoO_2−x can facilitate CO₂ adsorption/activation to generate *COOH as well as the subsequent protonation of *CO towards the formation of CH₄ because of the formation of a highly stable Mo−C−O−Mo intermediate.     

商用氧化铟锡玻璃:室温高效还原氮气的催化剂电极

NH₃作为一种必需的活化氮源,在化肥、染料、爆炸物和药物等的制造中起到了关键作用;同时,它也是一种在交通运输领域具有吸引力的无碳能源载体.工业上生产氨气使用典型的哈伯-博世工艺,但是此工艺涉及大量的能源消耗和碳排放,给环境带来巨大的压力.电化学氮还原反应(NRR)能够在温和环境下实现环境友好、节能的氨合成,但此过程需要高效的电催化剂.高效的NRR催化剂(Au、Ag、Pd和Ru)储量少、成本高,阻碍了它的实际应用.因此,设计和开发由地球上丰富的元素制成的具有成本效益的催化剂来代替NRR催化剂意义重大.本课题组最近的研究(Chem.Commun.,2018,54,12966-12969)表明,SnO2在环境条件下具有电催化氧化活性,但其低电导率限制了其性能,可通过氟掺杂或石墨烯杂化予以解决.氧化铟锡(ITO)作为一种含SnO2的材料,导电性好,可望用于NRR的高效电催化剂中.因此,本文采用商用氧化铟锡玻璃(ITO/G)作为催化剂电极,在温和环境条件下进行N₂-NH₃的电化学转化,并呈现出对生成氨气有较高的选择性.XRD和XPS结果表示,商用ITO/G中存在In,Sn和O元素;SEM显示ITO/G具有清晰的纳米薄膜结构和267 nm的截面厚度;相应的EDX谱图显示In,Sn和O元素分布均匀,且原子比为32.11:3.16:64.74.采用紫外-可见光谱及线性扫描伏安和恒电位极化等电化学测试研究了商用ITO/G的NRR活性.在0.5 M LiClO4电解液中测试时,于-0.40 V vs.RHE条件下,ITO/G的NH₃产率为1.06×10^-10 mol s^-1 cm^-2,其法拉第效率为6.17%.15N同位素标记实验证实了所测到的NH₃是由ITO/G催化的N₂电还原反应生成的.利用第一性原理计算探讨了在ITO催化剂上可能的NRR反应机理,确定了ITO催化剂的NRR活性位点、N₂化学吸附活性位点以及NRR的反应途径.此外,24 h恒电位(-0.40 V vs.RHE)极化测试和2 h恒电位极化(-0.40 V vs.RHE)测试后的XRD和SEM结果表明,该催化剂具有较高的电化学稳定性.综上所述,商用ITO/G用作在环境条件下将N₂转化为NH₃的有效催化剂电极,将为开发人工固定氮气的ITO基纳米结构提供一种研究途径.     

An Improved Stereo Matching Algorithm for Vehicle Speed Measurement System Based on Spatial and Temporal Image Fusion

This paper proposes an improved stereo matching algorithm for vehicle speed measurement system based on spatial and temporal image fusion (STIF). Firstly, the matching point pairs in the license plate area with obviously abnormal distance to the camera are roughly removed according to the characteristic of license plate specification. Secondly, more mismatching point pairs are finely removed according to local neighborhood consistency constraint (LNCC). Thirdly, the optimum speed measurement point pairs are selected for successive stereo frame pairs by STIF of binocular stereo video, so that the 3D points corresponding to the matching point pairs for speed measurement in the successive stereo frame pairs are in the same position on the real vehicle, which can significantly improve the vehicle speed measurement accuracy. LNCC and STIF can be used not only for license plate, but also for vehicle logo, light, mirror etc. Experimental results demonstrate that the vehicle speed measurement system with the proposed LNCC+STIF stereo matching algorithm can significantly outperform the state-of-the-art system in accuracy.     

甲烷在不同分子筛中吸附的理论对比研究

使用巨正则蒙特卡罗方法研究了CH₄分子在MOR和MFI分子筛中的物理吸附行为, 主要对比研究了这两种分子筛对CH₄分子在不同温度和压强下的物理吸附量、等量吸附热、 分子筛和CH₄以及CH₄和CH₄分子之间的相互作用能等物理量. 研究结果表明:在所有的温度和压力下, MOR分子筛对CH₄分子的吸附性能均优于相应的MFI分子筛, 这表明它是一种比MFI吸附性能更优异的吸附剂材料.从CH₄在这两种分子筛中的等量吸附热随吸附量的变化关系,分子筛和CH₄以及CH₄和CH₄之间的相互作用能分布曲线等角度出发分析了二者有不同吸附行为的原因.     

Lipase-catalyzed kinetic resolution of tetronic acid derivatives bearing a chiral quaternary carbon: total synthesis of (S)-(−)-vertinolide

We have developed a chemoenzymatic synthesis of (S)-vertinolide 1 with a chiral quaternary carbon atom at C5. In the kinetic resolution of tetronic acid precursor 6, lipase PS-D furnished the recovered alcohol 6 with an (R)-stereochemistry in a ratio of 95% ee, whereas lipase AY gave (S)-alcohol 6 with 93% ee. Chemical transformations of (S)-alcohol 6 provided (S)-vertinolide 1 in 33% yield in five steps with no loss of enantiomeric excess.     

Noise-induced enhancement of network reciprocity in social dilemmas

The network reciprocity is an important dynamic rule fostering the emergence of cooperation among selfish individuals. This was reported firstly in the seminal work of Nowak and May, where individuals were arranged on the regular lattice network, and played the prisoner’s dilemma game (PDG). In the standard PDG, one often assumes that the players have perfect rationality. However, in reality, we human are far from rational agents, as we often make mistakes, and behave irrationally. Accordingly, in this work, we introduce the element of noise into the measurement of fitness, which is determined by the parameter α controlling the degree of noise. The considered noise-induced mechanism remarkably promotes the behavior of cooperation, which may be conducive to interpret the emergence of cooperation within the population.     

Multiple bonding in Groups 13 and 14 homonuclear ethyne analogues

Hybrid density functional theory calculations have been carried out on model systems of Groups 13 and 14 alkyne analogues [M₂R₂]²⁻, Li₂[M₂R₂] and X₂R₂ (M=B, Al, Ga, In and Tl, X=C, Si, Ge, Sn and Pb and R=H, Me and Ph). The paper addresses both the nature of the bonding in these systems and the origin of the structural variations. Analysis of the orbitals and calculations of bond orders has identified the factors determining the adoption of a ‘classical’ linear, ethyne-like structure or a trans-bent geometry. The structural trends down each group and role of the substituent R group and the counter-ion have been also been investigated. It is found that all the elements below the first period of these groups adopt ‘non-classical’ trans-bent configurations in these molecules to minimise the steric repulsions between the two ends of the molecule whilst enhancing the bonding to the substituent even though this results in a weakened metal–metal bond as evidenced by bond lengthening and a reduction in the bond order. Complexation of the M₂R₂ ²⁻ ions by lithium reduces the electrostatic repulsions in the M₂R₂ ²⁻ complexes of the Group 13 elements by stabilisation of the π-like orbitals. Whilst the presence of Li⁺ is not responsible for the trans-bending, interactions between the Li atoms and the substituents are important in determining the extent of the distortion.     

Effect of tubular chiralities of single-walled ZnO nanotubes on electronic transport

The electronic transport properties of single-walled ZnO nanotubes with different chiralities are investigated by nonequilibrium Green's function combined with density functional theory. In this paper we consider three representative ZnO nanotubes, namely (3, 3) armchair, (5, 0) zigzag, and (4, 2) chiral, with a similar diameter of about 5.4 Å. Short nanotubes exhibit good conductance behavior. As the tube length increases, the conductance decreases at low bias and the nanotubes indicate semiconducting behavior. The current-voltage characteristics of the nanotubes longer than 3 nm depend weakly on the length of the tubes. The armchair and chiral ZnO nanotubes with the same length and diameter have almost overlapped current-voltage curves. The electron transport behaviors are analyzed in terms of the transmission spectra, density of states and charge population of these nanotubes. The results indicate that the resonant peaks above the Fermi level are responsible for electric currents. However, the zigzag ZnO nanotubes exhibit asymmetric current-voltage curves attributed to the built-in polarization field and give larger current than the armchair and chiral nanotubes at the same bias. The features explored here strongly suggest that the ZnO nanotubes are stable, flexible structures, which are valuable in Nano-Electromechanical System.