Asymmetric synthesis of 1,2-fluorohydrin: iridium catalyzed hydrogenation of fluorinated allylic alcohol

We have developed a simple protocol for the preparation of 1,2-fluorohydrin by asymmetric hydrogenation of fluorinated allylic alcohols using an efficient azabicyclo thiazole-phosphine iridium complex. The iridium-catalyzed asymmetric synthesis of chiral 1,2-fluorohydrin molecules was carried out at ambient temperature with operational simplicity, and scalability. This method was compatible with various aromatic, aliphatic, and heterocyclic fluorinated compounds as well as a variety of polyfluorinated compounds, providing the corresponding products in excellent yields and enantioselectivities.

We have developed a simple protocol for the preparation of 1,2-fluorohydrin by asymmetric hydrogenation of fluorinated allylic alcohols using an efficient azabicyclo thiazole-phosphine iridium complex.     

On the New Shear Constraint for Plane-Stress Orthotropic Plasticity Modeling of Sheet Metals

Experimental Mechanics - A shear constraint was very recently proposed by Abedini et al. (Int. J. Solids and Structures 151: 118–134 2018) to evaluate and calibrate advanced non-quadratic...     

Rationally Design of Near Infrared Light Responsive Micro‐Photoelectrodes for In Vivo Sensing of Neurotransmitter Molecules in Mouse Brain†

The accurate quantification of neurotransmitter molecules is an indispensable means to reveal the physiological mechanisms of neuro movement in molecular level. However, existing detection strategies cannot fully meet practical needs, and the on‐site and in vivo detection of neurotransmitters in brain remains a great challenge. Here, we report the development of a near infrared light responsive photoelectrochemical (PEC) detection method for in vivo quantification of neurotransmitter dopamine in mouse brain. Under guidance of density function theory calculations, a combination strategy of non‐metal cation doping and defect engineering is introduced to rationally design the micro‐photoelectrodes with excellent biocompatibility and stability and implements the in vivo PEC detection of dopamine in mouse brain. It opens up a new way for the accurate in vivo detection of biomolecules and allows researchers to make novel inquiries for long‐standing questions in a new way.     

微生物燃料电池阴极脱氮

微生物燃料电池(MFC)阴极电子受体的多样性可实现其阴极脱氮,从而将产生的电能合理利用,因此阴极脱氮成为了MFC的一个研究方向,同时也为实际废水中氮素的去除提供了新的可能。然而在反应过程中有众多因素会导致NOx-N与其他电子受体竞争阳极电子的现象,影响阴极反硝化过程对于电子的利用率,从而造成脱氮效率低等现实问题。目前已有许多研究通过优化MFC自身结构弥补产电的缺陷,及将与其他工艺系统耦合实现同步硝化反硝化等方法,取长补短以增加脱氮效率,降低对碳源的需求,以此解决微生物燃料电池阴极脱氮出现的问题。本文从MFC不同的脱氮历程、MFC工艺条件(pH、C/N、DO)、极室分隔材料等影响MFC阴极脱氮的因素及影响其阴极反硝化微生物群落构成等方面,进行了综述并预测未来研究方向。     

Quantum Decoherence of Gaussian Steering and Entanglement in Hawking Radiation and Thermal Bath

We study the effects of Hawking radiation and bath temperature on quantum steering and entanglement for a two-mode Gaussian state exposed in the background of a black hole and immersed in the two independent thermal baths. We find that both the effects can destroy the quantum steering and entanglement. Quantum steering always exists sudden death for any Hawking temperature and any bath temperature, but entanglement does not in zero-temperature thermal bath. Both the Hawking radiation and the asymmetry of thermal baths can induce the asymmetry of quantum steering, but the latter effect is much weaker than the former. An unintuitive result is that the observer who stays in the Hawking radiation or in the thermal bath with higher temperature has more stronger steerability than the other one. We also find that Hawking radiation and thermal noise can change the asymptotic behavior of steering and entanglement versus the squeezing parameter.

     

An improved evaluation of the neutron background in the PandaX-Ⅱ experiment

In dark matter direct detection experiments,neutron is a serious source of background,which can mimic the dark matter-nucleus scattering signals.In this paper,we present an improved evaluation of the neutron background in the PandaX-II dark matter experiment by a novel approach.Instead of fully relying on the Monte Carlo simulation,the overall neutron background is determined from the neutron-induced high energy signals in the data.In addition,the probability of producing a dark-matter-like background per neutron is evaluated with a complete Monte Carlo generator,where the correlated emission of neutron(s)andγ(s)in the(α,n)reactions and spontaneous fissions is taken into consideration.With this method,the neutron backgrounds in the Run 9(26-ton-day)and Run 10(28-ton-day)data sets of PandaX-II are estimated to be(0.66±0.24)and(0.47±0.25)events,respectively.     

A Chemically Soldered Polyoxometalate Single-Molecule Transistor

Polyoxometalates have been proposed in the literature as nanoelectronic components, where they could offer key advantages with their structural versatility and rich electrochemistry. Apart from a few studies on their ensemble behaviour (as monolayers or thin films), this potential remains largely unexplored. We synthesised a pyridyl-capped Anderson–Evans polyoxometalate and used it to fabricate single-molecule junctions, using the organic termini to chemically “solder” a single cluster to two nanoelectrodes. Operating the device in an electrochemical environment allowed us to probe charge transport through different oxidation states of the polyoxometalate, and we report here an efficient three-state transistor behaviour. Conductance data fits a quantum tunnelling mechanism with different charge-transport probabilities through different charge states. Our results show the promise of polyoxometalates in nanoelectronics and give an insight on their single-entity electrochemical behaviour.     

Sandwich-like Catalyst–Carbon–Catalyst Trilayer Structure as a Compact 2D Host for Highly Stable Lithium–Sulfur Batteries

Herein, we propose the construction of a sandwich-structured host filled with continuous 2D catalysis–conduction interfaces. This MoN-C-MoN trilayer architecture causes the strong conformal adsorption of S/Li₂S_x and its high-efficiency conversion on the two-sided nitride polar surfaces, which are supplied with high-flux electron transfer from the buried carbon interlayer. The 3D self-assembly of these 2D sandwich structures further reinforces the interconnection of conductive and catalytic networks. The maximized exposure of adsorptive/catalytic planes endows the MoN-C@S electrode with excellent cycling stability and high rate performance even under high S loading and low host surface area. The high conductivity of this trilayer texture does not compromise the capacity retention after the S content is increased. Such a job-synergistic mode between catalytic and conductive functions guarantees the homogeneous deposition of S/Li₂S_x, and avoids thick and devitalized accumulation (electrode passivation) even after high-rate and long-term cycling.     

Late-Stage Peptide Macrocyclization by Palladium-Catalyzed Site-Selective C−H Olefination of Tryptophan

Transition-metal-catalyzed C−H activation has shown potential in the functionalization of peptides with expanded structural diversity. Herein, the development of late-stage peptide macrocyclization methods by palladium-catalyzed site-selective C(sp²)−H olefination of tryptophan residues at the C2 and C4 positions is reported. This strategy utilizes the peptide backbone as endogenous directing groups and provides access to peptide macrocycles with unique Trp–alkene crosslinks.     

微波瑞利散射法测定空气电火花激波等离子体射流的时变电子密度

大气压空气电火花激波等离子体射流的电子密度在亚微秒时间尺度上瞬变,其电子密度的测定很难.基于微波瑞利散射原理,本文测量了空气电火花冲击波流注放电等离子体射流的时变电子密度.实验结果表明:测量系统的标定参数A为1.04 × 105 V·Ω·m–2;空气流注放电等离子体射流的电子密度与等离子体射流的半径和长度有关,结合高速放电影像展示的等离子体射流的等效半径和等效长度,测定的电子密度在1020 m–3的量级,且随时间先快速增长至峰值再成指数衰减.此外,本文还探讨了等离子体射流的不同等效尺度对测定结果的影响;分析结果表明,采用时变等效半径和时变等效长度的计算结果最有效,且第1个快速波峰是由光电离的电离波导致的.