Direct Transformation of Arenols Based on C—O Activation

In the view of substrate availability, atomic efficiency and cost, directly using arenols as coupling partners in cross‐coupling, would be one of the most attractive goals. Up to date, many efforts have been made to activate the C—O bond of phenols with different strategies, for example, through in‐situ formed intermediates, through a catalytic reductive dearomatization‐condensation‐rearomatization sequence or catalytic deoxygenation. In this review, we summarized recent advances in cross‐couplings of arenols as the electrophiles via C—O activation.     

固相萃取-HPLC法同时测定滇龙胆中7种苯甲酸酯

建立了固相萃取-HPLC法同时测定滇龙胆中抗老年痴呆的7种主要成分gentiside G,gentiside H,gentiside I,gentiside A,gentiside J,gentiside B,gentiside K的含量的方法。滇龙胆样品经乙醇提取环己烷萃取后,用硅胶固相萃取小柱净化,HPLC-DAD对7种苯甲酸酯进行定量检测。7种苯甲酸酯类化合物在一定范围内线性关系良好,相关系数均大于0.999,加样回收率为92.8%~104.6%,RSD为0.8%~4.7%。不同产地龙胆样品中云南产滇龙胆苯甲酸酯含量高于其他产地龙胆,7种化合物中,gentiside B含量最高达0.3425μg/g,gentiside G含量最低只有8.5μg/g。方法为滇龙胆药材的质量控制和资源开发利用提供科学依据。     

Influence of external load on friction coefficient of Fe-polytetrafluoroethylene

A coarse-grained molecular dynamics simulation model was developed in this study to investigate the friction process occurring between Fe and polytetrafluoroethylene(PTFE).We investigated the effect of an external load on the friction coefficient of Fe–PTFE using the molecular dynamics simulations and experimental methods.The simulation results show that the friction coefficient decreases with the external load increasing,which is in a good agreement with the experimental results.The high external load could result in a larger contact area between the Fe and PTFE layers,severer springback as a consequence of the deformed PTFE molecules,and faster motion of the PTFE molecules,thereby affecting the friction force and normal force during friction and consequently varying the friction coefficient.     

Identifying the viscoelastic properties of soft matter from the indentation response of a hard film-soft substrate system

The indentation technique is widely used in measuring the mechanical properties of soft matter at the microscale or nanoscale,but still faces challenges by these unique properties as well as the consequent strong surface adhesion, including the strong nonlinear effect, unclear judgment of the contact point, difficulties in estimating the contact area, and the risk of the indenter piercing the sample. Here we propose a two-step method to solve these problems: lay a hard film on a soft matter, and obtain the viscoelastic properties of this soft matter through the indentation response of this composite structure. We first establish a theoretical indentation model of the hard film-soft substrate system based on the theory of plates, elastic-viscoelastic correspondence principle and Boltzmann superposition principle. To verify the correctness of this method, we measure the mechanical properties of the methyl vinyl silicone rubber(MVSR) covered by a Cu nanofilm. Finally, we test the effectiveness and error sensitivity of this method with the finite element method(FEM). The results show that our method can accurately measure the mechanical properties of soft matter, while effectively circumventing the problems of the traditional indentation technique.     

Ba3V2S4O3: A Mott Insulating Frustrated Quasi‐One‐Dimensional S=1 Magnet

Through a solid‐state reaction, a practically phase pure powder of Ba₃V₂S₄O₃ was obtained. The crystal structure was confirmed by X‐ray single‐crystal and synchrotron X‐ray powder diffraction (P6₃, a=10.1620(2), c=5.93212(1) Å). X‐ray absorption spectroscopy, in conjunction with multiplet calculations, clearly describes the vanadium in charge‐disproportionated V^IIIS₆ and V^VSO₃ coordinations. The compound is shown to be a strongly correlated Mott insulator, which contradicts previous predictions. Magnetic and specific heat measurements suggest dominant antiferromagnetic spin interactions concomitant with a weak residual ferromagnetic component, and that intrinsic geometric frustration prevents long‐range order from evolving.