Isolation and Reactivity of Homoleptic Diphosphene Lead Complexes

Due to their limited capacity for π-backdonation, isolation of π-complexes of main-group elements remains a great challenge. We report herein the synthesis of a homoleptic diphosphene lead complex ( 2 ) from the degradation of P₄ with a bis(germylene)-stabilized Pb(0) complex. Structural and computational studies showed that 2 possesses significant π bonding interactions between Pb atom and diphosphene ligands, which is reminiscent of transition-metal diphosphene complexes. Consistent with its unique electronic structure, complex 2 can deliver Pb(0) atoms to perform redox reaction with an iminoquinone to produce a cyclic plumbylene ( 4 ) and perform 2,5-dimethyl-3,4-dimethylimidazol-1-ylidene (IMe₂Me₂) induced phosphorus cation abstraction to give an anionic PbP₃ complex ( 6 ).     

Palladium-Catalyzed Skeletal Rearrangement of Substituted 2-Silylaryl Triflates via 1,5-C−Pd/C−Si Bond Exchange

A palladium-catalyzed skeletal rearrangement of 2-(2-allylarylsilyl)aryl triflates has been developed to give highly fused tetrahydrophenanthrosilole derivatives via unprecedented 1,5-C−Pd/C−Si bond exchange. The reaction pathways can be switched toward 4-membered ring-forming C(sp²)−H alkylation by tuning the reaction conditions to give completely different products, fused dihydrodibenzosilepin derivatives, from the same starting materials. The inspection of the reaction conditions revealed the importance of carboxylates in promoting the C−Pd/C−Si bond exchange.     

High-Spin and Reactive Fe13 Cluster with Exposed Metal Sites

Atomically defined large metal clusters have applications in new reaction development and preparation of materials with tailored properties. Expanding the synthetic toolbox for reactive high nuclearity metal complexes, we report a new class of Fe clusters, Tp*₄W₄Fe₁₃S₁₂ , displaying a Fe₁₃ core with M−M bonds that has precedent only in main group and late metal chemistry. M₁₃ clusters with closed shell electron configurations can show significant stability and have been classified as superatoms. In contrast, Tp*₄W₄Fe₁₃S₁₂ displays a large spin ground state of S=13. This compound performs small molecule activations involving the transfer of up to 12 electrons resulting in significant cluster rearrangements.     

补偿效应研究的一个新视角

补偿效应与Arrhenius方程关系密切。本文为补偿效应研究提供了新视野。用几何图象分析了Arrhenius方程,指出过去认为此方程只表示速率与温度关系是不全面的,忽视了速率常数与活化能关系的研究。从图形看出,指前因子与活化能本身就具有互补关系,虽仅限于每两个不同活化能的情况。反应是一自组织过程。补偿效应的成立有必要条件和充分条件。欲实现补偿效应,从协同学角度考虑,E/T作为参变量必需小于一阈值,以使反应起活。并有一自变量做系列改变,以使A、E随其相似地连续变化,从而连通所有A、E的内在联系,1/T-lnk图中诸直线交于一点。指数分布是非均匀体系最具有普遍意义的分布函数。概率分析指出,补偿效应是A、E在固体表面和内部均呈相似指数分布的产物。对催化反应与非催化反应有普适性。在速率常数中体现为结构分布概率因子及能量分布概率因子。     

Effective moisture diffusivity and activation energy during convective drying of bread containing clove oil/orange oil

The aim of present study was to investigate the characteristic drying behaviour of bread with the convective drying method for increasing bread shelf life. Effective moisture diffusivity and activation energy were compared in detail. According to the results, bread samples were dried between 0 and 450 min for 40 °C, 0–180 min for 50 °C and 60 °C, respectively. The experimental data with high coefficient of determination (R²) changed between 0.889 and 0.998. The values of D_eff were obtained between 1.21 × 10^?9-1.22 × 10^?8 m²/s. Also, E_a values were found to be in range of 82.47–100.49 kJ/mol for bread samples which had additive-free and additive. When the bread samples without additives and the breads with essential oils were compared, it was found that the activation energy increased with the use of additives. Moisture content values decreased with the increase in time. Drying rate and moisture content relation showed the expected behaviour, thermally and morphologically.     

Kinetics of phenol hydrogenation over supported palladium catalyst

Kinetics of vapor phase hydrogenation of phenol to cyclohexanone over Pd/MgO system has been studied in a flow microreactor under normal atmospheric pressure. The reaction rate is found to be negative order with respect to the partial pressure of phenol and has increased from −0.5 to 0.5 with increasing temperature (473 to 563 K). The apparent activation energy (E_a) of the process is found to be close to 65 kJ per mol. On the basis of kinetic results a surface mechanism is proposed.     

茶碱对聚苯胺尿酸酶电极的生物电化学活性的抑制

用聚苯胺尿酸酶电极研究了茶碱对固定酶的影响，结果表明，茶碱对固定尿酶酶有明显的抑制作用，但这种抑制作用是可逆的，在茶碱的存在下，ＰＨ对酶电极的响应电流影响与无茶碱存在时不同；在０．２－０．５Ｖ之间，酶电极的响应电流随电位加而迅速升高，当电位进一步升高时，其变化速度减慢，茶碱使尿酶酶催化反应的活化能从无抑制剂存在的时的２９．９ｋＪ．ｍｏｌ＾－１提高到４７．８ｋＪ．ｍｏｌ＾－１，即抑制剂改变了尿酸催化     

萃取有机相中微乳液的稳定性研究

赊P507钾盐外，PSO7理、钠、按盐和P204的理、钠、钾、按以及有机接盐等与醇一油一水在一定条件下都能形成微乳液．因此，进一步搞清这些体系形成微乳液的结构、性质和稳定性，对革取化学研究是十分重要的．我们曾对PSO7（K）一醇一正庚烷一水四组分体系的结构参数［’j和物理化学性质［’］进行过研究，观察到辅助表面活性剂性质和含水量对微乳液结构有重要的影响·本文采用测定微乳液电导的变化，研究含有不同醇和不同量水时，P507（K）在革取有机相中形成微乳液颗粒的活化能（凸E），并用凸E的大小来描述和比较微乳液的界面膜强度…     

Effect of hydrostatic pressure on self-diffusion in metal nanoparticles

The thermodynamics approach has been developed to describe the self-diffusion in nano-sized solids. It has been established that identical homologous temperatures of metal nanoparticles with their fixed characteristic size give the identical coefficients of diffusion under different pressures. The dependence of the activation enthalpy of diffusion on pressure and on the characteristic size of nanoparticles is first obtained.