Enantiopure aryl-[1,2,5,6-tetrahydro-pyridinyl] methanols and their use for heterogeneous hydrogenation of ethyl pyruvate

Both enantiomers of two new chiral modifiers (naphthyl- and anthryl-[1,2,5,6-tetrahydro-pyridinyl] methanols, 4H and 5H) are obtained for the first time from inexpensive d-mannitol in 10 easy steps. Until now erythro-4H is the only synthetic chiral modifier available under both enantiomeric forms, which provide enantioselectivities almost as high as those obtained with natural cinchonidine, for which only one enantiomer is available. It is shown that the anthryl group may be less efficient than the naphthyl (the e.e.% drops from 75% with erythro-4H to 46% with erythro-5H) and that N-methyl substitution (trisubstituted nitrogen as in cinchonidine) leads also to a drop in the e.e.% (from 75% with 4H to 39% with 4Me).     

Transition Metal‐Free Reduction of Activated Alkenes Using a Living Microorganism

Microorganisms can be programmed to perform chemical synthesis via metabolic engineering. However, despite an increasing interest in the use of de novo metabolic pathways and designer whole‐cells for small molecule synthesis, the inherent synthetic capabilities of native microorganisms remain underexplored. Herein, we report the use of unmodified E. coli BL21(DE3) cells for the reduction of keto‐acrylic compounds and apply this whole‐cell biotransformation to the synthesis of aminolevulinic acid from a lignin‐derived feedstock. The reduction reaction is rapid, chemo‐, and enantioselective, occurs under mild conditions (37 °C, aqueous media), and requires no toxic transition metals or external reductants. This study demonstrates the remarkable promiscuity of central metabolism in bacterial cells and how these processes can be leveraged for synthetic chemistry without the need for genetic manipulation.     

安培环路定理的拓扑学描述

近年来拓扑学在量子力学中得到了广泛的运用.本文将安培环路定理积分式重新表达为一矢量场在轮胎参数面上的第一类陈数积分.数值模拟展示了该积分值为一整数即第一陈数,其代表矢量场的整体性质:当经历连续变换时,矢量场的局部数值发生改变但整体积分值即陈数仍保持不变;若陈数发生改变,则表明矢量场变换的连续性条件发生破坏,矢量场出现奇点.进一步通过高斯映射将该矢量场从参数轮胎面映射到单位球面上,并给出了第一陈数的直观几何意义.理论和数值结果揭示了安培环路定理的拓扑学本质,表明拓扑概念在经典物理学中也会有广泛应用.     

Solvent-free epoxidation of himachalenes and their derivatives by TBHP using [MoO2(SAP)]2 as a catalyst

Himachalenes, sesquiterpenes isolated from the essential oil of Cedrus atlantica, are abundant and relatively inexpensive natural molecules of high interest, of which classical chemical transformations have enlarged the application potential. Solvent-free epoxidation using aqueous TBHP as an oxidant and [MoO₂(SAP)]₂ as a catalyst is performed herein for the first time with this family of natural compounds and with related halogenated derivatives.     

Oxidative Mechanochemistry: Direct,Room‐Temperature,Solvent‐Free Conversion of Palladium and Gold Metals into Soluble Salts and Coordination Complexes

Noble metals are valued, critical elements whose chemical activation or recycling is challenging, and traditionally requires high temperatures, strong acids or bases, or aggressive complexation agents. By using elementary palladium and gold, demonstrated here is the use of mechanochemistry for noble‐metal activation and recycling by mild, clean, solvent‐free, and room‐temperature chemistry. The process leads to direct, efficient, one‐pot conversion of the metals, including spent catalysts, into either simple water‐soluble salts or metal–organic catalysts.     

Influence of the formulation of catalysts deposited on cordierite monoliths for acetic acid oxidation

Monolithic catalysts are prepared by washcoating cordierite monoliths with different sols (Pt/Al₂O₃, Pt/CeO₂, Pt/ZrO₂, Pt/Al₂O₃CeO₂, Pt/Al₂O₃ZrO₂, and Pt/CeO₂ZrO₂). These sols are prepared by a sol–gel process and characterized by specific surface area (S_BET), inductively coupled plasma, hydrogen chemisorption, high-resolution transmission electron microscopy, field emission scanning electron microscopy, oxygen storage capacity, X-ray diffraction, temperature-programmed reduction, CO₂ chemisorption, and the model reaction of 3,3-dimethylbutene isomerization. The catalytic performances of the monolithic catalysts are then evaluated for the acetic acid oxidation. The nature of catalyst coating has been found to influence the adherence with the cordierite monolith and the presence of cerium in the catalyst appears to increase the adherence of the latter. Pt/CeO₂, Pt/Al₂O₃CeO₂, and Pt/CeO₂ZrO₂ are found to be the most reducible catalysts (oxygen storage capacity and temperature-programmed reduction) and to have the lowest acidities (3,3-dimethylbutene isomerization). CO₂ chemisorption shows that these catalysts possess a good basicity. From the relation established between the catalytic activity and the redox and acid–base properties it has been concluded that the reducibility is the key factor for a good catalytic activity although the basicity has a significant influence on the catalytic performance.     

Improvement of HDS catalysts through the modification of the oxidic precursor with 1,5-pentanediol: Gas phase sulfidation and thiophene conversion

The performance, in thiophene HDS, of a CoMo/Al₂O₃ catalyst was successfully improved through chemical modification of its oxidic precursor by impregnation with 1,5-pentanediol solution. The gas phase activation with a H₂/H₂S mixture was followed by thermogravimetric analysis coupled with a rapid chromatograph; the catalysts were characterized at different steps of the activation using X-ray photoelectron spectroscopy (XPS). It appeared that the addition of the organic agent retards the sulfidation of the supported metals, leading to a simultaneous sulfidation of Co and Mo atoms. This induces the formation of smaller MoS₂ slabs and thus an increase in the number of active CoMoS sites, directly correlated with the better HDS performance of the modified solid. The role of 1,5-pentanediol is likely to inhibit, at low temperature, the adsorption of H₂S on the solid and thus the sulfidation of the supported metals.