雪菊精油对希氏肠球菌产酪胺及相关基因表达的影响

探讨不同质量浓度雪菊精油对希氏肠球菌（Enterococcus hirae）N47产酪胺的影响机制。利用反转录实时定量聚合酶链式反应分析E. hirae在雪菊精油作用下酪氨酸脱羧途径相关基因的表达情况；利用高效液相色谱法检测不同质量浓度雪菊精油对E. hirae产酪胺的影响。并将E. hirae接入到含不同质量浓度雪菊精油的熏马肠中发酵，评估香肠pH值、菌落总数和酪胺积累量。结果表明：在E. hirae纯培养体系和熏马肠体系中，雪菊精油通过抑制微生物的生长和酪氨酸脱羧途径中tyr DC、tyr P基因的表达，降低酪胺的积累量（P＜0.05）。当雪菊精油添加量为1/2最小抑菌浓度（minimal inhibitory concentration，MIC）和MIC时，熏马肠中酪胺的含量分别为78.52 mg/kg和45.83 mg/kg，较对照组分别减少了64.72%和79.41%。     

Insight into the Mechanism of Phenylacetate Decarboxylase (PhdB), a Toluene-Producing Glycyl Radical Enzyme

We recently reported the discovery of phenylacetate decarboxylase (PhdB), representing one of only ten glycyl-radical-enzyme reaction types known, and a promising biotechnological tool for first-time biochemical synthesis of toluene from renewable resources. Here, we used experimental and computational data to evaluate the plausibility of three candidate PhdB mechanisms, involving either attack at the phenylacetate methylene carbon or carboxyl group [via H-atom abstraction from COOH or single-electron oxidation of COO⁻ (Kolbe-type decarboxylation)]. In vitro experimental data included assays with F-labeled phenylacetate, kinetic studies, and tests with site-directed PhdB mutants; computational data involved estimation of reaction energetics using density functional theory (DFT). The DFT results indicated that all three mechanisms are thermodynamically challenging (beyond the range of many known enzymes in terms of endergonicity or activation energy barrier), reflecting the formidable demands on PhdB for catalysis of this reaction. Evidence that PhdB was able to bind α,α-difluorophenylacetate but was unable to catalyze its decarboxylation supported the enzyme's abstraction of a methylene H atom. Diminished activity of H327A and Y691F mutants was consistent with proposed proton donor roles for His327 and Tyr691. Collectively, these and other data most strongly support PhdB attack at the methylene carbon.     

Copper(II)/Silver(I)‐Catalyzed Sequential Alkynylation and Annulation of Aliphatic Amides with Alkynyl Carboxylic Acids: Efficient Synthesis of Pyrrolidones

A highly efficient protocol for the synthesis of pyrrolidones by the copper‐catalyzed alkynylation/annulation of aliphatic amides with alkynyl carboxylic acids is discussed in this paper. A broad range of easily accessible alkynyl carboxylic acids were introduced at the β‐methyl group of aliphatic amides with the assistance of an 8‐aminoquinolyl auxiliary group via decarboxylation to achieve the subsequent cyclic C N bond formation within one hour. High selectivity of β‐methyl groups over methylene groups was observed, and the extension of this catalytic system to the activation of methylene C H bonds failed. The substrates with two different groups at the α‐position of the aliphatic amides lead to the formation of diastereoisomers which is determined by ¹H NMR spectroscopy. The initially produced products with Z‐configurations can be easily transformed to the corresponding products with E‐configurations by the treatment with dilute p‐toluenesulfonic acid after the reaction. This catalytic tandem decarboxylative cyclization provides a new opportunity for the direct functionalization of sp³ C H bonds.

     

Direct Decarboxylative Alkynylation of α,α‐Difluoroarylacetic Acids under Transition Metal‐Free Conditions

An efficient and generally applicable protocol for decarboxylative coupling of α,α‐difluoroarylacetic acids with ethynylbenziodoxolone (EBX) reagents has been developed, affording α,α‐difluoromethylated alkynes bearing various functional groups in moderate to excellent yields. Remarkably, this potassium persulfate (K₂S₂O₈)‐promoted reaction employs water as solvent under transition metal‐free conditions, thus providing a green synthetic approach to α,α‐difluoromethylated alkynes.

     

Carbon-coated Ni-Co alloy catalysts: preparation and performance for in-situ aqueous phase hydrodeoxygenation of methyl palmitate to hydrocarbons using methanol as the hydrogen donor

Carbon-coated Ni, Co and Ni-Co alloy catalysts were prepared by the carbonization of the metal doped resorcinol-formaldehyde resins synthesized by the one-pot extended Stöber method. It was found that the introduction of Co remarkably reduced the carbon microsphere size. The metallic Ni, Co, and Ni-Co alloy particles (mainly 10–12 nm) were uniformly distributed in carbon microspheres. A charge transfer from Ni to Co appeared in the Ni-Co alloy. Compared with those of metallic Ni and Co, the d-band center of the Ni-Co alloy shifted away from and toward the Fermi level, respectively. In the in-situ aqueous phase hydrodeoxygenation of methyl palmitate with methanol as the hydrogen donor at 330 °C, the decarbonylation/decarboxylation pathway dominated on all catalysts. The Ni-Co@C catalysts gave higher activity than the Ni@C and Co@C catalysts, and the yields of n-pentadecane and n-C₆–n-C₁₆ reached 71.6% and 92.6%, respectively. The excellent performance of Ni-Co@C is attributed to the electronic interactions between Ni and Co and the small carbon microspheres. Due to the confinement effect of carbon, the metal particles showed high resistance to sintering under harsh hydrothermal conditions. Catalyst deactivation is due to the carbonaceous deposition, and the regeneration with CO₂ recovered the catalyst reactivity.     

The production of renewable transportation fuel through fed‐batch and continuous deoxygenation of vegetable oil derived fatty acids over Pd/C catalyst

Renewable fuels such as green diesel from renewable biomass have received attentions because of energy and environmental concerns. Deoxygenation, used to upgrade biomass derived oils has been applied intensively nowadays. To successfully improve this process, fed‐batch and following continuous processes on real biomass derived fatty acids need to be investigated. In this study, liquid‐phase deoxygenation of vegetable oil derived fatty acids was carried out over 5% Pd/C with cofeeding H₂. With sufficient hydrogen, complete hydrogenation of unsaturated fatty acids occurred, leading to successive deoxygenation of the saturated fatty acids with n‐alkane yields of 99% and 88% and average CO₂ selectivity of 94.9% and 94.6% in the fed‐batch and continuous mode, respectively. After hydrogenation is completed, lower than 5% of effective H₂ partial pressure was found to be favorable for the decarboxylation pathway and ideal for deoxygenation of biomass derived fatty acids. Copyright © 2015 John Wiley & Sons, Ltd.     

木质素热解中CO和CO2形成机理的理论研究

采用密度泛函理论方法(B3LYP)对含苯基的各种木质素模型化合物的脱羰基反应和脱羧基反应进行了理论研究。设计了8种模型化合物 R1-R8的8条脱羰基反应路径(1)-(8)和8种模型化合物 R9-R16的8条脱羧基反应路径(9)-(16)。计算了不同温度下各热解反应途径的标准热力学和动力学参数。计算结果表明,反应路径(1)-(4)的脱羰基反应能垒明显高于反应路径(5)-(8),CO 更可能通过苯基(对羟苯基、愈创木基和紫丁香基)乙醛的脱羰基反应而形成;反应路径(9)-(12)的脱羧基反应能垒低于反应路径(13)-(16),CO2的形成更可能通过苯基(对羟苯基、愈创木基和紫丁香基)甲酸的脱羧基反应而完成。     

Thermal behaviour of partially neutralised ethylene-maleic acid copolymer

As part of continuing studies on the cure of candidate polymers for waterborne coatings, the thermal behaviour of partially neutralised ethylene-maleic acid copolymer, EMA, has been examined. Films of EMA neutralised with a variety of bases were heated at 250°C. For this copolymer, as for poly(acrylic acid) at the same temperature, reflectance infrared spectroscopy has shown that heating led initially to anhydride formation. In the unneutralised state, or with the divalent ions calcium, magnesium, cobalt or zinc, further heating led to little or no further reaction. By contrast, the presence of univalent metal ions lithium, sodium and potassium caused a second reaction to occur, namely decarboxylation to yield keto crosslinks. This second reaction, however, did not occur to the extent that it does with poly(acrylic acid) under identical conditions. Possible reasons for this are discussed. Unlike poly(acrylic acid), EMA when partially neutralised was found not to form continuous films on the tin-plate substrate.