微波促进Wittig-Michael串级反应立体专一性合成ω-氨基-β-D-呋喃核糖酸衍生物

以D-核糖为原料, 在微波促进下, 利用2,3-O-异丙叉基-D-核糖2与叶立德3(Ph₃PCHCOOEt) 的Wittig反应和Michael加成, 立体专一性地合成了β-D-呋喃核糖酸酯类化合物, 再经叠氮化及还原反应, 得到ω-氨基-β-D-呋喃核糖酸衍生物. 在微波辐射下, 该Wittig-Michael串级反应的效率得到显著提高, 反应时间由12 h缩短为10 min, 收率达到91%. 反应具有非常好的β-立体选择性, 在碱性条件下处理后, α-异构体可转变成热力学稳定的β-异构体, 从而得到单一的β-异构体. 计算结果表明, β-异构体4b比α-异构体4a具有更高的热力学稳定性.     

气相色谱法测定电子烟烟液及气溶胶中双乙酰和乙酰丙酰

建立气相色谱法氢火焰离子化检测器测定电子烟烟液和气溶胶中双乙酰和乙酰丙酰含量的方法。样品以20 mL乙醇为萃取剂,涡旋振荡萃取10 min,采用气相色谱外标法进行定量分析。双乙酰和乙酰丙酰质量浓度在0.5~50 μg/mL范围内与色谱峰面积呈良好的线性关系,相关系数分别为0.999 6、0.999 4,方法检出限分别为0.044、0.052 μg/mL。烟液中双乙酰和乙酰丙酰测定结果的相对标准偏差为2.5%~4.3%(n=6),样品加标回收率为95.0%~102.5%;气溶胶中双乙酰和乙酰丙酰测定结果的相对标准偏差为3.1%~4.6%(n=6),样品加标回收率为92.7%~102.3%。气溶胶中双乙酰和乙酰丙酰理论浓度与实测浓度具有较强的相关性(对于双乙酰r~2=0.990 1,对于乙酰丙酰r~2=0.994 7),说明双乙酰、乙酰丙酰烟液通过雾化直接转移至气溶胶中。该方法准确度高,重现性好,检出限低,可满足电子烟样品的检测需求。     

希土永磁材料Nd-Fe-B氧化过程及抗氧化新体系的研究

Nd-Fe-B永磁体的热稳定性较差,易氧化,氧化使材料的结构受到破坏,永磁性能受到不可恢复的损失。氧化过程是分阶段的,在室温和干燥的空气中是稳定的,150℃左右受到破坏的主要原因是体系中钕的氧化,230℃以上铁开始氧化,温度升高使氧化加快,800℃左右氧化基本结束,最终产物主要是Fe_2O_3、Nd_2O_3和NdBO_3。新研制的Nd-Fe-B-Si四元体系的抗氧化能力有较大的提高,居里温度也提高了许多,是一种大有发展前途的新材料。     

Incorporation of an amide into 5-phosphonoalkyl-6-D-ribitylaminopyrimidinedione lumazine synthase inhibitors results in an unexpected reversal of selectivity for riboflavin synthase vs lumazine synthase

Several analogues of a hypothetical intermediate in the reaction catalyzed by lumazine synthase were synthesized and tested as inhibitors of both Bacillus subtilis lumazine synthase and Escherichia coli riboflavin synthase. The new compounds were designed by replacement of a two-carbon fragment of several 5-phosphonoalkyl-6-D-ribitylaminopyrimidinedione lumazine synthase inhibitors with an amide linkage that was envisioned as an analogue of a Schiff base moiety of a hypothetical intermediate in the enzyme-catalyzed reaction. The incorporation of the amide group led to an unexpected reversal in selectivity for inhibition of lumazine synthase vs riboflavin synthase. Whereas the parent 5-phosphonoalkyl-6-D-ribitylaminopyrimidinediones were lumazine synthase inhibitors and did not inhibit riboflavin synthase, the amide-containing derivatives inhibited riboflavin synthase and were only very weak or inactive as lumazine synthase inhibitors. Molecular modeling of inhibitor-lumazine synthase complexes did not reveal a structural basis for these unexpected findings. However, molecular modeling of one of the inhibitors with E. coli riboflavin synthase demonstrated that the active site of the enzyme could readily accommodate two ligand molecules.     

Task specific ionic liquid for direct electrochemistry of metal oxides

We present the first report on task specific ionic liquid (TSIL) for direct electrochemical detection of heavy metal oxides including cadmium oxide, copper oxide and lead oxide at room temperature. This TSIL based electrochemical sensor demonstrated a high sensitivity and selectivity towards the online monitoring of these trace metal oxide particulates, along with short detection time, low cost and high accuracy. This novel sensor platform opens new pathways for in-situ monitoring of metal oxide particulates for environmental sensing and decontamination applications.     

Catalytic adsorptive stripping voltammetric measurements of trace vanadium at bismuth film electrodes

Bismuth-coated glassy carbon electrodes have been successfully applied for catalytic adsorptive stripping voltammetric measurements of low levels of vanadium(V) in the presence of chloranilic acid (CAA) and bromate ion. The new protocol is based on the accumulation of the vanadium-chloranilic acid complex from an acetate buffer (pH 5.5) solution at a preplated bismuth film electrode held at −0.35 V (versus Ag/AgCl), followed by a square-wave voltammetric scan. Factors influencing the adsorptive stripping performance, including the CAA and bromate concentrations, solution pH, and accumulation potential or time have been optimized. The response compares favorably with that observed at mercury film electrodes. A linear response is observed over the 5-25 μg/L concentration range (2 min accumulation), along with a detection limit of 0.20 μg/L vanadium (10 min accumulation). High stability is indicated from the reproducible response of a 50 μg/L vanadium solution (n = 25; R.S.D. = 3.1%). Applicability to a groundwater sample is illustrated.     

Stable ultraviolet photoluminescence emission in n-type porous silicon

This very paper is focusing on the investigation of porous silicon preparation with n-type silicon wafer by means of electrochemical anodization in the dark and, particularly, on its stable ultraviolet photoluminescence emission. A lateral electrical potential was applied, for this purpose, on silicon wafers, driving the electrons away and letting holes appear on the surface of the silicon wafer to enhance the electrochemical etching process. Characterizations have been made with scanning electronic microscope, fluorescence spectrophotometer and Fourier transform infrared spectroscope. An ultraviolet photoluminescence emission of 370 nm is found in the as-prepared n-type porous silicon, which seems to be well associated with the formation of oxygen-related species (twofold coordinated silicon defect) during the anodic oxidation. The result characterized by photo-bleaching performance indicates that the ultraviolet photoluminescence emission is so stable—only 7% reduction within 3600 s. Meanwhile the morphology of as-prepared n-type porous silicon is investigated.     

Hydrogen bond and halogen bond inside the carbon nanotube

The hydrogen bond and halogen bond inside the open-ended single-walled carbon nanotubes have been investigated theoretically employing the newly developed density functional M06 with the suitable basis set and the natural bond orbital analysis. Comparing with the hydrogen or halogen bond in the gas phase, we find that the strength of the hydrogen or halogen bond inside the carbon nanotube will become weaker if there is a larger intramolecular electron-density transfer from the electron-rich region of the hydrogen or halogen atom donor to the antibonding orbital of the X-H or X-Hal bond involved in the formation of the hydrogen or halogen bond and will become stronger if there is a larger intermolecular electron-density transfer from the electron-rich region of the hydrogen or halogen atom acceptor to the antibonding orbital of the X-H or X-Hal bond. According to the analysis of the molecular electrostatic potential of the carbon nanotube, the driving force for the electron-density transfer is found to be the negative electric field formed in the carbon nanotube inner phase. Our results also show that the X-H bond involved in the formation of the hydrogen bond and the X-Hal bond involved in the formation of the halogen bond are all elongated when encapsulating the hydrogen bond and halogen bond within the carbon nanotube, so the carbon nanotube confinement may change the blue-shifting hydrogen bond and the blue-shifting halogen bond into the red-shifting hydrogen bond and the red-shifting halogen bond. The possibility to replace the all electron nanotube-confined calculation by the simple polarizable continuum model is also evaluated.     

Facile Synthesis of Fe3Pt-Ag Nanocomposites for Catalytic Reduction of Methyl Orange

The polyethyleneimine dithiocarbamate was employed as polymers to synthesize Fe₃Pt-Ag nanocomposites by using the seed deposition method. Fe₃Pt-Ag nanocomposites were utilized for the catalytic degradation of methyl orange(MO) in the presence of NaBH₄. Fe₃Pt-Ag nanocomposites showed good chemical catalytic activity and stability in pollutants degradation. Furthermore, Fe₃Pt-Ag nanocomposites can keep their efficiency till four cycles. The results suggest that the nanocatalysts with recyclability have broad prospects in environmental conservation applications.