A New Chemo‐Enzymatic Route to Side‐Chain Liquid‐Crystalline Polymers: The Synthesis and Polymerization of 6‐(4‐Methoxybiphenyl‐4′‐oxy)hexyl Vinyl Hexanedioate

A novel synthetic method combining chemo and enzymatic synthesis strategies was employed to prepare a vinyl acetate type monomer, 6‐(4‐methoxybiphenyl‐4′‐oxy)hexyl vinyl hexanedioate (VA‐LC). Homo‐ and copolymers of VA‐LC with maleic anhydride (MAn) were prepared by conventional free radical polymerization using 2,2′‐azobisisobutyronitrile (AIBN) and 1,1′‐azobis (cyclohexane carbonitrile) (AHCN) as an initiator at 95 and 60 °C, respectively. The thermal properties of the generated polymeric material were investigated by differential scanning calorimetry (DSC), and the optical texture was inspected by polarizing optical microscopy (POM). While the monomer VA‐LC does not exhibit liquid‐crystalline properties, poly(VA‐LC), and the alternating copolymer of VA‐LC with maleic anhydride both displayed such properties.

     

Azocalixarenes: Synthesis, Characterization, Complexation, Extraction, Absorption Properties and Thermal Behaviours

Azocalixarenes, which have a conjugated chromophore azo (–N=N–) group in p-positions, are synthesized in “one-pot” procedures in satisfactory yields. Their structures in the solid and solution are elucidated by UV–vis, FT-IR, ¹H and ¹³C NMR spectroscopic methods as well as elemental analysis techniques. Some of them are complexed with metal ions (alkali, alkaline-earth and transition metal ions) under neutral conditions. A wide variety of applications is expected by the functionalization of the side arms. The selective liquid–liquid extraction of various alkali, alkaline-earth and transition metal cations from the aqueous phase to the organic phase is carried out by using azocalixarenes. Furthermore, the synthesized azocalixarenes are utilized for selective extraction of Fe³⁺ cations from the aqueous phase to the organic phase. The effects of varying pH and solvent upon the absorption ability of azocalixarenes substituted with electron-donating and electron-withdrawing groups at their o-, m-, p-positions are examined. The thermal behaviours of azocalixarenes containing upper rim functionalized groups are investigated by means of thermogravimetry (TG), differential thermal analysis (DTA) and differential thermogravimetry (DTG).     

Trifluoromethyl- and difluoromethyl-β-lactams as useful building blocks for the synthesis of fluorinated amino acids, dipeptides, and fluoro-taxoids

Enantiopure 1-acyl-3-hydroxyl-4-CF₂H-azetidin-2-ones and 1-acyl-3-hydroxy-4-CF₃-azetidin-2-ones serve as versatile intermediates for the syntheses of CF₂- and CF₃-containing α-hydroxy-β-amino acids, dipeptides, and taxoid anticancer agents. Both enantiomers of 3-hydroxy-4-CF₂H-β-lactams can be obtained in high yields through the diethylaminosulfur trifluoride (DAST) reaction of the corresponding enantiopure 4-formyl-β-lactam that is prepared through [2+2] cycloaddition of acetoxyketene to a 3-methyl-2-butenaldimine, followed by enzymatic optical resolution and ozonolysis. (+)-3-Hydroxy-4-CF₃-β-lactams and (−)-3-hydroxy-4-CF₃-β-lactams can also be readily obtained in enantiopure form through [2+2] cycloaddition of a CF₃-imine with a ketene, followed by enzymatic optical resolution. Practical processes for the preparations of these enantiopure 3-hydroxy-4-R_f-β-lactams as well as their synthetic applications are described.     

Rapid liquid chromatographic-mass spectrometric analysis of withanolides in crude plant extracts by use of a monolithic column

Summary A rapid analytical method has been developed for the mutual resolution of three steroidal compounds, withaferin A, iochromolide, and withacnistin. Liquid chromatography was performed on a Chromolith analytical column (4.6 mm i.d.×50 mm), made from a cylindrical silica rod, operated at a flow rate of 4 mL min⁻¹ with a simple linear gradient prepared from 0.1% aqueous formic acid and 0.1% formic acid in acetonitrile. Under optimum conditions simultaneous separation of the compounds was achieved in less than 7 min, one eighth the time required for conventional LC separation. The overall analysis time was reduced without sacrificing chromatographic performance—essential for the resolution of positional isomers such as iochromolide and withacnistin. The column was coupled to a single-quadrupole mass spectrometer and the method was characterized by good performance in terms of repeatability, selectivity, linearity, and sensitivity. Detection limits in the single-ion-monitoring mode were 0.15 μg mL⁻¹ or below. Finally, the developed method was successfully applied to the determination of withanolides in extracts fromlochroma gesnerioides obtained by three different processes—traditional Soxhlet extraction and two faster methods, microwave-assisted extraction and pressurized solvent extraction.     

Voltammetric studies on the interactions between camazepam metabolic series and human serum albumin. Determination of oxazepam using adsorptive stripping voltammetry

The behaviour of oxazepam in adsorptive stripping voltammetry was studied taking into account those conditions which have an influence on the accumulation step (electrolyte, pH, time, potential, drop size and stirring rate), rest time and stripping step (pulse amplitude and scan rate). Oxazepam can be determined at a hanging mercury drop electrode by differential-pulse voltammetry in 0.008 M Britton-Robinson buffer at pH 2.0 with a ?0.50 V accumulation potential. Its detection limit was found to be 3.6 × 10^?10 M (30-s accumulation) and the relative standard deviation for oxazepam concentrations in the range 2.8 × 10^?8?4.0 × 10^?7 M is lower than 2.8% (80-s accumulation). In addition, a procedure using adsorptive stripping voltammetry was developed to study the interactions occurring between human albumin and the camazepam metabolic series (camazepam, temazepam and oxazepam). The interactions decreased in the order temazepam ? oxazepam ? camazepam and the groups and structural modifications favouring interaction were determined.     

能量选择中子成像技术及其应用

能量选择中子成像技术是利用特定范围波长(能量)的中子进行成像。在热/冷中子范围内(<25meV),能量选择中子成像技术主要基于布拉格边效应和衍射机制,相比常规中子成像技术不但可以显著提高图像对比度,而且能分析应变、应力、织构。在超热中子范围内(>1eV),能量选择中子成像技术主要基于中子共振吸收,中子截面随能量变化是同位素特有的,存在明显的共振吸收峰,因此可以进行同位素的“指纹”识别。能量选择中子成像技术在工程、材料、化学、物理、生物、考古等众多科研领域中有着非常广阔的应用前景。     

原子荧光光谱法测定砷过程中还原反应条件的优化

自然界中砷和砷的化合物一般可通过水、大气和食物等途径进入人体,危害人体健康,原子荧光光谱法测定砷含量被广泛应用。为准确测定样品中砷的含量,以原子荧光光谱法(AFS)测定土壤中总砷含量为例,重点研究高价态砷(Ⅴ)还原为低价态砷(Ⅲ)的实验条件,采用正交实验进行条件优化,建立适合的实验方法。通过设计L9(34)正交实验,高价态砷的还原反应与四个因素有关,即与反应温度、反应时间、盐酸加入量和硫脲的用量呈一定的正相关,结果表明,四个因素中硫脲用量的影响最为显著,其次是盐酸加入量、反应时间和反应温度。通过对四个因素的多水平检验,优化后的实验条件为：硫脲用量2.0 mL、盐酸加入量10%、反应时间20 min、温度20～35 ℃(即普通室温)。采用土壤标准物质验证优化后条件的可行性,得出砷的测定值在标准值范围内,RSD在2.2%～4.2%,精密度和准确性均满足质控要求。优化后的实验条件使得操作简便易行,提高了工作效率。     

基于化学计量学结合ICP-MS的党参道地性的研究及安全评价

微量元素与中药的功效和安全性密切相关,也是药材道地性研究的一部分,为探讨党参中重金属元素的安全性、风险性及道地性的相关性。本文采用电感耦合等离子体质谱法（ICP-MS）及原子荧光光谱法(AFS)测定来源于甘肃、山西、湖北、四川等产区的39批党参药材中的20种元素的含量,结果结合化学计量学分析对党参产区进行差异判别。通过单因子污染指数法和内梅罗综合污染指数法对其进行安全性评价,通过健康风险基于暴露量、危害指数法和暴露限值法对其进行风险评估。结果表明,重金属在各自范围内线性关系良好,加样回收率,仪器精密度和重复性良好,其中 Ba、Sr、Mn的含量最高。主成分分析显示39批药材分为三类,同一产区的党参能较好的聚在一起,元素含量差异与产区分布有一定规律,其中Cs、Ga、As、Co、Li、Pb、Hg、Se、V、Mn为关键的差异标志物,为产地元素特征分析鉴别提供依据。安全评价结果为39批党参药材污染等级为安全,但风险评估后DS-31、DS-32、DS-34、DS-36及 DS-37在人体长期蓄积中具有健康风险。结论：本研究方法高效、准确、简便,结合化学计量学可以对党参进行有效的产地判别,评价党参中元素的安全性及风险性,为党参道地性及健康评价提供了科学依据。     

粉末压片-X荧光光谱法测定过磷酸钙中硫含量

硫是过磷酸钙中重要营养指标之一,为准确快速测定过磷酸钙中硫的含量,试验采用粉末压片-X荧光光谱法,将过磷酸钙试样充分干燥后研磨至粒度小于74 μm,采用硼酸镶边,在压力18 Mpa条件下保压30 s,制成样片。通过在过磷酸钙样品中添加不同质量的纯物质硫酸钙（质量分数范围1.52 %～17.21 %）,经过专用混匀设备混合均匀后,与试样压片相同条件下压制标准样片,作为过磷酸钙中硫的标准样品,建立硫标准曲线,曲线线性相关系数R2为0.9995,采用经验系数法校正干扰,建立了粉末压片-波长色散X射线荧光光谱法测定过磷酸钙中硫含量的方法, 方法检出限为0.002 %。对3个不同硫含量的过磷酸钙样品采用本实验方法重复测量7次,RSD在1.4 %~3.1 %,方法精密度性好,同时用高温燃烧红外光谱法和电感耦合等离子发射光谱法对比,三者测量结果相对极差小于2.0 %,测量结果无显著性差异。此方法不需要对样品进行熔融或溶解,样品制备简单,数据准确度和稳定性好,分析效率高,适合大批量样品中硫的测定。     

锗元素测定方法综述

锗在国防工业、航空航天和通信等领域中的战略性,锗含量的测定对于保证材料质量和满足国际标准至关重要。本文综述了锗含量测定方法的多种技术,包括分光光度法、原子荧光光谱法、原子吸收光谱法、电感耦合等离子体原子发射光谱法、电感耦合等离子体质谱法以及滴定法。在每个检测方法的介绍中,详细探讨了方法的原理、前处理步骤以及应用范围,并分别总结了各个方法的优势和不足。最后,强调了锗含量测定方法的意义,特别是在满足出口监管和促进科学研究方面的作用。同时对锗元素的测定方法进行了展望,为未来的发展提供了参考方向。