不同前处理分析植物脂肪酸的气相色谱-质谱法研究

采用HCl-甲醇甲酯化、BF3-甲醇甲酯化以及硅烷化三种预处理提取植物中的脂肪酸,并使用气相色谱-质谱(GC-MS)方法进行分离和鉴定,从脂肪酸种类、回收率、甲酯化率、对仪器的影响和操做简易程度几个方面进行了比较。实验结果表明:相同的植物样品,HCl-甲醇甲酯化和BF3-甲醇甲酯化预处理后,GC-MS检测和识别的脂肪酸分别是32种和21种,而硅烷化预处理后只检测到了13种。HCl-甲醇甲酯化回收率大多高于85%,BF3-甲醇甲酯化的回收率高于50%,而十五烷酸的甲酯化率前者为88.20%,后者为81.23%。硅烷化可引起色谱柱固定相流失,影响其寿命,而甲酯化的影响甚微。HCl-甲醇甲酯化比BF3-甲醇甲酯化和硅烷化预处理检测和识别的脂肪酸种类多,操作简单,耗时短,GC-MS是理想的植物脂肪酸提取分析方法。     

外消旋化合物生物催化去对称化研究进展

手性化合物外消旋体的生物催化去对称化是目前生物与有机合成领域的重点、难点和热点,也是制备光学纯手性化合物的重要途径。我们将近年来发展起来的手性化合物生物催化去对称化的方法归纳为立体转化去对称化法、线性去对称化法、循环去对称化法、对映体收敛去对称化法和一步去对称化法五大类,对这五大类方法的原理、特点及其应用进展分别进行介绍并对其未来发展趋势进行展望。     

混合型稀土精矿循环化选工艺研究

针对目前包头混合型50稀土精矿化选工艺反应温度高、能耗大、盐酸利用率低等问题,通过研究稀土精矿的化选过程,设计了多级循环化选实验,考察了酸度、温度和循环级数对精矿中钙和稀土元素溶出情况的影响,确定了适合室温化选和高温化选的温度、 HCl酸度与循环次数,提出了混合型50稀土精矿多级循环化选工艺。该工艺可得到稀土品位大于67%, CaO含量小于1%的化选矿,化选温度可以降低至70℃,节约了能耗与酸耗,同时减少了化选废水的产生。     

高中化学新课程的校本化实施

高中化学新课程的校本化实施是指在遵照高中化学课程标准前提下,学校根据自身性质、特点和条件,将国家层面上规划的高中化学课程转变为适合本校学生学习需要的实践过程。高中化学新课程的校本化实施的外部条件有:国家要完善高中化学课程标准的修订;地方政府和师范院校要加大对高中化学新课程校本化实施的扶持。其内部运作可以从教学目标的校本化、教学内容的校本化、教学方式的校本化、教学评价的校本化等方面入手。     

官能化硅烷及其配位化合物的研究

硅原子具有空的3d轨道,可以作为电子接受体,这样就赋予了有机硅化合物独特的性质。在硅原子上引入官能化基团的小分子化合物称为官能化硅烷。近年来官能化硅烷及其配位化合物引起了化学工作者的重视,在光学、电学、催化等方面得到广泛的应用。按照官能化基团的不同,官能化硅烷可以分为含烯基、炔基、芳环等基团的π型官能化硅烷和含N、O、P、S等杂原子的官能化硅烷两类。本文概括了官能化硅烷合成方法,总结了其配合物的制备途径及研究进展,并对其研究和发展方向进行了展望。     

质子交换膜燃料电池梯度化膜电极

为实现质子交换膜燃料电池的高性能(高功率密度或大电流密度)、低成本(低铂载量)、长寿命发电,人们尝试在燃料电池的核心部件膜电极结构中引入梯度化设计的概念。梯度化膜电极包括膜电极中各组件的梯度化:气体扩散层的PTFE含量与孔隙率的梯度化,催化层的催化剂与Nafion用量的梯度化以及微孔层的疏水性与孔隙率的梯度化。梯度化膜电极中催化剂分布、孔隙率分布、亲/疏水性分布合理,具有良好的三相反应界面以及质子、电子、反应气体、水等多相物质高效传输通道,从而能满足在低铂载量、低加湿以及高电流密度条件下高性能稳定工作。本文整理了近几年来有关燃料电池梯度化膜电极研究的相关文献,梳理了梯度化膜电极研究发展脉络,归纳总结了各种梯度化膜电极的制备方法、性能以及构效关系,并展望了梯度化膜电极下一步研究方向,对高性能、低成本、长寿命的燃料电池开发具有指导意义。     

多元络合物显色反应中的有机溶剂化效应——镓(Ⅲ)-铬天青S-溴化十六烷基三甲铵-含氧有机溶剂体系

本文首次系统研究了醇等含氧有机溶剂对铬天青S(CAS)和多元络合物[Ga(Ⅲ)-CAS-CTAB]显色反应的溶剂化效应。有机溶剂化效应可以大幅度地提高多元络合物显色反应的灵敏度和有效地改善性质相近元素的反应选择性。测定了络合物的组成、溶剂化数、溶剂化常数、表观稳定常数。探讨了有机溶剂化效应的机理。     

基于C—H键官能团化的药物合成

过渡金属催化的C—H键官能团化是有机化学的重要研究内容,并被作为工具广泛应用于药物合成领域。本文阐述了C—H键官能团化的经典反应类型,着重综述了C—H键的芳基化、烯基化、烷基化、卤化、羟基化、胺化和C—H插入反应在药物合成中的应用,详细描述了具体药物的合成实例,并对重要的反应机理进行了分析,最后展望了C—H键官能团化在药物合成中的发展前景。     

超支化环糊精聚合物研究进展北大核心CSCD

超支化环糊精聚合物具备了超支化聚合物和环糊精各自的优点,两者的结合也为超支化环糊精聚合物带来了特殊的物理化学性质,现在已逐渐成为研究热点并在多个领域得到应用。本文简介了超支化聚合物和环糊精的基本特点,详细说明了超支化环糊精聚合物合成制备的方法,并从医药、生物学、新型材料、物化性质调控等方面介绍了超支化环糊精聚合物在近期的科研应用,最后总结了国内外发展情况,并结合现阶段研究,对超支化环糊精聚合物的发展前景进行展望。     

超支化环糊精聚合物研究进展

超支化环糊精聚合物具备了超支化聚合物和环糊精各自的优点,两者的结合也为超支化环糊精聚合物带来了特殊的物理化学性质,现在已逐渐成为研究热点并在多个领域得到应用。本文简介了超支化聚合物和环糊精的基本特点,详细说明了超支化环糊精聚合物合成制备的方法,并从医药、生物学、新型材料、物化性质调控等方面介绍了超支化环糊精聚合物在近期的科研应用,最后总结了国内外发展情况,并结合现阶段研究,对超支化环糊精聚合物的发展前景进行展望。     

Amyloid‐Like Fibrillogenesis through Supramolecular Helix‐Mediated Self‐Assembly of Tetrapeptides Containing Non‐Coded α‐Aminoisobutyric Acid (Aib) and 3‐Aminobenzoic Acid (m‐ABA)

Single‐crystal X‐ray diffraction studies of two terminally protected tetrapeptides Boc‐Ile‐Aib‐Val‐m‐ABA‐OMe ( I ) and Boc‐Ile‐Aib‐Phe‐m‐ABA‐OMe ( II ) (Aib=α‐aminoisobutyric acid; m‐ABA=meta‐aminobenzoic acid) reveal that they form continuous H‐bonded helices through the association of double‐bend (type III and I) building blocks. NMR Studies support the existence of the double‐bend (type III and I) structures of the peptides in solution also. Field emission scanning electron‐microscopic (FE‐SEM) and high‐resolution transmission electron‐microscopic (HR‐TEM) images of the peptides exhibit amyloid‐like fibrils in the solid state. The Congo red‐stained fibrils of peptide I and II , observed between crossed polarizers, show green‐gold birefringence, a characteristic of amyloid fibrils.     

Selective preparation of poly(p‐oxybenzoyl) by using fractional polycondensation

Selective preparation of poly(p‐oxybenzoyl) (POB) in the copolymerization system of p‐acetoxybenzoic acid (p‐ABA) and m‐acetoxybenzoic acid (m‐ABA) was examined by using reaction‐induced crystallization of oligomers. Polymer crystals mainly composed of p‐oxybenzoyl moiety were precipitated when the content of m‐ABA in the feed was 30 mol %. The formation of the polymer crystals was attributed to both the reactivity of monomer and the phase‐separation behavior of oligomer. Reactivity of p‐ABA was twice higher than that of m‐ABA, and thereby, the homo‐oligomers of p‐oxybenzoyl moiety were more rapidly formed in solution than do co‐oligomers at the early stage in polymerization. They were selectively precipitated by crystallization to form crystals because of low miscibility. Co‐oligomers containing m‐oxybenzoyl moiety were also formed in solution, but they were unable to be phase‐separated because of higher miscibility. Further polycondensation occurred between oligomers in the precipitated crystals, leading to the formation of POB. This polymerization proceeded with selecting certain monomers by crystallization and afforded a new methodology for fractional polycondensation. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2732–2743, 2006     

Dimer effect on fractional polycondensation of poly(p‐oxybenzoyl)

Selective preparation of poly(p‐oxybenzoyl) (POB) crystals was examined from the viewpoint of a dimer effect on fractional polycondensation. Four different copolymerization systems were chosen as the combinations of p‐acetoxybenzoic acid (p‐ABA), m‐acetoxybenzoic acid (m‐ABA), and their dimers. The crystals obtained from the copolymerization of the dimer of p‐ABA (p‐ABAD) and m‐ABA contained only 3.1 mol % of m‐oxybenzoyl moiety even at high content of m‐oxybenzoyl moiety in feed (χ_f) of 40 mol %. p‐Oxybenzoyl homo‐oligomers were more rapidly formed from p‐ABAD in the solution than from p‐ABA, and they were crystallized to form the crystals with segregating co‐oligomers. While co‐oligomers containing more m‐oxybenzoyl moiety were formed in the solution, afterward they were unable to be phase‐separated because of higher miscibility. The further polycondensation proceeded in the precipitated crystal, and finally the POB crystal was selectively formed. Lower polymerization temperature and concentration enhanced the fractionability, and the POB crystals containing less than 1 mol % m‐oxybenzoyl moiety were prepared at χ_f of 30 mol %, 270 °C, and a concentration of 0.5%. The dimer effect on the fractional polycondensation was clearly observed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1598–1606, 2008     

Synthesis of functional polyethylene graft copolymers by nitroxide‐mediated living radical polymerization

This paper describes a new method to prepare graft copolymers, such as polyethylene‐g‐polystyrene (PE‐g‐PS), with a relatively well‐controlled reaction mechanism. The chemistry involves a transformation process from the metallocene copolymerization of ethylene and m,p‐methylstyrene (m,p‐MS) to nitroxide‐mediated “living” free radical polymerization (LRFP) of styrene. The metallocene catalysis produces ethylene‐co‐m,p‐methylstyrene (EMS) random copolymers. Next, 1‐hydroxyl‐2,2,6,6‐tetramethylpiperidine (HO‐TEMPO) was synthesized by the reduction of TEMPO with sodium ascorbate. The macroinitiator (EMS‐TEMPO) was synthesized with the bromination reaction of EMS, and the following nucleofilic reaction with this functional nitroxyl compound. The resulting macroinitiator (EMS‐TEMPO) for LRFP was then heated in the presence of styrene to form graft copolymer. DSC, ¹H‐NMR, FTIR spectroscopy were employed to investigate the structure of the polymers. The results of Molau test showed that PE‐g‐PS could be a potential good compatilizer. Copyright © 2008 John Wiley & Sons, Ltd.     

Selective synthesis of poly(p‐oxybenzoyl) by fractional polycondensation: Enhancement of selectivity by shearing

The influence of shear flow, especially the timing for the application of shearing, was examined to enhance the selectivity for the preparation of poly(p‐oxybenzoyl) (Pp‐OB) by using hydrodynamically induced phase separation during polymerization of 4‐(4‐acetoxybenzoyloxy)benzoic acid (p‐ABAD) and m‐acetoxybenzoic acid (m‐ABA). The polymers containing few m‐oxybenzoyl (m‐OB) moieties were obtained as precipitates even at high content of m‐OB moiety in feed (χ_f) under shear flow. The content of m‐OB moiety in the precipitates (χ_p) prepared under shearing throughout the polymerization at the shear rate (γ) of 489 s^?1 was 6.3 mol % even at χ_f of 60 mol %. Especially, the Pp‐OB was obtained as the precipitates at χ_f of less than 50 mol %. The timing of the application of the shearing influenced the selectivity significantly, and the shearing just after the precipitation of the oligomers started was quite efficient to enhance the selectivity more. The χ_p of the precipitates prepared with shearing at γ of 489 s^?1 just after the precipitation was only 3.9 mol % even at χ_f of 60 mol %. The shear flow reduced the difference in the reactivity between p‐ABAD and m‐ABA, resulting in the decrease in the selectivity with regard to the formation of p‐oxybenzoyl homo‐oligomer. However, the shear flow enhanced the difference in the miscibility between homo‐oligomers and co‐oligomers. This change in the miscibility by shear flow brought about the more rapid precipitation of homo‐oligomers, leading to the enhancement of the selectivity. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Characterization of xylazine metabolism in rat liver microsomes using liquid chromatography–hybrid triple quadrupole–linear ion trap–mass spectrometry

ABSTRACT: Xylazine is an α₂‐adrenoceptor agonist and it is widely used in veterinary anesthesia in combination with ketamine. There is limited information on the metabolism of xylazine. A quantitative method for the determination of xylazine by HPLC‐ESI/MS/MS was developed. The method consisted of a protein precipitation extraction followed by analysis using liquid chromatography electrospray tandem mass spectrometry. The chromatographic separation was achieved using a Thermo Betasil Phenyl 100 × 2 mm column combined with an isocratic mobile phase composed of acetonitrile, methanol, water and formic acid (60:20:20:0.4) at a flow rate of 300 μL/min. The mass spectrometer was operating in selected reaction monitoring mode and the analytical range was set at 0.05–50 μm . The precision (%CV) and accuracy (%NOM) observed were 2.3–7.2 and 88.2–96.4%. In vitro metabolism studies were performed in rat liver microsomes and results showed moderate cytochrome P450 affinity (K_m = 10.1 μm ) and a low metabolic stability of xylazine with a half‐life of 4.1 min in rat liver microsomes. Five phase 1 metabolites were observed. The main metabolite observed was an oxidation of the thiazine moiety at m/z 235 and, to a lesser extent, we observed the formation of N‐(2,6‐dimethylphenyl)thiourea at m/z 181 and three distinctive hydroxylated metabolites at m/z 237. Further experiments with ketamine and ketoconazole strongly supported that the metabolism of xylazine to its main metabolite is mediated by CYP3A in rat liver microsomes. Copyright © 2013 John Wiley & Sons, Ltd.     

Influence of monofunctional reactants on the physical properties of dimer acid‐based polyamides

Dimer acid‐based polyamides were synthesized by condensation polymerization in the absence and presence of monofunctional reactants. Acetic acid, oleic acid and propyl amine were used as monofunctional reactants. The influences of the equivalent percentage (E%) and type of monofunctional reactant on the physical properties of dimer acid‐based polyamides such as glass transition temperature (T_g), melting point (T_m), heat of fusion (ΔH), degree of polymerization (DP), number average molecular weight (M_n), and kinematic viscosity were investigated. The molecular weight and viscosity of dimer acid‐based polyamides decreased with the increase in equivalent percentage of monofunctional reactant. Differential scanning calorimetry (DSC) studies showed that acetic acid and propyl amine had higher effect on the thermal properties of polyamides than that of oleic acid. In the case of polyamides prepared in the presence of acetic acid, the values of T_g, T_m, and ΔH of the polyamides increased remarkably with the increase in acetic acid content. On the contrary, propyl amine had a decreasing effect on the values of T_g, T_m, and ΔH of the polyamides. Incorporation of oleic acid into the polymer structure had no significant effect on the values of T_g and T_m of the dimer acid‐based polyamides. Copyright © 2006 John Wiley & Sons, Ltd.     

A Convenient Synthesis of the Echinacea‐Derived Immunostimulator and HIV‐1 Integrase Inhibitor (−)‐(2R,3R)‐Chicoric Acid

The Echinacea‐derived immunostimulator and HIV‐1 integrase inhibitor (−)‐chicoric acid (=2,3‐bis{[3‐(3,4‐dihydroxyphenyl)‐1‐oxoprop‐2‐enyl]oxy}butanedioic acid; 1a ) was conveniently prepared via a silane‐promoted Pd‐mediated chemoselective hydrogenolysis of its perbenzylated derivative 12a , which was generated from an efficient and reliable carbodiimide‐mediated coupling reaction between the caffeic acid dibenzyl ether derivative 7 and commercially available (+)‐dibenzyl L ‐tartrate ( 9a ). The other naturally occurring dextrorotatory chicoric acid ( 1b ) can be similarly prepared.     

How does a CC double bond cleave in the gas phase? Fragmentation of protonated ketotifen in mass spectrometry

In the literature, it is reported that the protonated ketotifen mainly undergoes C?C double bond cleavage in electrospray ionization tandem mass spectrometry (ESI‐MS/MS); however, there is no explanation on the mechanism of this fragmentation reaction. Therefore, we carried out a combined experimental and theoretical study on this interesting fragmentation reaction. The fragmentation of protonated ketotifen (m/z 310) always generated a dominant fragment ion at m/z 96 in different electrospray ionization mass spectrometers (ion trap, triple quadrupole and linear trap quadrupole (LTQ)‐orbitrap). The mechanism of the generation of this product ion (m/z 96) through the C?C double bond cleavage was proposed to be a sequential hydrogen migration process (including proton transfer, continuous two‐step 1,2‐hydride transfer and ion‐neutral complex‐mediated hydride transfer). This mechanism was supported by density functional theory (DFT) calculations and a deuterium labeling experiment. DFT calculations also showed that the formation of the product ion m/z 96 was most favorable in terms of energy. This study provides a reasonable explanation for the fragmentation of protonated ketotifen in ESI‐MS/MS, and the fragmentation mechanism is suitable to explain other C?C double bond cleavage reactions in mass spectrometry. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis of hetero‐telechelic polymers by self‐polyaddition of monomers containing both oxetanyl and carboxyl groups

The synthesis and self‐polyaddition of new monomers, o‐, m‐, and p‐[(3‐ethyloxetane‐3‐yl)methoxyethyl]benzoic acid (o‐EOMB, m‐EOMB, and p‐EOMB) containing both oxetanyl groups and carboxyl groups were examined. The reactions of o‐EOMB, m‐EOMB, and p‐EOMB in the presence of tetraphenylphosphonium bromide as a catalyst in o‐dichlorobenzene at 150–170 °C resulted in self‐polyaddition to give the corresponding hetero‐telechelic polymers poly(o‐EOMB), poly(m‐EOMB), and poly(p‐EOMB) with M_ns = 14,500–33,400 in satisfactory yields. The M_n of poly(o‐EOMB) decreased at higher reaction temperatures than 150 °C, unlike those of poly(m‐EOMB) and poly(p‐EOMB), possibly due to inter‐ or intraester exchange side reactions. It was also found that the thermal properties and solubilities of these polymers were supposed with the proposed structures. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7835–7842, 2008