顺反异构化过程及其机理

总结了分子中存在的顺反异构化过程及其机理,包括光致异构化、热致异构化和催化异构化。     

Development of general nuclear resonance fluorescence model

A model to simulate nuclear resonance fluorescence (NRF) reactions of various nuclear species and their various excitation levels was developed. There is a strong need for the simulation of NRF applications using general purpose radiation transport codes; however, NRF reaction cross section data are available only for a few excited states for certain nuclear species. In this study, based on the generalized gamma de-excitation model, an NRF model that can simulate NRF reactions associated with all the levels included in the nuclear structure database was developed. Absorption cross sections calculated by the developed NRF model agree with the experimental data typically within one order of magnitude. To illustrate that this model can be used for simulation studies on NRF applications, the demonstration of the developed NRF model for non-destructive nuclear material assay and isomer production is shown.     

重复结构单元含2个C＊的高分子的旋光异构体数目问题

在＂高分子物理＂课程中,关于高分子的构型异构的问题是核心教学内容之一,其中的＂旋光异构＂部分是一个学习和教学的难点。笔者尝试从＂构型基本单元＂和＂构型重复单元＂的概念出发来讲解高分子的旋光异构现象,从而,重复结构单元含1个手性碳原子（C＊）的高分子的旋光异构体数目问题得到了很好的理解。然而,当用这样的思路来分析重复结构...     

Beyond 16 Priority Pollutant PAHs: A Review of PACs used in Environmental Forensic Chemistry

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in soils and sediments, particularly in urbanized environments in which the concentrations of 16 (or so) PAHs are regulated. Distinguishing among the numerous PAH sources is of practical and legal concern and thereby is often an objective of environmental forensic chemistry studies. Studies of prospective sources and impacted soils and sediments that rely upon the 16 U.S. EPA Priority Pollutant PAHs are disadvantaged, as these few compounds generally lack the specificity to distinguish among different PAH sources in the environment. Advances in analytical and interpretive methods over several decades have shown that different PAH sources can be more defensibly distinguished using modified EPA Method 8270 that, among other improvements, measure many other polycyclic aromatic compounds (PACs) that co-occur with the Priority Pollutant PAHs in different sources and in the environment. The PACs include variously-alkylated PAHs and polycyclic aromatic sulfur heterocyclics (PASHs) homologs and individual isomers, which are herein reviewed. Collectively, these PACs provide a higher degree of specificity among PAC sources and can be used to understand the effects of weathering on PAH assemblages. Despite their diagnostic capacity, PACs should not be relied upon at the exclusion of other compound groups (e.g., petroleum biomarkers) in most environmental forensic chemistry studies. In light of these advances, source characterization studies that rely only upon the 16 (or so) Priority Pollutant PAHs warrant considerable caution.     

载气类型对气相色谱法分离顺-反脂肪酸异构体的影响

采用气相色谱-火焰离子化检测器,CP-Sil88毛细管柱为分析柱,考察在不同载气（氦气和氮气）和不同加热温度（等温180 ℃和梯度升温）条件下对不同食品基质中C18:1、C18:2和C18:3顺-反脂肪酸异构体分离度和定量的影响。结果显示,以氦气为载气,在起酥油、黄油、饼干和蛋糕4 种食品基质中,C18:1 13t,14t(6-8c)和C18:1 9c的分离度大于1.0,可清晰分辨并准确定量不同浓度C18:1的4t～13t,14t异构体,不会低估C18:1反式脂肪酸异构体总量。在植物油中,载气类型对C18:2顺反异构体的分离度和含量无影响;相比氮气,氦气在C18:3顺反异构体分离上具有一定优越性,但总量无显著差异。氦气作为同时测定食品中的反式脂肪酸、饱和脂肪酸、单不饱和脂肪酸和多不饱和脂肪酸的载气,定量准确且样品适用性广。     

粘质沙雷氏菌马来酸顺反异构酶表达纯化及酶学性质

从粘质沙雷氏菌(Serratia marcescens)中扩增得到马来酸顺反异构酶基因。将该基因连接到p ET24a载体上,并在Escherichia coli BL21(DE3)中实现了成功表达。酶学性质研究表明,重组酶的比酶活力为48.01 U/mg。其最适温度为37℃,最适p H为8.4。在最适反应条件下,Km值为4.20 mmol/L,Vmax为1.27 mmol/(L·min),kcat为4.38 s-1,催化效率kcat/Km为1.04 L/(mmol·s)。研究结果进一步显示,马来酸顺反异构酶具备良好的热稳定性(55℃半衰期为1.5 h)及高达99%以上的转化率,为马来酸顺反异构酶的进一步研究和工业应用制备高纯度的富马酸提供了理论基础和支持。     

纽曼式、透视式、楔型式与Fischer投影式的互换

在遵循R/S的最基本判断法则上,通过举例分析,对纽曼投影式、透视式、楔型式与Fischer投影式之间的相互转换,总结出了一套简便有效的经验方法。     

Separation and characterization of cis-trans isomers of α-tocotrienol by HPLC using a permethylated β-cyclodextrin phase

 The behaviour of α-, β-, γ- and δ-tocotrienols (structurally related to tocopherols with naturally trans-configurated double bonds in the side-chain) during HPLC on a permethylated β-cyclodextrin phase was studied. A newly developed isocratic HPLC method is described with an acetonitrile/water (58:42 by vol.) eluent and fluorescence detection at an emission wavelength of 330 nm (excitation wavelength = 295 nm). Each of the separately injected tocotrienols exhibited four peaks. The four separated components of α-tocotrienol were identified by spectroscopy (MS, ¹H-NMR, FTIR) to be structural side-chain isomers. The order of retention times was determined to be all-cis-α-tocotrienol followed by cis-trans-/trans-cis-α-tocotrienol (differentiation between the two compounds was not possible) with all-trans-α-tocotrienol as the last eluting isomer. Received: 27 June 1997     

C8芳烃异构体吸附分离工艺参数的测定与分析

研究了甲苯和C₈芳烃异构体在KBaX吸附剂、NaY吸附剂上的吸附性能,采用静态吸附平衡试验测定C₈芳烃异构体在吸附剂上吸附平衡参数,包括吸附剂对各芳烃组分的饱和吸附量与相对选择性系数,分析了饱和吸附量和相对选择性系数随温度和组分组成的变化;同时,采用动态穿透试验测定各组分的穿透曲线,借助Aspen软件拟合穿透试验数据,计算得到传质系数;进而,通过脉冲试验验证获得吸附过程性能参数的准确性,结果表明试验测定的吸附性能参数与模拟拟合结果吻合,说明试验测定的吸附性能参数可靠性良好。