Calculation of the proton affinities of polyfluorobenzenes and the activation energies for 1,2-hydrogen shifts in their carbocations

Isolated polyfluorobenzene (PFB) molecules and their protonated forms are investigated by the AM1 method with full geometry optimization. The proton affinities of PFB are estimated for different protonated positions. The proton affinity of PFB averaged over all isomers is shown to decrease monotonically as the number of fluorine atoms in the molecule increases. The relative populations of different isomers of arenonium ions (AI) formed by PFB protonation are determined. From the calculated data, the value of ⁺ for the F atom in theipso-position is estimated as 1.00. The activation energies of the 1,2-hydrogen shifts in AI are calculated. The dependences of the proton affinity and the activation energies of 1,2-hydrogen shifts on the number of halogen atoms are found to have distinct characters for PFB and polychlorobenzenes. The physical reasons for these difference are discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1878–1882, November, 1993.     

聚酰亚胺/二氧化硅纳米尺度复合材料的研究

通过正硅酸乙酯（ＴＥＯＳ）在聚酰胺酸（ＰＡＡ）的Ｎ，Ｎ’ 二甲基乙酰胺（ＤＭＡｃ），溶液中进行溶胶 凝胶反应，制备出不同二氧化硅含量的聚酰亚胺／二氧化硅（ＰＩ／ＳｉＯ２）复合薄膜材料．二氧化硅含量低于１０ｗｔ％的样品是透明浅黄色薄膜；二氧化硅含量高于１０ｗｔ％的样品是不透明棕黄色薄膜．利用红外光谱、扫描电镜、热失重分析、动态力学分析、热膨胀系数测试和应力 应变测试等方法研究了此类材料的结构与性能．结果表明，ＰＩ／ＳｉＯ２纳米复合材料具有较聚酰亚胺更高的热稳定性和更高的模量；线膨胀系数显著降低；拉伸强度和断裂伸长随二氧化硅含量而变化，分别在１０ｗｔ％和３０ｗｔ％附近出现最大值     

Hydrolysis rates of alkyl and aryl sulfinamides: evidence of general acid catalysis

Sulfinamides are important in enantioselective synthesis, as rare post-translational modifications of proteins and as isosteres of the amide bond. Little is known about the rates of hydrolysis for aliphatic sulfinamides or the mechanism of hydrolysis. In this Letter, we show that sulfinamides hydrolyse by predominantly a non-specific acid/base catalysis with phosphate buffer but by varying the buffer concentration, it was possible to determine the hydrolysis rates of a range of sulfinamides with water through non-linear least squares regression.     

Aromatic H／D Exchange Reaction Catalyzed by Groups 5 and 6 Metal Chlorides

Groups 5 and 6 metal chlorides such as MoCl5, WCI6, NbCl5 and TaCl5 were found to be simple and very efficientcatalysts for the aromatic H/D exchange reactions. Compared with other metal chlorides such as ZnCl2, SnCl4 and TiCl4, groups 5 and 6 metal chlorides showed better catalytic activity in the H/D exchange reaction of naphthalene with C6D6. Deuteration of anthracene using MoC15 as a catalyst proceeded within 24 h at room temperature. Other aromatic compounds such as toluene, diphenylmethane and 1,1,2-triphenylethane were also deuterated smoothly in C6D6 within 24 h at room temperature.     

Nitrofuran antibiotic residues in pork: The FoodBRAND retail survey

Use of nitrofuran drugs in food-producing animals has been prohibited within the EU because they may represent a public health risk. Monitoring compliance with the ban has focused on the detection of protein-bound nitrofuran metabolites which, in contrast to the parent compounds, are stable and persist in animal tissues. As part of the “FoodBRAND” project, an extensive survey of pork was undertaken across 15 European countries. Samples (n = 1500) purchased at retail outlets were analysed for the nitrofuran metabolites AOZ, AMOZ, AHD and SEM using LC–MS/MS determination of nitrobenzaldehyde derivatives. Limits of quantification for the method were 0.1 μg/kg (AOZ, AMOZ), 0.2 μg/kg (SEM) and 0.5 μg/kg (AHD). Of the 1500 samples tested, measurable residues of nitrofuran metabolites were confirmed in 12 samples (0.8% incidence overall) of which 10 samples were purchased in Portugal (AOZ, 0.3 μg/kg; AMOZ, 0.2–0.6 μg/kg) and one sample each in Italy (AMOZ, 1.0 μg/kg) and Greece (AOZ, 3.0 μg/kg).     

用选择离子流动管质谱测定汽油和柴油蒸汽成分

采用选择离子流动管质谱(SIFT／MS)装置，以H30^ 、N0^ 为初始离子对汽油和柴油蒸汽进行了研究，质谱分析表明，汽油和柴油主要由C—H化合物组成，包括烷烃、环烷烃、烯烃、炔烃、二烯烃以及芳香烃。在这几种成分中，烷烃都占有最大的比例；汽油蒸汽和柴油蒸汽最大的区别是柴油蒸汽中长链大分子的挥发性C—H化合物所占的比例远远高于汽油蒸汽。文中还给出了以H30^ 、N0^ 为初始离子所得到的汽油蒸汽的质谱图，以及汽油、柴油蒸汽中各种成分的定量分析结果。     

微型柱在线分离-ICP-MS法测定高纯氧化铕中的14个稀土杂质

研究了微型柱在线分离-电感耦合等离子质谱法（ICP-MS）测定高纯Eu2O3中痕量Tm的方法，研制了Cyanex272负载树脂微型分离柱，优化了分离Eu2O3基体的实验条件，在线分离测定时间为25min。建立了在线柱分离测定Tm，内标补偿法直接测定其余稀土杂质的高纯Eu2O3中14个稀土杂质的ICP-MS分析方法。方法检出限为0.01μg/g-0.15μg/g，加标回收率为91.5%-110%,相对标准偏差为1.7%-4.9%。可满足快速测定99.999%Eu2O3中14个稀土杂质的要求。     

Electrical interaction between two cylinders with an ion-penetrable charged membrane in an oil/water interface

The electrical interaction between two long, parallel cylinders each is covered by an ion-penetrable charged membrane immersed in an oil/water interface is investigated. The effects of contact angle, radius of cylinder, and membrane thickness on the electrical interaction force are examined. The results of numerical simulation reveal that the following conditions lead to a greater electrical interaction force: (i) a larger contact angle, i.e. a larger fraction of a cylinder in the oil phase; (ii) a larger cylinder radius; and (iii) a thinner membrane. For a fixed ionic strength, the electrical interaction force is insensible to the type of electrolytes in the water phase, in general. However, if two cylinders are close enough, then the higher the valence of counterions the greater the electrical interaction force.     

Chiral separation of β-amino alcohols by capillary electrophoresis using cyclodextrins as buffer additives. I. Effect of varying operating parameters

Summary Capillary electrophoresis has been used for the chiral analysis of two -amino alcohol pharmaceutical compounds. Capillary zone electrophoresis conditions were used with -cyclodextrin as a chiral mobile phase additive. The effects of variation of -cyclodextrin concentration, temperature, pH, background electrolyte composition and concentration have been investigated. Optimum separations were achieved for clenbuterol using -cyclodextrin at its solubility limit (16mM), the lowest practicable temperature (19°C), pH 4.0 and an electrolyte solution with a high ionic strength prepared from 0.1 M citric acid and 0.3 M Na₂HPO₄. For the development compound picumeterol and its (S)-enationmer, the optimum pH 4.0 buffer was prepared from 0.1 M citric acid and 0.2 M sodium acetate. Baseline separation with resolution greater than 2 was achieved for both compounds.This work was presented in part at the 2nd International Symposium on Chiral Discrimination, Rome, May 27–31, 1991.     

Simultaneous determination of tetrahydro-β-carbolines and β-carbolines

Summary Reversed-phase ion-pair HPLC with fluorimetric detectors connected in series was studied for the simultaneous determination of two tetrahydro--carbolines and two -carbolines. After additon of internal standards the samples were reacted with fluorescamine, and then subjected to serial extractions to remove their precursor (tryptamine) from the analytical system. This treatment not only suppressed the artefactual formation of tetrahydro--carbolines and -carbolines during analysis, but also effectively purified them. Under optimum conditions, using trifluoroacetic acid as counter ion, all analytes were separated within 14 min and without major interfering peaks. The quantitative ranges were 0.25–80.0 ng mL^–1 for both tetrahydro--carbolines and 0.1–30.0 ng mL^–1 for both -carbolines. Replicate spiking experiments showed that recovery from most of the samples tested was over 90% and the relative standard deviation ranged from 0.7 to 10.4% within and between assays. The proposed method was applicable to various materials such as soy sauce, vinegar, ketchup, tabasco, beer, wine, sake, whisky, brandy, cows' milk, coffee, cocoa, cheese, cigarette smoke and urine.