Electron excitation of the Schumann-Runge continuum, longest band, and second band electronic states in O2

We report measurements of differential and integral cross sections for electron excitation of the Schumann-Runge continuum, longest band, and second band electronic states in molecular oxygen. The energy range of the present study is 15-200 eV, with the angular range of the differential cross section (DCS) measurements from 2 to 130°. A generalized oscillator strength analysis is then employed in order to derive integral cross sections (ICSs) from the corresponding DCSs, and these ICSs are compared with relevant energy and oscillator strength scaled Born cross section (BEf-scaling [Y.-K. Kim, J. Chem. Phys. 126, 064305 (2007)]) results determined as a part of this investigation. Interestingly, while the present Schumann-Runge continuum and second band ICSs were in reasonable agreement with the respective BEf-scaling results, agreement for the longest band was poor below 100 eV with a possible reason for this apparently anomalous behavior being canvassed here. Finally, where possible all present data are compared with the results from earlier measurements and calculations with the level of agreement found being very good in some cases and marginal in others.     

Collapse transition of a square-lattice polymer with next nearest-neighbor interaction

We study the collapse transition of a polymer on a square lattice with both nearest-neighbor and next nearest-neighbor interactions, by calculating the exact partition function zeros up to chain length 36. The transition behavior is much more pronounced than that of the model with nearest-neighbor interactions only. The crossover exponent and the transition temperature are estimated from the scaling behavior of the first zeros with increasing chain length. The results suggest that the model is of the same universality class as the usual θ point described by the model with only nearest-neighbor interaction.     

Binding structures of propylene glycol stereoisomers on the Si(001)-2×1 surface: a combined scanning tunneling microscopy and theoretical study

The binding configuration of propylene glycol stereoisomer molecules adsorbed on the Si(001)-2×1 surface was investigated using a combination of scanning tunneling microscopy (STM) and density functional theory calculations. Propylene glycol was found to adsorb dissociatively via two hydroxyl groups exclusively as a bridge between the ends of two adjacent dimers along the dimer row. The chirality was preserved during bonding to Si atoms and was identifiable with STM imaging. The large number of propylene glycol conformers in the gas phase was reduced to a single configuration adsorbed on the surface at low molecular coverage.     

Quantification of human growth hormone by amino acid composition analysis using isotope dilution liquid-chromatography tandem mass spectrometry

We describe an accurate method for protein quantification based on conventional acid hydrolysis and an isotope dilution-HPLC-mass spectrometry (ID-HPLC-MS) method. Sample purity was confirmed using capillary zone electrophoresis, HPLC and MS. The analyte protein, human growth hormone (hGH), was effectively hydrolyzed by incubation with 8 M hydrochloric acid at 130 °C for 48 h, where at least 1 μM of hGH was treated to avoid possible degradation of released amino acids during hydrolysis. Using a reversed-phase column, the analytes (isoleucine, phenylalanine, proline and valine) were separated within 5 min using an isocratic eluent comprising 10% acetonitrile containing 0.1% trifluoroacetic acid. The detection limit (signal to noise ratio of 3) of amino acids was 5.5-6.2 fmol per injection. The quantification precision (RSD) of amino acids for intra- and inter-day assays was less than 0.98% and 0.39%, respectively. Comparison with other biochemical and instrumental methods revealed substantially higher accuracy and reproducibility of the ID-HPLC-MS/MS method as expected. The optimized hydrolysis and analytical conditions in our study were suitable for accurate quantification of hGH.     

基于粗粒化模型对有机溶剂的分子动力学模拟

在基于Boltzmann分布对四种基本构象进行Monte Carlo取样后, 通过与全原子模型的范德华势比较得到了Gay-Berne (GB)参数. 又在对用量化计算得到的分子体系的电势进行电荷、偶极矩和四极矩的拟合后, 得到了电多极展开势(EMP)参数. 利用得到的粗粒化参数, 基于粗粒化模型, 对CHCl₃及四氢呋喃(THF)两种有机溶剂进行了分子动力学模拟(MDS), 并将结果同全原子模拟进行了比较. 计算结果表明用粗粒化模型从整体上能重复全原子模型的模拟结果, 但在某些细节的计算与全原子模型有偏差, 其原因可能是目前工作仅考虑了单位点情况, 为此今后在对具有复杂结构的分子进行粗粒化模拟时还应考虑合理放置及增加相互作用位点.     

Iron-catalyzed bromination of aryl azides by N-bromosuccinimide:Efficient method for the synthesis of brominated aryl azides

An efficient and mild protocol for bromination of aryl azides with N-bromosuccinimide（NBS） under FeCl₃ catalysis in 1,2- dichloroethane was developed.It is proved to be an efficient method for obtaining brominated aryl azides.     

核壳结构型阻燃剂研究进展

通过微胶囊化技术可赋予阻燃剂以特殊的核壳结构,从而有效减小阻燃剂吸湿性,增加与基体相容性,明显提高阻燃高分子复合材料力学、耐水、阻燃等性能.本文扼要论述了核壳结构型卤系、氢氧化镁、红磷、无机磷系、有机磷系以及膨胀阻燃体系的研究现状,并阐述了该特殊阻燃剂的研究重点与发展趋势.     

不对称姜黄素类似物的合成及其清除自由基的研究

姜黄素类化合物中,非对称结构的单去甲氧基姜黄素具有一些特殊的生物活性.通过碱法合成2-单取代苯亚甲基环戊酮中间体,再用酸催化合成了10不对称的单羰基姜黄素类似物,多酚羟基的类似物可以不通过羟基保护直接合成,其中,除A1外其它9个为新化合物,并测试了所合成类似物对DPPH自由基的清除能力.结果表明类似物的酚羟基对自由基清...     

高效液相色谱法同时检测蜂蜜中的5类抗生素残留

建立了蜂蜜中氯霉素类、硝基咪唑类、喹诺酮类、磺胺类、四环素类5类共15种抗生素残留同时检测的高效液相色谱分析方法.蜂蜜经pH 2.0的磷酸水溶液溶解后直接用PCX固相萃取小柱净化富集,以乙腈-磷酸溶液(pH 2.5)作流动相,梯度洗脱,紫外检测器在274、315 nm波长下进行检测.15种抗生素在0.2 ～20.0 m...     

玄参、生地黄、紫草等六种中药中微量元素含量的测定

为了解中药中微量元素的含量与其药物的作用机制关系,用原子吸收分光光度计测定了玄参、生地黄、紫草、水牛角、牡丹皮、赤芍中铁(Fe)、镁(Mg)、铜(Cu)、钙(Ca)、锌(Zn)、铬(Cr)、钼(Mo)等7种微量元素的含量.结果表明,Ca的含量最高,Cu的含量几乎最低.这6种中草药含有多种对人体有益的微量元素,与它们的药...