Hydrogen bonding and π–π inter­actions in a laminar structure: benzene‐1,3‐dicarboxylic acid–4‐methyl­pyridine (1/2)

The title complex, C₈H₆O₄·2C₆H₇N, consists of two crystallographically independent 1:2 clusters of benzene‐1,3‐­dicarboxylic acid and 4‐methyl­pyridine. Each cluster, the components of which are linked by O—H⋯N hydrogen bonds, is almost planar by alignment of C—H⋯O hydrogen bonds. Herring‐bone ribbons of clusters are formed by other C—H⋯O hydrogen bonds, and these ribbons are further packed to form a laminar structure by π–π inter­actions.     

岩石破裂与渗流耦合过程细观力学模型

从岩石细观非均匀性的特点出发,应用弹性损伤力学、B iot渗流力学理论,对岩石破裂过程渗流-应力-损伤耦合模型进行了描述.算例表明,该模型能较好的模拟出岩石材料在水压和载荷作用下裂纹扩展路径不规则发展及稳态、瞬态渗流过程,裂纹扩展对渗流路径和流动过程起到明显的控制作用.     

利用原子的塞曼光谱对半导体激光器进行稳频

中性原子的超精细能级在磁场中产生塞曼分裂 ,另外 ,左旋和右旋圆偏振光激发下原子的跃迁选择定则不同 ,因此 ,原子在超精细塞曼能级间的吸收谱峰相对无磁场条件下的吸收谱峰有一定的移动。利用这一点 ,验证了一种简单、灵活的方法对半导体激光器进行稳频 ,使激光器的线宽稳到小于 1MHz。通过对实验结果的分析 ,发现由左旋和右旋圆偏振光激发引起的原子吸收谱峰移动之和与饱和吸收峰半高宽相等时 ,稳频效果最好     

基于传递矩阵法的热声发动机频率设计计算

介绍利用传递矩阵法计算热声发动机的工作频率的思路和方法。理论分析表明该方法是切实可行的 ,和其他方法得到了相互的印证。利用该方法的计算结果和已发表的试验结果进行了对比分析。研究结果表明 ,相比已有的计算方法而言 ,传递矩阵法更加简单直观 ,方便于采用计算机编程计算复杂结构的热声系统的工作频率。     

异质膜纳米通道的构建及其应用研究

从生物体离子通道中得到启发,研究人员开发了一系列仿生纳米通道,通过对内外表面的化学修饰,实现了在仿生纳米通道受限空间内离子转运的智能调控.目前的研究主要集中在均质膜方向,均质膜单一的结构和功能限制了其进一步发展,研发制备过程简单、稳定性好和功能多样的异质膜逐渐成为研究热点.与均质膜相比,异质膜被赋予单独使用均质膜时无法...     

Miniaturizing sample spots for matrix-assisted laser desorption/ionization mass spectrometry

The trend of miniaturization in bioanalytical chemistry is shifting from technical development to practical application. In matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), progress in miniaturizing sample spots has been driven by the needs to increase sensitivity and speed, to interface with other analytical microtechnologies, and to develop miniaturized instrumentation.We review recent developments in miniaturizing sample spots for MALDI-MS. We cover both target modification and microdispensing technologies, and we emphasize the benefits with respect to sensitivity, throughput and automation.We hope that this review will encourage further method development and application of miniaturized sample spots for MALDI-MS, so as to expand applications in analytical chemistry, protein science and molecular biology.     

An expeditious and high-yield formal synthesis of hirsutene using Rh(I)-catalyzed [(5+2)+1] cycloaddition

An expeditious and high-yield formal synthesis of hirsutene has been achieved. This synthesis features Rh(I)-catalyzed [(5+2)+1] cycloaddition to construct a bicyclic cyclooctenone, which can be efficiently transformed to bicyclic diketone, an advanced intermediate for racemic and asymmetric syntheses of hirsutene.     

One single standard substance for the determination of multiple anthraquinone derivatives in rhubarb using high-performance liquid chromatography-diode array detection

Due to the complexity of the chemical constitution of traditional Chinese medicines (TCMs), now there is a trend to establish methods, using multi-components analysis, for the effective quality control of TCMs. However, the limited availability of multiple reference substances hinders the wide popularization for routine quality control of TCMs. Using an easily available single component contained in the analyte as an internal standard to determine multiple analogues should be a practical option. In this study, we selected rhubarb rhizome as an example, and used emodin, the easily available active component, as the external standard to determine directly the content of emodin in rhubarb, and the same component as the internal standard to simultaneously determine the other six anthraquinones in rhubarb. Compared with the results obtained using the external standard method, this alternative method was found to have no statistically significant differences in our laboratory as verified by the F-test (p = 95%, n = 6). However, due to weak robustness caused by the fluctuation of relative response factors in different laboratories, such a method can only serve as a practical measure to solve the lack of so many chemical standard substances when relative response factors have been determined. This alternative method can then be used without reference substances. Once the corresponding chemical standards are available and are acceptable as well as cost-effective, then the external standard method for the simultaneous determination of multiple components (SDMC) in TCMs will prevail.