顶空固相微萃取-气相色谱-质谱法测定废水中痕量挥发性烷基硫化物

建立了顶空固相微萃取(HS-SPME)和气相色谱/质谱(GC/MS)联用测定人工湿地废水中的痕量挥发性烷基硫化物的方法。针对废水中两种主要的挥发性烷基硫化物(二甲基硫、二甲基二硫),详细研究了萃取纤维头的种类、萃取时间、萃取温度、pH值、离子强度、样品量及解析条件对HS-SPME的影响。载气为高纯氦气,流速为1.0mL/min,色谱柱为DB-5ms毛细管柱(0.25μm,30m×0.32mm),柱温:25℃(5min)■40℃(1min)■60℃(5min);在优化的实验条件下,本法测定二甲基硫及二甲基二硫的线性范围分别为10～10000ng/L和1～10000ng/L;检出限(3σ)分别为1.9ng/L和1.8ng/L;相对标准偏差小于10%;回收率分别为81.0%～94.6%和84.0%～100.9%。用二乙基硫为内标物质,将本法用于人工湿地废水中主要的烷基硫化物二甲基硫和二甲基二硫的测定,获得满意结果。     

A comparative study of various computational approaches in calculating the structure of pyridoxal 5'-phosphate (PLP)-dependent beta-lyase protein. The importance of protein environment

Various computational approaches, using molecular mechanics (Amber), semiempirical (AM1), density functional (B3LYP), and various ONIOM methods, have been comparatively investigated for the structure of Escherichia coli NifS CsdB protein. The structure of the entire monomer containing 407 amino acid residues and 579 surrounding water molecules has been optimized. The full geometry optimization in the "active site-only" approach (including only active site atoms) has been found to give the largest root-mean-square (RMS) deviation from the X-ray structure; a much better agreement has been achieved by keeping the atoms leading to the backbones of some amino acids frozen in their positions in the X-ray structure. The best agreement has been attained by including the surrounding protein in the calculations using the two-layer ONIOM (B3LYP:Amber) approach. The results presented in this study conclusively demonstrate the importance of the protein/active-site interaction on the active-site structure of the enzyme. The present theoretical study represents the largest system studied at the ONIOM level to date, containing 7992 atoms, including 84 atoms in the QM region and rest in the MM region.     

杂富勒烯的电子结构与性质关系的研究──Ⅱ.C_(57)X_3,C_(56)X_4(X=B、N、P)的位置异构体

用 CNDO／2方法在 586微机上计算了 C57X3C56X4（X=B、N、P）的 234个位置异构体的电子结构。在C57X3（X=B、N、P）位置异构体中，C57X3（1，2，9）（X=B、N、P）分别是最稳定的。对于C56X4（X=B、N、P）位置异构体，C56B4（1，2，9，8），C56N4（1，2，9，12）和C56P4（1，2，9，12）分别是最稳定的，但稳定性都比C60差。其氧化或还原性都比 C60好，将它们和 C60比较，与 X相距一个或两个键的 C原子电荷密度增加或减少较多，其余电或亲核反应性增加；X与 X，X与 C原子之间 Wiberg Order都减少较多，其键的强度削弱；邻近杂原子的 C与 C原子之间 Wiberg Order减少或增加很少，其键的强度稍有削弱或增强。     

不饱和类碳烯H2C(=)CLiBr的DFT研究

采用量子化学计算方法，在B3LYP／6－311G^*水平上全优化得到了不饱和类碳烯H2C＝CLiBr的平衡结构，结果表明，不饱和类碳烯H2C＝CLiBr只有两种平衡结构，对这两种平衡结构之间相互转化的过渡态进行计算，求得了转化势垒，根据计算得到的微观性质，采用统计热力学方法，研究了两种平衡结构之间相互转化的热力学性质，进而讨论了两种平衡结构在不同温度下的稳定性问题，在计算得到振动频率及强度的基础上，模拟了稳定平衡结构的红外光谱图。     

Pseudobond ab initio QM/MM approach and its applications to enzyme reactions

This perspective article mainly focuses on the development and applications of a pseudobond ab initio QM/MM approach to study enzyme reactions. The following aspects of methodology development are discussed: the approaches for the QM/MM covalent boundary problem, an efficient iterative optimization procedure, the methods to determine enzyme reaction paths, and the approaches to calculate free energy change in enzyme reactions. Several applications are described to illustrate the capability of the methods. Finally, future directions are discussed.     

纳米复合固体超强酸S_2O_8~(2-)/CoFe_2O_4催化合成癸二酸二乙酯

将硫酸钴、硫酸亚铁在NaOH溶液中与NaHCO3反应制得碱式碳酸盐前驱体 ,后者用 (NH4 ) 2 S2 O8浸渍、干燥 ,再经 5 0 0℃焙烧得到固体超强酸催化剂S2 O2 -8/CoFe2 O4 。产物经XRD、TEM、BET、TG DTA及化学法等检测 ,含硫量 4 5 2 % ,粒径为 4 2nm ,比表面积为 1 4 6m2 /g ,粒度均匀。催化剂的酸强度处于 -1 6 0 2和-1 4 5 2之间。以该固体酸为催化剂 ,由癸二酸和无水乙醇合成了癸二酸二乙酯。最佳反应条件为 :n(醇 )∶n(酸 ) =4 0∶1 0 ,癸二酸 0 1mol,催化剂 1 0 g ,反应时间 2 5h。在此反应条件下 ,酯化率可达 93 6%。     

Determination of rare earth impurities in high purity uranium by isotope dilution analysis

Summary An isotope dilution method for the determination of rare earth impurities in uranium has been developed and Ce, Nd, Sm, Eu and Gd have been determined in uranium oxide samples. The method involves isotopic dilution with enriched isotopes of the rare earths being measured, followed by the separation of rare earths from uranium. A mass spectrometer with thermionic source was used to determine the relative isotopic abundances in each of these rare earths. All these five elements were analysed selectively by preferential evaporation technique. Trace concentrations down to parts per billion range can be measured with good sensitivity and accuracy.

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Bestimmung von Verunreinigungen an Seltenen Erden in hochreinem Uran durch Isotopenverdünnungsanalyse

Zusammenfassung Eine Isotopenverdünnungsmethode wurde ausgearbeitet zur Bestimmung von Ce, Nd, Sm, Eu und Gd in Uranoxidproben. Das Verfahren umfaßt isotopische Verdünnung mit angereicherten Isotopen der zu bestimmenden Elemente und nachfolgende Abtrennung der Seltenen Erden von Uran. Die relativen Isotopenhäufigkeiten wurden mit Hilfe eines Massenspektrometers mit thermischer Ionenquelle bestimmt. Alle fünf Elemente wurden durch selektive Verdampfung analysiert. Spurenkonzentrationen bis herab zum ppb-Bereich konnten mit guter Empfindlichkeit und Genauigkeit erfaßt werden.

     

On the configuration interaction method for singlet states

The direct CI method, which avoids explicit calculation of the Hamiltonian matrix, is presented in a new form. The method is linked with Davidson's algorithm for iterative evaluation of the ground state eigenvector. The viability of the method is indicated by the test calculations on water which are described.     

Bacterial response to eukaryotic cells. Analysis of differentially expressed proteins using nano liquid chromatography-electrospray ionization tandem mass spectrometry

Host-bacteria interactions have mostly been investigated with regard to the host response or to activities of pathogenic bacteria. In contrast, we aim to identify reactions of non-pathogenic bacteria that result from their contact with host cells of the gastrointestinal tract. In a proteomic approach, the response of non-pathogenic human Escherichia coli bacteria on gut epithelial cells (rat IEC-6) was investigated in an in vitro co-culture model. For this purpose, a sensitive analytical procedure was developed based on the identification of two-dimensional polyacrylamide gel electrophoresis separated proteins by online nanoLC-electrospray ionization MS/MS using a quadrupole time-of-flight tandem mass spectrometer for accurate mass determination. We demonstrate here the efficiency of this technique by the identification of a total of 43 differentially expressed proteins, out of which 25 were up-regulated and 18 were down-regulated. They represent a wide range of molecular weight and different metabolic and physiological functions.     

Ag@Au core/shell triangular nanoplates with dual enzyme-like properties for the colorimetric sensing of glucose

Due to the serious harm of diabetes to human health, development of sensitive assays for glucose level is of high significance for early prevention and treatment of diabetes. Currently, most conventional enzyme-based glucose sensors suffer from high cost and low stability due to the inherent defects of natural enzymes. Herein, we develop a pure nanozyme-based glucose detection method using Ag@Au core/shell triangular nanoplates (TNPs), which combines glucose oxidase (GOD)- and horseradish peroxidase (HRP)-like activities of the Au shell and inherent plasmonic properties of Ag TNPs. The sensing mechanism is based on the fact that the Au shell possessed GOD-like activity, enabling the oxidation of glucose to produce H₂O₂, which can further etch the silver core, leading to the decrease of absorbance at 800 nm and the color change from blue to colorless. Compared with the previous nanozymes-based glucose sensors, our method avoids the use of enzymes and organic chromogenic agent. Moreover, the stability of the Ag@Au core/shell TNPs is much better than that of Ag TNPs due to the protection by the coating of the Au shell. This method was successfully applied to the detection of urine samples from patients with diabetes, indicating its practical applicability for real sample analysis.