The determination of chlorinated biphenyls,chlorinated dibenzodioxins,and chlorinated dibenzofurans by GC-MS

High resolution gas chromatography, with mass selective detection, has been used for the analysis of PCB on methyl 50 % octyl polysiloxane (SB 50 Octyl), methyl octadecyl polysiloxane, and a smectic polysiloxane (SB Smectic); and for the analysis of polychlorodibenzodioxins and polychlorodibenzofurans with 1 to 8 chlorine substituents on 100 % cyanopropyl siloxane (SP 2331), smectic polysiloxane (SB Smectic), a new polar stationary phase (DB-Dioxin). The analysis has also been performed by column coupling.     

Adrenaline recognition in water

Host molecule 1 displays a high affinity in water towards catecholamines and especially related structures such as beta-blockers with extended aromatic pi-faces (up to 7x10(3) M(-1) for each single complexation step or 5x10(7) M(-2) for both steps). The amphiphilic structural design leads to an extensive self-association of host molecules through their aromatic flanks. Above a cmc (critical micelle concentration) of 3x10(-4) M, host 1 forms micelles that produce a favorable microenvironment for hydrophobic interactions with the included guest molecules. Electrostatic attraction of the ammonium alcohol by the phosphonate anions is thus combined with hydrophobic contributions between the aromatic moieties. Ionic hydrogen bonds with polar OH or NH groups of the guest enforce the non-covalent interactions, and finally lead to increased specificity. Both its affinity and its selectivity towards adrenergic receptor substrates are greatly enhanced if the receptor molecule 1 is transferred from water into a lipid monolayer. Catecholamines and beta-blockers lead to drastically different effects at concentrations approaching the micromolar regime. Especially beta-blockers with minute structural changes can be easily distinguished from each other. In both cases, extensive hydrophobic interactions with a self-associated and/or self-organized microenvironment are largely responsible for the observed high efficiency and specificity.     

离子液体BMIBF4性质的研究

用最大气泡法和韦氏天平法, 在278.15～343.15 K范围内测定了离子液体BMIBF₄的表面张力和密度; 讨论了这个离子液体的体积性质和表面性质; 根据离子个头大又极不对称的特点, 提出了离子液体的空隙模型. 根据空隙模型计算的离子液体恒压热膨胀系数与实验值相比, 偏差在10%左右.     

烯烃加成反应活性与烷基极化效应的关系

烯烃的自由基加成和亲电加成速率受不同的因素控制.对于仅仅含烷基取代的简单烯烃:(1)与OH自由基加成速率-log kOH可由π键上烷基极化效应指数的几何平均值GMPEIπ关联:-log kOH=a bGMPEIπ c(GMPEIπ)2; (2)与亲电试剂加成速率log k可由π键两端碳原子所连基团极化效应指数PEI(L)和PEI(S)关联:log k=a bPEI(L) cPEI(S),其中的PEI(L)和PEI(S)分别表示极化效应较大和较小的一端.     

离子性指数、极化效应指数烷烃^13C NMR化学位移的 关系研究

定义了烷烃分子中碳原子的离子性指数(INI)，用离子性指数(INI)、极化效应指数(PEI)及N^i~H(i=αβΥ)结构信息参数研究了烷烃的^13CNMR化学位移模型，结果表明，烷烃^13CNMR化学位移(CS)可用下式来定量描述：CS=194.6156-37.7394(INI)+98.6505(ΣPEI)+27.1630(INI/ΣPEI)-652.9106(ΣPEI/INI)+0.7735N^α~H+2.2468N^β~H-0.1742N^γ~H。用上式估算了304个碳原子的化学位移，平均绝对误差仅为0.77δ，标准差0.9860δ，预测值与实验值非常吻合。     

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.     

Cs2CO3 Promoted coupling reactions for the preparation of skipped diynes

An improved methodology for the preparation of copper(I) alkynides has been developed using cesium carbonate as base. In the presence of cesium carbonate and CuI various 1-alkynes were converted smoothly to the corresponding copper alkynides which in situ reacted with propargylic halides in order to synthesize skipped diynes.     

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.

     

An investigation of the reliability of the Galerkin-Petrov method

It is shown that the Galerkin-Petrov method if applied in a controlled way yields reliable results for excited states of the same symmetry classifications as the ground state. Computations are performed for the 2¹ S and 3¹ S states of He. The problem of optimizing nonlinear parameters of the basis functions by means of the GP method is discussed. A special optimization scheme is suggested and numerically illustrated for someS states of He.     

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.