Formal total synthesis of hemibrevetoxin B by a convergent strategy

Concise construction of the trans-fused 7/7/6/6 tetracyclic ether part of hemibrevetoxin B (1) was achieved by a convergent strategy based on coupling reaction of an acyl anion equivalent, reductive cyclization of an α,ε-dihydroxyketone, and introduction of a methyl group at the central ring junction by the Nicolaou method. The resultant tetracyclic ether was transformed into the known intermediate, which was already converted to 1 by the Yamamoto group, thereby completing the formal total synthesis of 1.     

An efficient asymmetric synthesis of Fmoc-l-cyclopentylglycine via diastereoselective alkylation of glycine enolate equivalent

Stereoselective alkylation of the enolate derived from benzyl (2R,3S)-(−)-6-oxo-2,3-diphenyl-4-morpholinecarboxylate (1) with cyclopentyl iodide afforded anti-α-monosubstituted product, benzyl (2R,3S,5S)-(−)-6-oxo-2,3-diphenyl-5-cyclopentyl-4-morpholinecarboxylate (3) in 60% yield. Catalytic hydrogenolysis over PdCl₂ cleaved the auxiliary ring system to give l-cyclopentylglycine (4) in 84% yield. Subsequent protection of the α-amino function with Fmoc-OSu gave Fmoc-l-cyclopentylglycine (5) in high yield.     

镍电极开路电位测定微量硼氢根离子

实验采用循环伏安法，用镍电极代替铂铑等贵金属电极测定了碱性体系中不同硼氢根离子浓度下的开路电位，得出了研究电极的开路电位（-0．355～-0．280vs.SCE／V）与微量硼氢根离子浓度的对应关系，并用于监测电解偏硼酸钠制备硼氢化钠体系中微量硼氢根离子，同时计算了该方法的误差。结果表明，测量结果的相对标准偏差为2．2％；回收率为98．4％。该法简单、快速，可测定10^-5～10^-3mol／L范围的硼氢根离子浓度。     

Examination of the statistical method in the conjugated circuit theory

Summary The recently proposed statistical method for the calculation of resonance energies in the conjugated circuit theory is tested on the example of polyacenes. It is found that for the estimation of the resonance energy with a 10% average error, the method requires a sample consisting of about 20 (randomly chosen) Kekulé structures. Further increase of the sample size gives no significant gain in the accuracy of the method.

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Überprüfung der statistischen Methode in der Konjugierten-Ring-Theorie

Zusammenfassung Die unlängst vorgeschlagene statistische Methode in der Konjugierten-Ring-Theorie (conjugated circuit theory) wird am Beispiel der Polyacene getestet. Es wurde festgestellt, daß für die Abschätzung der Resonanzenergien bei einem mittleren Fehler von 10% für diese Methode ungefähr 20 (willkürlich gewählte) Kekulé-Strukturen nötig sind. Weitere Erhöhung dieser Anzahl bringt keine signifikante Verbesserung der Genauigkeit der Methode.

     

Fluorinated compounds for advanced IC interconnect applications: a survey of chemistries and processes

The semiconductor industry is now in the early stages of an unprecedented change in materials set for the integrated circuit (IC) interconnect structure. The traditional layers of aluminum conductors and silicon dioxide dielectrics are being replaced by copper thin films and a variety of low k candidates, respectively. In many cases, fluorine confers desirable properties on either the precursors or the final films. At the same time, fluorine presents some potentially adverse effects, which have led to a so-called “fear-of-fluorine” in interconnect applications. This paper will review the proposed uses of fluorinated compounds in the interconnect structures, covering both precursors and the resulting thin films. Both the status of technical studies, and the prospects for commercial implementation, will be addressed.     

压电石英晶体在电解质水溶液中的振荡性能研究(Ⅱ)——频率、频移特性

根据两面电极浸入液体中的压电晶体等效电路模型和Pierce振荡器振荡方程的解,得到晶体在电解质溶液中的振荡频率(F_1)与溶液电导率(x)的关系式:F_1=(1/2π)(1/C_1+1/C_2)(1/X_e)[(R_e~2+X_e~2)x~2+2R_ex+1]。以自行设计的Pierce晶体振荡器。研究了晶体和主振电路参数、输入电压及检测池外壳屏蔽接地对AT切9MHz石英晶体在KCl、Na_2SO_4水溶液中的频率、相对于纯水频移随溶液电导率变化的影响规律,结果与上式相符。     

脉冲激光引信用PFM和PWM式LD驱动电路的研究

 在激光引信的通讯系统中，针对引信用脉冲式半导体激光器驱动电路的脉冲宽度、频率、功率可调的需要，根据LD驱动电路的工作原理，建立了LD驱动电路的一般模型。然后用电子多频振荡器提供驱动信号，用双MOS驱动器来驱动半导体激光器，通过大量的实验、仿真、分析、比较，设计出了方便可调的大功率LD的驱动电路，该电路的脉冲频率和脉冲宽度可方便调整。并且该驱动电路的频率调节范围大（10Hz~20kHz）；脉冲宽度可以从几ns到几百ns进行调节，大大提高了激光引信通讯系统的性能与可靠性。     

基于开关控制的兴趣实验设计

设计了开关控制实验,专门对常见的开关特点及使用进行探讨,根据开关特点搭建相应的控制电路,用近似于工程项目的形式锻炼学生对开关的灵活应用,激发了学生实验的兴趣和积极性.     

Tuning the mesogenic properties of 5-alkoxy-2-(4-alkoxyphenyl)pyrimidine liquid crystals: the effect of a phenoxy end-group in two sterically equivalent series

Two sterically equivalent series of phenoxy-terminated 5-alkoxy-2-(4-alkoxyphenyl)pyrimidine liquid crystals were synthesised, and their mesogenic properties were characterised by polarised optical microscopy and differential scanning calorimetry (DSC). The phenoxy end-group causes a significant increase in melting point and inhibits – at least partially – the mesomorphism of these materials relative to the parent isomers; in most cases, the broad enantiotropic SmC phase formed by the parent isomers is suppressed by the addition of the phenoxy end-group. However, detailed analyses by small-angle X-ray scattering and monodomain 2D X-ray scattering suggest that these compounds form a SmA phase with a partially intercalated bilayer structure in which the phenoxy end-groups are nanosegregated. Such an intercalated bilayer structure might enable the tuning of smectogenic properties by appropriate substitution of the phenoxy end-groups.     

Zero Current Potentiometry for Measuring the Interface Potential at the Electrode/Solution Interface. Theoretical and Experimental Study

A novel electrochemical approach has been proposed to measure the interface potential at the electrode/solution interface based on reconstructing the three‐electrode system of a potentiostat. In this work, the method was investigated both theoretically and experimentally. Mathematical expressions, describing current? potential characteristics, were derived. Zero current potential E_zcp was defined as the potential at which the current is zero based on linear sweep voltammetry, and was determined from the I? E curve to measure the interface potential. The experimental results obtained with the couples Fe(CN)₆^3?/Fe(CN)₆^4? and Co(NH₃)₆³⁺/Co(NH₃)₆²⁺ as examples agreed well with the theory. The proposed approach exhibits an excellent performance for measuring the interface potential due to the advantages of rapidity, high stability and accuracy.