Synthesis of optically active β-alkyl aspartate via [3,3] sigmatropic rearrangement of α-acyloxytrialkylsilane

The synthesis of four types of optically active β-carbon-substituted analogs of threo-β-hydroxy aspartate (THA) and a β-carbon-substituted analog of threo-β-benzyloxy aspartate (TBOA), which are potent blockers of excitatory amino acid transporters in the mammalian central nervous system, via the chirality-transferring ester-enolate Claisen rearrangement of α-acyloxytrialkylsilane is described.     

Characterization of noise in inductively-coupled plasma emission spectrometry

The nebulizing process in inductively-coupled plasma emission spectrometry is a major source of the instrumental variability; an attempt has been made to isolate this source so that its influence on the final result could be evaluated. Direct measurements of the time-dependent variations of the sample supply to the plasma were achieved by using a device based on the light-scattering property of nebulized test solutions. The noise from the nebulizer and of the emission signal was characterized by autocovariance functions and power spectral densities. The types of noise observed showed f^{-$\text{1}\text{2}$} and f^{-$\text{1}\text{4}$} character, depending on the concentration of the test elements employed. Cross-covariance revealed a strong correlation between the noise sources considered. The applicability and limitations of possible correction and electronic filtering procedures are indicated.     

随机环境中选举模型的Hydrodynamic极限

本文研究随机环境中选举模型的Hydrodynamic极限。首先，我们通过图表示构造出随机环境中的选举模型，然后利用对偶关系得到了该粒子模型的宏观偏微分方程。     

表面活性剂-磺基水扬酸对镱原子吸收光谱的高增敏作用研究

本文就表面活性剂-磺基水杨酸对镱在乙炔-空气火焰中的高增敏作用进行了研究,结果表明,在十二烷基硫酸钠(SDS)与磺基水杨酸(SSA)共存时。镱的灵敏度增高50倍,其它稀土元素和一些阴离子对Yb的干扰得到了有效的抑制,对硫酸根和磷酸根尤其明显,同时也研究了该体系的增敏机理。在Yb-SDS-SSA体系中,镱的检出限为0.031μg/mL,在0.050～2.0μg/mL镱的浓度范围内,其相对标准偏差为3.0％。     

气相色谱法测定卷烟主流烟气气相物中的二氧化碳气体

采用热导检测器-气相色谱,外标法定量,测定了卷烟主流烟气气相物中的二氧化碳气体,实验结果表明：方法的准确度和精密度均很好,且测定数据可靠,结果令人满意。     

Zinc(II), Cobalt(II) and Nickel(II) Complexes of 5-Substituted-1,3,4-Thiadiazoles

Zn(II), Co(II) and Ni(II) complexes with some 5-substituted-1,3,4-thiadiazoles (L₁-L₄) have been prepared and characterized by conductivity, microanalysis, thermal analysis, infrared and electronic spectra measurements. All complexes behave as 1:1 electrolyte and the ligands are coordinated as bidentate molecules. The stability constants and energy of formation are determined and discussed on the basis of the ligands structure.     

Theoretical and experimental study of the structure and vibration spectra of 4,4′-carbonyl-di-morpholine

4,4′-Carbonyl-di-morpholine was synthesized and characterized by X-ray diffraction, the FTIR and NMR spectra. The extended MO calculations using density functional theory (DFT) and self-consistent field molecular orbital Hartree-Fock theory were carried out. The results of the calculations were compared with experimental data. The experimental and calculated results were supported each other. The performance of a hybrid B3LYP density functional was compared with the ab initio restricted Hartree-Fock method. With the basis sets of the 6-311G** quality, the DFT calculated bond lengths, dipole moments and harmonic vibrations were predicted in a very good agreement with available experimental data.     

The Mukaiyama-Michael addition of a β,β-dimethyl substituted silyl ketene acetal to α,β-unsaturated ketones using tetra-n-butylammonium bibenzoate as a nucleophilic catalyst

The Michael addition of a β,β-dimethyl substituted silyl ketene acetal [Me₂CC(OMe)OSiMe₃] to α,β-unsaturated ketones, namely, 2-cyclopentenone, 2-cyclohexenone, 3-methyl-2-cyclohexenone, isophorone, methyl vinyl ketone and mesityl oxide occurs smoothly in the presence of the nucleophilic catalyst, tetra-n-butyl ammonium bibenzoate (TBABB) in THF giving the corresponding 1,4-adducts in excellent yields.     

p-tert-Butyl thiacalix[4]arenes functionalized at the lower rim by o-, m-, p-amido and o-, m-, p-(amidomethyl)pyridine fragments as receptors for α-hydroxy- and dicarboxylic acids

A series of new p-tert-butyl thiacalix[4]arenes with o-, m-, p-amido and o-, m-, p-(amidomethyl)pyridine substituents at the lower rim in cone, partial cone, and 1,3-alternate conformations were synthesized. The ability of the obtained compounds to recognize the α-hydroxy (glycolic, tartaric) and dicarboxylic (oxalic, malonic, succinic, fumaric, and maleic) acids was investigated by UV-vis spectroscopy. Also, the efficiency and selectivity of binding, the association constants log K_a (10² to 10⁷ M⁻¹) and the stoichiometry were determined for the complexes of p-tert-butyl thiacalix[4]arenes with the acids. The receptors based on p-tert-butyl thiacalix[4]arenes with (amidomethyl)pyridine substitutes are most efficient in complexation in many cases.     

Solventless DBU-promoted Mannich-type reactions of α-amido p-tolylsulfones with diethyl fluoromalonates and diethyl malonates

Mannich-type reactions of α-amido p-tolylsulfones with diethyl fluoromalonates and diethyl malonates, respectively in presence of catalytic amount of DBU have been developed. A variety of α-amido p-tolylsulfones prepared from aromatic and aliphatic aldehydes reacts with diethyl fluoromalonates and diethyl malonates, respectively under mild reaction conditions to afford α-fluoro β-amino esters and β-amino esters in moderate to good yield.