硝酸镧与冠醚(2, 2)配合物的晶体及电子结构研究

用X-射线单晶衍射法测定了硝酸镧与冠醚(2,2)配合物的晶体结构,发现其具有与报道的Eu(NO_3)_3(2,2)配合物不同的配位方式.晶体属于三斜晶系,空间群P(?),晶胞参数为a=10.312(2)(?);b=12.745(3)(?);c=8.917(2)(?);α=103.79(2)°;β=112.73(2)°;γ=83.68(2)°;V=1049.5(5)(?)~3;F(000)=587.88;Z=2.结构用重原子法解出;R值为0.0292.用INDO法计算了配合物的净电荷分布,电子结构、键级.结果表明,镧与配位原子间的键具有一定程度的共价性.镧的5d轨道对共价性的贡献最大,而4f轨道基本上不参与成键.La-N比La-O(醚)间存在较强的作用,增大了配合物的稳定性.     

Total Synthesis of d,l-Isospongiadiol: An Intramolecular Radical Cascade Approach to Furanoditerpenes

A stereoselective oxidative free-radical cyclization of beta-keto ester polyenes 7 and 19 has been accomplished as a one-step entry to the tricarbocyclic synthons 8and 21 which contain five and six stereogenic centers, respectively. These key synthons possessing an axial carboethoxy group at C-4 were ultimately converted to the spongian skeleton (8--> 14 and 21 --> 25 -->14). The synthesis of d,l-isospongiadiol (3) from the common intermediate 14 was realized after introduction of the 2alpha-hydroxy group in the spongian A-ring via epoxidation of silyl enol ether 28 and subsequent desilylation.     

含1,3-亚丙基冠醚的合成

为了进一步研究亚丙基冠醚的络合行为,合成了三种含1,3-亚丙基冠醚,即2,3-苯并-1,4,7,11-四氧-环十三-2-烯(苯并-13-冠-4)(1)、2,3-苯并-1,4,8,11,14-五氧-环十七-2-烯(苯并-17-冠-5)(2)、2,3-苯并-1,4,7,10,14,17-六氧-环十九-2-烯(苯并-19-冠-6)(3)。通过元素分析、红外光谱、质谱、核磁共振谱和 X-衍射晶体结构分析,确证了它们的结构。     

Optimization of the electrokinetic supercharging preconcentration for high-sensitivity microchip gel electrophoresis on a cross-geometry microchip

We developed a novel on-line preconcentration procedure for microchip gel electrophoresis (MCGE), which enables application of electrokinetic supercharging (EKS) for highly sensitive detection of DNA fragments on a cross-geometry microchip. In comparison with conventional pinched injection using the cross microchip, the present approach allows loading a much larger amount of the sample by taking advantage of a newly developed operational mode. In order to obtain high preconcentration effect and prevent splitting of an enriched sample into subchannels, i.e., off the detector range, effects of the voltage applied on the reservoirs and the time of isotachophoretic preconcentration were examined. The optimal balance between the voltage and time was found for a high-sensitivity analysis of DNA fragments. After experimental optimization the detection limit of a 150 bp fragment was as low as 0.22 mg/L (S/N = 3) that is 10 times better than using the conventional pinched injection.     

DNA aggregation and cleavage in CGE induced by high electric field in aqueous solution accompanying electrokinetic sample injection

The phenomenon of peak area decrease due to high injection voltage (V_inj, e.g. 10–30 kV, 200–600 V/cm in the 50 cm capillary) was found in the analysis of very dilute DNA fragments (<0.2 mg/L) by using high‐sensitive electrokinetic supercharging‐CGE. The possibility of DNA cleavage in aqueous solution was suggested, in addition to the aggregation phenomenon that is already known. The analysis of intentionally voltage‐affected fragments (at 200 V/cm) also showed decreased peak areas depending on the time of the voltage being applied. Computer simulation suggested that a high electric field (a few kV/cm or more) could be generated partly between the electrode and the capillary end during electrokinetic injection (EKI) process. After thorough experimental verification, it was found that the factors affecting the damage during EKI were the magnitude of electric field, the distance between tips of electrode and capillary (D_e/c), sample concentration and traveling time during EKI in sample vials. Furthermore, these factors are correlating with each other. A low conductivity of diluted sample would cause a high electric field (over a few hundred volts per centimeter), while the longer D_e/c results in a longer traveling time during EKI, which may cause a larger degree of damage (aggregation and cleavage) on the DNA fragments. As an important practical implication of this study, when the dilute DNA fragments (sub mg/L) are to be analyzed by CGE using EKI, injection voltage should be kept as low as possible.     

Negishi偶联反应的研究进展

对有机锌试剂参与的Negishi偶联反应机理进行了简要概述,并详细综述了Negishi偶联反应的研究进展,主要介绍了Pd、Ni催化剂以及新型Fe、Co催化剂参与的Negishi偶联反应。展望了新型催化剂的发展趋势。     

自然循环过冷沸腾流动不稳定性的实验研究

本文以氟里昂作工质，对自然循环过冷沸腾流动不稳定性进行了实验研究．实验过程中发现自然循环系统内可能发生高频脉动和低频脉动二种类型的过冷沸腾流动不稳定性．通过实验研究揭示了这二种类型流动不稳定性的发生机理，证实高频脉动属于声波型脉动，低频脉动属于密度波型脉动．通过实验得出了判断系统稳定性的界限，并使用积分方程无因次分析方法得出了预测密度波型流动不稳定性的经验公式．     

计及污垢影响的换热器热优化

本文利用熵产生数方法研究了气体和液体传热介质的顺流、逆流换热器的热力学完善性，结果表明，如给定冷、热流体的入口温度，在综合考虑传热、流动阻力和污垢的情况下，可用优化方法确定其它参数。     

高精度TVD有限差分格式的自由梯度条件

1自由流条件守恒性气动方程组的高精度TVD有限差分格式一般通过使用通量限制器加入非线性的人工粘性来构成。在曲线坐标系中，通量限制器比较的两个因子与各自所在单元的界面雅可比转换行列式相关。为了消除畸变网格单元界面雅可比转换行列式的变化对通量限制器比较结果的影响，本文提出了高精度TVD格式的自由梯度性质，并分别就Osher和HartenTVD格式讨论了同时满足自由流和自由梯度的度量张量计算方法，使高精度TVD格式在畸变网格上得以实现。任意曲线坐标系中守恒型二维欧拉方程表示为其中，E、F为笛卡尔坐标系中的通量；J为坐标变…