皂甙分离和结构鉴定研究进展

本文对近十年来皂甙分离方法和结构签定技术进行了综述，尤其是对HPLC及1DNMR、2DNMR各种新技术在皂甙分离和结构鉴定方面的应用，作了较为详细的总结。     

羊水中痕量有机酸的气相色谱分析 Ⅰ.预分离方法的比较

本文研究了气相色谱分析羊水中痕量有机酸的各种预分离方法。对各种结构类型的标准有机酸水溶液进行回收实验以及实际的羊水样品分析表明,硅酸吸附法具有比较全面的优越性,是研究羊水中痕量有机酸较为理想的预分离方法。离子交换法对大多数有机酸也具有较高的回收率,但它的操作过程比较冗长。溶剂萃取法对柠檬酸、甘油酸等某些多元酸或羟基酸的回收不很理想,但对其它许多有机酸也可以取得较好的结果。所研究的方法均能分离除去羊水中大量的磷酸盐和硫酸盐,消除它们对有机酸气相色谱分析的干扰。     

人工培养菌种茯苓菌丝体多糖的分离、组成和分子量

由人工培育的茯苓菌种 (5·78号 )在含麸皮的培养液中于 2 5℃培养 1 8天得到茯苓菌丝体 .分别用9g LNaCl水溶液、热水、0 .5mol LNaOH和 88%甲酸从菌丝体中提取 7种多糖依次为 :ab PCM1、ab PCM2 I、ab PCM2 II、ab PCM3 I、ab PCM3 II、ab PCM4 I、ab PCM4 II,并从培养液中提取一种多糖ab PCM0 .红外光谱 (IR)、气相色谱 (GC)和1 3C NMR分析结果表明ab PCM0至ab PCM3 I多糖主要由α (1→ 3 ) D 葡萄糖、α D 甘露糖、β D 半乳糖和乙酰葡萄糖胺组成 ,而且随提取过程进行 ,葡萄糖含量逐渐增加 ,即从杂多糖到α 葡聚糖 .ab PCM3 II、ab PCM4 I和ab PCM4 II则主要是 β (1→ 3 ) D葡聚糖 .有趣的是 ,α 葡聚糖和 β 葡聚糖共存在该菌丝体的碱水提取液中 .由粘度法和光散射法测定了多糖的特性粘数 [η]和重均分子量Mw .ab PCM0、ab PCM1、ab PCM2 I、ab PCM2 II、ab PCM3 I和ab PCM4 II多糖的Mw 值分别为 7 7× 1 0 4、5 2× 1 0 4、5 0× 1 0 4、2 4 3× 1 0 4、65 2×1 0 4和 2 5 5× 1 0 4.     

Symbiodinolide, a novel polyol macrolide that activates N-type Ca channel, from the symbiotic marine dinoflagellate Symbiodinium sp.

A 62-membered novel polyol macrolide with a molecular weight of 2859 mu, symbiodinolide, was isolated from the symbiotic dinoflagellate Symbiodinium sp. Symbiodinolide exhibited a potent voltage-dependent N-type Ca²⁺ channel-opening activity at 7 nM and immediately ruptured the tissue surface of the acoel flatworm Amphiscolops sp. at 2.5 μM. The planar structure of symbiodinolide was elucidated by spectroscopic analysis and chemical degradations including hydrolysis and ethenolysis using the second-generation Grubbs' catalyst. Symbiodinolide was found to be a structural congener of zooxanthellatoxins. The relative stereochemistries of C26-C32, C44-C51, and C64-C66 parts, and the absolute stereochemistries of C69-73, C83-C103, and C3′-C18′ parts in symbiodinolide were established.     

Application of combined chromatographic techniques in the screening and purification of ecdysteroids

Summary Plants were found to contain ecdysteroids in concentrations in the order of 0.1% which are higher than those of the insects, and are adequate for the preparative production of ecdysteroids. A TLC screening method is elaborated for the qualitative and semiquantitative analysis of the ecdysteroid content of plants. The combined TLC method differentiates several characteristic ecdysteroids ranging from the apolar 2-deoxyecdysone to the polar 20,26-dihydroxyecdysone. A preparative purification method was developed consisting of solvent extraction, precipitation, crystallization and column liquid chromatography; these procedures permit the isolation of the main ecdysteroids in gram quantities. In some cases, droplet counter-current chromatography was also applied. Altogether, the isolation of thirteen ecdysteroids from five different plant species was accomplished by using a fast, simple and low-cost procedure, resulting in pure substances.     

Particle isolation for analysis of uranium minor isotopes in individual particles by secondary ion mass spectrometry

A new technique to measure ²³⁴U/²³⁸U and ²³⁶U/²³⁸U isotope ratios for individual particles in environmental samples was developed, which was a combination of particle isolation under scanning electron microscope (SEM) and secondary ion mass spectrometry (SIMS). The technique was verified by measuring ²³⁴U/²³⁸U and ²³⁶U/²³⁸U isotope ratios in individual particles in a simulated environmental sample containing uranium standard (NBL CRM U010) and Pb metal particles. When the uranium particles were not isolated, the relative deviations of the measured isotope ratios from the reference values increased with increasing the signal intensity ratio of ²⁰⁸Pb to ²³⁸U, which was due to the molecular ion interferences by the Pb particles co-existing in the sputtered area. By the isolation of individual uranium particles, the interferences were eliminated and the measured isotope ratios were in good agreement with the reference values. The maximum relative deviations among 20 particles were 8.9% for ²³⁴U/²³⁸U and 13.1% for ²³⁶U/²³⁸U isotope ratios, respectively. The technique was also successfully applied to the analysis of a real swipe sample containing various kinds of elements.     

Isolation, structure elucidation, and total synthesis of two new Chimonanthus alkaloids, chimonamidine and chimonanthidine

Two new tryptamine-related alkaloids, chimonamidine and chimonanthidine, were isolated from the seeds of Chimonanthus praecox Link. and their structures including absolute configuration were elucidated by spectroscopic analysis and biomimetic total synthesis from tryptamine.     

Aplyronine A, a potent antitumor macrolide of marine origin, and the congeners aplyronines B and C: isolation, structures, and bioactivities

Aplyronine A (2), a potent antitumor macrolide was isolated from the sea hare Aplysia kurodai together with the congeners aplyronines B (3) and C (4). The absolute stereostructure of aplyronine A (2) was determined by the instrumental analysis (mainly NMR and MS) and the enantioselective synthesis of the fragments obtained from chemical degradation of aplyronine A (2). The structures of aplyronines B (3) and C (4) were also elucidated. Cytotoxicity and antitumor activity of aplyronine A (2) were evaluated.     

强流离子源灯丝电源设计与分析

灯丝电源是中性束注入器等离子体发生器电源系统的重要组成部分,为了满足其低电压大电流输出特性要求,提出了带平衡电抗器双反星形整流电路的拓扑结构的电源设计方案。该拓扑结构与三相桥式整流电路相比较在采用相同器件下可达到更高功率,减少交流侧输入电流谐波并提高功率因素。分析了该拓扑结构下整流输出特性和所含的谐波分量,根据设计指标计算了整流变压器和平衡电抗器的相关参数,最后通过仿真和实验结果验证了这一拓扑结构的可行性。     

Pyridine Dimers and Their Low-Temperature Isomerization: A High-Resolution Matrix-Isolation Spectroscopy Study

The bonding between two neutral aromatic compounds, especially small ones, has been controversially debated in the last decades, and terms like “π-stacking” had to be revised. Surprisingly, despite of many experimental and computational work, there is still no clear consensus about the structure of and the bonding in the pyridine dimer. In this work, for different isomeric forms of the pyridine dimer, the structures and bonding were elucidated by combining high-resolution matrix-isolation spectroscopic results with quantum-chemical calculations. High-resolution IR spectra of Ne matrices at 4 K containing pyridine were recorded for different concentrations and upon annealing to 10 and 12 K, relying on three isotopologues of pyridine. The spectra show the presence of hydrogen-bonded, T-shaped, and stacked forms of weakly-bound pyridine dimers. Among these, the hydrogen-bonded isomer is identified as the lowest-energy form. The results provide for the first time conclusive information about the interaction between two pyridine dimers.