利用分子对称性简化天然有机产物合成设计的策略

本文综述了利用分子对称性简化天然有机产物合成设计的策略,讨论了具有下述四种对称性的分子的合成:一、对称中心和旋转对称轴;二、对称平面;三、潜在的对称性;四、局部的对称性。     

亚磺化脱卤试剂在有机合成中的应用

本文综述了亚磺化脱卤试剂在有机合成中的应用。特别是氟烷基化反应中的应用。     

Analysis of organic matter from witwatersrand basin (South Africa) by OTA and Py-GC-MSPreliminary results

Oxyreactive Thermal Analysis (OTA) and pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) have been performed on highly matured, uraniferous samples. Organic matter investigated by OTA gives two exothermic peaks on DTA curves. The dominant peak appearing at temperature higher than 500°C, confirm the high maturity of the organic matter. Results of analysis by Py-GC-MS complement the OTA results. The organic matter in all of the samples shows the same general pyrolysis characteristics. The pyrograms are dominated by low molecular mass aromatic hydrocarbons. The samples differ in relative abundances of the compounds. The changes in temperature and intensity of the lower-temperature peak in OTA method and differences in relative abundances of aromatic hydrocarbons were used to investigate differences in thermal maturity of the organic matter. This revised version was published online in July 2006 with corrections to the Cover Date.     

三甲基硅基化反应的研究

本文研究了以水玻璃作为硅酸盐阴离子,按Lentz方法进行的三甲基硅基化反应。在改变反应克分子比例时,可得到不同分子量和硅基化程度的硅树脂,由此说明,在硅基化反应时可能发生聚合、解聚和水解等副反应。对影响硅树脂产率的反应条件和三甲基硅基化树脂的一些物理性质也进行了讨论。     

Evaluation of the factors affecting extraction of organic compounds based on the acid-induced phase cloud point approach

On the basis of a better analytical exploitation of acid-induced cloud point approach, a systematic study on the phase behaviour of acid aqueous solutions of anionic surfactants and factors affecting anionic surfactant-mediated extractions was performed. The anionic surfactants investigated were alkylsulphonates (ASS) with alkylchain lengths comprised between 8 and 16 carbon atoms. The critical hydrochloric acid concentration (minimal acid concentration required to separation in two liquid phases) was found to increase as alkylchain length of the anionic surfactant increased from 10 to 14. Non-acid-induced liquid-liquid phase separation was observed for sodium octanesulphonate (SOS) or sodium hexadecyl sulphonate (SHS) in the hydrochloric concentration range 0-10 M. Acid aqueous solutions of sodium decylsulphonate (SDeS) and sodium dodecylsulphonate (SDoS) separated into two liquid phases at temperatures ranging between 10 and 80 °C, while temperatures >35 °C were required for sodium tetradecylsulphonate. The influence on extraction efficiency and concentrating ability of experimental variables such as hydrophobicity and concentration of surfactant, nature and concentration of analyte, hydrochloric acid concentration, time and temperature of extraction and time of equilibration and centrifugation was examined. Advantages provided by anionic surfactant-mediated extractions over the use of non-ionic surfactants (cloud point extractions) are discussed.     

Clays as selective catalysts in organic synthesis

Suitably modified smectite clays can be very selective catalysts for a wide range of organic reactions. While it has long been known that such materials can act as Bronsted and Lewis acids, it has been shown recently that they are also effective Diels-Alder catalysts. A selection of illustrative reactions is given which emphasises their wide range of use, their selectivity, and the ease of work-up after reaction. In each case, mechanistic information is presented, e.g., on the site of reaction (whether interlayer or surface), rate determining steps, etc. The regiochemical consequences of the restricted reaction space are stressed.Based on material presented at the Fourth International Symposium on Inclusion Phenomena and the Third International Symposium on Cyclodextrins, Lancaster, U.K., 20–25 July 1986.     

Comparative studies on a mesophilic and a thermophilic α-amylase

A comparative study was performed on thermal stability of mesophilic and thermophilic α-amylases, and the effects of various denaturing agents, organic solvents, and stabilizers were investigated. As expected, the thermophilic enzyme showed higher resistance toward denaturation in water as its natural medium, but such a difference could not be detected in nonaqueous environments. Furthermore, stability of these molecules was improved by including various stabilizing agents. Of the compounds tested, sorbitol provided the highest degree of protection, which was found to be owing to its effect on increasing T _m and its ability in totally preventing deamidation of amino acid residues in the protein molecules.     

酶的分子仿生研究进展

回顾了近几十年来印迹高分子和有机团簇对酶的仿生发展历程，总结了目前的 研究现状，探讨了电子效应和空间效应（柔性空间效应）对仿对酶在催化过程中实 现类似酶的识别和诱导契合的影响，并展望了酶的仿生发展趋势。     

Enzymatic polyesterification in organic media. Enzyme-catalyzed synthesis of linear polyesters. I. Condensation polymerization of linear hydroxyesters. II. Ring-opening polymerization of ϵ-caprolactone

With the object to synthesize polyesters by enzymatic catalysis in organic media, two directions have been investigated: (1) the condensation polymerization of linear ω-hydroxyesters and (2) the ring-opening polymerization of lactones. The commercially-available crude porcine pancreatic lipase (PPL), suspended in organic solvents, was the preferred enzyme for the reactions. In order to determine the optimal conditions for the condensation polymerization, the bifunctional methyl 6-hydroxyhexanoate was used as a model compound to study the influence of the following parameters: type of the enzymecatalyst, kind of solvent, concentration, temperature, duration, size of the reaction mixture, and stirring. Film-forming polyesters with a degree of polymerization (DP) up to about 100 were obtained from linear aliphatic hydroxyesters in n-hexane at reflux temperature (69°C). Yet concurrently with the intermolecular condensation polymerization, macrolactones were also formed by intramolecular reaction. Two aromatic hydroxyesters did not react under these conditions. For the ring-opening polymerization of lactones the reaction of ?-caprolactone with methanol as the preferred nucleophile, was studied. Polyesters with a DP of up to 35 were obtained in n-hexane at temperatures between 25 and 40°C. The degrees of polymerization of the polyesters were determined by comparative analyses of the end groups in the ¹H-NMR spectra and by determination of molecular weights either by vapor phase osmometry, gel permeation chromatography, or intrinsic viscosity. © 1993 John Wiley & Sons, Inc.