Properties and applications of β‐glycosidase from Bacteroides thetaiotaomicron that specifically hydrolyses isoflavone glycosides

To modify the glycan part of glycosides, the gene encoding β‐glycosidase was cloned from Bacteroides thetaiotaomicron VPI‐5482. The cloned gene, bt_1780, was expressed in Escherichia coli MC1061 and the expressed enzyme was purified using Ni‐NTA affinity chromatography. The purified enzyme, BTBG, showed optimal activity at 50 °C and pH 5.5. Interestingly, this enzyme did not have any hydrolysing activity on ordinary β‐linkage–containing substrates such as xylobiose, lactose and cello‐oligosaccharide, but specifically hydrolysed isoflavone glycosides such as daidzin, genistin and glycitin. Compared to a commercial beta glucosidase, BTBG selectively hydrolysed isoflavone glycosides in soybean extract mixture solution. These results suggest that BTBG may be a specialized enzyme for the hydrolysis of glycosides and that the substrate specificity of BTBG is applicable for the bioconversion of isoflavone glycosides in the food industry.     

由AEO_3硫酸化合成AES的研究

以氨基磺酸和氯磺酸作硫酸化剂,由AEO_3合成了AES,讨论了工艺条件对反应过程和产品质量的影响。     

均匀设计法在烷基糖苷合成中的应用

在烷基糖苷的合成反应中，影响糖苷得率的因素很多，且各因素之间又存在着相互牵制作用。为了探索合成的最佳条件，我们采用了均匀实验设计法。实验证明：它特别适用于多因素多水平的实验设计，同时减少了实验的次数，降低了实验的费用，提高了工作效率。     

合成十二烷基葡萄糖苷的工艺条件

采用对甲苯磺酸为催化剂 ,以D 葡萄糖和正十二醇为原料直接合成十二烷基糖苷 ,研究了工艺条件对反应速率、产物收率与色泽的影响。结果表明 ,催化剂用量对产物色泽无影响 ,适宜的工艺条件为 :正十二醇 /D 葡萄糖 (摩尔比 ) =4∶1,反应温度 110～ 12 0℃ ,反应时间 4h ,反应压力 4kPa ,搅拌速率大于 840r/min ,对甲苯磺酸 /D 葡萄糖 (摩尔比 ) =1.5 %,MgO为较好的中和剂。产物为乳白色 ,十二烷基糖苷总收率大于89%。     

Study of the coupling reactions between electrochemically generated aromatic radical anions and methyl, alkyl and benzyl radicals

Alkyl radicals produced in the indirect reduction of alkyl halides or alkyldimethylsulfonium salts by electrochemically generated aromatic radical anions couple fast with the latter and alkylated or dialkylated dihydro compounds are formed. Rate constants measured for the coupling reaction between on one hand methyl, primary, secondary and tertiary alkyl radicals as well as benzyl and cumyl radicals and on the other hand a wide spectrum of electrochemically generated aromatic radical anions are found to be about 1×10⁹ M⁻¹ s⁻¹. Previous measurements of coupling rate constants for primary alkyl radicals have been re-evaluated since they were affected by the presence of an S_N2 reaction occurring between the alkyl halides used as radical precursors and the aromatic radical anions. New experiments are also included using alkyldimethylsulfonium salts as precursors in order to prevent such S_N2 artefacts. It is concluded that sterical hindrance does not play a significant role for the radical-radical anion coupling reactions. In general the rate constants for the coupling reactions are all close to 10⁹ M⁻¹ s⁻¹.     

海明滴定法快速测定废水中的LAS含量

介绍了一种测定废水中LAS浓度的新方法。克服了常规方法亚甲基蓝比色法要绘制标准曲线，操作过程复杂等局限性。该方法测定过程简单，结果准确，标准偏差为1．4l，变异系数为3．92％。     

Exhaust Emissions from an Engine Fueled with Biodiesel from High-Oleic Soybeans

Biodiesel is a fuel comprising mono-alkyl esters of medium to long-chain fatty acids derived from vegetable oils or animal fats. Typically, engines operated on soybean-based biodiesel exhibit higher emissions of oxides of nitrogen (NOx) compared with petroleum diesel. The increase in NOx emissions might be an inherent characteristic of soybean oil’s polyunsaturation, because the level of saturation is known to affect the biodiesel’s cetane number, which can affect NOx. A feedstock that is mostly monounsaturated (i.e. oleate) helps to balance the tradeoff between cold flow and oxidative stability. Genetic modification has produced a soybean event, designated 335-13, with a fatty acid profile high in oleic acid (>85%) and with reduced palmitic acid (<4%). This high-oleic soybean oil was converted to biodiesel and run in a John Deere 4045T 4.5-L four-stroke, four-cylinder, turbocharged direct-injection diesel engine. The exhaust emissions were compared with those from conventional soybean oil biodiesel and commercial No. 2 diesel fuel. There was a significant reduction in NOx emissions (α = 0.05) using the high-oleic soybean biodiesel compared with regular soybean oil biodiesel. No significant differences were found between the regular and high-oleic biodiesel for unburned hydrocarbon and smoke emissions.     

Response of generalist and specialist insects to qualitative allelochemical variation

We examined the effects of a set of four biosynthetically related iridoid glycosides, aucubin, catalpol, loganin, and asperuloside, on larvae of a generalist,Lymantria dispar (Lymantriidae), the gypsy moth, and an adapted specialist, the buckeye,Junonia coenia (Nymphalidae). In general,L. dispar grew and survived significantly less well on artificial diets containing iridoid glycoside, compared to a control diet without iridoid glycosides. In choice tests, previous exposure to a diet containing iridoid glycosides caused larvae subsequently to prefer iridoid glycoside-containing diets even though they were detrimental to growth and survival. In contrast,J coenia larvae grew and survived better on diets with aucubin and catalpol, the two iridoid glycosides found in the host plantPlantago lanceolata (Plantaginaceae), than on diets with no iridoid glycoside or with loganin and asperuloside. The results of choice tests of diets with and without iridoid glycosides and between diets with different iridoid glycosides reflected these differences as well. These results are discussed in terms of (1) differences between generalists and specialists in their response to qualitative variation in plant allelochemical content, (2) the induction of feeding preferences, and (3) the evolution of qualitative allelochemical variation as a plant defense.     

HZSM-5固载苯并噻唑离子液体催化合成烷基糖苷及其动力学

以自制苯并噻唑离子液体([HBth]HSO4)为活性组分，HZSM-5分子筛为载体，通过过量溶剂浸渍法制备了固载型苯并噻唑离子液体催化剂([HBth]HSO4/HZSM-5)并用于催化合成烷基糖苷，通过傅立叶变换红外光谱、N2物理脱附、场发射电子显微镜和X射线衍射对催化剂结构进行表征，结果表明，[HBth]HSO4被成功地引入到HZSM-5载体的表面及孔道内。当催化剂用量为1.5 wt%，反应温度为105℃，醇糖摩尔比n(葡萄糖):n(辛醇)=6:1时，辛基糖苷得率达148.8%（产物质量/葡萄糖的质量?100%）。底物拓展及催化剂稳定性研究结果表明，[HBth]HSO4/HZSM-5对烷基糖苷及其衍生物都具有良好的催化效果，且催化剂能稳定循环使用四次，活性组分流失是催化剂失活的主要原因。通过对烷基糖苷催化合成机理和动力学的研究，确定了动力学方程。     

PROBING HIDDEN POLYMERIC INTERFACES USINGIR-VISIBLE SUM-FREQUENCY GENERATION SPECTROSCOPY

Understanding the molecular-level processes underlying interfacial phenomena is important in the area of adhesion. We briefly introduce IR-visible sum-frequency generation spectroscopy (SFG) using a total-internal-reflection geometry for the study of polymer-air, polymer-solid, and polymer-polymer interfaces. The following examples, predominantly of work done in our lab, illustrating differences in molecular structure and dynamic properties at interfaces are presented: the air- and solid-interface structure of an amorphous polystyrene (PS) and a semicrystalline polymer with side-chain crystallinity, poly(octadecyl acrylate) (PA-18); structure of a polymer-polymer interface between thin films of a semicrystalline polymer with side-chain crystallinity, poly(vinyl-N-octadecylcarbamate- co-vinyl acetate), and an amorphous PS; thermal order-to-disorder transitions of the air and solid interface of PA-18, and the interface of this polymer with PS; and dynamic surface-relaxation studies of a rubbed PS film.