9—冠—3衍生物载体锂离子选择性电极

报道了两种９－冠－３衍生物的合成，并以合成的化合物作载体研制了对锂离子响应的ＰＶＣ膜电极。以乙基－９－冠－３为载体的锂离子电极的能斯特响应为１０×１０－１～５２×１０－５ｍｏｌ／Ｌ，斜率为（５７４±０３）ｍＶ／ｐ［Ｌｉ］（２５℃），检测下限为２４×１０－５ｍｏｌ／Ｌ。电极具有良好的稳定性和重现性，用于实际样品测定，结果满意     

大黄素的吸附溶出伏安研究

研究了大黄素在甲醇、二氧六环和水的混合溶剂中以１％硼砂为支持电解质在静汞电极上的吸附伏安行为。建立了用微分脉冲吸附溶出伏安法测定其含量的新方法。在－０３０Ｖ（ｖｓＡｇ／ＡｇＣｌ）电位下吸附富集，可得一灵敏的还原溶出峰，峰电位－０７５Ｖ，浓度在５×１０－８～５×１０－９ｍｏｌ／Ｌ范围内与峰电流具有良好的线性关系，最低检出限为１×１０－９ｍｏｌ／Ｌ。该法用于含有大黄素体系的测定简便、快速、可靠。     

高效液相色谱法测定垃圾渗出液中的苯酚和对甲苯酚

介绍用气相色谱－质谱联用技术对垃圾渗出液中的酚类物质进行定性，然后用反相高效液相色谱法对苯酚和对甲苯酚进行定量分析。苯酚和对甲苯酚的线性范围分别为：５０×１０～４０×１０３ｍｇ·Ｌ－１，５０×１０２～１２×１０４ｍｇ·Ｌ－１；最低检出限为１６ｍｇ·Ｌ－１，４００ｍｇ·Ｌ－１；相对标准偏差为１１％和２９％。     

柑桔皮精油中β—胡萝卜素,维生素E和硒含量的测定

柑桔皮精油用ＫＯＨ皂化，用无水乙醚提取不皂化物，蒸去乙醚，残渣用无水乙醇溶解，超滤后取清液注入高效液相色谱仪，以反相柱分离，紫外可见分光检测器检测其中的β－胡萝卜素和维生素Ｅ。柑桔皮精油用正丁醇适当稀释后直接用平台石墨炉原子吸收法测定其中的硒。测定结果：柑桔皮精油中β－胡萝卜素，维生素Ｅ和硒的含量分别为０１６８×１０－３（ＲＳＤ＝５４％，ｎ＝５），１８１×１０－３（ＲＳＤ＝７２％，ｎ＝５）和０５５×１０－６（ＲＳＤ＝３７％，ｎ＝９）。     

兴奋剂马钱子碱的电化学氧化及其伏安法测定

以玻碳电极为工作电极，硫酸钾为支持电解质，在合适的ｐＨ条件下，通过循环伏安法，首次观测到了马钱子碱的不可逆氧化峰。在浓度为２０×１０－４～４０×１０－３ｍｏｌ／Ｌ范围内其峰电流与浓度呈线性关系，检测限为１０×１０－５ｍｏｌ／Ｌ。在正常人体的尿样中，采用标准加入法进行回收实验，其平均回收率为１００８％。该法简便、快速，用５０×１０－４ｍｏｌ／Ｌ的马钱子碱溶液重复测定１０次，相对标准偏差为１８％。对其反应机理作了初步探讨。     

吸附络合物体系的示波分析

Ｉｎ（Ⅲ）在ｐＨ４５７ＨＡｃＮａＡｃ０．１％ＶＣ０．０６％ＨＣｕＰ溶液中，用示波计时电位法可获得良好示波图，其切口电位为Ｅ＝０９０（Ｖｓ．ＳＣＥ），切口高度与Ｉｎ（Ⅲ）浓度在８００×１０－７～１４×１０－５ｍｏｌ／Ｌ范围内成正比，检出限可达５０×１０－７ｍｏｌ／Ｌ吸附络合物组成为Ｉｎ（Ⅲ）：铜铁试剂（ＨＣｕｐ）＝１∶１，条件稳定常数为５９×１０３     

密闭溶样两次金汞齐冷原子吸收光谱法测定煤中微量汞

建立了密闭溶样两次金汞齐冷原子吸收光谱法测定煤样中微量汞的方法，该法具有试剂空白低的特点，适合于测定煤样中的微量汞。研究表明，该法最低检出限为２５×１０－９，精密度为７３％，回收率平均为９９８１％。     

毕兹多克隆抗体的制备和分析应用

用琥珀酸酐－碳二亚胺法和氯磺化法合成了毕兹（Ｂｚ）的两种人工抗原Ｂｚ＿ＨＳ＿ｐｒｏｔｅｉｎ和Ｂｚ＿ＳＯ２＿ｐｒｏｔｅｉｎ。由Ｂｚ＿ＳＯ２＿ＢＳＡ（牛血清白蛋白）诱导出的抗血清能够用来测定１０－９ｍｏｌ·Ｌ－１的Ｂｚ，工作曲线的线性范围在３×１０－５～３×１０－９ｍｏｌ·Ｌ－１，相对标准偏差为１３６％（ｎ＝６），回收率在９０％～１１５％。     

土木香内酯的电化学研究

用单扫示波极谱法，在０１ｍｏｌ／ＬＬｉＣｌ中，土木香内酯有两个极谱还原波：Ｐ１（－１４１Ｖ）和Ｐ２（－１５１Ｖ）（ｖｓ．ＳＣＥ），峰Ｐ１的峰高与浓度在４３×１０－７～１２×１０－６ｍｏｌ／Ｌ和１３×１０－６～１５×１０－５ｍｏｌ／Ｌ范围内呈线性关系，可进行定量分析，用标准加入法能作定性分析，其检测限为２６×１０－７ｍｏｌ／Ｌ。测定了中药土木香中总内酯的含量，其结果令人满意。实验证明土木香内酯的电极过程为带有吸附性的不可逆的逐级电子反应过程，另外，还证明了Ｈ２Ｏ２可催化峰Ｐ１和羟基自由基可催化峰Ｐ２，讨论了土木香内酯清除由邻苯三酚自氧化产生的活性氧自由基（Ｏ－·２）的作用。     

蜂蜜中四环素族抗生素残留量的薄层色谱测定法

残留在蜂蜜中的四环素族抗生素在经Ｓｅｐ－ＰａｋＣ１８小柱固相萃取处理后，用高效正相薄层色谱予以分离，喷雾显色后用紫外灯进行定性分析；使用双波长薄层扫描仪进行定量测定。在蜂蜜中的添加量为００５０×１０－３、０１０×１０－３及０２０×１０－３时，强力霉素（ＤＣ）、土霉素（ＯＴＣ）和四环素（ＴＣ）的回收率分别为９１６％～１００３％、８４５％～１０３１％和７７０％～１０３２％。该法的测定低限可达到１０－３μｇ。     

Enantiomer separation by CEC——Enantiomer separation by packed-capillary electrochromatography

Three chiral compounds were successfully separated in a short time with two enantiomer separation models on packed-capillary electrochromatography (CEC). (i) 75 μm I.D. capillaries were packed with 5 μm β-cyclodextrin (β-CD) chiral stationary phase (CSP). Effects of voltage, pH and concentration of organic modifier on electroosmotic flow (EOF) and chiral separations were investigated systematically. Enantiomers of a neutral compound (benzoin) and a neutral drug (mephenytoin) were separated within a short time with high efficiency. Efficiency of 32 000 theoretical plates per meter and resolution (R_s) of 1.42 were achieved for enantiomers of benzoin using a βCD packed column with 6.2 cm packed length. Efficiency of 45 000 theoretical plates per meter and R_s of 3.40 were obtained for enantiomers of mephenytoin. Especially, the enantiomer separation of mephenytion was performed in just 3.4 min with R_s of 2.60. (ⅱ) 75 μm I.D. capillary was packed with octadecylsilica particles (ODS). Chiral separat     

Regioselectivity of olefin oxidation by iodosobenzene catalyzed by metalloporphyrins : control by the catalyst

The regioselectivity of the oxidation of three monosubstituted olefins, 6-phenoxyhex-1-ene, hex-1-ene and styrene, by iodosobenzene in the presence of various Fe-, Mn- or Cr-tetraaryl-porphyrins, was studied. It was found that, besides epoxides, known products from such systems, allylic alcohols and aldehydes were formed, the latter not being derived from the corresponding epoxides. The relative importance of these reactions greatly depends upon both the metal and porphyrin constituents of the catalyst. More particularly, the competition between epoxidation and allylic hydroxylation can be efficiently controlled by non-bonded interactions between the olefin and porphyrin substituents. No hydroxylation of the aromatic rings and no oxidative dealkylation of the ether function was detected.     

Glycosidase inhibition by macrolide antibiotics elucidated by STD-NMR spectroscopy

A glycosynthase approach was attempted to glycodiversify macrolide antibiotics, using DesR, a family-3 retaining beta-glucosidase involved in the self-resistance mechanism of methymycin production. STD-NMR was used to probe enzyme-substrate interactions. Analysis of competitive STD-NMR experiments between erythromycin A and a chromogenic substrate (pNP-beta-d-glucose) with the hydrolytically inactive nucleophile mutants led us to discover a family of unprecedented glycosidase inhibitors. Analysis of kinetic data with wild-type DesR determined that erythromycin is a competitive inhibitor of the glucosidase (IC50 = 2.8 +/- 0.3 microM and Ki = 2 +/- 0.2 microM) with respect to the hydrolysis of pNP-beta-d-glucose. Comparable inhibitory data was obtained for clarithromycin; however, the inhibitory effect of azithromycin was weak and no significant inhibition was observed with methymycin or d-desosamine. This report documents significant inhibition of glycosidases by macrolide antibiotics and provides insight into the design of novel glycosidase inhibitors based on the macrolactone ring of macrolide antibiotics.     

Membrane solubilization by detergent: resistance conferred by thickness

The commonly held model for membrane dissolution by detergents/surfactants requires lipid transport from the inner to the outer bilayer leaflet ('flip-flop'). Although applicable to many systems, it fails in cases where cross-bilayer transport of membrane components is suppressed. In this paper we investigate the mechanism for surfactant-induced solubilization of polymeric bilayers. To that end, we examine the dissolution of a series of increasingly thick, polymer-based vesicles (polymersomes) by a nonionic surfactant, Triton X-100, using dynamic light scattering. We find that increasing the bilayer thickness imparts better resistance to dissolution, so that the concentration required for solubilization, after a fixed amount of time, increases nearly linearly with membrane thickness. Combining our experimental data with a theoretical model, we show that the dominant mechanism for the surfactant-induced dissolution of polymeric vesicles, where polymer flip-flop across the membrane is suppressed, is the surfactant transport through the bilayer. This mechanism is different both qualitatively and quantitatively from the mechanisms by which surfactants dissolve pure lipid vesicles.     

Antibiotic recognition by binuclear metallo-beta-lactamases revealed by X-ray crystallography

Metallo-beta-lactamases are zinc-dependent enzymes responsible for resistance to beta-lactam antibiotics in a variety of host bacteria, usually Gram-negative species that act as opportunist pathogens. They hydrolyze all classes of beta-lactam antibiotics, including carbapenems, and escape the action of available beta-lactamase inhibitors. Efforts to develop effective inhibitors have been hampered by the lack of structural information regarding how these enzymes recognize and turn over beta-lactam substrates. We report here the crystal structure of the Stenotrophomonas maltophilia L1 enzyme in complex with the hydrolysis product of the 7alpha-methoxyoxacephem, moxalactam. The on-enzyme complex is a 3'-exo-methylene species generated by elimination of the 1-methyltetrazolyl-5-thiolate anion from the 3'-methyl group. Moxalactam binding to L1 involves direct interaction of the two active site zinc ions with the beta-lactam amide and C4 carboxylate, groups that are common to all beta-lactam substrates. The 7beta-[(4-hydroxyphenyl)malonyl]-amino substituent makes limited hydrophobic and hydrogen bonding contacts with the active site groove. The mode of binding provides strong evidence that a water molecule situated between the two metal ions is the most likely nucleophile in the hydrolytic reaction. These data suggest a reaction mechanism for metallo-beta-lactamases in which both metal ions contribute to catalysis by activating the bridging water/hydroxide nucleophile, polarizing the substrate amide bond for attack and stabilizing anionic nitrogen intermediates. The structure illustrates how a binuclear zinc site confers upon metallo-beta-lactamases the ability both to recognize and efficiently hydrolyze a wide variety of beta-lactam substrates.