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151.
Furton KG Hong YC Hsu YL Luo T Rose S Walton J 《Journal of chromatographic science》2002,40(3):147-155
Solid-phase microextraction (SPME) combined with gas chromatography (GC) is optimized and applied to the analysis of street-cocaine samples followed by the field-testing of isolated chemicals using certified detector dogs. SPME proves to be a very sensitive and rapid method for isolating odor chemicals from street-cocaine samples. SPME-GC and activated charcoal strip (ACS)-SPME-GC signature profile methods are developed for the detection and quantitation of cocaine-odor chemicals, including the optimization of controllable variables such as fiber chemistry, extraction time, and desorption time. The volatile odor chemicals in representative illicit cocaine samples are identified and quantitated by the ACS-SPME-GC signature profile method and direct injection. Field tests with drug detector dogs show methyl benzoate to be the dominant signature odor chemical along with cocaine on U.S. currency at a threshold level of approximately 1-10 microg when spiked or when 10 ng/s methyl benzoate is diffused from polymer bottles, which is required in order to initiate an alert. No other substance studied initiated consistent responses by the drug dogs. The results indicate that the microgram levels of cocaine that have been reported on circulated U.S. currency are insufficient to signal an alert from law-enforcement trained drug detector dogs. 相似文献
152.
153.
A strategy for design of bioimprinted proteins with glutathione peroxidase (GPX) activity has been proposed. The proteins imprinted with a glutathione derivative were converted into selenium-containing proteins by chemical modifying the reactive hydroxyl groups of serines followed by sodium hydrogen selenide displacement. These selenium-containing proteins exhibited remarkable GPX activities and the GPX activities of reduction of H2O2 by glutathione (GSH) were found to be 101-817 U μmol−1, which approaches the activity of a selenium-containing catalytic antibody elicited by a hapten similar to our template. The steady state kinetic study for imprinted protein catalysis revealed Michaelis-Menten kinetics for both H2O2 and GSH, e.g. the pesudo-first-order rate constant kcat (H2O2) and the apparent Michaelis constant Km (H2O2) at 1 mM GSH were calculated to be 784 min−1 and 1.24×10−3 M, respectively, and the apparent second-order rate constant kcat (H2O2)/Km (H2O2) was determined to be 6.33×105 (M min)−1. The kinetics and the template inhibition showed that the strategy might be a remarkably efficient one for generating artificial enzyme with GPX activity. 相似文献
154.
The adsorptive and electrochemical behaviors of medecamycin were investigated on a glassy carbon electrode (GCE) pretreated by anodic oxidation at +1.8 V for 5 min in 0.025 mol l–1 NH3-NH4Cl (pH 8.6) solution. An adsorptive stripping voltammetric method for the determination of medecamycin at the pretreated glassy carbon electrode has been developed. Medecamycin was accumulated in NH3-NH4Cl buffer (pH 9.0) at a potential of –0.7 V (vs. saturated calomel electrode (SCE)) for a certain time, and then determined by second-order differential anodic stripping voltammetry. The second-order differential anodic stripping peak current at +0.72 V was proportional to the concentration of medecamycin in the range 2.0 g ml–1 to 50.0 g ml–1. The detection limit (three times the signal-to-noise) was 1.0 g ml–1 and the relative standard deviation of the results was 3.28% for eight successive determinations of 10.0 g ml–1 medecamycin. This method has been applied to the direct determination of medecamycin in commercial tablets and spiked urine samples with satisfactory results. 相似文献
155.
Thermal activation of molecularly-wired gold nanoparticles on a substrate as catalyst 总被引:5,自引:0,他引:5
Luo J Jones VW Maye MM Han L Kariuki NN Zhong CJ 《Journal of the American Chemical Society》2002,124(47):13988-13989
The ability to prepare nanostructured metal catalysts requires the ability to control size and interparticle spatial and surface access properties. In this work, we report novel findings of an atomic force microscopic investigation of a controlled thermal activation strategy of gold catalysts nanostructured via molecular wiring or linking on a substrate surface. Gold nanocrystals of approximately 2 nm diameter capped by decanethiolate and wired by 1,9-nonanedithiolate on mica substrates were studied as a model system. By manipulating the activation temperature (200-250 degrees C), the capping/wiring molecules can be removed to produce controllable particle size and interparticle spatial morphology. The electrocatalytic activity of the activated nanostructures toward methanol oxidation, which is of fundamental importance to fuel cell catalysis, has been demonstrated. The novelty of the findings is the viability of a thermal activation strategy of core-shell nanostructured catalysts based on molecularly predefined interparticle spatial properties on a substrate, which upon further investigation may form the basis for spatially controllable nanostructured catalysts. 相似文献
156.
A new reagent proflavine-N, N, N', N'-tetraacetic acid (PTA) synthesized in our laboratory has been found useful as a chemiluminescence reagent for the determination of ruthenium (Ru) in pH 2.5 sulfuric acid solution containing acetone, it can be oxidized catalytically by hydrogen peroxide. With Ru(III) as catalyst, it emits light selectively. The linear range is between 2.0 x 10(-8) and 2.0 x 10(-5) g/ml. The detection limit and the recovery rate of the method are 1.0 x 10(-9)g/ml and 96.0-102%, respectively. The method has been satisfactorily applied to determine trace Ru(III) in synthesized sample. 相似文献
157.
钇对Ti-1100高温钛合金热稳定性和蠕变行为的影响 总被引:3,自引:1,他引:3
量了Ti1100和Ti1100/01%Y(质量分数)高温钛合金在600℃/100h空气中暴露后的拉伸性能及在600℃/150MPa/100h条件下的蠕变性能,利用透射电镜观察了合金室温及蠕变后的组织。结果表明,Ti1100合金加入01%的Y后,由于原始β晶粒得到细化,明显改善了其热稳定性;固溶在基体中的硅原子阻碍位错滑移和攀移,使蠕变中的回复过程难于实现;稀土还抑制α2相的长大,所形成的氧化物也阻碍位错的运动。这些均有利于提高Ti1100合金的抗蠕变性能。 相似文献
158.
Recycling Chiral Organocatalyst (4S)-Phenoxy-(S)-proline for Direct Asymmetric Aldol Reaction in Ionic Liquid (bmim)PF6 总被引:1,自引:0,他引:1
Room temperature ionic liquid (bmim)PF6 was evaluated for recycling an organocatalyst (4S)-phenoxy-(S)-proline for direct asymmetric aldol reactions. The desired aldol products were obtained with good yields up to 93.2% and enantioselectivities up to 88.5%, and isolation of the products by simple extraction allowed recycling the ionic liquid containing the immobilized catalyst in subsequent reactions without significant decrease of yields and enantioselectivities. 相似文献
159.
评述了液晶态分子在分析化学中的应用进展,包括其超分子的分子识别作用,液晶在色谱,光谱探针,核磁共振谱等分析化学领域中的应用。 相似文献
160.
Jiann-Kuan Luo Andrew S. Zektzer Raymond N. Castle Ronald C. Crouch John P. Shockcor Gary E. Martin 《Journal of heterocyclic chemistry》1993,30(2):453-460
Two novel heterocyclic ring systems, namely, [1]benzothieno[2,3-c]naphtho[1,2-f]quinoline and [1]benzothieno[2,3-c]naphtho[2,1-g]quinoline have been synthesized and characterized by inverse detected two-dimensional nmr methods. Unequivocal total assignments of the proton and carbon nmr spectra were made through the concerted utilization of HMQC (Heteronuclear Multiple Quantum Correlation) and a combination of HMBC (Heteronuclear Multiple Bond Correlation) and HMQC-TOCSY (HMQC with proton TOtal Correlation Spectroscopy). 相似文献