On NO3--H2O interactions in aqueous solutions and at interfaces

The constrained molecular-dynamics technique was employed to investigate the transport of a nitrate ion across the water liquid/vapor interface. We developed a nitrate-ion-water polarizable potential that accurately reproduces the solvation properties of the hydrated nitrate ion. The computed free-energy profile for the transfer of the nitrate ion across the air/water interface increases monotonically as the nitrate ion approaches the Gibbs dividing surface from the bulk liquid side. The computed density profiles of 1M KNO(3) salt solution indicate that the nitrate and potassium ions are both found below the aqueous interface. Upon analyzing the results, we conclude that the probability of finding the nitrate anion at the aqueous interface is quite small.     

Shape-coded silica nanotubes for biosensing

Shape-coded silica nanotubes (SNTs) were fabricated on the basis of template synthesis as a new dispersible microarray system. The template synthesis of shape-coded SNTs begins with the fabrication of a porous alumina film that has well-defined cylindrical pores with two or more different diameter segments by multistep anodization of an aluminum substrate. Then, SNTs were fabricated with a surface sol-gel method that can control the wall thickness of SNTs on the single-nanometer level. Attractively, the difference in optical reflectance between the segmented parts of individual silica nanotube makes it very convenient to identify each nanotube and enables these shape-coded SNTs to work as coding materials for biosensing.     

Electrical properties of polypyrrole wires measured by scanning probe microscope

Hybrid wires composed of metal and conducting polymer (polypyrrole, Ppy) were electrochemically synthesized using a template synthesis method. We showed that the dimensions of the hybrid wires can be tailored by controlling the time of electrolysis. The electrical properties of Ppy having different lengths were measured using a scanning probe microscope (SPM) tip as an electrode without aligning the hybrid wires on a substrate. Especially, temperature-dependent characteristics of the I-V curve were determined. As we expected, the shorter the Ppy wire is, the better the current response produced. The activation energy of each Ppy wire is determined. It is confirmed that the electrical properties of a single wire of Ppy can be measured by SPM.     

Chiral phosphoramide-catalyzed aldol additions of ketone trichlorosilyl enolates. Mechanistic aspects

The mechanism of the catalytic, enantioselective addition of trichlorosilyl enolates to aldehydes has been investigated. Kinetic studies using ReactIR and rapid injection NMR (RINMR) spectroscopy have confirmed the simultaneous operation of dual mechanistic pathways involving either one or two phosphoramides bound to a siliconium ion organizational center. This mechanistic dichotomy was initially postulated on the basis of catalyst loading studies and nonlinear effects studies. This duality explains the difference in reactivity and stereoselectivity of various classes of phosphoramides. Determination of Arrhenius activation parameters revealed that aldol addition occurs through the reversible albeit unfavorable formation of an activated complex, and natural-abundance 13C NMR kinetic isotope effect (KIE) studies have determined that the turnover limiting step is the aldol addition. A thorough examination of a range of phosphoramides has established empirical structure-activity selectivity relationships. In addition, the effects of catalyst loading, rate of addition, solvents, and additives have been studied and together allow the formulation of a unified mechanistic picture for the aldol addition.     

Chemical and biological evaluation on scopadulane-type diterpenoids from Scoparia dulcis of Vietnamese origin

From the aerial parts of Scoparia dulcis L. (Scrophulariaceae) grown in Vietnam, four scopadulane-type diterpenoids (4-7), of which 7 is new and was given the trivial name scopadulcic acid C, together with nine known compounds were isolated. Their structures were elucidated by spectroscopic analyses. The absolute configurations of 4-7 were ascertained by applying the modified Mosher's method to iso-dulcinol (6). The isolation of the lignans nirtetralin and niranthin for the first time from S. dulcis is also of chemotaxonomic interest. The cytotoxic activity in KB cells, inhibitory effect on LPS/IFNgamma-induced NO production, inhibition of multidrug resistance (MDR), and antibacterial and antifungal activities of the scopadulane-type diterpenoids 4-7 were examined in this study.     

Apparent 'electrocatalytic' activity of multiwalled carbon nanotubes in the detection of the anaesthetic halothane: occluded copper nanoparticles

The electrocatalytic detection of the anaesthetic halothane on a multiwalled carbon nanotube modified glassy carbon electrode is reported with a low limit of detection of 4.6 microM. A thorough investigation of the underlying cause of this apparent catalytic effect is undertaken by comparing the response of various carbon electrodes including glassy carbon, basal- and edge-plane pyrolytic graphite electrodes (bppg and eppg respectively) to increasing additions of halothane. The reduction of halothane is shifted by 250-300 mV to more negative potentials at an eppg electrode than that observed at the GC-CNT electrode. Therefore the results of this investigation show that, surprisingly, the electrocatalysis is not solely due to the introduction of edge-plane-like defect sites on the carbon nanotubes as is commonly found for many other substrates showing favourable voltammetry at nanotube modified electrodes. Instead, we reveal that in this unusual case the electroactive sites for the reduction of halothane are due to the presence of copper nanoparticles occluded within the carbon nanotubes during their production, which are never completely removed by standard purification techniques such as acid washing. This is only the third known case where apparent electrocatalysis by carbon nanotube modified electrodes is due to occluded metal-related nanoparticles within the nanotube structure, rather than the active sites being the edge-plane-like defect sites on the nanotubes. Furthermore this is the first case where the active sites are nanoparticles of copper metal, rather than metal oxide nanoparticles (namely oxides of iron(II)/(III)) as was found to be the case in the previous examples.     

Highly diastereoselective enolate addition of O-protected alpha-hydroxyacetate to (S(R))-tert-butanesulfinylimines: synthesis of taxol side chain

The taxol side chain (S(R),2R,3S)-N-tert-butanesulfinyl-O-Boc-3-phenylisoserine benzyl ester 4c was synthesized through a lithium enolate addition of O-Boc-alpha-hydroxyacetate benzyl ester 5c to benzylidene (S(R))-tert-butanesulfinamide 6a in excellent yield and diastereoselectivity. By similar approach, a series of enantiopure 3-substituted isoserine benzyl esters 4 useful for the semi-syntheses of taxol derivatives were also prepared in high to excellent yields and diastereoselectivities. The diastereoselective addition mechanism was discussed on the basis of the experimental observation.     

Continuous separation of microparticles by size with direct current-dielectrophoresis

Direct current-dielectrophoresis (DC-DEP), the induced motion of the dielectric particles in a spatially nonuniform DC electric field, is demonstrated to be a highly efficient method to separate the microparticles by size. The locally nonuniform electric field is generated by an insulating block fabricated inside a polydimethylsiloxane microchannel. The particle experiences a negative DEP (accordingly a repulsive force) at the corners of the block, where the local electric-field strength is the strongest. Thus, the particle deviates from the streamline and the degree of deviation is dependent on the DEP force (i.e., the particle size). Combined with the electrokinetic flow, mixed polystyrene particles of a few micrometers difference in diameter can be continuously separated into distinct reservoirs. For separating target particles of a specific size, it is required to simply adjust the voltage outputs of the electrodes. A numerical model based on the Lagrangian tracking method is developed to simulate the particle motion and the results showed a reasonable agreement with the experimental data.     

超高效液相色谱-荧光法测定大鼠尿液中的黄蝶呤、异黄蝶呤、酪氨酸和色氨酸

建立了一种大鼠尿液中黄蝶呤、异黄蝶呤、酪氨酸和色氨酸的超高效液相色谱-荧光分析方法(UPLCFLD),大鼠尿液利用甲醇和乙腈除蛋白后,采取C18固相萃取小柱进行净化,然后用UPLC-FLD法进行测定。黄蝶呤、异黄蝶呤、酪氨酸和色氨酸分别在0.01~10.0,0.005~10.0,0.5~100,0.5~200mg·L-1范围内与色谱峰面积呈线性关系,4种物质的仪器检测限分别为0.005,0.000 3,0.004和0.002mg·L-1,加标回收率除黄蝶呤在61.1%~78.0%之间,其余各物质回收率均在86.0%~110.0%之间,RSD小于10.5%。     

空气环境下煤粉流LIBS多元素同时检测中激光能量研究

考察了大气环境下激光诱导击穿光谱适用于煤粉流多元素同时检测的激光能量范围,分析了造成煤粉流测量谱线信号波动的原因,得到了适用于煤粉流多元素同时检测的激发区域功率密度范围和最佳功率密度。实验选取能量范围为20～160 mJ,粒径小于200 μm煤粉颗粒经下料口自由下落形成煤粉流束,通过螺杆式给粉机控制流量,波长1 064 nm脉冲激光聚焦后作用于下降的煤粉流束上,产生等离子体,光谱仪采集等离子体发射光谱信号,分析结果表明：实验台架下适于煤粉流LIBS检测的能量范围为30～60 mJ,对应激发前沿功率密度选取范围14.4～34.4 GW·cm-2,最佳测量功率密度19.5 GW·cm-2。