Kinetic Spectroelectrochemical Assay for Uric Acid in Human Urine

A spectroelectrochemical (SEC) assay for uric acid in human urine has been developed that is essentially reagent-free and involves relatively short analysis times of ∼12 min per specimen using a single-point standard addition approach. The SEC method was demonstrated to be selective for uric acid in human urine, avoiding interference through both the usual control parameters (electrolysis potential and measurement wavelength) and the relatively slow kinetics of a post-electrolysis reaction involving the oxidation product. Results from the SEC analysis of a split set of human urine specimens were well correlated to those obtained using a standard high-performance liquid chromatography method, suggesting the feasibility of clinical applications.     

Conformation dependence of DNA electrophoretic mobility in a converging channel

The electrophoresis of λ‐DNA is observed in a microscale converging channel where the center‐of‐masses trajectories of DNA molecules are tracked to measure instantaneous electrophoretic (EP) mobilities of DNA molecules of various stretch lengths and conformations. Contrary to the usual assumption that DNA mobility is a constant, independent of field and DNA length in free solution, we find DNA EP mobility varies along the axis in the contracting geometry. We correlate this mobility variation with the local stretch and conformational changes of the DNA, which are induced by the electric field gradient produced by the contraction. A “shish‐kebab” model of a rigid polymer segment is developed, which consists of aligned spheres acting as charge and drag centers. The EP mobility of the shish‐kebab is obtained by determining the electrohydrodynamic interactions of aligned spheres driven by the electric field. Multiple shish‐kebabs are then connected end‐to‐end to form a freely jointed chain model for a flexible DNA chain. DNA EP mobility is finally obtained as an ensemble average over the shish‐kebab orientations that are biased to match the overall stretch of the DNA chain. Using physically reasonable parameters, the model agrees well with experimental results for the dependence of EP mobility on stretch and conformation. We find that the magnitude of the EP mobility increases with DNA stretch, and that this increase is more pronounced for folded conformations.     

Preparation of Au Nanoparticles on Surface of Two Supports by Adsorption Phase Synthesis

By utilizing adsorption phase synthesis (APS), Au nanoparticles were prepared on the surface of SiO₂ with or without modification by Ni(OH)₂. TEM, XRD, and UV‐vis were employed to characterize the morphology of Au particles on the surface of two kinds of supports. The results showed that the average size of Au particles on the SiO₂ surface modified by Ni(OH)₂ was less than 5 nm. Due to high surface isoelectric point, Au particles formed in the adsorption layer were prone to distribute on the surface of SiO₂ modified by Ni(OH)₂. With content of Ni(OH)₂ in samples increasing, more Au particles with small size appeared on the support surface.     

Crystal Transformation of Nylon 11 Using in situ WAXD

Nylon I I is a high-performance semicrystalline polymer which was used widely in manyfields. In recent years, the curious ferroelectric and piezoelectric propel'ties of nylon I Iwere foundl'2. It is well known that piezoelectricity is related to the crystal form ofNylon I 1.The sample was mounteds in a capillary (diameter was Zmm) within a small ovenwith mica windows. The scattered intensity was recorded from Q = 0.2 to 6.5 A-] (Q =ursine/~) using steps of AQ=o.o5A-'. The values of the p…     

The origin of the high performance of tungsten carbides/carbon nanotubes supported Pt catalysts for methanol electrooxidation

The Pt supported on WC modified MWCNT catalysts (PtWC/MWCNT) were synthesized by the combination of organic colloidal and intermittent microwave heating (IMH) methods for the first. The results proved the better performance of the PtWC/MWCNT catalyst than that of Pt/C for methanol oxidation in terms of the onset potential and peak current density. The synergistic effect between Pt nanoparticles and WC and the structure effect of the MWCNTs could be the reasons to result in the high activity. The CO stripping test provided the evidence that the onset potential shift for methanol oxidation is consistent with the reduction in the overpotential for the CO oxidation on PtWC/MWCNT catalyst. Therefore, the mechanism of the high performance for methanol oxidation on PtWC/MWCNT catalyst is probably the easier oxidation of CO-like species which cause high overpotential for further oxidation of methanol.     

固相微萃取-气相色谱/质谱法测定博物馆空气中总挥发性有机物

采用固相微萃取-气相色谱/质谱(SPME-GC/MS)法测定博物馆室内空气中总挥发性有机物(TVOC)的含量,建立了一种更适合于博物馆室内空气中TVOC的检测方法.对7种挥发性有机物标样进行SPME-GC/MS定性定量分析,进样口温度230 ℃,柱温:起始温度45 ℃,保持3 min,以16 ℃/min的速率程序升温至250 ℃,保持5 min.结果表明,该方法在0.014～0.914 μg/L浓度范围内具有良好的线性关系,最低检出限在1.4～14 ng/L之间,相对标准偏差小于5.28%.该方法方便快捷、对待测物的选择性高、重复性好、采样无需电源、无需溶剂.     

Chemical constituents from Schisandra sphenanthera

The chemical constituents of the stems of Schisandra sphenanthera are described for the first time. This investigation has resulted in the isolation of a new phenolic glycoside （1）, along with seven known compounds. The structure of 1 was assigned by using spectroscopic techniques, including 2D NMR spectra.