NMR observations of 13C-enriched coenzyme B12 bound to the ribonucleotide reductase from Lactobacillus leichmannii

The 13C NMR resonance and one-bond 1H-13C coupling constants of coenzyme B12 enriched in 13C in the cobalt-bound carbon have been observed in the complex of the coenzyme with the B12-dependent ribonucleotide reductase from Lactobacillus leichmannii. Neither the 13C NMR chemical shift nor the 1H-13C coupling constants are significantly altered by binding of the coenzyme to the enzyme. The results suggest that ground-state Co-C bond distortion is not utilized by this enzyme to activate coenzyme B12 for C-Co bond homolysis.     

Synthesis of trifluoromethyl-promoted functional pyrazolo[1,5-a]pyrimidine and pyrazolo[5,1-d][1,2,3,5]tetrazine-4(3H)-ones

Ethyl 5-amino-3-trifluoromethyl-1H-pyrazole-4-carboxylate (1) was efficiently synthesized via the condensation of ethyl cyanoacetate and trifluoroacetic anhydride, followed by chloridization and the condensation with aqueous hydrazine. Its unique reactivity was exploited for the synthesis of trifluoromethylated pyrazolo[1,5-a]pyrimidine (5) and pyrazolo[5,1-d][1,2,3,5]tetrazine-4(3H)-ones (8a-j). Among them, 5 was firstly found to be a novel fluorescent molecule that might be exploited as an attractive fluorophore for possessing many binding sites, and its fluorescence intensity was obviously stronger than its methyl analogue. 8 were found to be a new chemical class of potential monocotyledonous Echinochloa crus-galli L. Beauv inhibitors, and were more active than their methyl analogues.     

Monolithic silica capillary column with coated cellulose tris(3,5-dimethylphenylcarbamate) for capillary electrochromatographic separation of enantiomers

Monolithic silica capillary columns were prepared by a sol-gel process in fused-silica capillaries with an inner diameter of 50 microm and were modified by coating of cellulose tris(3,5-dimethylphenylcarbamate). Influences of the factors in the modification process on enantiomer separations were investigated. The prepared columns were used to perform enantiomer separations by CEC. Fifteen and two pairs of enantiomers were separated under aqueous and nonaqueous mobile phases, respectively, and most of them were baseline-separated with very high column efficiencies. The Van Deemter curve was found flat under high linear velocity of the mobile phase, which indicated favorable kinetic properties of the prepared columns. Baseline separation of a pair of enantiomers was achieved in 90 s with high-column efficiency by short-end separation under high voltage.     

CE-LIF coupled with flow cytometry for high-throughput quantitation of fluorophores in single intact cells

We report a method of coupled CE-LIF detection with flow cytometry for high-throughput determination and quantitation of fluorophores in single intact K562/S (KS) cells. The membrane properties of KS cell including fluophore transport rate and apparent permeability coefficient were further quantitatively characterized. The method has advantages for accurate quantitation and unique capacity of high-throughput analysis. The strategy will be useful for the quantitation of fluorophores in the intact cells, such as measurement of multidrug resistance, quantitation of specific protein expression, and quantitative characterization of protein and enzyme functions.     

Capillary electrochromatography with zwitterionic stationary phase on the lysine-bonded poly(glycidyl methacrylate-co-ethylene dimethacrylate) monolithic capillary column

A polymer-based neutral monolithic capillary column was prepared by radical polymerization of glycidyl methacrylate and ethylene dimethacrylate in a 100 mum id fused-silica capillary, and the prepared monolithic column was subsequently modified based on a ring opening reaction of epoxide groups with 1 M lysine in solution (pH 8.0) at 75 degrees C for 10 h to produce a lysine chemically bonded stationary phases in capillary column. The ring opening reaction conditions were optimized so that the column could generate substantial EOF. Due to the zwitterionic functional groups of the lysine covalently bonded on the polymer monolithic rod, the prepared column can generate cathodic and anodic EOF by varying the pH values of running buffer during CEC separation. EOF reached the maximum of -2.0 x 10(-8) m2v(-1)s(-1) and 2.6 x 10(-8) m2v(-1)s(-1) with pH of the running buffer of 2.25 and 10, respectively. As a consequence, neutral compounds, ionic solutes such as phenols, aromatic acids, anilines, and basic pharmaceuticals were all successfully separated on the column by CEC. Hydrophobic interaction is responsible for separation of neutral analytes. In addition, the electrostatic and hydrophobic interaction and the electrophoretic migration play a significant role in separation of the ionic or ionizable analytes.     

Field emission properties and synthesis of carbon nanotubes grown by rf plasma-enhanced chemical vapor deposition

Plasma-enhanced chemical vapor deposition (PECVD) method was employed to grow the Fe-catalyzed carbon nanotubes (CNTs). The grown CNTs with a uniform diameter in the range of about 10-20 nm and the typical lengths beyond 1 μm resulted in a very high aspect ratio. The Raman and TEM results showed that the grown CNTs contained a large amount of carbonaceous particles and crystal defects, such as pentagon-heptagon pair defects. XPS measurement indicated that the CNTs had CH covalent bonds. Field emission characteristics exhibited the low turn-on threshold field of 2.75 V/μm and the maximum emission current density of 7.75 mA/cm² at 6.5 V/μm. The growth mechanism of CNTs and the effects of hydrogen plasma on their structure were discussed.     

Jet formation in shock-heavy gas bubble interaction

The influences of the acoustic impedance and shock strength on the jet formation in shock-heavy gas bubble interaction are numerically studied in this work. The process of a shock interacting with a krypton or a SF 6 bubble is studied by the numerical method VAS2D. As a validation, the experiments of a SF 6 bubble accelerated by a planar shock were performed. The results indicate that, due to the mismatch of acoustic impedance, the way of jet formation in heavy gas bubble with different species is diversified under the same initial condition. With respect to the same bubble, the manner of jet formation is also distinctly different under different shock strengths. The disparities of the acoustic impedance result in different effects of shock focusing in the bubble, and different behaviors of shock wave inside and outside the bubble. The analyses of the wave pattern and the pressure variation indicate that the jet formation is closely associated with the pressure perturbation. Moreover, the analysis of the vorticity deposition, and comparisons of circulation and baroclinic torque show that the baroclinic vorticity also contributes to the jet formation. It is concluded that the pressure perturbation and baroclinic vorticity deposition are the two dominant factors for the jet formation in shock-heavy gas bubble interaction.     

On Dirichlet Problem for a Class of Delayed Reaction–Diffusion Equations with Spatial Non-locality

We consider a very general class of delayed reaction–diffusion equations in which the reaction term can be non-monotone as well as spatially non-local. By employing comparison technique and a dynamical system approach, we study the global asymptotic behavior of solutions to the equation subject to the homogeneous Dirichlet condition. Established are threshold results and global attractiveness of the trivial steady state, as well as the existence, uniqueness and global attractiveness of a positive steady state solution to the problem. As illustrations, we apply our main results to the local delayed diffusive Mackey–Glass equation and the nonlocal delayed diffusive Nicholson blowfly equation, leading to some very sharp results for these two particular models.     

一种新型酶生物燃料电池阳极构建及性能研究

通过酸化碳纳米管(CNTs)和β-环糊精(β-CD)之间的范德华力作用, 实现CNTs的β-CD功能化. β-CD具有内腔疏水、外壁亲水的环状结构, 其内腔容易与二茂铁(Fc)形成稳定的主客体包合结构, 实现Fc在碳纳米管上的高效固载; 再将CNTs-β-CD-Fc复合物与葡萄糖氧化酶(GOD)混合, 采用戊二醛实现酶分子间的交联, 形成GOD/CNTs-β-CD-Fc复合物, 然后将其涂覆到玻碳电极(GC)上, 得到一种新型的酶生物燃料电池阳极(GOD/CNTs-β-CD-Fc/GC). 采用同步热分析法、傅里叶变换红外光谱和透射电子显微镜对所制备的CNTs-β-CD-Fc复合物进行了表征, 采用循环伏安法研究了GOD/CNTs-β-CD-Fc/GC电极对葡萄糖氧化的催化性能. 结果表明: 在同等实验条件下, 没有固载Fc的GOD/CNTs- β-CD/GC电极基本无催化电流, 而GOD/CNTs-β-CD-Fc/GC电极表现出比GOD/CNTs-Fc/GC电极更为优越的电催化性能. 进一步以GOD/CNTs-β-CD-Fc/GC电极或GOD/CNTs-Fc/GC电极为酶阳极, 商用催化剂E-TEK Pt/C电极(E-TEK Pt/C/GC)为阴极, 构建葡萄糖/氧气生物燃料电池(EBFC), 结果表明前者的最大功率密度(33 μW·cm^-2, 0.18 V)几乎是后者的三倍(11.7 μW·cm^-2, 0.16 V). 通过记录开路电位随时间的变化研究了EBFC的稳定性, 以GOD/CNTs-β-CD-Fc/GC电极为阳极的EBFC在连续工作9 h后仍保留了92%的开路电位, 表明该电池具有良好的连续工作稳定性. 我们提出的这种新型生物燃料电池阳极的构造方法, 为构建高性能、高稳定性的葡萄糖/氧气EBFC提供了新的思路.     

Direct Synthesis of High Purity Silicon Wires by Electrorefining in Molten KF-NaF Eutectic

The electrochemical synthesis silicon wires by electrorefining metallurgical grade silicon in thermally dried and pre-electrolyzed molten KF-NaF eutectic were studied at temperatures 800-900 oC using cyclic voltammetry and ac impedance. One oxidation peak at -0.14 V could be attributed to the reaction of Si to Si⁴⁺. A cathodic peak occurred at -0.56 V in the cyclic voltammogram and one response semicircle in the ac impedance spectrum was observed, supporting a one-step electrochemical reduction process of Si⁴⁺→Si. The electrochemical reaction of silicon was controlled by the diffusion process. The purity of electrorefined silicon wires was up to 99.999% by ICP-MS analysis.