Chemical Reactions and Kinetics of the Carbon Monoxide Coupling in the Presence of

The chemical reactions and kinetics of the catalytic coupling reaction of carbon monoxide to diethyl oxalate were studied in the presence of hydrogen over a supported palladium catalyst in the gaseous phase at the typical coupling reaction conditions. The experiments were performed in a continuous flow fixed-bed reactor. The results indicated that hydrogen only reacts with ethyl nitrite to form ethanol, and kinetic studies revealed that the rate-determining step is the surface reaction of adsorbed hydrogen and the ethoxy radical (EtO-). A kinetic model is proposed and a comparison of the observed and calculated conversions showed that the rate expressions are of rather high confidence.     

Synthesis of new 1,3-bis（phenylethynyl）disilazanes

Three new 1,3-bis(phenylethynyl)disilazanes were synthesized from the reaction of 1,3-dichlorodisilazanes with (phenylethy- nyl)lithium,and characterized by infrared (IR) spectra,nuclear magnetic resonance (NMR) and mass spectrometry (MS).     

吸附式增湿饱和器

本文介绍了美国GE公司DPG—300分流湿度发生器的工作原理。针对该发生器的增湿饱和度不够的缺陷,提出了改进措施。改进的方法是通过在增湿饱和器内放置能够吸附水的吸附材料而实现的。     

Probing the kinetic landscape of transient peptide-protein interactions by use of peptide (15)n NMR relaxation dispersion spectroscopy: binding of an antithrombin peptide to human prothrombin

Protein-ligand interactions may lead to the formation of multiple molecular complexes in dynamic exchange, affecting the kinetic and thermodynamic characteristics of the binding equilibrium. We followed the dissociation kinetics of the transient and specific complex of an antithrombotic peptide N-acetyl-Asp(55)-Phe-Glu-Glu-Ile-Pro(60)-Glu-Glu-Tyr-Leu-Gln(65) with human prothrombin by use of (15)N NMR relaxation dispersion spectroscopy of the peptide. Every one of the five (15)N-labeled adjacent residues of the peptide exhibited apparently different kinetic exchange and relaxation behaviors, which were especially evident at different concentrations of prothrombin. Binding-induced (15)N relaxation dispersion of residues Phe(56), Glu(57), Glu(58), and Ile(59) can be fitted phenomenologically to a two-site on-and-off exchange mechanism with physically feasible relaxation and kinetic parameters obtained for residues Phe(56), Glu(58), and Ile(59), independent of the prothrombin concentration. The apparent kinetic parameters of Glu(57) show some dependence on the concentration of prothrombin and the extracted transverse relaxation rate for Glu(57) in the bound state was severalfold higher than that expected for a protein-peptide complex with a size of approximately 72 kDa. In addition, the equilibrium population of the bound peptide obtained for Glu(57) was inconsistent with those for Phe(56), Glu(58), and Ile(59) and with the prothrombin/peptide ratios used in the experiments. These discrepancies can be explained by the presence of two conformations for the peptide-protein complex exchanging at a rate of approximately 100 s(-)(1). In all, our study shows that fast dissociation of protein-peptide complexes can be studied quantitatively using peptide (15)N NMR relaxation dispersion measurements without a precise knowledge of the peptide and protein concentrations. In addition, protein titration was found to improve the accuracy of quantitative analysis and may make it possible to determine the rate of conformational changes within the protein-peptide complex.     

Optimization of the electrokinetic supercharging preconcentration for high-sensitivity microchip gel electrophoresis on a cross-geometry microchip

We developed a novel on-line preconcentration procedure for microchip gel electrophoresis (MCGE), which enables application of electrokinetic supercharging (EKS) for highly sensitive detection of DNA fragments on a cross-geometry microchip. In comparison with conventional pinched injection using the cross microchip, the present approach allows loading a much larger amount of the sample by taking advantage of a newly developed operational mode. In order to obtain high preconcentration effect and prevent splitting of an enriched sample into subchannels, i.e., off the detector range, effects of the voltage applied on the reservoirs and the time of isotachophoretic preconcentration were examined. The optimal balance between the voltage and time was found for a high-sensitivity analysis of DNA fragments. After experimental optimization the detection limit of a 150 bp fragment was as low as 0.22 mg/L (S/N = 3) that is 10 times better than using the conventional pinched injection.