Assembled dendritic titanium catalysts for enantioselective hetero-Diels-Alder reaction of aldehydes with Danishefsky's diene

A new type of dendritic 2-amino-2'-hydroxy-1,1'-binaphthyl (NOBIN)-derived Schiff-base ligands have been synthesized and applied to the titanium-catalyzed hetero-Diels-Alder reaction of Danishefsky's diene with aldehydes. These reactions afforded the corresponding 2-substituted 2,3-dihydro-4H-pyran-4-ones in quantitative yields and with excellent enantioselectivities (up to 97.2 % ee). The disposition of the dendritic wedges and the dendron size in the ligands were found to have significant impact on the enantioselectivity of the reaction. The recovered dendritic catalyst could be reused without further addition of the Ti source or a carboxylic acid additive for at least three cycles, retaining similar activity and enantioselectivity. The high stability of this type of assembled dendritic titanium catalyst may be attributed to the stabilization effect of large-sized dendron units in the catalyst molecule. The other important phenomenon observed with this catalyst system is that a higher degree of asymmetric amplification has been achieved by attachment of the dendron unit to the chiral ligand, which represents a new advantage of dendrimer catalysts for asymmetric reactions using chiral ligands of lower optical purity.     

聚甲醛自然老化的SEM研究

对户外曝晒3～36个月的聚甲醛(POM)老化形态进行了研究,讨论了老化层厚度,裂纹宽度、裂纹深度及断口形态与老化时间的关系。结果表明:POM的老化导致了材料内部结构由韧性变成脆性而几乎完全丧失物理机械性能。     

A comparison of the stochastic theory of the crystal growth and the Stefan problem

The stochastic theory of the crystal growth is compared with the solution of the Stefan problem in the case of Sn solidification. It is shown that the stochastic theory gives the same results as the solution of the Stefan problem if kinetic processes at the solidification front are very rapid.     

PREPARATION OF POLYSULFONAMIDE/TiO2 NANOCOMPOSITES BY SOL-GEL

Polysulfonamide (PSA) was synthesized at room temperature, the polymerization based on terephthaloyl chloride and 3,3 '-diaminodiphenylsulfone in the common solvent N,N -Dimethyl-acetamide (DMAc). Polysulfonamide/titanium oxide nanocomposites were prepared by sol-gel method. Tetrabutyl titanate(TBT) was added into the polysulfonamide solution, at the same time ,some water was mixed to make the TBT hydrolyze. In the process, hydrochloric acid was used to catalyze the reaction. The polysulfonamide chemistry structure was characterized by FT-IR spectrum. Atomic force microscopy (AFM) was employed to observe the microstructure of the composite film. The thermal property was investigated by TGA.The results show that we have succeeded to synthesize the polysulfonamide, TiO2particles were well distributed in the composite film and average size was about 20 nm on average, the heat-resistance of nanocomposite was batter than the pure polysulfonamide.     

Vascular endothelial and smooth muscle cell culture on NaOH-treated poly(epsilon-caprolactone) films: a preliminary study for vascular graft development

Tissue engineering offers the potential of providing vessels that can be used to replace diseased and damaged native blood vessels. The endothelization of a synthetic vascular graft minimizes the failures associated with blood clotting and platelet activation. The aim of this study was to culture vascular-derived endothelial and smooth muscle cells on both untreated and NaOH-treated poly(epsilon-caprolactone) (PCL) films, a biocompatible and bio-resorbable polymer, and to evaluate the behavior of both cell types as a preliminary study for vascular graft development. PCL films were prepared by hot pressing; characterized by DSC, IR, SEM, and scanning force microscopy; and treated with NaOH to increase the surface hydrophilicity before cell culture. Endothelial and smooth muscle cells, isolated from pig cava vein, were characterized by immunofluorescence and confocal microscopy studies of endothelial nitric oxide synthase and alpha-smooth muscle actin. Good adhesion, growth, viability and morphology of both the endothelial and smooth muscle cells on PCL films were obtained, but a light stimulation of mitochondrial activity was observed during short culture times. NaOH treatment improved the adhesion and enhanced the proliferation in both cell types. This verified the possible use of this modified polymer as a support in the preparation of a synthetic vascular graft. [Diagram: see text] SEM micrograph of smooth muscle cells cultured on NaOH-treated PCL film. (Original magnification: 1000x).     

Investigation of Tomato Plant Defence Response to Tobacco Mosaic Virus by Determination of Methyl Salicylate with SPME-Capillary GC-MS

Headspace SPME was applied to investigation of tomato plant defence response to tobacco mosaic virus (TMV) by determination of compounds emitted from tomato plants at the extraction conditions of 25 °C and 15 min. It was found that TMV-inoculated tomato plant released large amount of methyl salicylate (MeSA) as response to TMV and MeSA concentration changed dramatically with time after inoculation. Gaseous MeSA as a signaling compound could induce in surrounding tomato plants to produce salicylic acid (SA) and synthesize and release MeSA. These results show that MeSA might be an airborne plant-signalling molecule in tomato plant response to TMV. The present method provided low detection limit of 2.0 ng L^–1 and needed little sample preparation time (15 min), so the method makes it easy to find the critical times of tomato plant response to TMV by fast determination of MeSA released from tomato plant.     

Method development for the quantitation of ABT-578 in rabbit artery tissue by 96-well liquid-liquid extraction and liquid chromatography/tandem mass spectrometric detection

Quantitative determination of drug concentrations in tissue samples can provide critical information for drug metabolism, kinetics, and toxicity evaluations. For analysis of tissue samples using liquid chromatography/tandem mass spectrometric (LC/MS/MS) detection, homogenization is a critical step in achieving good assay performance. Assay performance can be closely evaluated by spiking the drug directly into tissue samples prior to homogenization. It is especially important to include this assay evaluation for the analysis of artery tissue samples because artery tissue is very elastic, making it quite a challenge to develop an effective procedure for homogenization. An LC/MS/MS assay in 96-well format using liquid-liquid extraction was developed for analyzing ABT-578 in rabbit artery samples. Tissue quality control samples were prepared by spiking ABT-578 stock solutions directly into the tissue before homogenization. The usage of the tissue control samples gives a thorough evaluation of the sample preparation process that includes both homogenization and sample extraction. A 20% blood in saline solution was used as a homogenization solution. Calibration standards were made by spiking ABT-578 into rabbit whole blood. Blood quality control samples were also prepared by spiking ABT-578 into rabbit whole blood. These blood QC samples were used to confirm the validity of the calibration curve. A lower limit of quantitation of 0.050 ng/mL was achieved. The linear dynamic range of blood standards was from 0.050-30.3 ng/mL with the correlation coefficient (r) ranging from 0.9969-0.9996. Overall %CV was between 1.3 and 7.0%, and analytical recovery was between 98.2 and 105.8% for blood QC samples. The %CVs for tissue QC samples were between 6.7 and 13.0%, and analytical recovery after correction was between 93.5 and 114.3%.