测定本体粘度的拉伸蠕变方法

测量高聚物粘度的方法很多。对高粘度样品经常采用拉伸蠕变方法,这时测定的是拉伸粘度习η_T: σ=η_T(?)_f其中σ是拉伸应力,(?)_f是由此引起的拉伸流动的应变速率。由于高聚物是粘弹性材料。因此必须设法区分弹性形变和流动形变,才能得到η_T值。Bueche和Kraus等曾分别用拉伸蠕变方法研究聚甲基丙烯酸甲酯和聚顺丁二烯的本体粘度。他们所用的处理方法有三     

Design and synthesis of 2-alkylbenzimidazole derivatives as novel non-peptide angiotensin Ⅱ AT1 receptor antagonists

A series of 2-alkylbenzimidazole derivatives 9a-n have been designed and synthesized as a novel class of non-peptide angiotensin Ⅱ AT1 receptor antagonists. The synthesized compounds were evaluated for their antagonism of angiotensin Ⅱ, induced contraction in the rabbit thoracic aortic ring and the results showed that compounds 9a, 9g and 9j exhibited potent antagonistic activity of AT1 receptor.     

Structural characterization of a novel self-assembly heterohexanuclear complex: [Ni2Ag4(μ-dppm)4(pymt)6](SbF6)2 · 2DMF · H2O

A novel heterohexanuclear complex [Ni₂Ag₄(μ-dppm)₄(pymt)₆](SbF ₆)₂ · 2DMF · H₂O (1), was synthesized by self-assembly with [Ag₂(μ-dppm)₂(MeCN)₂](SbF₆) ₂ and [Et₄N][Ni(pymt)₃] (dppm = bis(diphenylphosphino)methane, pymt = pyrimidine-2-thiolate) as components and characterized by IR spectra, elemental analysis, ¹H-NMR spectrum, ³¹P-NMR spectrum and Visible-Ultraviolet spectrum. Structure of the complex was determined by X-ray analysis.     

Theoretical study of structure and stability of fullerene derivative: C50O

A total of eight possible isomers of C₅₀O, an oxide of fullerene C₅₀ (D_5h), have been investigated by B3LYP/3‐21G calculations. The isomer, which has an annulene‐like structure with oxygen bridging across a [5,6] type C? C bond at the site between the pole and the equatorial belt, is found being the ground state of C₅₀O. Four isomers are relatively more stable and the energy differences between them are not large. This result indicates that more than one C₅₀O isomer will coexist once C₅₀O is synthesized. The relative stabilities of the C₅₀O isomers may be determined mainly by the strain release and by the formation of the cyclic phenylene substructure at the equatorial belt of the cage. The calculated nucleus independent chemical shifts (NICS) of the C₅₀O isomers will be useful because from them one can expect outstanding NMR properties that can lead to their identification and characterization. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Solid-phase synthesis of 1,2-diheterocyclic-substituted (E)-olefins from a supported selenium resin

A library of 1,2,3-triazoles, isoxazoles, 1,2,4-oxadiazoles, and isoxazoline-containing 1,2-di-heterocyclic-substituted compounds with three points of diversity linked by an E double bond were prepared. Key steps include a 1,3-dipolar cycloaddition and Porco's two-step, one-pot condensation and alpha-alkylation reaction of selenium resins.     

Influence of the water molecule on cation-pi interaction: ab initio second order Møller-Plesset perturbation theory (MP2) calculations

The influence of introducing water molecules into a cation-pi complex on the interaction between the cation and the pi system was investigated using the MP2/6-311++G method to explore how a cation-pi complex changes in terms of both its geometry and its binding strength during the hydration. The calculation on the methylammonium-benzene complex showed that the cation-pi interaction is weakened by introducing H(2)O molecules into the system. For example, the optimized interaction distance between the cation and the benzene becomes longer and longer, the transferred charge between them becomes less and less, and the cation-pi binding strength becomes weaker and weaker as the water molecule is introduced one by one. Furthermore, the introduction of the third water molecule leads to a dramatic change in both the complex geometry and the binding energy, resulting in the destruction of the cation-pi interaction. The decomposition on the binding energy shows that the influence is mostly brought out through the electrostatic and induction interactions. This study also demonstrated that the basis set superposition error, thermal energy, and zero-point vibrational energy are significant and needed to be corrected for accurately predicting the binding strength in a hydrated cation-pi complex at the MP2/6-311++G level. Therefore, the results are helpful to better understand the role of water molecules in some biological processes involving cation-pi interactions.     

Synthesis of monofluorinated analogues of lysophosphatidic acid

Lysophosphatidic acid (LPA, 1- or 2-acyl-sn-glycerol 3-phosphate) displays an intriguing cell biology that is mediated via interactions both with G-protein coupled seven transmembrane receptors and with the nuclear hormone receptor PPARgamma. Synthesis and biological activities of fluorinated analogues of LPA are still relatively unknown. In an effort to identify receptor-selective LPA analogues and to document in detail the structure-activity relationships of fluorinated LPA isosteres, we describe a series of monofluorinated LPA analogues in which either the sn-1 or the sn-2 hydroxy group was replaced by fluorine, or the bridging oxygen in the monophosphate was replaced by an alpha-monofluoromethylene (-CHF-) moiety. The sn-1 or sn-2 monofluorinated LPA analogues were enantiospecifically prepared from chiral protected glycerol synthons, and the alpha-monofluoromethylene-substituted LPA analogues were prepared from a racemic epoxide with use of a hydrolytic kinetic resolution. The sn-2 and sn-1 fluoro LPA analogues were unable to undergo acyl migration, effectively "freezing" them in the sn-1-O-acyl or sn-2-O-acyl forms, respectively. The alpha-monofluoromethylene LPA analogues were unique new nonhydrolyzable ligands with surprising enantiospecific and receptor-specific biological readouts, with one compound showing a 1000-fold higher activity than native LPA for one receptor subtype.     

制备方法对WO_3/ZrO_2结构的影响

用XRD、比表面测定、LRS定性和定量的方法对用Zr（OH）4和已晶化的ZrO2作载体制得的两类WO3／ZrO2催化剂进行了表征．揭示了样品比表面、载体物相、活性组分的存在状态与制备方法、WO3含量、焙烧温度之间的关系．结果表明，WO3能单层分散在ZrO2上；单层覆盖在Zr（OH）4上的WO3使载体在焙烧时晶粒生长受阻，形成介稳的四方ZrO2，并阻止载体微粒间的烧结，使从Zr（OH）4出发制得的WO3／ZrO2比表面明显增大，在WO3含量达到单层分散容量时以上作用表现得最充分；WO3与Zr（OH）4（或四方ZrO2）在高温（～800℃）可能发生了某种化学结合，开创出超强酸位．用以上观点可对文献中已报导的主要实验事实作出较满意的解释.