Carbonat-isostere Anionen [SnX3]5− in den Verbindungen Rb6[SnX3]O0,5 und Cs6[SnX3]O0,5 mit X = As,Sb und Bi

Carbonate Isostructural Anions [SnX₃]^5? in the Compounds Rb₆[SnX₃]O_0.5 and Cs₆[SnX₃]O_0.5 with X = As, Sb, and Bi The metallic shining compounds Rb₆[SnX₃]O_0.5 and Cs₆[SnX₃]O_0.5 with X = As, Sb, and Bi were prepared from the melt starting from adequate mixtures of the elements and SnO₂. They crystallize in the hexagonal system (space group P6₃/mmc, No. 194, Z = 2) with the lattice constants mentioned in ?Inhaltsübersicht”?. In the structures of the isotypic compounds tin and the main group(V) elements build up trigonal planar anions [SnX₃]^5? with X = As, Sb, and Bi isostructural to the carbonate anion, oxygen forms isolated O^2? ions. The bond lengths Sn? X are significantly shortened with respect to the sums of Pauling covalent radii. The atoms of the units [SnX₃]^5? are coordinated by alkali metal cations forming trigonal prisms and the O^2? anions occupy octahedral holes.     

Stabilization ofEscherichia coli penicillin G acylase by polyethylene glycols against thermal inactivation

The effects of five polyethylene glycol (PEG) compounds of different molecular weight on the thermal stability of penicillin G acylase (PGA) obtained from a mutant ofEscherichia coli ATCC 11105 have been investigated. The molecular weights of PEG compounds were 400, 4000, 6000, 10,000, and 15,000. The thermal inactivation mechanisms of both native and PEG-containing PGA were considered to obey first order inactivation kinetics during prolonged heat treatments. Optimal concentrations of PEGs at molecular weights of 400,4000, 6000,10,000, and 15,000 were found to be 250,150,150,100, and 50 mM, respectively. The greatest enhancement of thermostability was observed with PEG 4000 and PEG 6000, as a nearly 20-fold increase above 50°C. PGA showed almost the same temperature activity profile and optimal temperature values both in the presence and absence of PEG. The addition of PEGs did not cause any change in the optimal temperature value of PGA, but the parametersV _m ,K _m , the activation energy, and thek _cat values of enzyme were markedly decreased because of the mixed inhibition by PEG compounds. The type of inhibition was found to be hyperbolic uncompetitive.     

Liquid-liquid equilibria for mixtures of (ethylene carbonate + aromatic hydrocarbon + cyclohexane)

Liquid-liquid equilibrium data for mixtures of (ethylene carbonate + benzene + cyclohexane) at temperatures 303.15 and 313.15 K and (ethylene carbonate + BTX + cyclohexane) at temperature 313.15 K are reported, where the BTX is benzene, toluene and m-xylene. The compositions of liquid phases at equilibrium were determined by gas liquid chromatography. The selectivity factors and partition coefficients of ethylene carbonate for the extraction of benzene, toluene and m-xylene from (ethylene carbonate + BTX + cyclohexane) are calculated and presented. The obtained results are compared with the selectivity factors and partition coefficients of ethylene carbonate for the extraction of benzene from (ethylene carbonate + benzene + cyclohexane). The liquid-liquid equilibrium data were correlated with the UNIQUAC and NRTL activity coefficient models. The phase diagrams for the studied mixtures are presented and the correlated tie line results have been compared with the experimental data. The comparisons indicate the applicability of the UNIQUAC and NRTL activity coefficients model for liquid-liquid equilibrium calculations of the studied mixtures. The tie line data of the studied mixtures also were correlated using the Hand method.     

Application of the essential work of fracture concept to nanostructured polymer materials

The first part of the paper deals with a critical discussion of the methodical basis of essential work of fracture (EWF) concept with respect to the specimen geometry (especially the notch depth) and application to polymers. In the second part, an in situ testing device, which combines a tensile testing machine with an optical strain-field measuring system, has successfully demonstrated possibility of characterization of fracture behaviour of polystyrene-polybutadiene block copolymers and block copolymer/homopolymer blends as examples of nanostructured polymer materials. It has been shown that knowledge of the time evolution of the strain field close to the crack tips leads to a simple verification of the basic precondition for the applicability of the EWF concept, the precondition “plastic zone coalescence-before-stable crack propagation”.     

Effect of monomer concentration on characteristics of methacrylic acid-grafted polyethylene film prepared by photografting

The effect of monomer concentration on photografting of methacrylic acid (MAA) onto linear low-density polyethylene (PE) film (thickness=30 μm) was investigated at 60 °C in water solvent together with the location of MAA-grafted chains. Xanthone was used as a photoinitiator which was coated on the film sample earlier. The higher percentage of grafting and graft efficiency were afforded for the system with the higher monomer concentration. The resultant MAA-grafted films were subjected to measurements of pH-responsive character and ability to adsorb cupric ion in order to understand the characteristics of function introduced. The grafted samples exhibited the pH-responsive character, where they shrank and swelled in acidic and alkaline media, respectively. The pH-responsive character of the grafted films was higher for the samples prepared in the system with a higher monomer concentration. Moreover, the grafted samples exhibited the ability to adsorb cupric ion, and the ability was reduced when the sample was prepared in the system with a higher monomer concentration. The different extents of the pH-responsive character and ability to adsorb cupric ion of the resulting grafted PE films were discussed in terms of location of grafted chains in the film substrate, which was determined by a scanning electron microscope and an attenuated total reflection infrared spectroscopy.     

Towards advanced circuit board materials: adhesion of copper foil to ultra‐high molecular weight polyethylene composite

Polyethylene based composites are attractive materials for advanced circuit board applications because of their unique combination of properties: low dielectric constant and loss factor, light weight, high flexural modulus and low thermal expansion coefficient controlled in all spatial directions. This investigation describes a process to consolidate chopped fibers of ultra‐high molecular weight polyethylene concurrently with its bonding to a copper foil. Bonding is affected by a thin sheet of low‐density polyethylene, incorporating a crosslinking agent with a concentration gradient across the sheets thickness. In this single step process, the composite material is formed and bonded to the metal foil, achieving good adhesion without the use of extraneous glue. Copyright © 2002 John Wiley & Sons, Ltd.     

相转移催化合成增塑剂BBP和水杨醛的研究

相转移催化合成增塑剂ＢＢＰ和水杨醛的研究郭锡坤，高文华，曾东宇（汕头大学化学系，汕头５１５０６３）关键词相转移催化，季铵盐，聚乙二醇，邻苯二甲酸丁苄酯，水杨醛，增塑剂邻苯二甲酸丁苄酯（增塑剂ＢＢＰ）是一种优良的增塑剂．邻羟基苯甲醛（水杨醛）不仅是重要...     

Small angle neutron scattering studies on nonaqueous dispersions of calcium carbonate Part 2. Determination of the form factor for concentric spheres

Colloidal dispersions of calcium carbonate, stabilised primarily by a surface active agent, in both toluene and dodecane have been examined by small angle neutron scattering. A model has been developed to simulate the scattering behaviour of the particles and is based on the idea of a concentric sphere with a homogeneous layer of adsorbed material surrounding a core particle. Computations based on the model show a wide variation of scattering behaviour with variation of the coherent scattering length of the dispersion medium. These predictions were confirmed by experiment. A method is described for analysis of the experimental data which leads to a determination of the thickness of the adsorbed layer, the radius of the core particle and the standard deviation of core particle radius.     

用TMS—2型热机分析仪测量热释蠕变

对已经商品化的Perkin-Elmer TMS-2型热机分析仪进行改进,用来测量聚合物材料的热释蠕变行为。按照7SCr分步加载的程序,用弯曲法测量了-83～300℃温度范围内低密度聚乙烯的玻璃化转变松弛过程,并从TSCr谱上计算其相应的分子参数,实验结果与用扭转的TSCr方法所得结果相等,因此这是一种研究聚合物材料松弛行为的方便可行的技术。     

Kinetic and computational studies on aminolysis of bicyclic carbonates bearing alicyclic structure giving alicyclic hydroxyurethanes

Aminolysis of bicyclic carbonates, which consist of five-membered cyclic carbonate and five- or six-membered alicyclic groups, was examined. Kinetic studies revealed that the aminolysis of the bicyclic carbonate with cyclohexane ring proceeded more smoothly than that of the bicyclic carbonate with cyclopentane ring. Computational calculation suggested that the different reaction rates originate from the distinct ring-strain of the cyclic carbonate groups affected by the conformation of the alicyclic groups.