聚氯乙烯表皮成分对加成型硅橡胶固化的影响

采用流变学方法研究了双组分加成型硅橡胶在不同聚氯乙烯(PVC)表皮上的固化动力学,并利用红外光谱、核磁共振波谱、电感耦合等离子体质谱仪等手段分析了PVC表皮成分,以确定导致双组分加成型硅橡胶不固化的具体原因。 结果表明,PVC表皮中导致硅橡胶不固化的主要元素为P元素。 在固定硅橡胶厚度为1 mm的情况下,当PVC表皮中的P元素质量分数低于3×10^-3%时,浇注在其上的双组分加成型硅橡胶依然能固化;而当PVC表皮中的P元素质量分数超过约2.4×10^-2%时,虽然浇注在其上的双组分加成型硅橡胶的中间层依然能固化,但与PVC表皮接触部分的硅橡胶不固化,且不固化层厚度随P元素质量分数增加而增加。 本文还研究了在P元素质量分数低于3×10^-3%的PVC表皮上,降低硅橡胶厚度至微米级时的固化行为,在P元素质量分数低于3×10^-3%的PVC表皮上,当硅橡胶厚度低于2 μm时,硅橡胶出现不完全固化现象。 双组分加成型硅橡胶在含有P元素的PVC表皮表面的固化行为主要是由硅橡胶样品中铂催化剂总含量及PVC表皮中的P元素含量确定的,同时也会受到双组分加成型硅橡胶反应速率以及铂催化剂、P元素在硅橡胶中的扩散速率的影响。     

Raman spectroscopic characterization of the magnesium content in amorphous calcium carbonates

A series of Mg‐bearing synthetic amorphous calcium carbonates (ACC) were characterized by Raman spectroscopy. The spectra showed a systematic increase in the carbonate ν₁ peak position from the control samples that contained 0.0 mol % MgCO₃ to samples that contained up to 43 mol % MgCO₃. The relationship is best described by the function: mol % MgCO₃ = (ν₁ – 1079.66) / 0.2017. The Mg content is equally well‐predicted by a correlation with the instrumentally corrected ν₁ full width at half maximum that is quantified by: mol % MgCO₃ = (ν₁ – 23.26) / 0.1969. An analysis of the Raman data collected for ACC combined with insights from crystalline materials suggests that compositional dependencies arise from changes in the local metal–oxygen bonds as Mg substitutes for Ca. The calibrations described here provide a rapid and nondestructive means of determining the Mg content of ACC, with additional advantages of minimal sample preparation and a high degree of lateral spatial resolution (approximately 1 µm). This method may be appropriate for investigations of heterogeneous samples such as biominerals. Copyright © 2011 John Wiley & Sons, Ltd.     

抗氧化剂抗脂质过氧化机制的ESR研究

以NADH诱导的心肌线粒体损伤体系为模型,在体外用ESR研究了谷胱甘肽(GSH)、超氧化物歧化酶(SOD)及辣根过氧化物酶(HRP)的抗氧化机制.结果表明,低浓度的GSH可部分抑制体系中自由基的生成;SOD与HRP以适当比例共同作用,可完全抑制体系中自由基的生成,较好地防止脂质过氧化的发生.     

统计优化迭代法测量质子交换波导折射率分布

提出了一种用于拟合测量渐变波导的折射率分布的新的理论处理。该方法把统计优化手段导入循环迭代法 ,可适用于费米函数这一类曲线变化范围大、且有多个自变量的函数。实验上用焦磷酸质子交换制备了LiNbO3波导样品 ,用该方法对退火后的折射率分布作了测量拟合 ,折射率拟合值与实验值的均方差为± 8.2× 10 - 4。     

Highly regio- and enantioselective thermal [2 + 2] cycloaddition of coumarin in a crystalline inclusion complex under high vacuum

Coumarin and thiocoumarin, which are usually thermally unreactive for dimerization, were dimerized in their inclusion crystalline complexes under thermal and high vacuum conditions.     

Interfacial synthesis of pyramidal lead sulfide crystallites with high energy {331} facets

Single crystals of PbS in the form pyramids with a high proportion of high energy {331} faces are obtained by the use of a novel reaction technique at the interface of water and toluene. The pyramids spontaneously form a monolayer spread across the entire water-toluene interface. The influence of deposition parameters such as temperature, solution concentration, reaction time on the nature and properties of interfacial films are studied. In addition, the effect of solvo-static parameters such as column height and interfacial area are investigated. The obtained films are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM).     

Enzymatic profiling system in a small-molecule microarray

[reaction: see text] We have developed a microarray-based strategy for detection of three major classes of hydrolytic enzymes on the basis of their catalytic activities. This enables the sensitive detection of proteins not merely by their bindings but rather by their enzymatic activities. This may provide a valuable tool for screening, identification, and characterization of new enzymes in a high-throughput fashion.     

Catalytic enantioselective intermolecular reductive aldol reaction to ketones

We describe the first example of a catalytic enantioselective intermolecular reductive aldol reaction. Three types of reactions were studied: (1) reactions between acetophenone and methyl acrylate; (2) reactions between symmetric ketones and β-substituted α,β-unsaturated esters; and (3) reactions between acetophenone derivatives and an allenic ester. Although only moderate enantioselectivity was obtained in the first reaction type, high to excellent enantioselectivity was realized in the enantio-induction at the α-position in the second reaction type and at the δ-position in the third reaction type. Specifically, the third reaction type afforded the corresponding tertiary alcohols with up to 99% ee. Pre-activation of the nucleophile by silyl enolate formation is not necessary in these one-pot catalytic enantioselective reductive aldol reactions.     

Decorating Mn3O4 nanoparticle on NiO nanoflake arrays for high-performance electrochemical biosensors

Journal of Solid State Electrochemistry - Substrate materials play a significant role in the improvement of electrochemical biosensors. In the present work, NiO nanoflake arrays were fully and...     

MgB_2(001)面超导结构的电子浓度第一原理分析

采用密度范函理论计算了金属化合物MgB2(001)薄膜结构的电子能带结构和状态密度,计算的交换相关能分别采用LDA和GGA。规范保守赝势的计算结果表明,晶格常数与实验值误差在很小的范围内,分析了引起MgB2(001)面结构超导转变时电子浓度和偏态密度的变化情况,发现构成该超导体结构的成键有三种,着重从结构的电子浓度变化分析了其超导特性,六角蜂窝状结构中硼原子间相互作用为sp2杂化的共价键,镁原子和硼原子之间是离子键结合,镁原子层是金属键结合,镁原子的价电子部分转移到硼原子的pz轨道,部分电子为镁原子层共用。MgB2的超导机制为强烈的电子-声子耦合,为B原子间强烈的共价作用形成,是传统S波超导体。对Mg元素同一主族的其它硼化物进行布居分析,发现MgB2中Mg原子电子转移明显强于BeB2和CaB2,说明电子浓度是引起超导转变的一个重要因素。