Controlling nanoparticle formation via sizable cages of supramolecular soft materials

We present a new generic strategy to fabricate nanoparticles in the "cages" within the fibrous networks of supramolecular soft materials. As the cages can be acquired by a design-and-production manner, the size of nanoparticles synthesized within the cages can be tuned accordingly. To implement this idea, both selenium and silver were chosen for the detailed investigation. It follows that the sizes of selenium and silver nanoparticles can be controlled by tuning the pore size of the fiber networks in the material. When the concentration of the gelator is high enough, monodisperse nanoparticles can be prepared. More interestingly, the morphology of the nanoparticles can be altered: silver disks can be formed when the concentrations of both the gelator and silver nitrate are sufficiently low. As the fiber network serves as a physical barrier and semisolid support for the nanoparticles, the stability in the aqueous media and the ease of application of these nanoparticles can be substantially enhanced. This robust surfactant-free approach will not only allow the controlled fabrication of nanoparticles, but also can be applied to the fabrication of composite materials for robust applications.     

A simple method for thermoanalysis of evolved gases

Thermoanalytical processes involving the splitting-off of ammonia, water, halogens, inorganic acids or acid anhydrides can be simply observed by using a specimen-holder in which specific reactions with the decomposition products can be induced. A special glass or quartz double crucible can be used for this purpose; the products arising in the lower part of the crucible can be oxidized selectively with reagents placed in the upper part, or can be bound or transformed into other compounds. This double crucible is also suitable for studying reactions taking place between solid and gaseous substances.     

电化学噪声测量分析系统设计与实现

根据电化学噪声原理,利用微机技术设计实现了电化学噪声测量分析系统。该系统具有高灵敏度,自动选择量程,多回路自动测量,可调整采样参数等功能,并在时／频域内对所测量的电化学噪声进行分析。     

应用相图边界理论勾画多元恒温截面相图

根据相图的边界理论,可以确定恒温截面图中紧邻相区及其边界关系,进而可以根据有限的实验数据,比较直接地勾画出整个恒温截面图。本文以5元相图和8元相图为例加以说明。     

Surface diffusion as a rate-enhancing mechanism in macromolecular association: The effectiveness of one- and two-dimensional surface sliding

The effective rate for a macromolecular association can be increased if the molecules can be held together loosely by nonspecific surface forces while they search for the specific reactive sites. In this way steric constraints can be relieved. In extreme cases, a specific interaction site can be surrounded by extensive surfaces either essentially linear (e.g. a DNA site) or two-dimensional (e.g. a membrane-bound receptor). If ligands can bind nonspecifically and search these surfaces in a lower-dimensional diffusion process, very substantial rate enhancements can be achieved under suitable conditions. The ranges of concentration and affinity of such nonspecific surfaces that can produce rate enhancements are derived and discussed. It is found that under the expected conditions in the living cell, such rate enhancements will be fairly modest. Nonetheless, nonspecific surface diffusion may play an important role.     

Slow diffusion by singlet state NMR spectroscopy

Small diffusion coefficients can be measured by using populations of singlet states that have a relaxation time constant, T(s), which can be much longer than the longitudinal relaxation time, T1. Spatial information can be encoded with pulsed field gradients in the manner of stimulated echo sequences. Singlet states can be excited via double-quantum coherences to enhance the efficiency of phase encoding and decoding.     

表面能与晶体生长/溶解动力学研究的新动向

界面现象使物质在结晶过程中出现了临界现象.但最近的研究指出在物质溶解过程中,在表面能量的控制下也存在着临界现象以及尺寸效应.实验发现,当晶体自身小到一 定的程度时(通常在纳米尺度上并和临界蚀坑的大小相近),在溶解过程中其速度会自发降 低,反应被抑制乃至停止.尽管在热力学上表面能的因素可以赋予小颗粒晶体较大的溶解度 ,但表面能却也能通过对临界条件的控制而使这些微粒在动力学上不被溶解.这个发现不仅 解决了纳米颗粒在水溶液中稳定性的问题,而且还从动力学的角度解释了生物矿物选择纳米 尺度作为其基本构成单元的原因.由于表面能和晶体生长/溶解的动力学有着密切的关系, 我们可以通过对表面能的调节来修改它们的动力学速度和晶体的形貌.反过来,也可以用动力学的方法来测定表面能及表面吸附/脱附常数等.相对于常规的界面研究手段,通过生 长和溶解动力学途径所得的数据有着很好的可靠性及重复性.我们认为,晶体生长和溶解的 动力学和表面能的研究相结合,不仅为界面研究提供了新的思路和方法,而且也会推动晶体生长和材料科学的发展.     

稀土氧化物对中高碳钢堆焊金属中夹杂物变质作用的热力学分析

采用热力学方法,研究了稀土氧化物对中高碳钢堆焊金属中夹杂物的变质作用。夹杂物生成的热力学分析表明,在堆焊熔池中,稀土氧化物可以被碳还原成稀土元素,稀土元素可以与氧、硫生成稀土氧化物、稀土硫化物和稀土硫氧化物,从而达到脱氧、脱硫、净化堆焊熔池的作用;稀土氧化物还可以直接与硫作用,生成稀土硫氧化物,起到脱硫的效果。     

问题、项目引领式教学法在高校有机化学教学中的应用

问题、项目引领式教学法可分为问题引领式与项目引领式教学两个部分。问题引领式教学法可用于课程的基础部分教学;项目引领教学法主要用于学生已掌握一定的基础知识之后,教师有针对性地提出一些目前亟待解决的小的项目让学生提出思路及解决办法。通过两种方法的互相补充,可显著提高学生对有机化学这门课程的学习兴趣,也能使有机化学的理论知识与实践能力更紧密地联系在一起,从而提高该课程的教学效果,同时也激发学生创新的潜能。     

Field-free molecular alignment control by phase-shaped femtosecond laser pulse

In this paper, we theoretically show that the field-free molecular alignment can be controlled by shaping the femtosecond laser pulse with a periodic phase step modulation, involving the maximum degree and temporal structure of the molecular alignment. We show that the molecular alignment can be completely suppressed or reconstructed as that by the transform-limited laser pulse, the temporal structure of the alignment transient can be controlled with a desired shape, and the molecular alignment and antialignment for any temporal structure can be switched. Furthermore, we also show that both the degree and direction of the molecular alignment at a fix time delay can be continuously modulated.     

Light activated patterning of dye-labeled molecules on surfaces

This Communication describes a novel method for patterning proteins, ligands, or other organic/inorganic species onto solid substrates. The process works by linking the moiety of interest to a fluorophore that can be subsequently photobleached and bound to the interface. The technique can be performed in aqueous solution and allows several species to be addressed onto the surface simultaneously by using different frequencies of light. Because the method can be used with fluorophores excited by visible light, shorter and more damaging wavelengths can be avoided.     

Regio‐ and Stereoselective Modification of Chiral α‐Amino Ketones by Pd‐Catalyzed Allylic Alkylation

Chiral α‐amino ketones are excellent nucleophiles for stereoselective palladium‐catalyzed allylic alkylations. Both chiral as well as achiral allylic substrates can be applied, while the stereochemical outcome of the reaction is controlled by the chiral ketone enolate. The substituted amino ketones formed can be reduced stereoselectively, and up to five consecutive stereogenic centers can be obtained. This approach can be used for the synthesis of highly substituted piperidine derivatives.     

胆固醇/卵磷脂/壳聚糖体系中碳酸钙模拟生物矿化的研究

本文采用X射线衍射、红外光谱和扫描电子显微镜等方法研究了胆固醇／卵磷脂／壳聚糖体系中碳酸钙模拟生物矿化过程。通过改变有机基质的组成,使有机基质的模板作用 也发生改变,从而使生成方解在一重型里面在酸钙的模板可生成球霰石型的碳酸钙。文中还进一步探讨了体系中壳聚糖、卵磷脂、胆固醇三者的协同作用对生成碳酸钙晶型的影响。     

A method for the determination of technetium in environmental waters

A method is described which can be used to determine technetium-99 levels in a range of water types. Ruthenium isotopes which may interfere in the analysis are removed from the sample by precipitation before concentration of pertechnetate onto an ion-exchange column. Other nuclides can be removed from the column using NaOH before elution of the technetium using NaSCN. The technetium in the NaSCN eluent can then be extracted into butan-2-one which can be evaporated onto a planchette. Technetium-99m is used as a yield tracer and after this has decayed away to negligible levles the amount of technetium on the planchette can be determined by measuring the rate of beta radiation emission from the final concentrate.     

Die Reaktivdestillation: Moderne Trenn‐ und Reaktionstechniken

In a reactive distillation column, both the chemical conversion and the distillative separation of the product mixture are carried out simultaneously. Through this integrative strategy, chemical equilibrium limitations can be overcome, higher selectivities can be achieved and heat of reaction can be directly used for distillation. Moreover, azeotropic mixtures and mixtures of closely boiling components can be separated by reactive distillation. Increased process efficiency and reduction of investments and operational costs are the direct results of this approach.     

Separation of different forms of transferrin by isoelectric focusing to detect effects on the liver caused by xenobiotics

Several genetic variants and also isoforms of transferrin differing in carbohydrate structure can be separated by polyacrylamide or agarose gel isoelectric focusing. Numerous blood plasma or serum samples can be analyzed in parallel in each gel. Studies of the heterogeneity of transferrin have already revealed many results of importance to different fields of human medicine. Gene typing can give important and useful information for paternity determination and in forensic medicine. The gene type C 2 seems to have increased frequency in certain malfunctions. Futhermore, functional abnormalities of liver cells can be revealed by determination of the concentrations of transferrin isoforms differing mainly in their carbohydrate parts. The isoforms can be quantified with zone immunoelectrophoresis assay. Thus valuable information can be obtained about important modulated regulations of cell and membrane functions, even when these are disturbed by disease and xenobiotics. The information may be useful e.g. in the detection of individuals suffering from toxic effects, to identify toxic agents and exposure conditions. Studies of house painters revealed that exposure to different types of paints had an effect on transferrin. Determination of the concentration of the isotransferrin with pI 5.7 in blood samples from alcoholics can be used as a marker for the detection of liver dysfunction and for the monitoring of therapy treatments. In addition, by analyzing the isotransferrins a rare genetic abnormality can be detected.     

Nucleophilic transition metal based cyclization of allenes

Allenes bearing a pro-nucleophile can be cyclized on treatment with a wide variety of transition metal catalysts and reagents: palladium, cobalt, ruthenium, silver, rhodium, lanthanides, gold. The nucleophilic groups can be nitrogen, oxygen or carbon based and can form rings of various sizes, often with good control of stereochemistry. A variety of mechanisms can be proposed for these reactions and the metal complex can be used to introduce a variety of functional groups during cyclization. Several heterocyclic natural products have been prepared using a selection of these reactions.     

Indirect Electroorganic Syntheses—A Modern Chapter of Organic Electrochemistry [New Synthetic Methods (59)]

The electrochemical formation and regeneration of redox agents for organic syntheses (indirect electrolysis) widens the potential of electrochemistry, as higher or totally different selectivities can often be obtained while at the same time the energy input can be lowered significantly. Higher current densities can also be obtained by preventing otherwise often encountered electrode inhibition. New types of redox catalysts can be formed in-situ and can be regenerated after reaction with the substrates. This principle is of increasing importance also for the application of already known redox agents with regard to environmental protection, since large amounts of a product can be generated in a closed circuit using only relatively small amounts of the redox reagent. Consequently the operation of such a process can be greatly simplified, and the release of ecologically objectionable spent reagents into the environment can be prevented. The broad spectrum of redox catalysts currently in use includes, inter alia, metal salts in very low or high oxidation states, halogens in various oxidation states, and, in particular, a wide variety of transition-metal complexes. A great deal of progress has recently been made in the application of organic electron transfer agents, since compounds have been found that are sufficiently stable in both the reduced as well as the oxidized state.     

SCTA and Adsorbents

Sample controlled thermal analysis (SCTA) can be used in several manners with respect to adsorbents. Almost 70% of adsorbent synthesis procedures involve a thermal step that can be adapted to a sample controlled method. In this respect, SCTA has been used for the preparation of activated alumina, calcination of zeolites and activation of carbons. The thermodesorption of adsorbed molecules can also be carried out using a sample controlled method. Here, both the surface area and pore volume of adsorbents can be assessed. Finally, SCTA can be highly beneficial in the thermal pretreatment of adsorbents prior to adsorption. This revised version was published online in July 2006 with corrections to the Cover Date.