四氟乙烯齐聚体的反应 四氟乙烯四、五聚体和芳香胺的反应

前已报道四氟乙烯四聚体(全氟-3,4-甲基己烯-3)(1)、五聚体(全氟-3,4-二甲基-4-乙基己烯-2)(2)和脂肪烷氧以及脂肪胺的亲核反应.本文报道化合物1,2和芳香胺如苯胺、β-萘胺的反应.由于烯烃1、2双键处于分子中间,因而当亲核试剂进攻时,双键容易发生重排,生成的末端基烯烃更具反应性,故导致一取代、二取代、三取代以及环化降解等复杂产物.     

CSTR和批式反应器中酶法拆分萘普生的比较

比较了批式反应器和连续流动搅拌反应器中酶动力学拆分萘普生的不同之处。从宏观反应器平衡角度,推导出了在ＣＳＴＲ中不同于在批式反应器中的酶立体选择性,产物对映体过量值和反应转化率的定量关系式,并通过脂肪酶催化的萘一甲酯的不对称水解反应得到了证实。     

CALCULATION OF THE YOUNG''''S MODULUS OF AN ADSORBED POLYMER LAYER

Polymer layers adsorbed to a surface or in a confined environment often change their mechanical properties. There is even the possibility of solidification of the confined layer. To judge the stiffness of such a layer, we used the Hertz model to calculate the Young's modulus of the polymer layer in the confinement of AFM experiments with silicon nitride tip with a radius of curvature of R≈50 nm and a glass sphere attached to the cantilever R = 5μm. Since there is no visible indentation of the layer in the AFM experiments, the layer is either penetrated very easily, or the indentation is too small to be seen in a force curve. The latter would be the case for a polymer layer with a Young's modulus above 4×108 Pa in case of an experiment with a silicon nitride tip and 4×105 Pa in case of a glass sphere.     

Heterostructured Tin oxide-pillared tetratitanate with enhanced photocatalytic activity

Here we point out that the nanocrystals well ordered in compact hexagonal networks are highly stable compared to the same nanocrystals either isolated on a substrate or ordered in a less compact manner. The emergence of unexpected collective physical intrinsic properties results in the nanocrystals being ordered over a long distance in colloidal crystals called supracrystals. Some morphologies of nanocrystals ordered, at the micrometer scale, in 3D superlattices called supracrystals are similar to those obtained with atoms in nanocrystals. From a comparison between vibrational and magnetic properties of supracrystals and aggregates composed of the same nanocrystals, it is proposed that nanocrystals in a supracrystal could behave as atoms in a nanocrystal. From these data a possible analogy between nanocrystals in a supracrystal and atoms in nanocrystals is proposed.     

Study of Viscosity-temperature Properties of Oil and Gas-condensate Mixtures in Critical Temperature Ranges of Phase Transitions

Transport of oil and gas-condensate mixtures of various compositions is found to be accompanied by a slight increase in viscosity in the coldest period when ground temperatures at depth of a condensate pipeline reach 0 – minus 4°С. Fall in temperature of oil fluids under study to minus 10 – minus 30°С is accompanied by a sharp increase in all structural and rheological parameters of the mixture. Even a slight amount of oil added to a gas-condensate mixture causes a significant decrease in viscosity in the negative temperature range. As a result, cloud and pour point of a mixture falls, its amount decreases, the structure of paraffin deposits changes.     

Solvent‐Dependent Self‐Discrimination of Bis(2‐hydroxyphenyl)diamides

Solvent‐dependent, self‐discrimination of diamides is described. Mixing a solution of (R)‐ 1 a and (S)‐ 1 a , which are valine‐derived, bis(2‐hydroxyphenyl)diamide‐bearing, multiple hydrogen‐bonding modules, in dichloromethane immediately led to the formation of a thick suspension comprising a 1:1 heterochiral aggregate of 1 a . The solubility of heterochiral 1 a was substantially lower in halogenated solvents than in ethyl acetate. A perusal of racemic crystal structures obtained from chloroform and ethyl acetate revealed a significant difference in the crystal‐packing pattern, which is likely to be the basis for the pronounced difference in solubility. Specific self‐discrimination of 1 a in an ensemble of eight structurally related molecules showcased the specific aggregation through the hydrogen‐bonding network of the bis(2‐hydroxyphenyl)diamide framework. The low solubility of heterochiral 1 a in halogenated solvent was exploited to achieve high stereoselectivity in a catalytic asymmetric reaction by using a low enantiomeric excess sample of 1 a .     

A novel method that improves sensitivity of protein detection in PAGE and Western blot

We have developed a simple and inexpensive method that improves sensitivity of protein and antigen detection in standard PAGE procedures. Our technique uses a sample microloader device with a funnel‐like structure, filled with a 4% stacking gel. When attach to the top of a polyacrylamide slab gel, the proteins in a sample are concentrated by electrophoresis into a small volume as they emerge from the device's narrow outlet. Our microloader has several advantages over previous devices, including simple assembly, high versatility, and absence of cross‐contamination between lanes. Addition of this device to a slab gel results in a fivefold increase in the sensitivity of antigen detection in a Western blot. As a result, less protein is required for loading and signal detection. Our protocol is a straightforward modification of a standard experimental technique, and is especially useful when only limited sample quantities are available.     

Some practical aspects of free energy calculations from molecular dynamics simulation

In this work, we address two critical aspects of calculation of the free energy differences in molecular systems from molecular simulations. The first aspect involves checking whether the calculated free energy difference depends significantly on the extent of perturbation used for accomplishment of a given transformation. The second aspect of interest is to verify if the sampling errors in calculating the free energy differences between the wild-type molecule and a mutated one in its free state and in a complex are similar, or not, for a finite-length dynamic simulation. The reliability of the free energy estimates obtained from molecular simulations using thermodynamic cycles depends in part on this fact. For investigating these aspects, we use a self-transformation scheme in which a transformation of a part of a molecular system into itself is considered. We perform MD simulations of DNA fragments in which a part of a specific base is subjected to such a self-transformation. Results indicate that the estimated free energy differences do not depend significantly on the extent of perturbation used to achieve the transformation. Interestingly, the variation in the cumulative free energy difference, ΔA, with the coupling parameter, λ, depends significantly on the extent of perturbation. We examine the physical basis of the observed nature of the variation of the accumulated free energy difference, ΔA, against the λ value in the case of a self-transformation. In a thermodynamic cycle, the sampling errors due to the finite-length simulation for the molecular system are found to be similar to each other for the two perturbations (free and in a complex) justifying the use of such approach in calculating ΔΔA in molecular complexes. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 877–885, 1999     

Photochemical and thermal isomerization processes of a chiral auxiliary based donor-acceptor substituted chiroptical molecular switch: convergent synthesis,improved resolution and switching properties

A new type of chiroptical molecular switch is presented where irradiation employing different wavelengths of light induces a reversible helix inversion of a sterically overcrowded alkene bearing a second chiral entity in the form of a stereogenic center present in a pyrrolidine unit. The additional stereogenic center in the chiral auxiliary group has a distinct influence on the switching selectivity of this system and greatly facilitates the resolution of the different diastereoisomers, which is a considerable improvement compared with previously reported systems. In addition, the pyrrolidine stereogenic center causes small energetic differences between the various states of the switch system resulting in a small but significant directional preference in the helix inversion steps.     

Mathematical model development and simplification for multi-route complex chemical mechanism

A complete inventory and a clearly defined structure of any complex reaction mechanism are difficult to obtain. This paper addresses a complex catalytic cycle of dehydrogenation of butane in theoretical and computational beliefs. Mathematically, simplification is done by “model reduction,” that is, the rigorous way of approximating and representing a complex model in simplified form. Firstly, a simple single-route mechanism has been considered then a complex system is discussed in detail. The most practical and helpful way to represent a complicated system is using a simple model so that the model may be improved and transformed into a more accurate one that can be solved numerically. To reduce the complexity of a higher dimensional complex system, need to be a split reaction mechanism in different available routes. With the help of the concept of the multi-route model, we can reduce a complicated higher-dimensional system to a low-dimensional manifold and investigate each route independently. For model development and standardization, sensitivity analysis is a powerful tool used in this paper. The influence of parameters on target output is discussed through graphical results depicted in the symbology toolbox in MATLAB.     

Measurement of bubble size distribution in protein foam fractionation column using capillary probe with photoelectric sensors

Bubble size is a key variable for predicting the ability to separate and concentrate proteins in a foam fraction ation process. It is used to characterize not only the bubble-specific interfacial a rea but also coalescence of bubbles in the foam phase. This article describes the development of a photoelectric method for measuring the bubble size distribution in both bubble and foam columns for concentrating proteins. The method uses a vacuum to withdraw a stream of gas-liquid dispersion from the bubble or foam column through a capillary tube with a funnel-shaped inlet. The resulting sample bubble cylinders are detected, and their lengths are calculated by using two pairs of infrared photoelectric sensors that are connected with a high-speed data acquisition system controlled by a microcomputer. The bubble size distributions in the bubble column 12 and 1 cm below the interface and in the foam phase 1 cm above the interface are obtained in a continuous foam fractionation process for concentrating ovalbumin. The effects of certain operating conditions such as the feed protein concentration, superficial gas velocity, liquid flow rate, and solution pH are investigated. The results may prove to be helpful in understanding the mechanisms controlling the foam fractionation of proteins.     

Synthesis and evaluation as a visible‐light polymerization photoinitiator of a new dye‐linked bis(trichloromethyl)‐1,3,5‐triazine

A dye‐linked initiator consisting of a merocyanine dye, which has an absorption maximum at 460 nm, and a substituted bis(trichloromethyl)‐1,3,5‐triazine initiator was prepared in order to achieve an efficient photopolymerization in a visible‐light region. The spectroscopic studies clearly showed that the dye‐linked initiator exhibit a marked increase in the efficiency of fluorescence quenching than a simple mixture of the dye/initiator. These results are reasonably explained in terms of the efficiency of electron transfer between the dye and the initiator. The relative photoinitiating efficiency of dye‐linked initiators in photopolymerization of acrylate monomers was evaluated and the results clearly indicated that the dye‐linked photoinitiator exhibited a marked increase in the photoinitiating efficiency of photopolymerization of acrylates compared to a simple mixture of the dye/initiator in photopolymer coatings particularly at a lower concentration of the initiator. This was explained in terms of the active quenching sphere of the dye/initiator system. Superior photosensitivity in the linked compound at a lower concentration indicates that this would be particularly useful as a visible‐light photoinitiator in holographic‐recording photopolymers. Copyright © 2004 John Wiley & Sons, Ltd.     

Highly Efficient Self-Assembly of Metallacages and Their Supramolecular Catalysis Behaviors in Microdroplets

Developing a new strategy to improve the self-assembly efficiency of functional assemblies in a confined space and construct hybrid functional materials is a significant and fascinating endeavor. Herein, we present a highly efficient strategy for achieving the supramolecular self-assembly of well-defined metallacages in microdroplets through continuous-flow microfluidic devices. The high efficiency and versatility of this approach are demonstrated by the generation of five representative metallacages in different solvents containing water, DMF, acetonitrile, and methanol in a few minutes with nearly quantitative yields, in contrast to the yields obtained with the hour-scale reaction time in a batch reactor. A ring-opening catalytic reaction of the metallacages was selected as a model reaction for exploring supramolecular catalysis in microdroplets, whereby the catalytic yield was enhanced by 2.22-fold compared to that of the same reaction in the batch reactor. This work illustrates a new promising approach for the self-assembly of supramolecular systems.     

Nicotinic Acetylcholine Receptor Agonists: A Milestone for Modern Crop Protection

The destruction of crops by invertebrate pests is a major threat against a background of a continuously rising demand in food supply for a growing world population. Therefore, efficient crop protection measures in a vast range of agricultural settings are of utmost importance to guarantee sustainable yields. The discovery of synthetic agonists selectively addressing the nicotinic acetylcholine receptors (nAChRs), located in the central nervous system of insects, for use as insecticides was a major milestone in applied crop protection research. These compounds, as a result of their high target specificity and versatility in application methods, opened a new innovative era in the control of some of the world′s most devastating insect pests. These insecticides also contributed massively to extending our knowledge of the biochemistry of insect nicotinic acetylcholine receptors. The global economic success of synthetic nAChR agonists as insecticides renders the nicotinic acetylcholine receptor still one of the most attractive target sites for exploration in insecticide discovery.     

Benefits of the implementation of a metrological structure for water analyses

Traceability of measurements still often remains a non-operational notion for end-user chemists. A practical project, sponsored by the French Ministry of Research, has been conducted to evaluate and to demonstrate possible benefits of the implementation of a metrological structure for improvement of the quality of water analyses. LNE (Laboratoire National d'Essais) was in charge of the build up of the traceability chain in a concrete case of determination of some heavy metals (cadmium and lead) in a groundwater. Pure solutions for calibration and a matrix RM have been certified by LNE and then used by 46 labs (mainly French) in a inter-laboratory study. Results have shown a measurable bias in lead analysis in the groundwater for all methods in routine use by laboratories. This project has demonstrated the interest of a metrological approach for method calibration, method validation and estimation of measurement uncertainty.     

Combinatorial Approach to Chiral Tris‐ligated Carbophilic Platinum Complexes: Application to Asymmetric Catalysis

A straightforward methodology for the synthesis of libraries of chiral tris‐ligated cationic platinum complexes and their in situ evaluation as asymmetric carbophilic catalysts in a model domino hydroarylation/cyclization reaction of a 1,6‐enyne was developed. A catalyst‐generation process based on a combination of a monodentate and a bidentate phosphorus ligand allowed the formation of 108 chiral complexes. One‐pot screening of the stereoinduction obtained with this library in a test domino addition/cyclization reaction validated this approach and stressed the key role played by the monodentate ligand partner in obtaining high enantioselectivities. In the case of two challenging substrate/nucleophile combinations, the combinatorial approach resulted in a significant gain in enantioselectivity.     

C60笼内内陷粒子的运动

研究C60笼内内陷粒子的量力力学运动, 导出运动能量与波函数, 以内陷CO分子为例做了计算, 解释了分子对微波的吸收现象。     

Chalcogenide-Lewis acid mediated reactions of electron-deficient alkynes with aldehydes

Reactions of but-3-yn-2-one (2) with aldehydes 1 in the presence of a Lewis acid and dimethyl sulfide (3 a) predominantly gave (E)-alpha-(halomethylene)aldols 4-5 in high yields, while reactions of methyl propiolate (6 a) mainly afforded (Z)-3-halogeno-2-(hydroxymethyl)acrylates 7-8 in low to moderate yields. A reaction of dimethyl acetylenedicarboxylate (10) with 1 a in the presence of TiCl(4) and 1,1,3,3-tetramethylthiourea (3 c) produced maleate (E)-11 (40 %) and butenolide 12 (40 %). When a reaction of 6 a with 1 a was carried out in the presence of TiBr(4) and 3 a (0.2 equiv) at -20 degrees C for 60 h, 3-(methylthio)-2-(hydroxyalkyl)acrylate 9 a was obtained in an 8 % yield. Experiments were conducted in order to elucidate the formation mechanism of 9 a, and it was made clear that 9 a was formed via the processes of the Michael addition of sulfide 3 a to alkynoate 6 a and an aldol reaction with 1 a and demethylation.     

Compression of Polymer Brushes Under a Lateral Force

Summary: The influence of a lateral force (or lateral shear) acting on chains in a polymer brush is investigated theoretically. Brushes consisting of chains with temperature dependent anisotropic interactions between monomers (main‐chain mesogenic groups) are considered. It is shown that a lateral force applied to polymer brush induces its compression. In contrast to a conventional brush, the compression of brush, capable of forming a liquid crystalline (LC) state, can be caused by comparatively small shear forces. Moreover, such shear forces can induce a phase transition of a brush into the tilted LC state with a several‐fold decrease in brush thickness. These results allow us to predict a possibility to observe a decrease in brush thickness in a real experiment with reasonably values of shear rate.

Model of a chain in a polymer brush under an influence of lateral force p.