Tandem Stille/Suzuki-Miyaura coupling of a hetero-bis-metalated diene. Rapid, one-pot assembly of polyene systems

[structure: see text]. The synthesis of a hetero-bis-metallo 1,3-butadiene is reported, and its use as an orthogonal Stille and Suzuki-Miyaura coupling partner is detailed. The tin/boron diene participated successfully in a one-pot, sequential Stille and Suzuki-Miyaura coupling protocol, and its utility was demonstrated in the two-step construction of the pentaene side chain of the Fusarium metabolite lucilactaene.     

高分子单链凝聚成与线团相互穿透的多链凝聚态

高分子单链凝聚态由于链内链结构单元间存在范德化吸引作用,高分子链呈打圈链构象,而多链凝聚态由于链内链单元间的吸引作用被与相互穿透的近邻链的单元间吸引作用所屏蔽,高分子链呈高斯链构象。本文简要介绍单链凝聚态试样的制备方法,单链单晶体、单链玻璃体、溶胀的单链高弹态拉伸等的实验观察,并提出从单链凝聚态到多链凝聚态的转变过程问题,即高分子线团的相互穿透过程,目前还缺少基础了解。     

Role of chain stiffness on the conformation of single polyelectrolytes in salt solutions

Conformation of single polyelectrolytes in tetravalent salt solutions is investigated under the framework of a coarse-grained model, using Langevin dynamics simulations. The chain size, studied by the radius of gyration, shows three different variational behaviors with salt concentration, depending on the chain stiffness. According to the size variations, polyelectrolytes of fixed chain length are classified into three categories: (1) flexible chain, for which the variation shows a curve similar to a tilted L, (2) semiflexible chain, whose curve resembles U, and (3) rigid chain, for which the curve is a straight line. The wormlike chain model with persistence length predicted by the Odijk-Skolnick-Fixman theory is found to be able to qualitatively describe the end-to-end distance at low salt concentration not only for semiflexible and rigid chains but also for flexible chain. In a low salt region, a flexible polyelectrolyte extends more significantly than a semiflexible chain, in reference of the size of their uncharged counterparts, and in a high salt region, regardless of chain stiffness, a chain attains a dimension comparable to that of its neutral polymer. The chain stiffness influences both the local and the global chain structures. A flexible chain exhibits a zigzagged local structure in the presence of salt ions, and the condensed structure is a disordered, random globule. A semiflexible chain is locally smooth, and the condensed structure is orderly packed, taking a form such as hairpin or toroid. Moreover, the chain stiffness can also affect the nature of the coil-globule transition. The transition occurred in a discrete manner for semiflexible chain, whereas it occurred in a continuous way for flexible chain. This discrete feature happened not only at low salt concentration when a semiflexible chain collapsed but also at high salt concentration when the collapsed chain is reexpanded. At the end, the effects of chain stiffness and salt concentration on the conformation of single polyelectrolytes are summarized in a schematic state diagram.     

液晶离聚物--分子设计与热性能

综述了液晶离聚物的分子设计与液晶热性能的关系,一般主链液晶,离子在链中浓度增加,玻璃化温度（Ｔｇ）和熔点（Ｔｍ）下降,离子在端基,对Ｔｇ和Ｔｍ影响不大;离子对侧链淮晶的影响,取决于主链的柔顺性和离子在链中的位置等。一般情况下,无论对主链还是侧链液晶离聚物,随着离子在链中浓度增加,液晶相向各向同性液体转化温度（Ｔｉ）降低。     

Studies on Single Chain Structure of Konjac Glucomannan

1INTRODUCTION The single chain structure of KGM is the ele-mentary acting unit of its biological function and viscoelasticity of mechanical properties.The re-search method of saccharide chain and the com-plexity of its structure have restricted the study on structure-activity relationship.Therefore,the studies concerning KGM both at home and abroad mainly focus on its application,whereas less on its structure.Previous researches were only related to the determination and distribution as…     

高分子链空间构象分布的复杂性——Θ条件下能量与尺寸的分布

通过高分子链的模型的计算来研究高分子链构象的尺寸与能量的分布．结果表明，高分子的链构象在小尺寸范围布居数增多；高分子的链构象在小尺寸范围存在比较稳定的链构象状态；在小尺寸范围比较稳定的链构象多具有类似棒状等非球形结构；高分子的链构象的尺寸与能量的分布显示熵弹性具有不对称性．     

Response analysis in biochemical chain reactions with negative feedforward and feedbackward loops

Finite difference equations can be used to study the responses of biochemical chain reactions at any step of the chain to an external stimulus. In this study, we developed mathematical models for two hypothetical chain reactions involving loops to study the responses in the chain as the length of the chain gets longer, so called transient and steady state responses. The first model is for a chain with a negative feedforward loop, and the second one is for a chain that has a negative feedback loop. Although both of the models have the same steady state equations and values, we showed that the chain with negative feedforward and negative feedback loops can produce significantly different behaviors. The former can bring the chain into oscillations with various periods and eventually chaos when the feedback is strong enough as the length of the reaction chain increases, whereas the latter is not capable of producing oscillations and more complicated dynamics.     

N-烷基化聚对苯二甲酰对苯二胺梳状高分子中烷基侧链对刚性主链堆积行为的影响

基于聚对苯二甲酰对苯二胺(PPTA), 采用N-烷基化方法制备了系列PPTACns(烷基侧链碳原子数n=8, 10, 12, 14, 16, 18)刚性主链梳状高分子, 利用DSC, XRD和FTIR等方法研究了其主链堆积行为、 分子链构象及热性能等与烷基侧链长度及结晶特性之间的关系. XRD和DSC结果表明, 当烷基侧链碳原子数达到14时, 烷基侧链发生结晶. XRD结果显示, PPTACns具有层状结构, 烷基侧链长度对主链层间距影响显著. FTIR研究发现, 烷基侧链的聚集状态对PPTACns分子链的构象产生较大影响, 伴随着烷基侧链结晶的熔融, PPTACns的分子链构象发生显著改变. 烷基侧链处于熔融状态的PPTACns的ν_C=O和γ_C-H谱带峰位与烷基侧链不结晶的PPTACn接近.     

Mesoscopic dynamic Monte Carlo simulations of the adsorption of proteinlike HP chains within laterally constricted spaces

Two-dimensional dynamic Monte Carlo simulations are applied to the protein-like HP chain model to investigate the influence of lateral confinement of the adsorbed chain on adsorption thermodynamics and the ensemble of accessible chain conformations. The structure of the model makes it possible to enumerate all possible chain conformations and thereby define with precision the relation between adsorption thermodynamics and changes in accessible chain conformations resulting from the adsorption process. Lateral confinement of the adsorbed chain is shown to dramatically reduce the number of accessible energy states and unique chain conformations such that, under certain conditions, adsorption is predicted to actually stabilize the chain against denaturation. Lateral confinement preferentially eliminates expanded conformations of the adsorbed chain, shifting the equilibrium from the unfolded state toward the native state. As a result, the conformational entropy of the adsorbed chain is predicted to be lower than that of the chain free in solution. The protein-like HP chain responds to an increase in the hydrophobicity of the sorbent surface by strongly favoring those conformations that minimize the overall internal energy of the system. As a result, adsorption severely destabilizes the native-state conformation. The ability of our simulation results to provide insights into underlying mechanisms for nonspecific protein adsorption is illustrated through qualitative comparison with activity data for hen egg-white lysozyme adsorbed on silica at different surface concentrations.     

扫描探针显微技术研究聚苯乙烯单链颗粒的力学响应

首先通过极稀溶液滴膜的方法得到了聚苯乙烯的单链颗粒 .之后 ,采用稍浓溶液得到了既有单链聚苯乙烯颗粒又有多链 (上千根 )聚苯乙烯颗粒的样品 .力调制技术显示单链聚苯乙烯颗粒比多链聚苯乙烯颗粒软 ;另一方面 ,对多链聚苯乙烯颗粒和聚苯乙烯本体的纳米压印实验结果表明二者的模量是近似的 .因此 ,可以得出单链聚苯乙烯颗粒比本体聚苯乙烯软 ,这说明存在于聚苯乙烯单链颗粒中的分子链内的缠结点密度不如存在于本体中的分子链间的缠结点密度大     

高分子链形状与尺寸关联的Monte Carlo模拟

运用MonteCarlo方法对线型高分子链格点模型的构型进行了模拟,研究了构型的尺寸(采用平方末端距R²,平方回转半径S²来表征)和形状(由非球形因子A表征)之间的关联.对任何长度的高分子链,其关联系数CA,R²和CA,S²均为正值,表明高分子链的形状与尺寸之间存在正关联,即尺寸小的构型其非球形因子A一般也小,反之尺寸大的构型其非球形因子A一般也大.关联系数CA,R²和CA,S²均随链长的增大而减小,近似地与链长的倒数(n^-1)成正比.研究还表明,关联系数的极限值(链长n很大时)与格点的类型无关,与链样本产生的方式也无关,但与链是否考虑排斥体积有关,考虑了排斥体积后,关联系数增大.     

近壁模型高分子链的计算机模拟

采用简立方格点上的普通无规行走 (NRW)和自避行走 (SAW )为模型链 ,研究了不可穿透的刚性壁附近高分子的构象性质 ,得出近壁链的构象熵和尺寸随一端点与壁之间距离z0 的变化 .所用的计算机模拟技术包括精确计数和MonteCarlo模拟 .数值结果表明 ,近壁链的构象熵降低遵循一种简单规律 ,即当链长愈长或一端愈接近于壁时 ,与长度相同的自由链相比 ,链因壁限制所致构象熵的降低愈大 .当链十分接近于壁时 ,其均方末端距〈R2 〉(尤其是与壁垂直的分量〈R2z〉)大于自由链的相应值 ;随z0 增大 ,〈R2 〉及〈R2z〉开始减小 ,通过某一极小值 ,然后上升 ;当z0 →∞时 ,趋于自由链的极限值 .换言之 ,近壁模型链的线团经历一个收缩再逐渐扩张的过程     

端基附壁高分子模型链的塌缩转变

借MonteCarlo和模拟退火方法研究了端基附壁高分子尾形链在不同温度下的形态变化 ,链的模型采用有最近邻相互吸引作用的自避行走 .计算机实验结果表明 ,对于端基附壁的高分子尾形链 ,与自由链一样 ,当温度逐渐降低时高分子链会发生从松散的无规线团到紧密球体的塌缩转变 .计算机模拟得到了端基附壁链的均方末端距及其分量 ,均方回转半径及分布随温度的变化 .由于刚性壁的影响 ,使得有限链长的高分子尾形链与自由链相比 ,其表示链尺寸 温度关系的曲线要稍低 .模拟还发现 ,在高温时壁对链形状的影响比较大 ,壁垂直方向上尺寸明显大于平行方向的尺寸 ,后者接近于自由链的尺寸分量 .然而 ,低于θ温度时 ,尤其是完全塌缩之后 ,壁对链形状的影响已经很小 .     

The dependence of the rules governing gas-phase combustion on the competition between chain propagation and chain termination reactions

The competition between chain propagation and chain termination reactions was shown to play an important role in gas-phase combustion. Conditions under which this competition to a substantial extent determined the critical ignition conditions and the rate of the process were analyzed. Examples that showed that ignoring the role played by chain propagation, chain termination, and chain branching reactions in branched-chain processes led to conclusions that contradicted experimental data were considered.     

The relative contributions of self-heating and chain branching to the kinetics of hydrogen oxidation outside the ignition region close to the third limit

It is shown that, in hydrogen-oxygen mixtures, under the conditions when the rate of reaction chain termination is higher than the rate of chain branching, the characteristic reaction time is hundreds of seconds even in the immediate vicinity of the third ignition limit. The self-heating of the mixtures therefore does not exceed several degrees and, contrary to the accepted views, cannot result in thermal combustion. Ignition observed in the third limit region is caused by a higher rate of chain branching compared with chain termination; that is, it is a chain reaction. Self-heating only becomes substantial during the development of chain combustion.     

Calculation of hydrophile-lipophile balance for polyethoxylated surfactants by group contribution method

Based on Davies' group contribution method, hydrophile-lipophile balance (HLB) values were calculated by effective chain length (ECL) instead of actual chain length of straight alkyl chain, polyoxyethylene (EO) chain, and polyoxypropylene (PO) chain. Linear equations were adopted for the effective chain length of straight alkyl chain and PO chain; a Gamma probability density function (PDF) was used to describe the contribution of each EO group to HLB and the effective chain length of EO chain could be obtained by integrating Gamma PDF. The HLB values of 224 nonionic surfactants were calculated and the average absolute error is less than 1.5, which is much better than the results obtained by Davies.     

Nascent crystallization of a growing chain on a catalyst surface: a nonequilibrium molecular dynamics simulation study

The growing chain molecular dynamics (GCMD) simulation method, a new nonequilibrium molecular dynamics code, is proposed to simulate the polymer chain aggregation behavior during polymerization on a catalyst surface. We found that the growing chain crystallizes on the surface in two stages: the nucleation stage and the crystal growth stage. In the first part of the nucleation period, the short polymerizing chain first absorbs on the surface and can be in either an ordered or disordered structure. Still in the nucleation period, when the chain reaches a degree of polymerization, about 100 bonds, the chain folds into a stable nucleus on the substrate with 3-5 stems. In the crystal growth stage where the polymerization also proceeds, we observed a stem elongation process in combination with a chain folding process. In the stem elongation step, the number of stems in the nucleus remains constant, and all the stems expand together to a length of ca. 5-25 ns. In the subsequent chain folding step, the stem length decreases about 20 bonds within a period of ca. 0.1-0.5 ns. During chain growth, the elongation process and the folding process occur in an alternating and repeated fashion. The crystallization mechanism of the polymerizing chain was discussed.     

THE SPATIAL DISTRIBUTION AND MOMENTS OF CIRCULAR FREELY JOINTED CHAIN

The spatial distribution function and second moments of circular freely jointed chain are derived based on an analytical method. The circular Gauss chain, which is simple for long chains, is compared with the circular freely jointed chain, which is exact for short chains. It is shown that the Gauss chain model predicts a more compact configurational distribution than the exact freely jointed chain. The two chain models, however, become closer to each other when the chain length increases. It is found that the difference of the mean square radius of gyration calculated with these two chain models is a constant, independent of the chain length.     

Analysis of reduced monoclonal antibodies using size exclusion chromatography coupled with mass spectrometry

Size-exclusion chromatography (SEC) has been widely used to detect antibody aggregates, monomer, and fragments. SEC coupled to mass spectrometry has been reported to measure the molecular weights of antibody; antibody conjugates, and antibody light chain and heavy chain. In this study, separation of antibody light chain and heavy chain by SEC and direct coupling to a mass spectrometer was further studied. It was determined that employing mobile phases containing acetonitrile, trifluoroacetic acid, and formic acid allowed the separation of antibody light chain and heavy chain after reduction by SEC. In addition, this mobile phase allowed the coupling of SEC to a mass spectrometer to obtain a direct molecular weight measurement. The application of the SEC-MS method was demonstrated by the separation of the light chain and the heavy chain of multiple recombinant monoclonal antibodies. In addition, separation of a thioether linked light chain and heavy chain from the free light chain and the free heavy chain of a recombinant monoclonal antibody after reduction was also achieved. This optimized method provided a separation of antibody light chain and heavy chain based on size and allowed a direct measurement of molecular weights by mass spectrometry. In addition, this method may help to identify peaks eluting from SEC column directly.     

界面层中模型高分子链构象的统计理论

高分子自由链在溶液、熔体或固体中的构象有完整的理论和实验工作 ,已是成熟的知识[1～ 4] .近年来 ,受限大分子构象的探索已成为新的热点[5] .界面是一种最简单的限制 ,将对其附近的高分子产生显著的影响 .除理论家的重视以外 ,界面附近高分子构象问题还与许多应用领域相关 .例如 ,液体高分子的表面张力 ,固体高分子的粘附 ,滑移 ,磨蚀等力学特性 ,甚至它们的光学和电学性质都与界面上的组成和分子构象相关[6] .ｄｅＧｅｎｎｅｓ[7] 最早强调界面附近的分子链构象问题的重要性 .他首先从理论上猜测长链的链端若与界面有强吸引作用 ,则它们…