Reconfigurable self-assembly through chiral control of interfacial tension

From determining the optical properties of simple molecular crystals to establishing the preferred handedness in highly complex vertebrates, molecular chirality profoundly influences the structural, mechanical and optical properties of both synthetic and biological matter on macroscopic length scales. In soft materials such as amphiphilic lipids and liquid crystals, the competition between local chiral interactions and global constraints imposed by the geometry of the self-assembled structures leads to frustration and the assembly of unique materials. An example of particular interest is smectic liquid crystals, where the two-dimensional layered geometry cannot support twist and chirality is consequently expelled to the edges in a manner analogous to the expulsion of a magnetic field from superconductors. Here we demonstrate a consequence of this geometric frustration that leads to a new design principle for the assembly of chiral molecules. Using a model system of colloidal membranes, we show that molecular chirality can control the interfacial tension, an important property of multi-component mixtures. This suggests an analogy between chiral twist, which is expelled to the edges of two-dimensional membranes, and amphiphilic surfactants, which are expelled to oil-water interfaces. As with surfactants, chiral control of interfacial tension drives the formation of many polymorphic assemblages such as twisted ribbons with linear and circular topologies, starfish membranes, and double and triple helices. Tuning molecular chirality in situ allows dynamical control of line tension, which powers polymorphic transitions between various chiral structures. These findings outline a general strategy for the assembly of reconfigurable chiral materials that can easily be moved, stretched, attached to one another and transformed between multiple conformational states, thus allowing precise assembly and nanosculpting of highly dynamical and designable materials with complex topologies.     

通过合金和去合金过程制备一种海绵状的纳米多孔铂以及对氧的电催化还原

采用一种简易的方法制备了海绵状的球形纳米多孔铂,首先是用循环伏安法在玻碳电极上电沉积得到铂铜合金,然后在浓硝酸中刻蚀合金去掉铜．用到场发射扫描电镜、X射线光电子能谱、X射线衍射和循环伏安法对其进行了表征．也对制备此种铂催化剂的条件进行了优化．此种铂修饰电极对氧的还原表现出很高的电催化活性,其氧的还原峰电流是相应纳米铂修饰电极的四倍．这种制备海绵状纳米多孔结构的方法以及所得到得到铂修饰电极可能在燃料电池和生物传感器等领域有着很大的应用前景．     

六角螺系统的 Harmonic 指标

图G的 Harmonic指标定义为图G 中所有边uv 的权重2du＋dv 的和,用 H（G）表示;二阶Harmonic指标被定义为图G中所有二长路uvw的权重3du＋dv＋dw 的和,用2H（G）表示;其中du表示G中点u的度数。该文研究了六角螺链和六角螺系统的 Harmonic 指标,发现它们的极图不唯一。通过研究二阶 Harmonic指标,确定了六角螺链的极图,发现六角螺系统的极图是一类特定的图。并且找到一个关于Harmonic 指标的极图和二阶 Harmonic 指标的极图的关系。最后,提出一个关于 Harmonic 指标的开放新问题。     

Formation of massive black holes through runaway collisions in dense young star clusters

A luminous X-ray source is associated with MGG 11--a cluster of young stars approximately 200 pc from the centre of the starburst galaxy M 82 (refs 1, 2). The properties of this source are best explained by invoking a black hole with a mass of at least 350 solar masses (350 M(o)), which is intermediate between stellar-mass and supermassive black holes. A nearby but somewhat more massive cluster (MGG 9) shows no evidence of such an intermediate-mass black hole, raising the issue of just what physical characteristics of the clusters can account for this difference. Here we report numerical simulations of the evolution and motion of stars within the clusters, where stars are allowed to merge with each other. We find that for MGG 11 dynamical friction leads to the massive stars sinking rapidly to the centre of the cluster, where they participate in a runaway collision. This produces a star of 800-3,000 M(o) which ultimately collapses to a black hole of intermediate mass. No such runaway occurs in the cluster MGG 9, because the larger cluster radius leads to a mass segregation timescale a factor of five longer than for MGG 11.     

关于六角系统的两个猜想

对Gutman提出的关于六角系统的三个猜想,举例说明了该六角系统中的复盖与1－因子关系的两个猜想是不成立的,而六角系统的复盖问题与有机化学中六隅芳香体系有密切联系。     

Drying-mediated self-assembly of nanoparticles

Systems far from equilibrium can exhibit complex transitory structures, even when equilibrium fluctuations are mundane. A dramatic example of this phenomenon has recently been demonstrated for thin-film solutions of passivated nanocrystals during the irreversible evaporation of the solvent. The relatively weak attractions between nanocrystals, which are efficiently screened in solution, become manifest as the solvent evaporates, initiating assembly of intricate, slowly evolving structures. Although certain aspects of this aggregation process can be explained using thermodynamic arguments alone, it is in principle a non-equilibrium process. A representation of this process as arising from the phase separation between a dense nanocrystal 'liquid' and dilute nanocrystal 'vapour' captures some of the behaviour observed in experiments, but neglects entirely the role of solvent fluctuations, which can be considerable on the nanometre length scale. Here we present a coarse-grained model of nanoparticle self-assembly that explicitly includes the dynamics of the evaporating solvent. Simulations using this model not only account for all observed spatial and temporal patterns, but also predict network structures that have yet to be explored. Two distinct mechanisms of ordering emerge, corresponding to the homogeneous and heterogeneous limits of evaporation dynamics. Our calculations show how different choices of solvent, nanoparticle size (and identity) and thermodynamic state give rise to the various morphologies of the final structures. The resulting guide for designing statistically patterned arrays of nanoparticles suggests the possibility of fabricating spontaneously organized nanoscale devices.     

健康要素的六角模型探索

从健康概念三种水平上的释义开始,提出了从系统科学视角阐述的健康的定义;讨论了健康科学的学科性质与特点;以精神健康、心理健康、生理健康、行为健康、社会适应健康、环境健康六个要素构建了关于人的整体健康的六角理论模型,并对该模型的具体化与潜在价值进行了讨论。     

六角晶系钡铁氧体纳米晶的制备和表征

采用柠檬酸sol gel工艺 ,制备了Zn2 Z型 ,Zn2 W型 ,Co2 Z型 ,M型平面六角晶系的钡铁氧体钠米晶 .采用X射线衍射分析 (XRD) ,透射电镜分析 (TEM)和热分析对其物相组成、显微结构、反应过程等进行研究 ,发现采用本工艺 ,在 75 0℃的较低温度下 ,就可形成均匀单一的铁氧体纳米晶 ,并深入分析了其反应机制 ;对Zn2 Z型铁氧体的吸波特性进行了研究 ,结果表明 :在X波段 (8～ 12GHz)和Ku波段 (12～ 18GHz) ,有多个吸收峰 ,最大吸收量达 6 5dB ,10dB的带宽达到 6 .5GHz ,说明这是一种优质的宽频微波吸收材料 ,并探究了纳米吸波材料的吸波机理 .     

超六边形斑图的4种形成途径

为了减弱在斑图形成时实验条件的限制,获得同一斑图的多种形成途径,利用双水电极介质阻挡放电装置,在空气/氩气混合气体放电中,观察到了超六边形斑图的4种形成途径.在不同气压和氩气含量下,研究了4种斑图包括不规则六边形斑图、六边形斑图、四边形斑图和四六边形共存斑图到超六边形斑图的演化.实验发现随气压及氩气含量的变化,它们向超六边形斑图演化时的出现范围由大到小依次是六边形斑图、四六边形共存斑图、不规则六边形斑图和四边形斑图.     

六角网格系统下字符的显示

六角网格系统下的图形显示优于矩形网格系统.基于六角网格的优点,根据矩形网格系统下字符显示的原理,探讨了六角网格系统下点阵字符与轮廓字符的显示,并对这两种字符显示方法的优缺点作了比较.     

Recent development of peptide self-assembly

Amino acids are the building blocks to build peptides and proteins. Recent development in peptide synthesis has however enabled us to mimic this natural process by preparing various long and short peptides possessing different conformations and biological functions. The self-assembly of short designed peptides into molecular nanostructures is becoming a growing interest in nanobiotechnology. Self-assembled peptides exhibit several attractive features for applications in tissue regeneration, drug delivery, biological surface engineering as well as in food science, cosmetic industry and antibiotics. The aim of this review is to introduce the readers to a number of representative studies on peptide self-assembly.     

三维自组装石墨烯的细胞相容性研究

针对石墨烯的二维平面结构不利于细胞在材料上延伸生长和黏附的问题,通过水热法合成自组装石墨烯,搭建利于细胞生长和黏附的三维结构.利用扫描电子显微镜、透射电子显微镜、傅里叶红外光谱、拉曼光谱、X线光电子能谱和接触角测试仪对样品的表面形貌、微观结构、化学键、原子组态和亲水性能进行测试,并通过形体外细胞实验研究了L929小鼠肺部成纤维细胞在材料上的黏附和增殖生长等行为.实验结果表明:自组装石墨烯具有孔径为1~3μm的孔洞,材料整体呈网状结构,为多层石墨烯片层的堆叠;样品中部分C元素分别与H和O元素结合生成多种官能团;三维自组装石墨烯的亲水性和表面细胞增殖生长情况均优于二维石墨烯,更适于作为组织支架促进细胞生长.     

Recent development of peptide self-assembly

Amino acids are the building blocks to build peptides and proteins. Recent development in peptide synthesis has however enabled us to mimic this natural process by preparing various long and short peptides possessing different conformations and biological functions. The self-assembly of short designed peptides into molecular nanostructures is becoming a growing interest in nanobiotechnology. Self- assembled peptides exhibit several attractive features for applications in tissue regeneration, drug delivery, biological surface engineering as well as in food science, cosmetic industry and antibiotics. The aim of this review is to introduce the readers to a number of representative studies on peptide self-assembly.     

N-烷基-2-巯基乙酰胺自组装膜阻隔溶液离子跨膜输运能力

采用自组装手段，将3种不同链长的N-烷基-2-巯基乙酰胺分子(HSCH2CONH(CH2)nCH3，n＝6，11，17)组装于多晶金(Au)表面，形成自组装单分子膜(SAMs)．接触角测量值表明，SAMs具有与长链硫醇形成的自组装单分子膜相近的润湿性和致密性．循环伏安和阻抗测量表明，SAMs的缺陷随分子链长的增加而降低，界面电荷传输阻力亦随分子链长的增加而增加，界面氧化还原反应随着链长的增加逐渐转化为完全的动力学控制过程．SAMs有效阻隔了溶液离子、电子等的跨膜输运．     

用乙酰胺合成六方形貌介孔氧化硅纤维

以正硅酸乙酯(TEOS)为硅前驱体,乙酰胺(CH3CONH2)为助溶剂,十六烷基氯化吡啶(C16PyC l)为结构导向剂,在酸性溶液中合成六方形貌的介孔氧化硅纤维,经小角X射线衍射(SXRD)、扫描电子显微镜(SEM)和低温N2吸附-脱附技术等表征。结果表明:合成的样品为六角状外形的氧化硅纤维,直径约4~7μm,长度约几十微米。六角状纤维的孔道具有与MCM-41类似的六方结构;煅烧后样品的吸附数据显示出吸附-脱附等温线为典型的IV型,吸附-脱附滞后环为H2型,孔道的孔径分布较宽;BJH最可几孔径为2.96 nm和3.50 nm,表明样品具有特殊的双孔道结构;计算的BET表面积为1 060 m2.g-1。     

六角密堆积结构的有效介电常数

本文导出一般形式的Rayleigh方程和混杂介质的有效介电常数公式，计算了介电粒子构成的六角密堆积结构的有效介电常经，从理论上讲．笔者的计算可准确到任意高阶矩，因而结果是精确的。     

等能量六角系统的算法设计

针对一类特殊的六角系统图,设计了一种算法,该算法可以得出该类图中是否含有等能量的图.结果表明:利用该算法,当sum≥29时,能找到能量相等的异构六角系统图.该结论在化学图论领域中具有实际应用意义.     

一类六角系统的完美匹配

对于峰、谷点均位于其凸包的边界上的一类六角系统,本文给出了一个较简单的求完美匹配的算法。     

六方纳米介孔二氧化硅纤维的合成

以十六烷基氯化吡啶(C16PyCl)为模板剂,原硅酸四乙酯(TEOS)为硅源,乙酰胺为助剂,在酸性条件下合成了六方纳米介孔二氧化硅纤维,并使用扫描电镜(SEM)、小角X射线衍射(SXRD)和N2气体吸附仪对其进行了表征。结果表明合成样品呈六方纤维外形,纤维直径约3~5μm,纤维长度约几十微米。六方纤维具有MCM-41的六方孔道结构;煅烧后的样品显示典型的IV型吸附等温线和H2型滞后环,孔径分布较宽,具有双孔道结构,BJH最可几孔径为2.96/3.50 nm,BET表面积为1 060 m2.g-1。