抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

A revolution in novel nanoparticles and colloidal building blocks has been enabled by recent breakthroughs in particle synthesis These new particles are poised to become the ‘atoms’ and ‘molecules’ of tomorrow’s materials if they can be successfully assembled into useful structures Here, we discuss the recent progress made in the synthesis of nanocrystals and colloidal particles and draw analogies between these new particulate building blocks and better-studied molecules and supramolecular objects We argue for a conceptual framework for these new building blocks based on anisotropy attributes and discuss the prognosis for future progress in exploiting anisotropy for materials design and assembly

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Anisotropy of building blocks and their assembly into complex structures

Journal of Physics Condensed Matter: Preface

A challenging goal in materials chemistry and physics is spontaneously to form intended superstructures from designed building blocks. In fields such as crystal engineering and the design of porous materials, this typically involves building blocks of organic molecules, sometimes operating together with metallic ions or clusters. The translation of such ideas to nanoparticles and colloidal-sized building blocks would potentially open doors to new materials and new properties, but the pathways to achieve this goal are still undetermined. Here we show how colloidal spheres can be induced to self-assemble into a complex predetermined colloidal crystal-in this case a colloidal kagome lattice-through decoration of their surfaces with a simple pattern of hydrophobic domains. The building blocks are simple micrometre-sized spheres with interactions (electrostatic repulsion in the middle, hydrophobic attraction at the poles, which we call 'triblock Janus') that are also simple, but the self-assembly of the spheres into an open kagome structure contrasts with previously known close-packed periodic arrangements of spheres. This open network is of interest for several theoretical reasons. With a view to possible enhanced functionality, the resulting lattice structure possesses two families of pores, one that is hydrophobic on the rims of the pores and another that is hydrophilic. This strategy of 'convergent' self-assembly from easily fabricated colloidal building blocks encodes the target supracolloidal architecture, not in localized attractive spots but instead in large redundantly attractive regions, and can be extended to form other supracolloidal networks.

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Directed self-assembly of a colloidal kagome lattice

Controlling interparticle interactions, aggregation and cluster formation is of central importance in a number of areas, ranging from cluster formation in various disease processes to protein crystallography and the production of photonic crystals. Recent developments in the description of the interaction of colloidal particles with short-range attractive potentials have led to interesting findings including metastable liquid-liquid phase separation and the formation of dynamically arrested states (such as the existence of attractive and repulsive glasses, and transient gels). The emerging glass paradigm has been successfully applied to complex soft-matter systems, such as colloid-polymer systems and concentrated protein solutions. However, intriguing problems like the frequent occurrence of cluster phases remain. Here we report small-angle scattering and confocal microscopy investigations of two model systems: protein solutions and colloid-polymer mixtures. We demonstrate that in both systems, a combination of short-range attraction and long-range repulsion results in the formation of small equilibrium clusters. We discuss the relevance of this finding for nucleation processes during protein crystallization, protein or DNA self-assembly and the previously observed formation of cluster and gel phases in colloidal suspensions.

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Equilibrium cluster formation in concentrated protein solutions and colloids

We report observations of a temperature-induced orientational transition in a freely suspended nematic film of the liquid crystal 4-ethyl-2-fluoro-4′-[2-(trans-4-n-pentylcyclohexyl)-ethyl]-biphenyl (I52). The transition is from a high-symmetry state, where the molecules are perpendicular to the film boundaries (homeotropic alignment), to a lower-symmetry state, where the molecules are inclined (tilted alignment), and occurs as the temperature of the sample is raised. A previous study by Faetti and Fronzoni (1978) discovered a similar transition in freely suspended nematic films of N-(p-methoxybenzylidene)-p-n-butylaniline, except that it occurred as the temperature was lowered, a result that we confirm here. In order to explain both orientational transitions and the temperature-independent alignment of other nematics, we have generalized a model by Parsons (1978) that is based on competition between polar and quadrupolar contributions to the surface free energy. By considering the effects of smectic ordering and ionic impurities, we can account for all of the various observations.

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Temperature-induced orientational transitions in freely suspended nematic films

The smectic potential in a liquid crystal with a reentrant nematic phase: NMR of solutes

Order-disorder transitions in colloidal systems are an attractive option for making switchable materials. Electric-field-driven order-disorder transitions are especially attractive for this purpose because the tuning parameter is easily and externally controllable. However, precise positional control of 3D structure is immensely challenging. Using patterned electrodes, we demonstrate that ac electric fields-dominantly dielectrophoresis (DEP) coupled with an electrohydrodynamic mechanism consisting of induced-charge electro-osmosis (ICEO)-can be used to template colloidal order dynamically in three dimensions. We find that the electric field geometry dictates the location, size, and shape of colloidal patterns and can produce patterns with surprising complexity.

Dynamic templating of colloidal patterns in three dimensions with nonuniform electric fields.

Colloidal particle coordinates in three dimensions can be obtained in 3D samples with a combination of the increased resolution and optical sectioning capabilities of confocal microscopy and fluorescently labeled model core-shell silica colloids. In this work we show how this capability can be used to analyze structure formation in electrorheological fluids on a quantitative basis. We find body-centered-tetragonal (BCT) crystals for colloidal particles in an electric field. Metastable sheet like structures were identified as an intermediate phase prior to BCT crystal formation. Due to finitesize effects induced by the electrode surface the sheets are not randomly oriented, but grow preferentially with a 60 o tilt with respect to the electric field. Preliminary measurements indicate that flow-aligned sheets form under shear. Finally, we show that in the case that the ionic strength is very low, electric-field-induced dipolar interactions can be present in addition to long-range repulsions between the colloids leading to interesting metastable and equilibrium structures with possibilities for applications in photonic bandgap crystals as well as in model ER studies. Electrorheological (ER) [1] and magnetorheological (MR) fluids have been studied since the 1950’s with a view to developing wide-ranging applications that relate to the reversible millisecond field-responsive control of the apparent fluid viscosity. Commercial ER and MR fluids are “messy” systems of odd-shaped and polydisperse sub-millimeter particles in a fluid suspension. The detailed physical mechanisms and the role of variables such as size and shape polydispersity, the role of a mobile surface-charge layer in the ER case, and the role of Brownian motion, are only now beginning to be understood (see [2] for a recent review). Moreover, while rheological measurements have yielded a lot of information, there is yet only limited information about the kinds of structures formed [3-5] and their dynamics. In this paper, we describe a technique and two model systems for studying the kinetics of the ER response.

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Monodisperse colloidal suspensions of silica and pmma spheres as model electrorheological fluids: a real-space study of structure formation

We study theoretically the effect of an external field on the nematic–smectic-A transition close to the
tricritical point, where fluctuation effects govern the qualitative behavior of the transition. An external
field suppresses nematic-director fluctuations by making them massive. For a fluctuation-driven firstorder
transition, we show that an external field can drive the transition second order. In an appropriate
liquid-crystal system, we predict the required magnetic field to be of order 10 T. The equivalent electric
field is of order 1 V�mm.

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Anand Yethiraj

Papers

Temperature-induced orientational transitions in freely suspended nematic films

The smectic potential in a liquid crystal with a reentrant nematic phase: NMR of solutes

Dynamic templating of colloidal patterns in three dimensions with nonuniform electric fields.

Monodisperse colloidal suspensions of silica and pmma spheres as model electrorheological fluids: a real-space study of structure formation

External-Field-Induced Tricritical Point in a Fluctuation-Driven Nematic–Smectic-ATransition