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

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Self-assembled monolayers of thiolates on metals as a form of nanotechnology.

The field of self-assembled monolayers (SAMs) has witnessed tremendous growth in synthetic sophistication and depth of characterization over the past 15 years.1 However, it is interesting to comment on the modest beginning and on important milestones. The field really began much earlier than is now recognized. In 1946 Zisman published the preparation of a monomolecular layer by adsorption (self-assembly) of a surfactant onto a clean metal surface.2 At that time, the potential of self-assembly was not recognized, and this publication initiated only a limited level of interest. Early work initiated in Kuhn’s laboratory at Gottingen, applying many years of experience in using chlorosilane derivative to hydrophobize glass, was followed by the more recent discovery, when Nuzzo and Allara showed that SAMs of alkanethiolates on gold can be prepared by adsorption of di-n-alkyl disulfides from dilute solutions.3 Getting away from the moisture-sensitive alkyl trichlorosilanes, as well as working with crystalline gold surfaces, were two important reasons for the success of these SAMs. Many self-assembly systems have since been investigated, but monolayers of alkanethiolates on gold are probably the most studied SAMs to date. The formation of monolayers by self-assembly of surfactant molecules at surfaces is one example of the general phenomena of self-assembly. In nature, self-assembly results in supermolecular hierarchical organizations of interlocking components that provides very complex systems.4 SAMs offer unique opportunities to increase fundamental understanding of self-organization, structure-property relationships, and interfacial phenomena. The ability to tailor both head and tail groups of the constituent molecules makes SAMs excellent systems for a more fundamental understanding of phenomena affected by competing intermolecular, molecular-substrates and molecule-solvent interactions like ordering and growth, wetting, adhesion, lubrication, and corrosion. That SAMs are well-defined and accessible makes them good model systems for studies of physical chemistry and statistical physics in two dimensions, and the crossover to three dimensions. SAMs provide the needed design flexibility, both at the individual molecular and at the material levels, and offer a vehicle for investigation of specific interactions at interfaces, and of the effect of increasing molecular complexity on the structure and stability of two-dimensional assemblies. These studies may eventually produce the design capabilities needed for assemblies of three-dimensional structures.5 However, this will require studies of more complex systems and the combination of what has been learned from SAMs with macromolecular science. The exponential growth in SAM research is a demonstration of the changes chemistry as a disciAbraham Ulman was born in Haifa, Israel, in 1946. He studied chemistry in the Bar-Ilan University in Ramat-Gan, Israel, and received his B.Sc. in 1969. He received his M.Sc. in phosphorus chemistry from Bar-Ilan University in 1971. After a brief period in industry, he moved to the Weizmann Institute in Rehovot, Israel, and received his Ph.D. in 1978 for work on heterosubstituted porphyrins. He then spent two years at Northwestern University in Evanston, IL, where his main interest was onedimensional organic conductors. In 1985 he joined the Corporate Research Laboratories of Eastman Kodak Company, in Rochester, NY, where his research interests were molecular design of materials for nonlinear optics and self-assembled monolayers. In 1994 he moved to Polytechnic University where he is the Alstadt-Lord-Mark Professor of Chemistry. His interests encompass self-assembled monolayers, surface engineering, polymers at interface, and surfaces phenomena. 1533 Chem. Rev. 1996, 96, 1533−1554

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Formation and Structure of Self-Assembled Monolayers.

Department of Materials Science, University of Patras, 26504 Rio Patras, Greece, Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation, 48 Vass. Constantinou Avenue, 116 35 Athens, Greece, Institut de Biologie Moleculaire et Cellulaire, UPR9021 CNRS, Immunologie et Chimie Therapeutiques, 67084 Strasbourg, France, and Dipartimento di Scienze Farmaceutiche, Universita di Trieste, Piazzale Europa 1, 34127 Trieste, Italy

Chemistry of Carbon Nanotubes

Small but strong: A review of the mechanical properties of carbon nanotube–polymer composites

Solid lubricants fill a special niche in reducing wear in situations where the use of liquid lubricants is either impractical or inadequate, such as in vacuum, space technology or automotive transport. Metal dichalcogenides MX2 (where M is, for instance, Mo or W and X is S or Se) are widely used as solid lubricants. These materials are characterized by a layered structure with weak (van der Waals) inter-layer forces that allow easy, low-strength shearing1,2. Within the past few years, hollow nanoparticles (HNs) of MX2 with structures similar to those of nested carbon fullerenes and nanotubes have been synthesized3,4. Here we show that these materials can act as effective solid lubricants: HN-WS2 outperforms the solid lubricants 2H-MoS2 and 2H-WS2 in every respect (friction, wear and lifetime of the lubricant) under varied test conditions. We attribute the outstanding performance of HN-WS2 to its chemical inertness and the hollow cage structure, which imparts elasticity and allows the particles to roll rather than to slide.

Hollow nanoparticles of WS2 as potential solid-state lubricants

The force required to separate a carbon nanotube from a solid polymer matrix has been measured by performing reproducible nanopullout experiments using atomic force microscopy. The separation stress is found to be remarkably high, indicating that carbon nanotubes are effective at reinforcing a polymer. These results imply that the polymer matrix in close vicinity of the carbon nanotube is able to withstand stresses that would otherwise cause considerable yield in a bulk polymer specimen.

Measurement of carbon nanotube-polymer interfacial strength

A technique to investigate the adhesion of carbon nanotubes to a polymer matrix is described. Carbon nanotubes bridging across holes in an epoxy matrix have been drawn out using the tip of a scanning probe microscope while recording the forces involved. A full force-displacement trace could be recorded and correlated with transmission electron micrographs observations prior and subsequent to the tip action. Based on these experiments, an approximate calculation of the nanotube-polymer interfacial shear strength has been performed.

Detachment of nanotubes from a polymer matrix

Spin-based properties, applications, and devices are commonly related to magnetic effects and to magnetic materials. Most of the development in spintronics is currently based on inorganic materials. Despite the fact that the magnetoresistance effect has been observed in organic materials, until now spin selectivity of organic based spintronics devices originated from an inorganic ferromagnetic electrode and was not determined by the organic molecules themselves. Here we show that conduction through double-stranded DNA oligomers is spin selective, demonstrating a true organic spin filter. The selectivity exceeds that of any known system at room temperature. The spin dependent resistivity indicates that the effect cannot result solely from the atomic spin-orbit coupling and must relate to a special property resulting from the chirality symmetry. The results may reflect on the importance of spin in determining electron transfer rates through biological systems.

Spin Specific Electron Conduction through DNA Oligomers

Human brain wrinkling has been implicated in neurodevelopmental disorders and yet its origins remain unknown. Polymer gel models suggest that wrinkling emerges spontaneously due to compression forces arising during differential swelling, but these ideas have not been tested in a living system. Here, we report the appearance of surface wrinkles during the in vitro development and self-organization of human brain organoids in a microfabricated compartment that supports in situ imaging over a timescale of weeks. We observe the emergence of convolutions at a critical cell density and maximal nuclear strain, which are indicative of a mechanical instability. We identify two opposing forces contributing to differential growth: cytoskeletal contraction at the organoid core and cell-cycle-dependent nuclear expansion at the organoid perimeter. The wrinkling wavelength exhibits linear scaling with tissue thickness, consistent with balanced bending and stretching energies. Lissencephalic (smooth brain) organoids display reduced convolutions, modified scaling and a reduced elastic modulus. Although the mechanism here does not include the neuronal migration seen in vivo, it models the physics of the folding brain remarkably well. Our on-chip approach offers a means for studying the emergent properties of organoid development, with implications for the embryonic human brain. Wrinkling in human brain organoids suggests that brain development may be mechanically driven, a notion supported only by model gels so far. Evidence in this simple living system highlights roles for cytoskeletal contraction and nuclear expansion.

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Sidney R. Cohen

Papers

Hollow nanoparticles of WS2 as potential solid-state lubricants

Measurement of carbon nanotube-polymer interfacial strength

Detachment of nanotubes from a polymer matrix

Spin Specific Electron Conduction through DNA Oligomers

Human Brain Organoids on a Chip Reveal the Physics of Folding.