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

In this article, the effects of size and confinement at the nanometre size scale on both the melting temperature, Tm, and the glass transition temperature, Tg, are reviewed. Although there is an accepted thermodynamic model (the Gibbs–Thomson equation) for explaining the shift in the first-order transition, Tm, for confined materials, the depression of the melting point is still not fully understood and clearly requires further investigation. However, the main thrust of the work is a review of the field of confinement and size effects on the glass transition temperature. We present in detail the dynamic, thermodynamic and pseudo-thermodynamic measurements reported for the glass transition in confined geometries for both small molecules confined in nanopores and for ultrathin polymer films. We survey the observations that show that the glass transition temperature decreases, increases, remains the same or even disappears depending upon details of the experimental (or molecular simulation) conditions. Indeed, different behaviours have been observed for the same material depending on the experimental methods used. It seems that the existing theories of Tg are unable to explain the range of behaviours seen at the nanometre size scale, in part because the glass transition phenomenon itself is not fully understood. Importantly, here we conclude that the vast majority of the experiments have been carried out carefully and the results are reproducible. What is currently lacking appears to be an overall view, which accounts for the range of observations. The field seems to be experimentally and empirically driven rather than responding to major theoretical developments.

https://iopscience.iop.org/article/10.1088/0953-8984/17/15/R01/pdf

Effects of confinement on material behaviour at the nanometre size scale

Supercooled liquids and glasses are important for current and developing technologies. Here we provide perspective on recent progress in this field. The interpretation of supercooled liquid and glass properties in terms of the potential energy landscape is discussed. We explore the connections between amorphous structure, high frequency motions, molecular motion, structural relaxation, stability against crystallization, and material properties. Recent developments that may lead to new materials or new applications of existing materials are described.

Perspective: Supercooled liquids and glasses

We survey results of computer simulations for the structure and dynamics of supercooled polymer melts and films. Our survey is mainly concerned with features of a coarse grained polymer model?a bead?spring model?in the temperature regime above the critical glass temperature Tc of the ideal mode-coupling theory (MCT). We divide our discussion into two parts: a part devoted to bulk properties and a part dealing with thin films. The discussion of the bulk properties focuses on two aspects: a comparison of the simulation results with MCT and an analysis of dynamic heterogeneities. We explain in detail how the analyses are performed and what results may be obtained, and we critically assess their strengths and weaknesses. In discussing the application of MCT we also present first results of a quantitative comparison which does not rely on fits, but exploits static input from the simulation to predict the relaxation dynamics. The second part of this review is devoted to extensions of the simulations from the bulk to thin films. We explore in detail the influence of the boundary condition, imposed by smooth or rough walls, on the structure and dynamics of the polymer melt. Geometric confinement is found to shift the glass transition temperature Tg (or Tc in our case) relative to the bulk. We compare our and other simulation results for the Tg shift with experimental data, briefly survey some theoretical ideas for explaining these shifts and discuss related simulation work on the glass transition of confined liquids. Finally, we also present some technical details of how to perform fits to MCT and give a brief introduction to another approach to the glass transition based on the potential energy landscape of a liquid.

https://iopscience.iop.org/article/10.1088/0953-8984/17/32/R02/pdf

Computer simulations of supercooled polymer melts in the bulk and in confined geometry

The Flash DSC 1, a power compensation twin-type, chip-based fast scanning calorimeter (FSC): First findings on polymers

The ultrasensitive differential scanning calorimetry is used to observe the glass transition in thin (1-400 nm) spin-cast films of polystyrene, poly (2-vinyl pyridine) and poly (methyl methacrylate) on a platinum surface. A pronounced glass transition is observed even at a thickness as small as 1-3 nm. Using the high heating (20-200 K/ms) and cooling (1-2 K/ms in glass transition region) rates which are typical for this technique, we do not observe appreciable dependence of the glass transition temperature over the thickness range from hundreds of nanometers down to 3 nm thick films. The evolution of calorimetric data with film thickness is discussed in terms of broadening of transition dynamics and loss of transition contrast.

/pdf/glass-transition-in-ultrathin-polymer-films-calorimetric-2hq7zc6vmz.pdf

Glass transition in ultrathin polymer films: calorimetric study.

The equipment for an ultrasensitive, fast, thin-film differential scanning calorimetry [(TDSC) or nanocalorimetry] technique is described. The calorimetric cell (∼0.30 cm2) operates by applying a short (∼10 ms) dc current pulse (∼10 mA) to a thin (∼50 nm) patterned metal strip, which is supported by a thin (∼50 nm) SiNx membrane. The calorimeter operates at high heating rates (15–200 K/ms) and is very sensitive (30 pJ/K). The design of the calorimeter, the timing/synchronization methods, as well as the choice of key components of the instrument are discussed. Comparisons are made between two dc pulsing circuits that generate the current, a battery powered system and a system based on discharge of an assembly of charged capacitors (recommended). Design concepts for the differential as well as a simplified nondifferential technique are discussed and evaluated via experiments on thin films of indium. The differential design shows an increase in sensitivity, making it suitable for small samples. The custom made electronic circuits are also described, including the design of a preamplifier with low (28×) and high (700×) gain options, which are also compared using experimental data. Noise considerations are critical for the method. Simple models which describe noise levels in the calorimetric data are given and methods for reducing noise are discussed in detail. The sources of noise in the instrument are discussed in terms of both fundamental factors such as Johnson noise of the metal strip, as well as the limiting attributes of the sensing and pulsing circuits and instrumentation. These limiting attributes include spurious signals generated by desorption of ambient gases from the sensor, ground loops, switching regulators, and missing codes in analog-to-digital converter instruments. Examples of the experimental data of heat capacity Cp(T) of various thin films of indium, tin, and polystyrene are presented. A complete data set of raw experimental values is included for a 20 nm sample of Sn which shows the values of current and voltage of both the sample and reference sensors, as well as the differential voltage and the final values of the heat capacity.

Ultrasensitive, fast, thin-film differential scanning calorimeter

Ultrasensitive, thin-film, differential scanning calorimetry is used to determine the glass-transition temperature of 3−400 nm thick, spin-cast films of polystyrene, poly (2-vinyl pyridine), and poly (methyl methacrylate) on a platinum surface. The technique used here is modified to characterize the glass transition over a time scale of seconds rather than milliseconds. No appreciable dependence of the glass-transition temperature on thickness is observed over the entire range used. The results are discussed in comparison with previous calorimetric measurements, characterized by the glass-transition time scale of milliseconds.

/pdf/probing-glass-transition-of-ultrathin-polymer-films-at-a-49tha0tcml.pdf

Probing Glass Transition of Ultrathin Polymer Films at a Time Scale of Seconds Using Fast Differential Scanning Calorimetry

http://allen.matse.illinois.edu/pdf/allen_tca_062603.pdf

Glass transition of thin films of poly(2-vinyl pyridine) and poly(methyl methacrylate): nanocalorimetry measurements

We report the synthesis of silver-decanethiolate (AgSC10)lamellarcrystals.Nanometer-sizedAgclustersgrown on inert substrates react with decanethiol vapor to form multi- layer AgSC10 lamellar crystals with both layer-by-layer and in- plane ordering. The crystals have strong (010) texture with the layersparalleltothesubstrates.Thesynthesismethodallowsfor a precise control of the number of layers. The thickness of the lamellae can be manipulated and systematically reduced to a single layer by decreasing the amount of Ag and lowering the annealing temperature. The single-layer AgSC10 lamellae are two-dimensional crystals and have uniform thickness and in-plane ordering. These samples were characterized with nanocalori- metry, atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray reflectivity (XRR), Fourier transform infrared spectroscopy (FTIR), and Rutherford backscattering spectroscopy (RBS).

Mikhail Efremov

Papers

Glass transition in ultrathin polymer films: calorimetric study.

Ultrasensitive, fast, thin-film differential scanning calorimeter

Probing Glass Transition of Ultrathin Polymer Films at a Time Scale of Seconds Using Fast Differential Scanning Calorimetry

Glass transition of thin films of poly(2-vinyl pyridine) and poly(methyl methacrylate): nanocalorimetry measurements

SynthesisandCharacterizationofSingle-LayerSilver-Decanethiolate Lamellar Crystals