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

Crystalline metal-organic frameworks (MOFs) are formed by reticular synthesis, which creates strong bonds between inorganic and organic units. Careful selection of MOF constituents can yield crystals of ultrahigh porosity and high thermal and chemical stability. These characteristics allow the interior of MOFs to be chemically altered for use in gas separation, gas storage, and catalysis, among other applications. The precision commonly exercised in their chemical modification and the ability to expand their metrics without changing the underlying topology have not been achieved with other solids. MOFs whose chemical composition and shape of building units can be multiply varied within a particular structure already exist and may lead to materials that offer a synergistic combination of properties.

The Chemistry and Applications of Metal-Organic Frameworks

Mobility — the transport of people and goods — is a socioeconomic reality that will surely increase in the coming years. It should be safe, economic and reasonably clean. Little energy needs to be expended to overcome potential energy changes, but a great deal is lost through friction (for cars about 10 kWh per 100 km) and low-efficiency energy conversion. Vehicles can be run either by connecting them to a continuous supply of energy or by storing energy on board. Hydrogen would be ideal as a synthetic fuel because it is lightweight, highly abundant and its oxidation product (water) is environmentally benign, but storage remains a problem. Here we present recent developments in the search for innovative materials with high hydrogen-storage capacity.

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Hydrogen-storage materials for mobile applications

This critical review provides a processing-structure-property perspective on recent advances in cellulose nanoparticles and composites produced from them. It summarizes cellulose nanoparticles in terms of particle morphology, crystal structure, and properties. Also described are the self-assembly and rheological properties of cellulose nanoparticle suspensions. The methodology of composite processing and resulting properties are fully covered, with an emphasis on neat and high fraction cellulose composites. Additionally, advances in predictive modeling from molecular dynamic simulations of crystalline cellulose to the continuum modeling of composites made with such particles are reviewed (392 references).

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Cellulose nanomaterials review: structure, properties and nanocomposites

[Liu, Chang; Li, Feng; Ma, Lai-Peng; Cheng, Hui-Ming] Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, Shenyang 110016, Peoples R China.;Cheng, HM (reprint author), Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, 72 Wenhua Rd, Shenyang 110016, Peoples R China;cheng@imr.ac.cn

Advanced Materials for Energy Storage

Although measurements of crystallinity index (CI) have a long history, it has been found that CI varies significantly depending on the choice of measurement method. In this study, four different techniques incorporating X-ray diffraction and solid-state 13C nuclear magnetic resonance (NMR) were compared using eight different cellulose preparations. We found that the simplest method, which is also the most widely used, and which involves measurement of just two heights in the X-ray diffractogram, produced significantly higher crystallinity values than did the other methods. Data in the literature for the cellulose preparation used (Avicel PH-101) support this observation. We believe that the alternative X-ray diffraction (XRD) and NMR methods presented here, which consider the contributions from amorphous and crystalline cellulose to the entire XRD and NMR spectra, provide a more accurate measure of the crystallinity of cellulose. Although celluloses having a high amorphous content are usually more easily digested by enzymes, it is unclear, based on studies published in the literature, whether CI actually provides a clear indication of the digestibility of a cellulose sample. Cellulose accessibility should be affected by crystallinity, but is also likely to be affected by several other parameters, such as lignin/hemicellulose contents and distribution, porosity, and particle size. Given the methodological dependency of cellulose CI values and the complex nature of cellulase interactions with amorphous and crystalline celluloses, we caution against trying to correlate relatively small changes in CI with changes in cellulose digestibility. In addition, the prediction of cellulase performance based on low levels of cellulose conversion may not include sufficient digestion of the crystalline component to be meaningful.

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Cellulose crystallinity index: measurement techniques and their impact on interpreting cellulase performance

1354 Ó WILEY-VCH Verlag GmbH, D-69469 Weinheim, 1999 0935-9648/99/1611-1354 $ 17.50+.50/0 Adv. Mater. 1999, 11, No. 16 [6] J. Kido, H. Hayase, K. Hongawa, K. Nagai, K. Okuyama, Appl. Phys. Lett. 1994, 65, 2124. [7] J. Kido, W. Ikeda, M. Kimura, K. Nagai, Jpn. J. Appl. Phys. 1996, 35, L394. [8] T. Sano, M. Fujita, T. Fujii, Y. Hamada, K. Shibata, K. Kuroki, Jpn. J. Appl. Phys. 1995, 34, 1883. [9] L. Liu, W. Li, Z. Hong, J. Peng, X. Liu, C. Liang, Z. Liu, J. Yu, D. Zhao, Synth. Met. 1997, 91, 267. [10] N. Takada, T. Tsutsui, S. Saito, Jpn. J. Appl. Phys. 1994, 33, L863. [11] W. R. Dawson, J. L. Kropp, M. W. Windsor, J. Chem. Phys. 1966, 45, 2410. [12] G. A. Crosby, R. E. Whan, R. M. Alire, J. Chem. Phys. 1961, 34, 743. [13] G. A. Crosby, Mol. Cryst. 1966, 1, 37. [14] T. Forster, Discuss. Faraday Soc. 1959, 27, 7. [15] A. Dogariu, R. Gupta, A. J. Heeger, H. Wang, Synth. Met. 1999, 100, 95. [16] Y. Yang, Q. Pei, A. J. Heeger, J. Appl. Phys. 1996, 79, 934. [17] M. Uekawa, Y. Miyamoto, H. Ikeda, K. Kaifu, T. Nakaya, Synth. Met. 1997, 91, 259. [18] M. Uekawa, Y. Miyamoto, H. Ikeda, K. Kaifu, T. Nakaya, Bull. Chem. Soc. Jpn. 1998, 71, 2253. [19] C. Wu, J. C. Sturm, R. A. Register, J. Tian, E. P. Dana, M. E. Thompson, IEEE Trans. Electron Devices 1997, 44, 1269. [20] M. R. Andersson, G. Yu, A. J. Heeger, Synth. Met. 1997, 85, 1275. [21] M. A. Baldo, D. F. O'Brien, Y. You, A. Shoustikov, S. Sibley, M. E. Thompson, S. R. Forrest, Nature 1998, 395, 151. [22] V. Cleave, G. Yahioglu, P. Le Barny, R. H. Friend, N. Tessler, Adv. Mater. 1999, 11, 285. [23] Z. Bao, Y. Feng, A. Dodabalapur, V. R. Raju, A. J. Lovinger, Chem. Mater. 1997, 9, 1299. [24] F. Pschenitzha, J. C. Sturm, Appl. Phys. Lett. 1999, 74, 1913. [25] J. A. Rogers, Z. Bao, V. R. Raju, Appl. Phys. Lett. 1998, 72, 2716. [26] S. Chang, J. Bharathan, Y. Yang, R. Helgeson, F. Wudl, M. B. Ramey, J. R. Reynolds, Appl. Phys. Lett. 1998, 73, 2561. [27] G. Parthasarathy, P. E. Burrows, V. Khalfin, V. G. Kozlov, S. R. Forrest, Appl. Phys. Lett. 1998, 72, 2138. [28] J. D. Joannopoulos, P. R. Villeneuve, S. Fan, Nature 1997, 386, 143. [29] A. Dodabalapur, E. A. Chandross, M. Berggren, R. E. Slusher, Science 1997, 277, 1787. [30] K. Ohta, A. Ishii, H. Muroki, I. Yamamoto, K. Matsuzaki, Mol. Cryst. Liq. Cryst. 1985, 116, 299. [31] J. C. de Mello, H. F. Wittmann, R. H. Friend, Adv. Mater. 1997, 9, 230. [32] N. C. Greenham, I. D. W. Samuel, G. R. Hayes, R. T. Phillips, Y. A. R. R. Kessener, S. C. Moratti, A. B. Holmes, R. H. Friend, Chem. Phys. Lett. 1995, 241, 89.

A Simple and Complete Purification of Single‐Walled Carbon Nanotube Materials

Reversible Lithium-Ion Insertion in Molybdenum Oxide Nanoparticles

The crystallinity index of cellulose is an important parameter to establish because of the effect this property has on the utilization of cellulose as a material and as a feedstock for biofuels production. However, it has been found that the crystallinity index varies significantly depending on the choice of instrument and data analysis technique applied to the measurement. We introduce in this study a simple and straightforward method to evaluate the crystallinity index of cellulose. This novel method was developed using solid state 13C NMR and subtraction of the spectrum of a standard amorphous cellulose. The crystallinity indexes of twelve different celluloses were measured and the values from this method were compared with the values obtained by other existing methods, including methods based on X-ray diffraction. An interesting observation was that the hydration of the celluloses increased their crystallinity indexes by about 5%, suggesting that addition of water increased cellulose order for all the cellulose samples studied.

Measuring the crystallinity index of cellulose by solid state 13C nuclear magnetic resonance

We have synthesized, characterized, and computationally validated the high Brunauer–Emmett–Teller surface area and hydrogen uptake of a new, noncatenating metal–organic framework (MOF) material, NU-111. Our results imply that replacing the phenyl spacers of organic linkers with triple-bond spacers is an effective strategy for boosting molecule-accessible gravimetric surface areas of MOFs and related high-porosity materials.

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Philip A. Parilla

Papers

Cellulose crystallinity index: measurement techniques and their impact on interpreting cellulase performance

A Simple and Complete Purification of Single‐Walled Carbon Nanotube Materials

Reversible Lithium-Ion Insertion in Molybdenum Oxide Nanoparticles

Measuring the crystallinity index of cellulose by solid state 13C nuclear magnetic resonance

Designing Higher Surface Area Metal-Organic Frameworks: Are Triple Bonds Better than Phenyls?