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

This critical review will be of interest to the experts in porous solids (including catalysis), but also solid state chemists and physicists. It presents the state-of-the-art on hybrid porous solids, their advantages, their new routes of synthesis, the structural concepts useful for their ‘design’, aiming at reaching very large pores. Their dynamic properties and the possibility of predicting their structure are described. The large tunability of the pore size leads to unprecedented properties and applications. They concern adsorption of species, storage and delivery and the physical properties of the dense phases. (323 references)

Hybrid porous solids: past, present, future

New materials capable of storing hydrogen at high gravimetric and volumetric densities are required if hydrogen is to be widely employed as a clean alternative to hydrocarbon fuels in cars and other mobile applications. With exceptionally high surface areas and chemically-tunable structures, microporous metal–organic frameworks have recently emerged as some of the most promising candidate materials. In this critical review we provide an overview of the current status of hydrogen storage within such compounds. Particular emphasis is given to the relationships between structural features and the enthalpy of hydrogen adsorption, spectroscopic methods for probing framework–H2 interactions, and strategies for improving storage capacity (188 references).

/pdf/hydrogen-storage-in-metal-organic-frameworks-9ols7xj8jh.pdf

Hydrogen storage in metal–organic frameworks

Metal-organic framework-5 (MOF-5) of composition Zn4O(BDC)3 (BDC = 1,4-benzenedicarboxylate) with a cubic three-dimensional extended porous structure adsorbed hydrogen up to 4.5 weight percent (17.2 hydrogen molecules per formula unit) at 78 kelvin and 1.0 weight percent at room temperature and pressure of 20 bar. Inelastic neutron scattering spectroscopy of the rotational transitions of the adsorbed hydrogen molecules indicates the presence of two well-defined binding sites (termed I and II), which we associate with hydrogen binding to zinc and the BDC linker, respectively. Preliminary studies on topologically similar isoreticular metal-organic framework-6 and -8 (IRMOF-6 and -8) having cyclobutylbenzene and naphthalene linkers, respectively, gave approximately double and quadruple (2.0 weight percent) the uptake found for MOF-5 at room temperature and 10 bar.

/pdf/hydrogen-storage-in-microporous-metal-organic-frameworks-2xcgwp5q23.pdf

Hydrogen Storage in Microporous Metal-Organic Frameworks

A neutron diffraction determination of the critical exponent β for the n = 4 system holmium☆

Dynamics of molecular hydrogen in the complex trans-[bis[bis(diphenylphosphino)ethane]](.eta.2-dihydrogen)hydridoiron(1+) tetrafluoroborate(1-) in the solid state as revealed by neutron-scattering experiments

Nature of guest species within alkaline earth-ammonia intercalates of titanium disulfide

The effects of pore size reduction on the dynamics of hydrogen sorption in metal–organic materials (MOMs) were elucidated by studying SIFSIX-2-Cu and its doubly interpenetrated polymorph SIFSIX-2-Cu-i by means of sorption, inelastic neutron scattering (INS), and computational modeling. SIFSIX-2-Cu-i exhibits much smaller pore sizes, which possess high H2 sorption affinity at low loadings. Experimental H2 sorption measurements revealed that the isosteric heat of adsorption (Qst) for H2 in SIFSIX-2-Cu-i is nearly two times higher than that for SIFSIX-2-Cu (8.6 vs. 4.6 kJ mol−1). The INS spectrum for H2 in SIFSIX-2-Cu-i is rather unique for a porous material, as only one broad peak appears at low energies near 6 meV, which simply increases in intensity with loading until the pores are filled. The value for this rotational transition is lower than that in most neutral metal–organic frameworks (MOFs), including those with open Cu sites (8–9 meV), which is indicative of a higher barrier to rotation and stronger interaction in the channels of SIFSIX-2-Cu-i than the open Cu sites in MOFs. Simulations of H2 sorption in SIFSIX-2-Cu-i revealed two hydrogen sorption sites in the MOM: direct interaction with the equatorial fluorine atom (site 1) and between two equatorial fluorine atoms on opposite walls (site 2). The calculated rotational energy levels and rotational barriers for the two sites in SIFSIX-2-Cu-i are in good agreement with INS data. Furthermore, the rotational barriers and binding energies for site 2 are slightly higher than that for site 1, which is consistent with INS results. The lowest calculated transition for the primary site in SIFSIX-2-Cu is also in good agreement with INS data. In addition, this transition in the non-interpenetrating material is higher than any of the sites in SIFSIX-2-Cu-i, which indicates a significantly weaker interaction with the host as a result of the larger pore size.

Dramatic effect of pore size reduction on the dynamics of hydrogen adsorbed in metal–organic materials

Conversion of methane into higher hydrocarbons is a process of enormous technological importance, which would benefit from a better understanding of the nature of the surface intermediates formed during methane activation. Currently methane is converted into hydrocarbons mainly by an indirect route[1, 2] via syn gas[3] as the intermediate. Alternative routes, such as oxidative coupling of methane[4±7] over metal oxide catalysts and methane homologation[8±10] on transition metal catalysts have also been extensively investigated. In a previous study we[11] have observed the formation of various CxHy surface intermediate species after methane decomposition on single-crystal Ru(0001) and Ru(1120) model catalysts, observed by high-resolution electron energy loss spectroscopy (HREELS). In this study we used INS to investigate the surface intermediate species formed during the decomposition of methane on Ru/Al2O3 and Ni/SiO2 catalysts. We relate these findings to our previous work on idealized single-crystal model catalysts. The present work represents a step in the effort to bridge the gap between surface science and real-world catalysts in terms of the type of material and pressure used. Inelastic neutron scattering (INS)[12±14] vibrational spectroscopy is a technique that can be directly applied to high surface-area catalysts from ambient to high pressures. This method can also provide accurate quantitative information, has high sensitivity to hydrogenous species, and is not limited by the selection rules of other vibrational spectroscopies. Herein we report the first experimental evidence of the formation of ethylidyne, vinylidene, and methylidyne (CxHy) species from methane on supported metal catalysts. Shown in Figure 1 is the difference INS vibrational spectrum after methane decomposition on Ru/Al2O3. The rather modest resolution, especially at higher frequencies, and poor statistics are the result of having to use a difference spectrum and of the relatively small amount of H in the sample. Nonetheless, the rate was defined as the number of doublings between day 5 and day 9 (determined as the logarithm in base 2 of the increase in the DNA amount) divided by the elapsed time (4 days).

Characterization of C2 (CxHy) Intermediates from Adsorption and Decomposition of Methane on Supported Metal Catalysts by in situ INS Vibrational Spectroscopy

Juergen Eckert

Papers

A neutron diffraction determination of the critical exponent β for the n = 4 system holmium☆

Dynamics of molecular hydrogen in the complex trans-[bis[bis(diphenylphosphino)ethane]](.eta.2-dihydrogen)hydridoiron(1+) tetrafluoroborate(1-) in the solid state as revealed by neutron-scattering experiments

Nature of guest species within alkaline earth-ammonia intercalates of titanium disulfide

Dramatic effect of pore size reduction on the dynamics of hydrogen adsorbed in metal–organic materials

Characterization of C2 (CxHy) Intermediates from Adsorption and Decomposition of Methane on Supported Metal Catalysts by in situ INS Vibrational Spectroscopy