Observation of nanometer-Xe clusters embedded in Al crystals.

The structure of Xe precipitates with sizes in several nanometers embedded in Al is known to be stable and its structure is well confirmed. But knowledge about the structure of Xe precipitates with nanometer sizes is very limited. There are difficulties in observing such small structures embedded in a crystalline matrix. An off-Bragg condition is used to observe diffraction patterns, dark-field, and high-resolution transmission electron microscopy images. The structure of Xe precipitates with sizes of about 2 nm and smaller is observed and confirmed. They are in an fcc structure and their orientation relationship with the Al matrix is similar to that of larger crystalline Xe precipitates or in an undefined structure. The lattice spacing or atomic distance in such nanometer-sized Xe precipitates is smaller than those of larger Xe precipitates embedded in Al matrix. There is a trend that as the size becomes smaller, the precipitates are more likely to have an undefined structure.     

Membrane structure and its correlation with membrane permeability

Methods for the investigation of pore and molecular structure of synthetic membranes are reviewed. Membranes are classified as coarse-porous, fine-porous, and solution-diffusion membranes, on one hand; and homogeneous, asymmetric, and composite on the other, Pore structure of synthetic membranes can be elucidated in detail only by electron and raster electron microscopic investigations. Inspection of molecular structure requires diversely specific test probes such as low-energy neutron scattering and/or diffraction, and gas sorption and permeability measurements, as well as thermodynamic and thermomechanical analysis. Other methods used to elucidate pore and molecular structure of synthetic membranes are discussed and, concurrently, membrane structure is correlated with membrane permeability.     

双发光MOFs的比率型传感和可视化检测应用*

通过[Cu(NH₃)₄]²⁺和EDTA-Ca配合物,引出金属有机骨架(MOFs),揭示刚性多齿配体使MOFs形成无限延展多孔结构的本质。从单一荧光引出双荧光,到比率型荧光传感和可视化检测应用。MOFs丰富的金属离子和配体组成以及多孔结构,为实现双荧光奠定了基础。镧系金属的电子结构使其可以发出可见光。基于此,通过几个多发光MOFs,特别是镧系金属MOFs的比率型荧光和可视化传感应用,将教学知识点与科学前沿结合到一起,一方面加深学生对知识点的理解和掌握,另一方面激发学生运用知识,探索未知的兴趣。     

On the structure and stretching of microhydrated DNA

The structure of short double-stranded DNA oligomers in complex with varied amounts of water is investigated with classical molecular dynamics. Free simulations are performed first and mechanical stress is switched on afterward, resembling the conditions of single-molecule conductivity experiments. Water as well as counterions are seen to contribute to the stabilization of double-stranded DNA structure, and a collapse of the native DNA structure is observed upon the removal of a certain amount of water. Pulling with a moderate external force provides additional support to the double-stranded DNA structure, whereas larger forces lead to the overstretching transition followed by the separation of DNA strands, in a manner similar to that observed in fully hydrated DNA.     

Quantum control by means of hamiltonian structure manipulation

A traditional quantum optimal control experiment begins with a specific physical system and seeks an optimal time-dependent field to steer the evolution towards a target observable value. In a more general framework, the Hamiltonian structure may also be manipulated when the material or molecular 'stockroom' is accessible as a part of the controls. The current work takes a step in this direction by considering the converse of the normal perspective to now start with a specific fixed field and employ the system's time-independent Hamiltonian structure as the control to identify an optimal form. The Hamiltonian structure control variables are taken as the system energies and transition dipole matrix elements. An analysis is presented of the Hamiltonian structure control landscape, defined by the observable as a function of the Hamiltonian structure. A proof of system controllability is provided, showing the existence of a Hamiltonian structure that yields an arbitrary unitary transformation when working with virtually any field. The landscape analysis shows that there are no suboptimal traps (i.e., local extrema) for controllable quantum systems when unconstrained structural controls are utilized to optimize a state-to-state transition probability. This analysis is corroborated by numerical simulations on model multilevel systems. The search effort to reach the top of the Hamiltonian structure landscape is found to be nearly invariant to system dimension. A control mechanism analysis is performed, showing a wide variety of behavior for different systems at the top of the Hamiltonian structure landscape. It is also shown that reducing the number of available Hamiltonian structure controls, thus constraining the system, does not always prevent reaching the landscape top. The results from this work lay a foundation for considering the laboratory implementation of optimal Hamiltonian structure manipulation for seeking the best control performance, especially with limited electromagnetic resources.     

A study of the adsorption properties of modified layered silicate

The composition and structure of vermiculite samples modified successively with hydrochloric acid and chitosan are studied with the use of X-ray fluorescence and X-ray-diffraction analyses, as well as IR spectroscopy. The adsorption characteristics of the samples with respect to nitrogen and different dyes are determined, and the parameters of their porous structure are calculated. It is shown that the acid treatment of initial vermiculite drastically increases the content of silicon (in the form of amorphous silica), changes the layered structure of the silicate, and substantially enhances its specific surface area and pore volume.     

Structure and properties of hydroxylated surfaces of oxides

A review of works dealing with the IR spectra and structure of hydroxylated surfaces of oxides is presented. Influence of crystal structure and other factors on OH stretching modes, as well as data about bending vibrations of hydroxy groups are discussed. Experimental results are compared with data of computer simulations.     

The influence of polymer structure on the electrical and mechanical properties of some synthetic films

Various physico-chemical properties of films prepared from PP/PE blends are investigated and compared with those of homopolymers. Crystallographic structure and morphology of films are correlated with the properties studied. Special emphasis is made toward investigation of dependences between the structure and the properties: electrical, mechanical as well as water sorption.     

溶胶凝胶法制备铜铁矿结构p型透明导电氧化物薄膜

铜铁矿结构p型透明导电氧化物(transparent conducting oxide, TCO)薄膜是一类在电子学领域具有广泛应用前景的新材料,因其可与n-TCO薄膜形成真正意义上的“透明器件”而备受关注。本文介绍了铜铁矿结构p-TCO的结构特性以及溶胶凝胶法的基本原理和特点;系统地介绍了溶胶凝胶法制备铜铁矿结构p-TCO薄膜的工艺;分析比较了有机醇盐、无机盐溶胶体系的优缺点;最后讨论了进一步的发展方向,指出溶胶凝胶法是一种高效可行的制备p-TCO薄膜的方法。     

Molecular Dynamics Simulation of Structure II Clathrate Hydrates of Xenon and Large Hydrocarbon Guest Molecules

Molecular dynamics (MD) simulations of structure II clathrate hydrates are performed under canonical (NVT) and isobaric–isothermal (NPT) ensembles. The guest molecule as a small help gas is xenon and gases such as cyclopropane, isobutane and propane are used as large hydrocarbon guest molecule (LHGM). The dynamics of structure II clathrate hydrate is considered in two cases: empty small cages and small cages containing xenon. Therefore, the MD results for structure II clathrate hydrates of LHGM and LHGM + Xe are obtained to clarify the effects of guest molecules on host lattice structure. To understand the characteristic configurations of structure II clathrate hydrate the radial distribution functions (RDFs) are calculated for the studied hydrate system. The obtained results indicate the significance of interactions of the guest molecules on stabilizing the hydrate host lattice and these results is consistent with most previous experimental and theoretical investigations.     

Effect of phosphate activating group on oligonucleotide formation on montmorillonite: the regioselective formation of 3',5'-linked oligoadenylates

The effects of amine structure on the montmorillonite-catalyzed oligomerization of the 5'-phosphoramidates of adenosine are investigated. 4-Aminopyridine derivatives yielded oligoadenylates as long as dodecamers with a regioselectivity for 3',5'-phosphodiester bond formation averaging 88%. Linear and cyclic oligomers are obtained and no A5'ppA-containing products are detected. Oligomers as long as the hexanucleotide are obtained using 2-aminobenzimidazole as the activating group. A predominance of pA2'pA is detected in the dimer fraction along with cyclic 3',5'-trimer; no A5'ppA-containing oligomers were detected. Little or no oligomer formation was observed when morpholine, piperidine, pyrazole, 1,2,4-triazole, and 2-pyridone are used as phosphate-activating groups. The effects of the structure of the phosphate activating group on the oligomer structure and chain lengths are discussed.     

Proton-mediated electron configuration change in high-spin iron(II) porphyrinates

The synthesis, molecular structure, and electronic structure characterization of two five-coordinate high-spin imidazolate-ligated iron(II) porphyrinates are reported. Their electronic structure, as deduced from M?ssbauer spectra obtained in strong magnetic fields, is distinctly different from that of the analogous imidazole-ligated species. The resulting electronic structure models are consistent with all observed differing features in the two classes.     

New laser plasma process to obtain solid coatings and their structural characteristics

Carbon nitride coatings are synthesized in the new laser plasma of powerful optical pulsating discharge using acetonitrile as a precursor. A high-pressure and -temperature C₃N₄ cubic phase with a spinel structure type is obtained. The microhardness of coatings of this structure type is ~45 gPa. The chemical composition and structure of the coatings are characterized by a complex of spectroscopic (IR, Raman, EDS) techniques as well as microscopic (AFM and XRD) techniques.     

Rational material design of Li-excess metal oxides with disordered rock salt structure

This review article summarizes recent research development on a new class of electrode materials with a cation-disordered rock salt structure for energy storage applications. Historically, oxide-based electrode materials with the disordered rock salt structure are regarded as “electrochemically inactive.” However, recent experimental and theoretical research reveals that many oxides with the disordered rock salt structure can be utilized as high-capacity electrode materials, which deliver a much larger reversible capacity compared with traditional and cation ordered layered materials used for practical battery applications. For these emerging electrode materials, higher energy density is achieved relying on anionic and/or cationic redox as multi-electron reactions. Moreover, this anionic/cationic redox for Li-excess materials with the rock salt structure is effectively activated for nano-sized materials. These new trends for the material design on high-capacity electrode materials are highlighted and the future direction to design Li/Na insertion materials for energy storage applications is outlooked.     

Clusters as crystal fragments of silicon bulk

Silicon clusters of 13 to 43 atoms were studied with the semi-empirical method SINDO1. Crystalline structures of face-centered cubic (fcc), hexagonal close packed (hcp) and diamond type and noncrystalline structures of icosahedral type were compared. Noncrystalline structures are most stable for clusters up to 13 atoms. Clusters with 19 and more atoms of the fcc structure are preferable to the less dense diamond structure. With more than 35 Si atoms, the diamond structure is favored over the hcp structure. The binding energy of fcc and hcp structures decreases and that of the diamond structure increases with increasing cluster size. A similar trend is observed for the HOMO-LUMO energy gap which is taken as a measure of the band gap.     

平朔气煤的煤岩显微组分结构研究

用显微光度计、扫描电子显微镜(SEM)、傅立叶变换红外光谱(FTIR)、X射线衍射光谱(XRD)和X光电子能谱(XPS)等测试手段研究了平朔气煤的等密度梯度离心分离(DGC)显微组分富集物的结构。结果表明,镜质组和稳定组结构相似,含氧基团基本相同,但丝质组结构则不同,它含有较多的羧基和羰基。根据实验结果讨论了三种显微组分的大分子结构,认为它们是由许多结构相似而又不相同的结构单元所构成。镜质组和稳定组的单元核心主要为脂环、缩聚芳环,环数为5—6个;丝质组单元核心主要为缩聚芳环,环数为7—8个,环缩合程度最高,芳香层片在空间排列规则,相互定向程度大。     

Using ESI-MS to probe protein structure by site-specific noncovalent attachment of 18-crown-6

A new method for probing the equilibrium structures and folding states of proteins utilizing electrospray ionization mass spectrometry is described. Protein structure is explored as a function of side-chain availability as determined by a specific interaction between lysine and 18-crown-6 ether (18C6). Various intramolecular interactions are competitive with the lysine/18C6 interaction and can prevent noncovalent attachment of 18C6. Changes to protein structure modify these inhibiting intramolecular interactions, which leads to a change in the number of 18C6s that attach to the protein. Experiments conducted with cytochrome c, ubiquitin, and melittin reveal that the method is sensitive to changes in both tertiary and secondary structure. In addition, the structure of each charge state can be examined independently. Experiments can be performed under conditions where the pH and amount of organic cosolvent are varied. Control experiments conducted with pentalysine, which lacks structural organization, are also presented.     

Electronic structure,Fermi surface,and chemical bonding in new layered oxyselenide: HgCuSeO

A full-potential FLAPW-GGA method is used to study for the first time the electronic structure of new layered HgCuSeO oxyselenide with a tetragonal structure. The band structure, density of electron states, Fermi surface, and effective atomic charges are obtained and analyzed; the coefficients of low-temperature heat capacity and paramagnetic Pauli susceptibility are estimated. It is shown that the new layered HgCuSeO phase can be characterized as non-magnetic ionic metal.     

Incorporation of FT-IR spectral data in a computer-assisted prediction of globular protein structure

Currently, much effort is being directed to the determination of the three-dimensional structure of proteins. Two classes of research are of interest; spectrometric techniques which include Fourier transform infrared (FT-IR) spectrometry, and non-spectrometric prediction schemes. The spectra obtained using FT-IR spectrometry, are analyzed to determine the percentages of alpha-helices, beta-pleated sheets, and non-structured coils in a protein. Unfortunately, FT-IR, as well as other spectrometric techniques, cannot be used to determine the exact secondary structure of a protein reliably. Non-spectrometric prediction methods yield information on the exact secondary structure, but are not always accurate. Most prediction methods relate the primary amino acid sequence to the secondary structure of a protein, allowing sequential secondary structure information for the protein examined to be obtained. The goal of this research is to incorporate FT-IR with a prediction method, resulting in an improvement in the accuracy of the prediction.     

Water cavities of sH clathrate hydrate stabilized by molecular hydrogen: phase equilibrium measurements

In this experimental phase equilibrium study, we show for the first time that it is possible to stabilize structure sH of hydrogen clathrate hydrate with the help of some selected promoters. It was established that the formation pressures of these systems are significantly higher than that of structure sII of hydrogen clathrate hydrate when tetrahydrofuran (THF) is used as a promoter. Although no experimental evidence is available yet, it is estimated that the hydrogen storage capacity of structure sH can be as high as 1.4 wt % of H2, which is about 40% higher compared to the hydrogen storage capacity in structure sII.