铌源和掺杂位置对LiFePO4/C电化学性能的影响

使用Nb2O5和Nb(OC6H5)5为铌源对LiFePO4/C中的锂位和铁位分别掺杂,采用碳热还原法合成掺杂Nb的磷酸铁锂系列材料。运用X射线衍射仪、扫描电镜、循环伏安、交流阻抗谱和恒电流充放电测试等对材料进行表征。结果表明:相比掺杂位置,铌源对材料的颗粒形貌和粒径分布影响更大,而颗粒大小对材料的电化学性能,尤其是大倍率性能的提高有重要作用;掺杂在Li位的Nb元素比在Fe位能更好的稳定晶体结构,从而有利于提高循环性能。     

Connectivity and binding‐site recognition: Applications relevant to drug design

Here, we describe a family of methods based on residue–residue connectivity for characterizing binding sites and apply variants of the method to various types of protein–ligand complexes including proteases, allosteric‐binding sites, correctly and incorrectly docked poses, and inhibitors of protein–protein interactions. Residues within ligand‐binding sites have about 25% more contact neighbors than surface residues in general; high‐connectivity residues are found in contact with the ligand in 84% of all complexes studied. In addition, a k‐means algorithm was developed that may be useful for identifying potential binding sites with no obvious geometric or connectivity features. The analysis was primarily carried out on 61 protein–ligand structures from the MEROPS protease database, 250 protein–ligand structures from the PDBSelect (25%), and 30 protein–protein complexes. Analysis of four proteases with crystal structures for multiple bound ligands has shown that residues with high connectivity tend to have less variable side‐chain conformation. The relevance to drug design is discussed in terms of identifying allosteric‐binding sites, distinguishing between alternative docked poses and designing protein interface inhibitors. Taken together, this data indicate that residue–residue connectivity is highly relevant to medicinal chemistry. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

Formation Sites and Microscopic Conformation Study on the Konjac Glucomannan Molecular Helices

<正>In this work,the formation sites,helical parameters and hydrogen bond positions of Konjac glucomannan molecular helices were investigated using molecular dynamic simulation method.To our interest,the KGM chain is mainly composed by local left and right helix structures. The formation sites of KGM chain might locate at the chain-segments containing acetyl groups,and the left helix is the favorable conformation of KGM.Temperature-dependent molecule conformation study indicates that the right helix is dominant when the temperature is lower than 343 K,above which,however,the left helix is dominating(right helix disappears).In addition,intramolecular hydrogen bonds in the left helix can be found at the-OH groups on C(2),C(4)and C(6)of mannose residues;comparably,the intramolecular hydrogen bonds in the right helix can be mainly observed at the-OH groups on C(4)and C(6)of the mannose residues and C(3)of the glucose residues.In conclusion,molecular dynamic simulation is an efficient method for the microscopic conformation study of glucomannan molecular helices.     

Ab-initio approach to study hydrogen diffusion in 9Cr steels

We calculate the equilibrium energies and migration barriers of Fe, Cr and H interstitial defects in α-FeX(X=Cr)$\mathrm{\alpha }\mathrm{-}\mathrm{FeX}(\mathrm{X}=\mathrm{Cr})$. We use the ab-initio electronic structure code, SIESTA, coupled to the monomer method to find activated states (or migration barriers), in order to study atomic defects diffusion. Ab-initio calculations reveal that in the presence of Cr the H migration barriers are higher than in pure α-Fe$\mathrm{\alpha }\mathrm{-}\mathrm{Fe}$. On the other hand, our permeation tests on 9%Cr–91%Fe alloys reveal a permeation coefficient 10 times lower and a diffusion coefficient 200 times lower than in pure, annealed iron. Focusing on our experimental results, we explore very simple model of new H trapping sites and possible migration paths that can explain the experimental observations.     

In situ FTIR spectra of pyridine adsorbed on SiO2–Al2O3, TiO2, ZrO2 and CeO2: general considerations for the identification of acid sites on surfaces of finely divided metal oxides

Exposure of strong Lewis (coordinatively unsaturated metal atoms) and Bronsted (proton donor OH-groups) acid sites on solid surfaces is a prime demand for potential adsorptive and catalytic applications. In situ FTIR spectroscopy of small adsorbed base molecules, often NH₃, pyridine, CH₃CN, NO or CO molecules, has been well established as a powerful surface analytical technique for characterization of nature, strength and concentration of acid sites. Pyridine (Py) has been preferred as an IR probe molecule of finely divided metal oxide surfaces at room (RT) and higher temperature regimes, since it is (i) more selective and stable than NH₃; (ii) much more strongly adsorbed than CO and CH₃CN; and (iii) relatively more sensitive to the strength of Lewis acid sites than NO. In the present work, in situ IR spectra of Py adsorbed at ≥RT on characterized alumina, silica, silica–alumina, titania, zirconia and ceria were measured, and compared with RT-spectra of liquid and gas phase Py obtained under identical spectroscopic conditions, in order to characterize spectral consequences of mutual Py–Py interactions in the adsorbed phase. It has been concluded that the availability of Lewis acid sites can be unequivocally monitored by formation of coordinated Py molecules giving rise to IR-absorption(s) due to the ν_8a mode of νCCN vibrations at 1630–1600 cm⁻¹, where the higher the frequency assumed, the stronger the acidity of the site. Formation of pyridinium surface species (PyH⁺) is identifiable by (i) an ν_8a-absorption at ≥1630 cm⁻¹; (ii) an ν_19b-absorption at 1550–1530 cm⁻¹; as well as (iii) νN⁺---H and δN⁺---H absorptions occurring, respectively, near 2450 and 1580 cm⁻¹, and, thus, the availability of Bronsted acid sites. Moreover, products and IR-characteristics of Py surface reactions at >RT have been identified, and used to imply nature of surface base sites (OH⁻and O²⁻) involved in formation of acid–base site pairs.     

Noncollinear spin density functional theory for spin‐frustrated and spin‐degenerate systems

We have implemented ab initio linear combinations of Gaussian‐type orbital calculations with generalized localized spin density approximation (GLSDA) for a dimer of equilateral H₃ as a model of the noncollinear magnetic clusters. It has been found that the GLSDA solution with the three‐dimensional noncollinear spin structure is, contrary to prior band calculations by other groups, the ground state near the O_h conformation. Further computational results are compared to that of ab initio generalized Hartree–Fock. The difference between them and the influence of the correlation correction were discussed. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001     

Induced Chiral Metal Surfaces in Asymmetric Hydrogenations?

On the basis of reviewed works and our experiences we propose that during the reduction of the surface the adsorbing substrates and the chiralcompounds induce the formation of chiral surface sites in dia- or enantioselective hydrogenation reactions catalyzed by precious metal     

液相色谱/电喷雾质谱(LC/ESI/MS)在蛋白质分析鉴定中的应用

对液相色谱／电喷雾质谱（LC／ESI／MS）在蛋白质分子量测定、一级结构的分析、蛋白质和多肽纯度的鉴定、肽质量酶谱、蛋白质分子内二硫键的定量和定位、磷酰化位置的测定以及在蛋白质组中的应用等方面进行了综述和讨论。