NiSO_4·6H_2O晶体聚集体形貌及结晶学模型的建立

对四方晶系水溶性晶体NiSO4·6H2O（镍矾）进行生长实验,得到其晶体聚集体形貌.基于单偏光显微镜下的形貌观察和分析,以结晶学、晶体形貌学基本原理为基础,探讨该晶体聚集体形貌中蕴含的结晶学规律,并建立了该晶体聚集体的结晶学模型.在该模型中,晶体发育单形{110},{114},{100},{103},形成聚集体形貌时,...     

多铁材料MnSb2O6中自旋涨落的ESR研究

具有手性晶体结构的MnSb₂O₆其基态为螺旋磁序,对外磁场有着响应丰富的铁电性.本文通过助熔剂法制备了高质量MnSb₂O₆单晶.电子自旋共振谱(ESR)的结果表明其共振场具有类似铁磁材料的各向异性温度依赖关系.这一结果表明MnSb₂O₆基态的螺旋磁序在外磁场中形成了随磁场方向转动的圆锥磁序相(conical phase).对共振峰半高宽的进一步拟合得到一个意外小的临界指数,这表明MnSb₂O₆中的磁矩具有二维特征并且存在着较强的竞争相互作用.     

Effect of crystallographic orientations on transport properties of methylthiol-terminated permethyloligosilane molecular junction

The understanding of the influence of electrode characteristics on charge transport is essential in the field of molecular electronics. In this work, we investigate the electronic transport properties of molecular junctions comprising methylthiol-terminated permethyloligosilanes and face-centered crystal Au/Ag electrodes with crystallographic orientations of (111) and (100), based on the ab initio quantum transport simulations. The calculations reveal that the molecular junction conductance is dominated by the electronic coupling between two interfacial metal-S bonding states, which can be tuned by varying the molecular length, metal material of the electrodes, and crystallographic orientation. As the permethyloligosilane backbone elongates, although the σ conjugation increases, the decreasing of coupling induced by the increasing number of central Si atoms reduces the junction conductance. The molecular junction conductance of methylthiol-terminated permethyloligosilanes with Au electrodes is higher than that with Ag electrodes with a crystallographic orientation of (111). However, the conductance trend is reversed when the electrode crystallographic orientation varies from (111) to (100), which can be ascribed to the reversal of interfacial coupling between two metal-S interfacial states. These findings are conducive to elucidating the mechanism of molecular junctions and improving the transport properties of molecular devices by adjusting the electrode characteristics.     

Crystal structure and magnetic properties of Mn substituted ludwigite Co3O2BO3

The needle shape single crystals Co_3−x Mn_xO₂BO₃ with ludwigite structure have been prepared. According to the X-ray diffraction data the preferable character of distinct crystallographic positions occupation by Mn ions is established. Magnetization field and temperature dependencies are measured. Paramagnetic Curie temperature value Θ=−100 K points out the predominance of antiferromagnetic interactions. Spin-glass magnetic ordering takes the onset at T_N=41 K. The crystallographic and magnetic properties of Co₃O₂BO₃:Mn are compared with the same for the isostructural analogs Co₃O₂BO₃ and CoO₂BO₃:Fe.     

晶体取向对定向凝固平界面失稳行为的影响

采用丁二腈-丙酮透明模型合金研究了不同晶体取向的晶粒在定向凝固条件下的平界面失稳过程.实验选择了三个界面失稳后具有不同生长形态的典型晶粒作为研究对象, 分别为择优生长枝晶、倾斜枝晶和海藻晶.结果表明可发展为择优生长枝晶的晶粒的平界面失稳孕育时间和初始扰动波长最小,海藻晶次之, 倾斜枝晶最大,这与以往的解析结果和相场模拟结果一致. 同时,实验观察发现可发展为择优生长枝晶和倾斜枝晶的晶粒的界面非稳态演化过程与海藻晶显著不同,这表明平界面失稳的非稳态演化过程与晶体取向相关.     

The balance of flexibility and rigidity in the active site residues of hen egg white lysozyme

The crystallographic temperature factors(B factor) of individual atoms contain important information about the thermal motion of the atoms in a macromolecule.Previously the theory of flexibility of active site has been established based on the observation that the enzyme activity is sensitive to low concentration denaturing agents.It has been found that the loss of enzyme activity occurs well before the disruption of the three-dimensional structural scaffold of the enzyme.To test the theory of conformational flexibility of enzyme active site,crystal structures were perturbed by soaking in low concentration guanidine hydrochloride solutions.It was found that many lysozyme crystals tested could still diffract until the concentration of guanidine hydrochloride reached 3 M.It was also found that the B factors averaged over individually collected data sets were more accurate.Thus it suggested that accurate measurement of crystal temperature factors could be achieved for medium-high or even medium resolution crystals by averaging over multiple data sets.Furthermore,we found that the correctly predicted active sites included not only the more flexible residues,but also some more rigid residues.Both the flexible and the rigid residues in the active site played an important role in forming the active site residue network,covering the majority of the substrate binding residues.Therefore,this experimental prediction method may be useful for characterizing the binding site and the function of a protein,such as drug targeting.     

新型1,5-苯并硫氮衍生物的合成和晶体结构

以β-二甲胺基苯丙酮盐酸盐为原料, 经过羟醛缩合, 与邻氨基硫酚的环化, 最后与氯乙酰氯的[2＋2]环加成反应, 合成了8种未见文献报道的新化合物, 其结构经IR, 1H NMR和MS及元素分析确证. 利用单晶X射线衍射法测定了化合物4e的晶体结构.     

Planigon tessellation cellular automata

Cellular automata (CA) do not find as wide a use in chemical complexity determined by a crystal structure as in homogeneous reacting systems. A reason for this is discussed, and a superposition of planigons and parallelogons or Wigner‐Seitz tessellations is suggested that is derived from a crystallographic plane and is capable of representing chemical complexity at a single crystal face in terms of CA. The interplay between growth and form of two‐dimensional negative crystals is discussed in these terms as a particular example. © 1999 John Wiley & Sons, Inc.     

A crystallographic model for the orientation dependence of low cyclic fatigue property of a nickel-base single crystal superalloy

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