Crystal structure of hexagonal SrAl2O4 at 1073 K

The crystal structure of SrAl₂O₄ at 1073 K was determined from conventional X-ray powder diffraction data using direct methods, and it was further refined by the Rietveld method. The structure was hexagonal (space group P6₃, Z=6) with a=0.89260(3) nm, c=0.84985(2) nm and V=0.58639(3) nm³. Final reliability indices were R_wp=7.87%, R_p=5.87% and R_B=4.19%. The [AlO₄] tetrahedra are linked to form trigonally distorted rings and they are joined in layers. These layers are stacked with a two-layer repeat and connected by the tetrahedral apices. All of the Sr atoms occupy the centers of the rings when viewed along the c-axis. The structure is described as a stuffed derivative of tridymite.     

Relationship of rotational correlation time from EPR spectroscopy and protein-membrane interaction

A study was carried out to determine if rotational correlation time of spin-labeled hen egg lysozyme (HEL) interacting with ultrafiltration membranes could be used to infer protein-membrane interaction. Polysulfone and cellulosic membranes, which have notably different adsorption properties, and membranes with varying pore sizes were used in this study. Based on this study, it was determined that the rotational correlation time does reflect variations in protein adsorption and pore plugging on membranes. The rotational correlation times for the highly adsorbent polysulfone (2.82 × 10⁻⁸ s) were significantly higher than those obtained from proteins on cellulosic membranes (0.62 × 10⁻⁸ s) and from those in solution (0.17 × 10⁻⁸ s). Rotational correlation time was also increased due to steric hindrance associated with pore plugging, although it was not as significant as the adsorption effect. This study indicates that the rotational time constant can be used to infer the type of protein-membrane interaction.     

均三氮苯类除草剂结构与活性的理论研究

利用Gaussian03程序包中的B3LYP方法,选择6-31G基组对均三氮苯类除草剂及类似衍生物2-(4-溴苄氨基)-4-甲基-6-三氟甲基-1,3,5-三氮苯进行了量子化学计算,从理论上讨论了它们的空间结构、电子结构特征与活性的关系.计算结果表明:三氮苯环与N(7)和N(8)原子形成了共轭结构,分子活性大小与LUMO轨道的得电子能力以及在LUMO轨道中占主要成分的原子有重要关系.N(7)和N(8)连接单个具有推电子能力的基团,有利于生物活性的提高.对于2-(4-溴苄氨基)-4-甲基-6-三氟甲基-1,3,5-三氮苯中,N(8)和C(9)是重要的活性部位,和传统的均三氮苯类除草剂分子相比,与D1蛋白上不同的氨基酸残基发生了键合作用.     

Rapid Synthesis of Nanocrystalline TiO2/SnO2 Binary Oxides and Their Photoinduced Decomposition of Methyl Orange

A rapid and simple method, the so-called stearic acid method (SAM) was developed to prepare nanostructured TiO₂/SnO₂ binary oxides by combustion of stearic acid precursors. The preparative process was studied by Fourier transform infrared spectroscopy (FT-IR). During the preparative process, metal precursors were dispersed in stearic acid at molecular level. Microstructure of the samples was investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), BET specific surface area measurement and the results were compared with those obtained by conventional sol-gel method. The photocatalytic decomposition of methyl orange was used as a model system to determine the relative influences of the preparation method and the concentration of SnO₂ on the photocatalytic activities. It was found that preparative methods affected the crystalline structure of TiO₂/SnO₂ powders and the anatase phase of TiO₂ was stabilized by the addition of SnO₂ in SAM. The samples prepared by SAM showed better dispersity, larger specific surface area and the TiO₂/SnO₂ (r=0.15, SAM) catalyst showed higher photocatalytic activity than Degussa P25.     

对MDTA中测样品热容量的准恒温法的评述

对用调制差热分析（ＭＤＴＡ）准恒温法测样品热容量的情形进行了讨论。通过结合最基本的热传导定律和ＭＤＴＡ模型，指出了目前国际上测量样品热容量的准恒温法只能得到在所测温度范围内的物质热容量平均值，调制温度的幅度越大或调制频率越高，所得到的热容量数据越平滑。在所测温度范围内样品热容量基本不变时，用ＭＤＴＡ准恒温法较好；但当样品热容量在所测温度范围内有明显变化时，用传统差热分析法（ＤＴＡ）更好一些。     

Quality assurance system for a decomposition method as demonstrated for the Wickbold combustion technique

 A five-step model for a quality assurance system is developed for an internal quality control check. It includes the quality control of the decomposition method and the detection method as steps belonging together. The Wickbold combustion technique as decomposition method in combination with atomic absorption spectrometry was chosen. The vaporization of the elements mercury, arsenic, lead, antimony and selenium is based on combustion in an oxyhydrogen flame. To check the efficiency of the analytical system, the uncertainty of results was calculated on the basis of the "Guide to the Expression of Uncertainty in Measurement". Received: 13 January 1997 · Accepted: 29 March 1997     

紫荆花红色素开发利用的研究

首次报道紫荆花红色素的提取纯化方法及红色素的理化性质，并与玫瑰茄红色素作对比研究，证实同属于花青甙类化合物，又经急性毒性试验证明其毒性极低，故紫荆花天然红色素具有开发利用的价值。     

Quantum chemical calculations of the isomer shift in iron(II) complexes of 1,2,4-triazoles with a 1 A 1 ⇔ 5 T 2 spin transition

DFT calculations have been performed to determine the isomer shift for a series of iron(II) clusters with nitrogen-containing ligands which serve as models of coordination units in Fe(II) complexes with 1,2,4-triazoles possessing a ¹ A ₁ ? ⁵ T ₂ spin transition. Good agreement has been found between the theoretical and experimental values of the isomer shift for both low-and high-spin phases. Our calculations confirmed the hypothesis about relationship between the experimentally observed differences in the isomer shift for the low-spin phases of the complexes and variations of the Fe-N mean bond length.     

Preparation and Characterization of N-4-Nitrophenyl-L-prolinol Nanocrystals in Sol-Gel Matrices

Organic nanocrystals of N-4-nitrophenyl-l-prolinol (NPP) have been grown in sol-gel matrices prepared from silicon alkoxide precursors. Our process is based on the control of the nucleation and growth kinetics of the dye in the pores of dense gels. Nanocomposites gel-glasses are obtained with a high optical quality due to the small size of the nanocrystals (10-20 nm). Differential scanning calorimetry experiments evidenced clearly the melting point of NPP nanocrystals, which is registered 51°C above that of NPP powder. Micro-Raman and solid state NMR spectroscopies allowed us to demonstrate that our nanocrystallization process does not chemically modify NPP molecules. We specified also the nature of interactions existing between the NPP nanocrystals and the xerogels. These strong interactions, which explain the important increase of the melting point of the nanocrystals in comparison to the NPP powder, are hydrogen bonds between nitro groups of NPP and uncondensed silanol functions of the silicate network.     

乙基乙酰胺热解反应机理的MO研究

对于烷基乙酰胺的初始热解反应机理, 通常认为与酯类的热解反应相类似。Maccoll和Nagra通过对该热解反应的动力学研究, 认为两者存在不同。差异之一, 烷基乙酰胺存在两种可能的热解途径【参见本文(129页)前述反应方程(1),(2)】。而在酯类热解反应中(2)的活化能过高, 且四元环过渡态极不稳定。差异之二, 极性溶剂(比如乙酸)对酰胺热解反应的催化作用不明显, 而对酯类等气相热解反应的催化作用是十分显著的。为此, 我们用MINDO/3分子轨道法对乙基乙酰胺的初始热解反应进行了较全面的研究。用能量梯度法对此反应的反应物、中间体和生成物的平衡几何构型进行了全优化。(如图1所示)用极小能量途径法分别寻找反应(1)和反应(2)的初始过渡态, 继而用Powell法全优化过渡态的几何构型, 计算所得的过渡态TS1、TS2和TS3分别见图2a, 图3a和图4a。为了确证这些过渡态, 进行了振动分析研究, 结果表明这些过渡态的力常数矩阵的诸本征值中均只有一个负值, 且虚振动模式展示了走向各自的反应物和生成物的趋势, (如图2b,图3b和图4b所示)。它们的总能量及反应(1)和反应(2)的活化能列于表1. 对整个热解反应(1)作了内禀反应坐标(IRC)理论分析, 反应历程见图5所示. 与IRC相应的总能偶极矩以及部分关键的键长和原子净电荷变化一并列于表2.本文研究结果表明, 在乙基乙酰胺的初始反应中主反应即反应(1)与酯类反应相类似, ...