Chlorine-radical Induced Oxidation of Glyoxal and Glyoxal-S（IV） Adducts in the Aqueous Phase

A laser flash photolysis study of the reactivity of Clwith glyoxal, glyoxal mono- and dibisulfite adducts, 1-hydroxy-2, 2-diol-ethanesulfonate and 1, 2-dihydroxy-1, 2-ethanedi sulfonate in the aqueous phase was carried out. The obtained rate constants can be used for atmospheric modeling.     

Diorgano, Dichloro－tin （IV） Complexes of 4－X－Benzohydroxamic Acid （X=CI, OCH3）： Synthesis, Characterization, Antitumor Activity in Vitro and the Crystal Structure of trans－ [Me2Sn（L2） 2]

A series of diorganotin (IV) derivatives of R2SRL2 (R = Me, Et, n-Bu, ph or CI; L = Ll or L2) and their corresponding mixed-ligand complexes RESn (L1)(L2) have been prepared and the structure of trans-MeESn (L2)2 was characterized by FT-IR, ^1H, ^13C and ^ll9Sn NMR spectroscopies,MS, elemental analysis, melting points and X-ray diffIaction. The structure-activity relationships were discussed.     

Molecular Dynamics Studies of the Kinetics of Phase Changes in Clusters II: Crystal Nucleation from Molten (RbCl)256 and (RbCl)500 Clusters

Molecular dynamics computer simulations have been carried out to study the effects of cluster size and temperature on the nucleation rate of rubidium chloride clusters in the temperature range of 500-650 K. Clusters with 256 and 500 RbCl molecules have been studied and the results are compared with those obtained from 108 molecule clusters. The melting point (MP) of the clusters was observed to increase with the size of the clusters and can be described by a linear equation MP=997-405 N^−1/3, where N is the number of molecules in the cluster. The nucleation rate is found to decrease with increasing cluster size or increasing nucleation temperature. Both classical nucleation theory and diffuse interface theory are used to interpret our observed results.     

纳米粒子相变的分子动力学研究：Cu453的性质、结构与结晶成核

Molecular dynamics （MD） computer simulations have been carried out to study the structures, properties and crystal nucleation of nanoparticles with 453 Cu atoms. Structure information was analyzed from the MD simulations, while properties of nanoparticles of Cu453, such as melting point, freezing temperature, heat capacity and mo- lar volumes, have been estimated. The face center cubic （FCC） phase and icosahedron （Ih） phase were observed during the quenching process, and nucleation rates of crystallization to FCC crystal of Cu453 at temperatures of 650, 700, 750, and 800 K were analyzed. Both classical nucleation theory （CNT） and diffuse interface theory （DIT） were used to interpret our observed nucleation rates. The free energy and diffuse interface thickness between the liquid and the FCC crystal phases were estimated by the CNT and DIT respectively, and the results show that the DIT does not work properly to the system.     

Simulations of NaCl Aggregation from Solution: Solvent Determines Topography of Free Energy Landscape

The partition-enabled analysis of cluster histograms (PEACH) method is used to calculate the free energy surface of NaCl aggregation using cluster statistics from MD simulations of small systems (40–90 ions plus solvent) in four solvents. In all cases (pure methanol, pure water, and two methanol/water mixtures) NaCl clusters show a transition from amorphous to rocksalt structure with increasing cluster size. The crossover sizes, and the apparent kinetic barrier to ordering, increase with increasing water content. Implications for the proposed two-step mechanism of NaCl crystal nucleation (in which the ordered structure emerges from a large disordered cluster), and how this mechanism might depend on solvent and on degree of supersaturation, are discussed. In pure water, nonideal crowding effects that promote clustering are identified from systematic concentration-dependent deviations between simulation results and the PEACH model fit. In contrast, the ability of PEACH to fit aggregation statistics in mixed solvents is consistent with negligible interactions between ions in different clusters. © 2018 Wiley Periodicals, Inc.     

2，2，3-三甲基丁烷(C7H16)晶体的成核动力学

High temperature solid phase I of 2,2,3-trimethylbutane(C7H16)(TMB) was investigated by X-ray powder diffraction. The electron diffraction technique for observing the kinetics of phase transitions in the condensed matter has been applied to study the freezing of TMB clusters with diameter of~13nm. Cluster beams were generated from the supersonically expanded TMB vapor with mole fraction of 0.01 in neon carrier gas. The freezing evolution was monitored by electron diffraction in interval of 7-9 μs. Clusters with an average size of ~5,500 molecules were observed to freeze into the solid phase I at a nucleation rate of 3.5 × 1028 m-3•s- 1 at the freezing temperature of clusters, ～170K. The estimated growth rate of postcritical nuclei indicates that the observed nucleation in the present experiment corresponds to mononuclear freezing of the clusters into single crystals of solid phase I.     

表面能与晶体生长/溶解动力学研究的新动向

界面现象使物质在结晶过程中出现了临界现象.但最近的研究指出在物质溶解过程中,在表面能量的控制下也存在着临界现象以及尺寸效应.实验发现,当晶体自身小到一 定的程度时(通常在纳米尺度上并和临界蚀坑的大小相近),在溶解过程中其速度会自发降 低,反应被抑制乃至停止.尽管在热力学上表面能的因素可以赋予小颗粒晶体较大的溶解度 ,但表面能却也能通过对临界条件的控制而使这些微粒在动力学上不被溶解.这个发现不仅 解决了纳米颗粒在水溶液中稳定性的问题,而且还从动力学的角度解释了生物矿物选择纳米 尺度作为其基本构成单元的原因.由于表面能和晶体生长/溶解的动力学有着密切的关系, 我们可以通过对表面能的调节来修改它们的动力学速度和晶体的形貌.反过来,也可以用动力学的方法来测定表面能及表面吸附/脱附常数等.相对于常规的界面研究手段,通过生 长和溶解动力学途径所得的数据有着很好的可靠性及重复性.我们认为,晶体生长和溶解的 动力学和表面能的研究相结合,不仅为界面研究提供了新的思路和方法,而且也会推动晶体生长和材料科学的发展.     

Comparison of the Nucleation Kinetics Obtained from the Cumulative Distributions of the Metastable Zone Width and Induction Time Data

A linearized integral model based on classical nucleation theory is applied in this work to determine the interfacial energy and pre-exponential factor using a linear plot from the cumulative distributions of the metastable zone width (MSZW) data for some systems reported in the literature, including isonicotinamide, butyl paraben, dicyandiamide, and salicylic acid. Based on the same criterion for the nucleation point, the interfacial energy and pre-exponential factor are determined using the conventional linear regression method from the cumulative distributions of the induction time data for the same systems. The results indicate that the interfacial energy and pre-exponential factor calculated from the MSZW data are consistent with those calculated from the induction time for the studied systems.     

二氧化硫分子通过增强二次成核促进纤维的生长:基于分子动力学的模拟研究

空气污染是一种常见的现象. 空气污染物是诱发各类疾病的重要因素之一. 以二氧化硫分子为代表,研究了它与Aβ_17～42原纤维之间的相互作用. 伞形抽样模拟表明,二氧化硫分子的引入减少了纤维的解离自由能. 分析各氨基酸残基结合二氧化硫的频数得知,二氧化硫分子更容易动态地结合到疏水性氨基酸残基的骨架上,同时也容易结合到带电的氨基酸残基上进而削弱盐桥相互作用,但是对这些相互作用的削弱是非常微小的,不足以破坏原纤维的结构. 通过非线性主方程分析,我们发现二氧化硫分子加速了Aβ_17～42二次成核过程,同时缩短了迟滞时间而加速纤维的聚集过程. 通过这些计算,我们定量地揭示了空气污染物与蛋白质相互作用的特征,期望我们的结果为当今社会评估污染物的健康效应提供宝贵的参考信息.     

超临界水中碳酸钠团簇成核与生长分子动力学模拟

应用分子动力学方法研究了碳酸钠颗粒在超临界水中的成核与生长过程. 计算了温度为700-1100 K、压力在23-30 MPa下碳酸钠的团聚过程, 计算时间为1 ns. 对体系结合能与径向分布函数的分析表明, 碳酸钠成核过程主要受静电作用的影响. 在超临界态下, 水分子与Na⁺和CO₃^2- 之间的静电作用降低, Na⁺与CO₃^2- 能够很容易碰撞形成Na₂CO₃小团簇. 在Na₂CO₃整个成核过程中, 单个离子的碰撞在前50 ps 内完成, 同时离子碰撞速率达到10³⁰ cm^-3·s^-1. 另外, 在成核阶段温度的影响比压力更加明显, 温度越高, 离子碰撞速率越快, 形成的初始团簇越多. 而压力对Na₂CO₃团簇的进一步生长影响较大.     

Na_5P_3O_(10)-Ca(OH)_2-CO_2-H_2O体系纳米CaCO_3的成核与生长

通过化学分析、SEM显微分析技术结合RosinRamiler概率统计理论从介观层次研究Na5P3O10CaOH2CO2H2O体系纳米CaCO3的合成反应及其成核和生长过程。结果表明Na5P3O10对CaOH2的碳化反应具有抑制作用。随着Na5P3O10的增加体系中CaCO3的成核速率B0逐渐增大。在Na5P3O10=0ppm时CaCO3结晶的生长由长程扩散和凝聚生长控制Na5P3O10=380.4760.9ppm时前期受短程扩散和界面反应控制、后期受长程扩散控制。Na5P3O10的存在抑制了纳米CaCO3的晶体生长。