Impact of Water Molecules on the Isomerization of CH3S（OH）CH2 to CH3S（O）CH3： A Computational Investigation

The isomerization of CH3S（OH）CH2 to CH3S（O）CH3 in the absence and presence of water has been investigated at the G3XMP2//B3LYP/6-311 ＋ G（2df, p） level. The naked isomerization, the reaction without water, gives the high barrier height （21.56 kcal.mol^-1）. Three models are constructed to describe the water influence on the isomerization, that is, water molecules are the catalyst and the microsolvation, and water molecules act as the catalyst and microsolvation simultaneously. Our results show that the isomerization barrier heights of CH3S（OH）CH2 to CH3S（O）CH3 are reduced by 12.32, 11.04, and 7.80 kcal.mol^-1, respectively, when one, two, and three water molecules are performed as catalyst, in contrast to the naked isomerization. Moreover, the rate constants of the isomerization are calculated using the transition state theory with the Wigner tunneling correction over the temperature range of 240-425 K. We find that the rate constant of a single water molecule as the catalyst is 1.58 times larger than the naked isomerization at 325 K, whereas it is slower by 6 orders of magnitude when water molecule serves as the microsolvation at 325 K, compared to naked reaction. So the water-catalyzed isomerization of CH3S（OH）CH2 to CH3S（O）CH3 is predicted to be the key role in lowering the activation energy. The isomerization involving water molecules acting as mierosolvation is unfavorable under atmospheric conditions.     

水团簇构象稳定性起源和本质的密度泛函理论与量子分子动力学研究

寻找确定分子体系构象稳定性的关键因素是至关重要的, 但即使对最简单的分子, 其稳定性的起源和本质仍存在很大的争议. 本文以水团簇为例, 采用量子分子动力学产生185个八聚水分子团簇模型, 并运用基于密度泛函理论的两个能量分解方法寻找其稳定性的决定因素. 我们发现不同水团簇的稳定性与其立体排斥能和交换相关能成良好的线性关系.本文还采用双变量模型模拟水团簇的稳定性, 取得了更好的结果(相关系数大于0.99). 本工作对揭示包括水分子团簇在内的通过弱相互作用组成的分子络合物的稳定性起源和本质提供了有益启示.     

Preparation,Crystal Structure,Thermal Decomposition and Explosive Properties of K2（tza）2（H2O） （tza=Tetrazole-1-acetic Acid）

A new energetic compound based on the tetrazole-1-acetic acid (tza) and potassium(I) salt, K2(tza)2(H2O), was synthesized and characterized by elemental analysis and FT-IR spectrum. Its crystal structure was determined by single-crystal X-ray diffraction analysis. The results show that the crystal belongs to the orthorhombic system, space group Pna21 with a = 1.11972(17) nm, b = 0.46647(7) nm, c = 2.5158(4) nm, V = 1.3140(3) nm3, K2C6H8N8O5, Mr = 350.40 g·mol-1, Dc = 1.771 g·cm-3, μ(MoKα) = 0.759 mm-1, F(000) = 712, Z = 4, R = 0.023 and wR = 0.0527 for 2961 observed reflections (I > 2σ(I)). The K(I) cation is six-coordinated with four O atoms from three carboxylate groups, one O atom from one H2O molecule and one N atom from tetrazolyl ring, in which each tza is coordinated in a tridentate chelating bridging coordination mode. The thermal decomposition mechanism of the title complex was studied by DSC and TG-DTG techniques. Under nitrogen atmosphere at a heating rate of 10 K·min-1, the thermal decomposition of the complex contains one main exothermic process between 191.7 and 243.8 ℃ in the DSC curve. Its combustion heat was mensurated by oxygen bomb calorimetry. The non-isothermal kinetics parameters were calculated by the Kissinger's method and Ozawa-Doyle's method, respectively. The sensitivity properties of K2(tza)2(H2O) were also determined with standard methods, which was very sensitive to flame.     

Hydrothermal Synthesis,Crystal Structure and Thermal Stability of a Binuclear Copper（Ⅱ） Complex with 3-（Pyridin-2-yl）-1,2,4-triazole

One novel binuclear copper(Ⅱ) complex [Cu 2 (Hpt) 2 (CO 3) 2 (H 2 O) 2 ]·H 2 O with copper carbonate and 3-(pyridin-2-yl)-1,2,4-triazole (Hpt) was hydrothermally synthesized and characterized by IR and X-ray diffraction analysis.The complex crystallizes in triclinic,space group P2 1 /n with a=0.6862(1),b=0.7805(1),c=1.1983(2) nm,α=72.03(2),β=107.72(3),γ=75.28(2)o,V=0.5884 nm 3,D c=2.105 g/cm 3,Z=1,F(000)=357,GOOF=1.041,the final R=0.01859 and wR=0.04348.The whole molecule is composed of two cooper ions,two Hpt molecules,two carbonate and three water molecules,forming a binuclear structure.The crystal structure shows that the cooper ion is coordinated with three nitrogen atoms from two Hpt molecules,two oxygen atoms from one carbonic acid and one water molecule,forming a distorted square pyramidal geometry.The TG analysis result shows that the title complex is stable under 131.0 ℃.     

金刚石表面纳米尺度水分子的相变观测

水是自然界中最重要的物质之一,研究界面或受限体系的水分子动力学具有重要的科学意义.近些年新兴的基于氮-空位(NV)色心的纳米磁共振技术可以同时观测纳米尺度的核磁信号和温度.本文利用单个NV色心成功探测到金刚石表面纳米尺度水分子分别在固态和液态条件下的核磁信号,并通过改变温度成功观测到该纳米尺度水层的固-液相变.实验结果表明,基于NV色心的核磁共振技术可以有效地探测纳米尺度物质的结构和动力学行为,为纳米尺度受限体系相关科学的研究提供新的探测手段.     

界面水分子扩散对超高分子量聚乙烯摩擦学性能影响的反应分子动力学模拟研究

采用基于反应力场(ReaxFF)的分子动力学模拟方法,研究了摩擦界面水分子向超高分子量聚乙烯(UHMWPE)基体扩散和渗透的基本过程.分子模拟结果表明：摩擦过程中,水分子稳定吸附在Fe板表面,并与聚乙烯链形成分子内摩擦,使聚乙烯分子产生剪切变形.当Fe板表面存在纳尺度外凸结构时,其在UHMWPE表面的耕犁作用更为显著,使摩擦界面的内摩擦力显著增加.当摩擦速度增加时,摩擦界面原子温度显著升高.在水润滑条件下,界面水分子逐渐扩散到UHMWPE基体中,引起相邻聚乙烯链之间的原子距离增加,这导致聚乙烯链之间的相互作用强度降低.此外,摩擦界面处还伴随着水分子中氢氧键断裂,并引起相应原子的电荷跃变.此时,水氧原子与Fe原子形成Fe―O化合物,且具有与Fe₂O₃相似的晶体结构.水分子扩散进入UHMWPE内时,还引起其周围聚乙烯分子的电荷发生改变,造成UHMWPE表层原子电荷分布不均匀.     

静电场中水分子的扩散与液固相变

扩散与相变是本科阶段基础物理教学的重要内容.本文以体相水分子系统为例,基于分子动力学模拟,研究静电场环境下水分子的扩散和相变.在较小电场强度情况下,水分子表现出显著的大角度跳跃转动,且转动频次随电场呈先增加后减小的非单调行为.这种大角度跳跃转动的反常电场依赖性与水分子扩散系数随电场强度变化的非单调性存在较强相关性.在电场强度较大时,水分子系统发生液固相变,即电致结冰,并观察到了两种冰相沿电场方向的层状混合堆叠结构.该分子动力学模拟有助于学生从微观层次理解分子扩散与相变等物理现象的分子机制,可作为教学实例培养本科生的科研实践能力.