聚偏二氯乙烯构象分布的理论研究

在MP2/6-311++G**水平下, 对2,2,4,4-四氯戊烷与2,2,4,4,6,6-六氯庚烷旋转异构体构象进行几何优化和能量计算. 结果表明, 对于2,2,4,4-四氯戊烷, 采用gauche-gauche排列的旋转异构体的能量较低; 2,2,4,4,6,6-六氯庚烷旋转异构体中, 采用trans-gauche-trans-gauche排列的构象能量较低. 反之, 完全采用trans-trans排列的旋转异构体构象能量较高, 不稳定. 通过比较模型分子不同旋转异构体构象的能量差值可以得到一级和二级特征的相互作用能差, 进而计算统计权重参数. 在此基础上, 应用计算得到的模型分子的几何构型与统计权重参数, 分别构建针对—CH2—和—CCl2—中心的聚偏二氯乙烯的6态旋转异构态模型. 通过旋转异构态模型可以计算聚偏二氯乙烯分子中各种构象的分布.     

纳米银六角阵列在掺氧氮化硅中的局域表面等离激元共振特性仿真

通过COMSOL Multiphysics 和 Lumerical FDTD solution对不同尺寸纳米银六角阵列在非晶态掺氧氮化硅(a-SiN_x:O)介质中的局域表面等离激元共振(LSPR)特性进行仿真, 计算结果表明半径为25 nm的纳米银六角阵列形成的局域表面等离激元(LSP)与厚度为70 nm的a-SiN_x:O的蓝光发射(460 nm)的共振效果最为显著, 随着纳米银颗粒尺寸的增大其消光共振峰红移. 在460 nm波长激发下半径为25 nm的纳米银阵列在a-SiN_x:O中的极化强度和表面极化电荷的分布模拟证明了该阵列在460 nm激发下形成的LSP为偶极子极化模式, 通过对该尺寸的纳米银阵列的LSP 在a-SiN_x:O中的最强垂直辐射空间计算, 获得了银颗粒上方a-SiN_x:O的最佳厚度为30 nm, 仿真结果对硅基蓝光发射器件(450–460 nm)的设计提供了重要的理论参考.     

一种新的硅基晶体 BaH2SiO4的结构和性能

本文报道了采用水热法生长BaH₂SiO₄单晶的实验结果,它属三斜晶系,空间群为P1,晶包参数为:a=7.079,b=7.362,c=7.5824?,α=89.64°,β=88.785°,γ=88.23°。原子力显微镜(AFM)和P-E铁电回线测量显示该材料具有铁电性,沿(010)方向极化强度和娇顽力分别为0.882μC·cm^-2 and 1.12kV·cm^-1,研     

稀土与N-对甲基苯磺酰甘氨酸和邻菲咯啉配合物的合成与晶体结构

Three new lanthanide complexes with the formulae [Eu2（TsGly）6（phen）2（H2O）2] （1）, [Ln（TsGly）2（phen）2-（H2O）2]C1·2H2O [Ln=Er（2a） and Yb （2b）, TsGly=N-p-tolylsulfonylglycinate, phen= 1,10-phenanthroline] were synthesized. Crystallographic data for 1： monoclinic, P21/n, a= 1.29791（16） nm, b= 1.9034（2） nm, c= 1.7596（2） nm,β=93.410（3）°, V=4.3394（9） nm^3, Z=4, R1 =0.0326, wR2=0.0771; and for 2b： triclinic, P1, a= 1.2674（2） nm, b= 1.4405（2） nm, c= 1.4809（3） nm, a= 113.256（3）°, β= 108.253（3）°, γ=94.739（3）°, V=2.2922（7） nm°3, Z=2, R1=0.0292, wR2=0.0669. X-ray diffractional analysis reveals that compound 1 adopts dinuclear structure with fourfold bridging TsGly ligands between the Eu（Ⅲ） centers, while compound 2b features an unusual mononuclear structure.     

Spectral, structural, and electrochemical properties of ruthenium porphyrin diaryl and aryl(alkoxycarbonyl) carbene complexes: influence of carbene substituents, porphyrin substituents, and trans-axial ligands

A wide variety of ruthenium porphyrin carbene complexes, including [Ru(tpfpp)(CR(1)R(2))] (CR(1)R(2) = C(p-C(6)H(4)Cl)(2) 1 b, C(p-C(6)H(4)Me)(2) 1 c, C(p-C(6)H(4)OMe)(2) 1 d, C(CO(2)Me)(2) 1 e, C(p-C(6)H(4)NO(2))CO(2)Me 1 f, C(p-C(6)H(4)OMe)CO(2)Me 1 g, C(CH==CHPh)CO(2)CH(2)(CH==CH)(2)CH(3) 1 h), [Ru(por)(CPh(2))] (por=tdcpp 2 a, 4-Br-tpp 2 b, 4-Cl-tpp 2 c, 4-F-tpp 2 d, tpp 2 e, ttp 2 f, 4-MeO-tpp 2 g, tmp 2 h, 3,4,5-MeO-tpp 2 i), [Ru(por)[C(Ph)CO(2)Et]] (por=tdcpp 2 j, tmp 2 k), [Ru(tpfpp)(CPh(2))(L)] (L = MeOH 3 a, EtSH 3 b, Et(2)S 3 c, MeIm 3 d, OPPh(3) 3 e, py 3 f), and [Ru(tpfpp)[C(Ph)CO(2)R](MeOH)] (R = CH(2)CH==CH(2) 4 a, Me 4 b, Et 4 c), were prepared from the reactions of [Ru(por)(CO)] with diazo compounds N(2)CR(1)R(2) in dichloromethane and, for 3 and 4, by further treatment with reagents L. A similar reaction of [Os(tpfpp)(CO)] with N(2)CPh(2) in dichloromethane followed by treatment with MeIm gave [Os(tpfpp)(CPh(2))(MeIm)] (3 d-Os). All these complexes were characterized by (1)H NMR, (13)C NMR, and UV/Vis spectroscopy, mass spectrometry, and elemental analyses. X-ray crystal structure determinations of 1 d, 2 a,i, 3 a, b, d, e, 4 a-c, and 3 d-Os revealed Ru==C distances of 1.806(3)-1.876(3) A and an Os==C distance of 1.902(3) A. The structure of 1 d in the solid state features a unique "bridging" carbene ligand, which results in the formation of a one-dimensional coordination polymer. Cyclic voltammograms of 1 a-c, g, 2 a-d, g-k, 3 b-d, 4 a, b, and 3 d-Os show a reversible oxidation couple with E(1/2) values in the range of 0.06-0.65 V (vs Cp(2)Fe(+/0)) that is attributable to a metal-centered oxidation. The influence of carbene substituents, porphyrin substituents, and trans-ligands on the Ru==C bond was examined through comparison of the chemical shifts of the pyrrolic protons in the porphyrin macrocycles ((1)H NMR) and the M==C carbon atoms ((13)C NMR), the potentials of the metal-centered oxidation couples, and the Ru==C distances among the various ruthenium porphyrin carbene complexes. A direct comparison among iron, ruthenium, and osmium porphyrin carbene complexes is made.     

Primary and secondary phosphane complexes of metalloporphyrins: isolation, spectroscopy, and X-ray crystal structures of ruthenium and osmium porphyrins binding phenyl- or diphenylphosphane

[Ru(II)(por)(PH(n)Ph(3-n))2], [Os(II)(por)(CO)(PH(n)Ph(3-n))] (n=1, 2), and [Os(II)(F20-tpp){P(OH)Ph2}(PHPh2)] (F20-tpp=5,10,15,20-tetrakis(pentafluorophenyl)porphyrinato dianion) were prepared from the reaction of [M(II)(por)(CO)] (M=Ru, Os) or [Os(VI)(por)O2] with the respective primary/secondary phosphane and characterized by 1H NMR, 31P NMR, UV/Vis, and IR spectroscopy, mass spectrometry, and elemental analysis. The reaction of [Os(VI)(por)O2] with PHPh2 also gave minor amounts of [Os(II)(por){P(OH)Ph2}2]. [Ru(II)(F20-tpp)(PH2Ph)2] exhibits a remarkable stability toward air and shows a reversible metal-centered oxidation couple at E(1/2)=0.39 V versus [Cp2Fe](+/0) in the cyclic voltammogram. The structures of [Ru(II)(F20-tpp)(PH2Ph)2] x 2CH2Cl2, [Ru(II)(4-Cl-tpp)(PHPh2)2] x 2CH2Cl2 (4-Cl-tpp=5,10,15,20-tetrakis(p-chlorophenyl)porphyrinato dianion), [Ru(II)(F20-tpp)(PHPh2)2], and [Os(II)(F20-tpp){P(OH)Ph2}2] were determined by X-ray crystallography and feature Ru-P distances of 2.3397(11)-2.3609(9) A and an Os-P distance of 2.369(2) A.     

A molecular-dynamics simulation study on the dependence of Lennard-Jones gas-liquid phase diagram on the long-range part of the interactions

The particle-transfer molecular-dynamics technique is adopted to construct the Lennard-Jones fluid gas-liquid phase diagram. Detailed study of the dependence of the simulation results on the system size and the cutoff distance is performed to test the validity of the simulation technique. Both the traditional cutoff plus long-range correction (CPC) and Ewald summation methods are used in the simulations to calculate the interactions. In the intermediate range of temperatures, the results with the Ewald summation method are almost the same as those with the CPC method. However, in the range close to the critical point, the results with the CPC method deviate from those with the Ewald summation. Compared with the results obtained via the Ewald summation in a smaller system, simply increasing the system size in the CPC scheme may not give better results.     

A practical method to avoid bond crossing in two-dimensional dissipative particle dynamics simulations

Dissipative particle dynamics (DPD) simulation technique is an effective method targeted on mesoscopic simulations in which the interactions between particles are soft. As a result, it inevitably causes bond crossing and interpenetration between particles. Here we develop a practical method based on the two-dimensional DPD model which can extremely reduce the possibility of bond crossing. A rigid core is added to each particle by modifying the form of the conservative force in DPD so that the particles cannot penetrate each other. Then by adjusting the spring constant of the bond, we can impose a simple geometry constraint so that the bond crossing can hardly take place. Furthermore, we take into account an analytic geometry constraint in the polymerization model of DPD by which we can successfully avoid the severe bond crossing problem during bond generation in two dimensions. A parabola fitting between the pressure and the particle number density shows that our modified DPD model with small rigid cores can still be mapped onto the Flory-Huggins model, and the mesoscopic length scale of our simulations does not change. By analyzing the mean-square displacement of the innermost monomer and the center of mass of the chains, we find a t(8/15) power law of the polymer dynamics in our model instead of the Rouse prediction supporting the recent results in literature.     

Molecular dynamics simulation study on adsorption and diffusion processes of a hydrophilic chain on a hydrophobic surface

Molecular dynamics simulations are applied to investigate the adsorption and diffusion processes of a single hydrophilic poly(vinyl alcohol) (PVA) chain with different chain lengths on a hydrophobic graphite surface. It is expected that the chain and the surface "dislike" each other because one is hydrophilic and the other is hydrophobic. But surprisingly, a short PVA chain is well adsorbed on the surface, accompanied by large changes in the chain configuration. With increasing degree of polymerization (N), the chain turns gradually from two-dimensional adsorption to possessing certain height in the direction perpendicular to the surface. Moreover, the adsorption energy increases and the diffusion coefficient decreases with increasing N. In particular, for N = 20 in equilibrium, the hydroxyls of this short chain are close to the graphite surface in the stable adsorption configuration. In addition, we change the effective dielectric constant to 76.0 to mimic good solvent condition. The chain configurations and the diffusion coefficients both vary in contrast to the foregoing results.