应用分子动力学模拟和拉曼光谱对钙、镁、氯离子 水化现象的研究

应用分子动力学方法,模拟了298 K下,密度为1.0 g/cm~3的水溶液中Ca²⁺,Mg²⁺,Cl~-的水化现象,得到了相应离子周围水分子的微观分布情况.发现在钙离子周围,水分子以其氧离子去靠近中心离子;而在氯离子周围,水分子则以其中的一个氢原子去靠近中心离子.通过分析三种离子的径向分布函数、配位数曲线、水化数、水化半径,发现Ca²⁺的水化数和水化半径均大于Mg²⁺,即Ca²⁺的水合能力比Mg²⁺强.与以往研究结果相比,本文计算所得的自扩散系数更接近实验所得结果.为了使模型更好的代表真实水溶液体系,本文还应用分子动力学和拉曼光谱法研究了不同浓度的CaCl₂水溶液.分子动力学研究发现随着浓度的升高,CaCl₂溶液中Ca²⁺,Cl~-的配位数分别呈降低趋势.同时,随着浓度的升高,Ca²⁺,Cl~-的自扩散系数也呈现降低的趋势.作者推断这是由于浓度的升高,加剧了离子的微观反...     

硝酸钾电解质溶液水化结构的分子动力学模拟

应用分子动力学方法对硝酸钾溶液中离子团簇的结构和离子的水化性质进行模拟研究．水分子采用简单点电荷模型，钾离子被看作带电硬球，硝酸根离子采用刚性四节点模型，同时考虑了节点间的库仑长程作用和L-J相互作用，库仑长程作用采用EWALD求和方法处理，得到了溶液中各种离子对的微观构型和径向分布函数，考察了溶液浓度对离子水化性质的影响．研究表明, 在KNO3溶液中存在一定程度的离子缔合，在高离子浓度情形，可以观察到二聚体、三聚体、溶剂分离阴阳离子对以及其它更复杂的离子团簇构型；离子水化数随离子浓度的升高而降低，对不同浓度的溶液得到的K+的水化数为5?7，NO3-的水化数为3.5?4.7，与蒙特卡罗模拟结果和飞行时间中子衍射实验的测量结果一致．     

Nuclear quadrupolar relaxation in ionic crystals

The nuclear quadrupolar relaxation time of alkali halide crystals is investigated by the Heitler-London approximation. We use the Slater determinant which is constructed by the Hartree-Fock wave functions of the free ions. The charge distribution around an ion is not spherically symmetrical because of mutual overlap of the atomic wave functions of nearest-neighbor ions. Moreover, the charge distribution around an ion changes its shape during thermal vibrations of the ions, because the degree of the overlap depends upon the distance apart of the ions. Therefore, the quadrupolar interaction in alkali halide lattices is the resultant of a combination of the thermal vibration with the charge overlap. As illustrations of the theory, we have computed the quadrupolar relaxation time of the ³⁹K and the ³⁵Cl nuclei in the KCl crystal, and the ²³Na nucleus in the NaCl crystal. The theoretical results are in good agreement with those of experiments. We have also computed the ratio of the quadrupolar relaxation time of the metal nucleus to that of the halogen nucleus for some alkali halide crystals. After computing the same ratio by the covalent model and the deformation model, we have compared these results with the available experimental data. Finally, by using the same overlap model as that mentioned previously, we have developed a formula which gives the chemical shift of ionic crystals.     

KCdF3晶体中Cr3+-Li+中心局域结构研究

利用零场分裂参量与晶体结构之间的定量关系,研究了双掺杂晶体KCdF₃:Cr³⁺,Li⁺的局域结构。指出,对于KCdF₃:Cr³⁺,Li⁺晶体,四角晶场的形成包含两个方面:(1)由于电荷补偿而产生的等效电荷形成的四角对称晶场;(2)Cr³⁺的局域结构发生晶格畸变而产生的四角对称晶场。事实上,当Cr³⁺和Li⁺掺入KCdF₃晶体时,Cr³⁺代替了Cd²⁺离子;由于Cr³⁺离子与Cd²⁺离子的半径不同、电荷不同、质量不同,导致Cr³⁺的局域结构发生晶格畸变,由此而产生四角对称晶场;由于电荷补偿,Li⁺离子取代了[001]方向与Cr³⁺离子邻近的Cd²⁺离子,由此产生的等效电荷而形成的四角晶场。这样,Cr³⁺的局域结构由O_h对称变为C_4v点对称。文中建立了ZFS参量和晶体结构之间的定量关系。在考虑晶格畸变和等效电荷的基础上,研究了KCdF₃:Cr³⁺,Li⁺晶体的ZFS参量,理论结果和实验符合很好。得到了F^-离子向中心离子分别移动为ΔR₁=0.00268nm,ΔR₂=0.001nm,ΔR₃=0.00165nm。     

Aqueous electrolyte surfaces in strong electric fields: molecular insight into nanoscale jets and bridges

Exposing aqueous surfaces to a strong electric field gives rise to interesting phenomena, such as formation of a floating water bridge or an eruption of a jet in electrospinning. In an effort to account for the phenomena at the molecular level, we performed molecular dynamics simulations using several protocols on both pure water and aqueous solutions of sodium chloride subjected to an electrostatic field. All simulations consistently point to the same mechanisms which govern the rearrangement of the originally planar surface. The results show that the phenomena are primarily governed by an orientational reordering of the water molecules driven by the applied field. It is demonstrated that, for pure water, a sufficiently strong field yields a columnar structure parallel to the field with an anisotropic arrangement of the water molecules with their dipole moments aligned along the applied field not only in the surface layer but over the entire cross section of the column. Nonetheless, the number of hydrogen bonds per molecule does not seem to be affected by the field regardless of its strength and molecule’s orientation. In the electrolyte solutions, the ionic charge is able to overcome the effect of the external field tending to arrange the water molecules radially in the first coordination shell of an ion. The ion–water interaction interferes thus with the water–electric field interaction, and the competition between these two forces (i.e., strength of the field versus concentration) provides the key mechanism determining the stability of the observed structures.     

NMR relaxation of protons in tissues and other macromolecular water solutions

Nuclear magnetic resonance (NMR) longitudinal (T₁) and transverse (T₂) relaxation parameters have been evaluated for protein solutions, cellular suspensions and tissues using both data from our laboratory and the extensive literature. It is found that this data can be generalized and explained in terms of three water phases: free water, hydration water, and crystalline water. The proposed model which we refer to as the FPD model differs from similar models in that it assumes that free and hydration water are two phases with distinct relaxation times but that T₁ = T₂ in each phase. In addition there is a single correlation time for each rather than a distribution as assumed in most other models. Longitudinal decay is predicted to be single exponent in character resulting from a fast exchange between the free and hydration compartments. Transverse decay is predicted to be multiphasic with crystalline (T₂ 10 μsec), hydration (T₂ 10 sec) and free (T₂ 100 sec) water normally visible. The observed or effective transverse relaxation times for both the hydration and free water phases are greatly affected by the crystalline phase and are much shorter than the inherent relaxation times.     

Electronic structure and spectrum of endofullerene cation [Ce@C<Subscript>60</Subscript>]<Superscript>+</Superscript>

The electronic structure, the equilibrium geometric configuration, and the charge distribution are calculated for the positive endofullerene ion [Ce@C₆₀]⁺. It is shown that the equilibrium distance from the Ce atom to each of the six nearest C atoms almost coincides with the sum of the cerium ionic radius and the carbon atomic radius. The spectrum of electronic transitions in the visible and UV regions is presented.     

有机分子的结构与排列方式对原子电荷分布及静电作用的影响

对由两个相同的长直链分子(CH3(CH2)5—R(R=COOH,CH3,OH)、CH3(CH2)4—COOH))呈镜面对称分布组成的四种模型,及由两个CH3(CH2)5COOH分子平行分布组成的模型进行了量化计算,研究了分子间距、功能团、链长及排列方式对原子电荷分布及分子静电相互作用的影响.结果表明:1)分子中不同位置的亚甲基团(—CH2—)的C原子电荷各不相同.2)原子电荷不仅受到分子链长及功能团的影响,同时,当分子间距及排列方式发生改变时,原子电荷也发生改变;双分子模型较单分子模型的原子电荷变化较大.3)分子间静电作用由尾基功能团的极性决定,由强到弱为—COOH—OH—CH3,分子中其他原子对静电作用的贡献较小;分子链长的增加导致尾基功能团中电荷减少,从而使得分子间静电作用减弱.     

Ab Initio Investigation of the Microspecies and Energy in Hydrated Strontium Ion Clusters

Quantum chemistry calculations were used to study the structure and energy of strontium (Sr) ion hydrated clusters [Sr(H₂O)_1?25]²⁺. The saturated hydration number of the first hydration layer of Sr²⁺ was 8, and the hydration distance was 2.58 Å. The second hydration layer had 1–9 hydration numbers, and the hydration distance was in the range of 4.4–4.6 Å. This work also developed the relationship between the thermodynamic data (average water binding energy E_n and successive water binding energy ΔE_n,n?1, etc.) of the aforementioned low-energy structure and the hydration structures. The first hydration layer was formed by the strong electrostatic interaction between Sr²⁺ and water molecules, and the decrease in ΔE_n,n?1 was relatively large. Hydrogen bonds were formed between water molecules of the second hydration layer and water molecules of the inner layer, and the decrease in ΔE_n,n?1 was relatively small. When one water molecule was added beyond the second hydration layer, ΔE_n,n?1 was close to the hydrogen bond energy 8.88 kcal/mol (37.1 kJ/mol) of dimer water molecule, indicating that there was very weak interaction between Sr²⁺ and the water molecules beyond the second hydration layer.     

N2H4在NiFe(111)合金表面吸附稳定性和电子结构的第一性原理研究

采用基于色散校正的密度泛函理论进行了第一性原理研究, 详细分析了肼(N₂H₄)在Ni₈Fe₈/Ni(111)合金表面稳定吸附构型的吸附稳定性和电子结构及成键性质. 通过比较发现, 肼分子以桥接方式吸附在表面的两个Fe原子上是最稳定的吸附构型, 其吸附能为-1.578 eV/N₂H₄. 同时发现, 肼分子在这一表面上吸附稳定性的趋势为: 桥位比顶位吸附更有利, 且在Fe原子上比在Ni原子上的吸附作用更强. 进一步分析了不同吸附位点上稳定吸附构型的电子结构、电荷密度转移以及电子局域化情况. 结果发现: 相同吸附位点的电子态密度图基本一致, 并且N原子的p轨道和与之相互作用的表面原子的d轨道之间存在态密度上的重叠; 吸附后电荷密度则主要从肼分子转移到表面原子之上; 在电子局域化函数切面图中也发现吸附后电子被局域到肼分子的N原子和相邻的表面原子之间. 这些电子结构的表征都充分说明肼分子与表面原子之间通过电荷转移形成了强烈的配位共价作用.     

Layered lattice gas model for the metal-electrolyte interface

Several models of the diffuse double layer in liquid electrolytes are discussed. These models all involve partitioning the space charge region into a number of planar layers parallel to the metal electrode, with ionic liquid lattice gas, as opposed to idea gas, response in each layer. Each layer may contain both ions and solvent molecules. Several difficulties implicit in the earlier work of Liu on such a model are pointed out. These problems seem to have caused the appearance of an initial charge-free region in Liu's results. A layer model involving Liu's original assumptions of point ionic charges and point dipoles is discussed in detail and is shown to be electrostatically inconsistent. It is replaced by a layer model in which ionic charge resides on each basic layer, with each such layer surrounded symmetrically by charge layers representing the effect of finite-extent permanent dipoles. This model leads, as it should, to Gouy-Chapman behavior in the continuum limit. Finally, a method of including ion hydration effects explicitly in such a model is proposed.     

砷和砷酸铁水化结构和红外光谱理论研究

水体中砷的去除与其水化作用密切相关,而不同质子化砷和砷酸铁水化特征相关报道甚少,且缺乏不同质子化砷和砷酸铁水化层红外光谱解析。在B3LYP/6-311G(d, p)计算水平上比较不同质子化砷酸根[H_mAsO₄]m-3(m=0～2)和铁-砷酸盐络合物种[FeH_mAsO₄]m+(m=0-2)水化能,利用约化密度梯度函数图形化分析其与水分子相互作用的强度、类型和位置,并解析不同质子化砷酸根和砷酸铁水化层红外光谱特征。结果表明,随着氢质子化,砷酸根[H_mAsO₄]m-3(m=0～2)水化能力减弱,而铁-砷酸盐络合物种[FeH_mAsO₄]m+(m=0～2)水化能力随着氢质子化增强。当水分子中1个氢与[H_mAsO₄]m-3(m=0～2)中1个氧相互作用时倾向形成氢键;而水分子中2个氢同时分别与[H_mAsO₄]m-3(m=0～2)中两个氧相互作用时,相互作用变弱,以范德华力相互作用;水分子通过其氢与砷酸根中氧形成的氢键强于水分子通过其氧与质子化砷酸根中氢形成的氢键。未质子化O_N倾向与2~4个水分子形成氢键,而质子化O_P最多与2个水分子形成氢键且O_P…H_W氢键弱于O_N…H_W氢键。红外光谱中,2 954,3 114,3 179,3 252和3 297 cm-1是AsO3-₄第一水化层中水分子Ow-Hw伸缩振动峰,3 277,3 324和3 376 cm-1是HAsO2-₄第一水化层中水分子的Ow-Hw伸缩振动峰,3 189,3 277,3 306和3 383 cm-1是H₂AsO-₄第一水化层中水分子Ow-Hw伸缩振动峰;[FeH_mAsO₄]m+(m=0～2)第一水化层中水分子Ow-Hw伸缩振动对应区域依次是2 500~3 060,2 660~3 200和2 900~3 360 cm-1。因此,随质子化,[H_mAsO₄]m-3(m=0～2)和[FeH_mAsO₄]m+(m=0～2)第一水化层中水分子的Ow-Hw伸缩振动峰蓝移;相对于[H_mAsO₄]m-3(m=0～2),[FeH_mAsO₄]m+(m=0～2)第一水化层水分子的弯曲振动峰和伸缩振动峰都明显红移。[FeH_mAsO₄]m+(m=0～2)第一水壳层形成Fe-Ow-Hw…Ow-Hw…O_N-As氢键桥,该氢键桥中Ow-Hw具有特殊吸收峰,伸缩振动峰依次位于2 195,2 526和2 673 cm-1,质子化导致明显蓝移但峰强度几乎无变化;而其弯曲振动峰随质子化红移且强度明显降低;独立O_P-H伸缩振动峰不受Fe络合影响,而O_P-H…Ow中O_P-H伸缩振动峰位置因Fe络合而发生明显蓝移。该研究有助于更好地解析不同PH下砷和砷酸铁在水中溶解性,可用于红外光谱监测水溶液中砷和砷酸铁水化特征。     

Investigation of the relationship between the ionic conductivity and the local structures of singly and doubly doped ceria compounds using EXAFS measurement

The oxide ionic conductivity measurements of singly and doubly doped ceria compounds were carried out. Singly and doubly doped ceria used in this study were Ce_0.8Ln_0.2O_1.9 (Ln=Y, Sm, Nd, or La) and Ce_0.8La_0.1Y_0.1O_1.9, respectively. Lattice constants of these compounds were in proportion to the ionic radius of the dopant(s). The doubly doped ceria compound showed oxide ionic conductivity comparative to the average of that of each corresponding singly doped sample. This finding indicates that the conductivity is influenced by both dopants in the doubly doped compounds. The extended X-ray absorption fine structure (EXAFS) study showed that the coordination number of oxide ions at the nearest neighbor of cation was related to the ionic conductivity. It was found that the conductivity gave the highest value when oxygen vacancies were randomly distributed in the lattice. This indicates that the local structure seriously affects oxide ionic conduction in singly and doubly doped ceria compounds.     

Poisson-Fokker-Planck model for biomolecules translocation through nanopore driven by electroosmotic flow

A non-continuous electroosmotic flow model (PFP model) is built based on Poisson equation, Fokker-Planck equation and Navier-Stokse equation, and used to predict the DNA molecule translocation through nanopore. PFP model discards the continuum assumption of ion translocation and considers ions as discrete particles. In addition, this model includes the contributions of Coulomb electrostatic potential between ions, Brownian motion of ions and viscous friction to ion transportation. No ionic diffusion coefficient and other phenomenological parameters are needed in the PFP model. It is worth noting that the PFP model can describe non-equilibrium electroosmotic transportation of ions in a channel of a size comparable with the mean free path of ion. A modified clustering method is proposed for the numerical solution of PFP model, and ion current translocation through nanopore with a radius of 1 nm is simulated using the modified clustering method. The external electric field, wall charge density of nanopore, surface charge density of DNA, as well as ion average number density, influence the electroosmotic velocity profile of electrolyte solution, the velocity of DNA translocation through nanopore and ion current blockade. Results show that the ion average number density of electrolyte and surface charge density of nanopore have a significant effect on the translocation velocity of DNA and the ion current blockade. The translocation velocity of DNA is proportional to the surface charge density of nanopore, and is inversely proportional to ion average number density of electrolyte solution. Thus, the translocation velocity of DNAs can be controlled to improve the accuracy of sequencing by adjusting the external electric field, ion average number density of electrolyte and surface charge density of nanopore. Ion current decreases when the ion average number density is larger than the critical value and increases when the ion average number density is lower than the critical value. Our numerical simulation shows that the translocation velocity of DNA given by the PFP model agrees with the experimental, results better than that given by PNP model or PB model.     

On a hydration model utilized in the discussion of dielectric spectra of aqueous solutions

A solution model is discussed which allows the microwave part of the permittivity spectrum of aqueous solutions to be related to characteristics of the hydration water. The parameters, which can be derived from measured dielectric spectra thereby are the hydration water relaxation time, the number of hydration water molecules per molecule of solute, the static orientational polarizability of the hydration water, and a quantity, which refers to the distribution of hydration water relaxation times. The (continuum) model, appropriate for solutions of (nearly) spherically shaped solute particles, has regard to internal electric fields resulting from polarization charges at interfaces. Possible errors in the parameter values are indicated, which may arise if the internal fields are only incompletely taken into account. Previously measured spectra for a series of aqueous solutions of 1,4-diazabicyclo[2,2,2]octane have been evaluated on the basis of the present model. The results for these (favourable) solutions are presented to show, that the found dependence of the parameter values on solute concentration is consistent with the idea of the proposed hydration model.     

四磷酸镧钾的晶体结构

四磷酸镧钾(KLa[PO₃]₄)晶体属单斜晶系,空间群为P2₁。晶胞参数a=8.106(3)?, b=8.551(2)?,c=7.326(3)?,β=92.18(6)°晶胞内分子数z=2。全矩阵最小二乘法修正给出1026个独立反射点的R=0.061,R_w=0.062。基本的结构单元为(PO₃)_n螺旋带,它们由共角的四面体构成。十二面体LaO₈是彼此分立,K原子占据不规则空隙多面体中心。最短的La—La距为7.063?。 关键词：     

Characterization of NOx species in dehydrated and hydrated Na- and Ba-Y, FAU zeolites formed in NO2 adsorption

Adsorbed ionic NO_x species formed upon the interaction of NO₂ with dehydrated or hydrated Na- and Ba-Y, FAU zeolites were characterized using FT-IR/TPD, solid state NMR, and XANES techniques. NO₂ disproportionates on both dehydrated catalyst materials forming NO⁺ and NO₃⁻ species. These ionic species are stabilized by their interactions with the negatively charged zeolite framework and the charge compensating cations (Na⁺ and Ba²⁺), respectively. Although the nature of the adsorbed NO_x species formed on the two catalysts is similar, their thermal stabilities are strongly dependent on the charge compensating cations. In the presence of water in the channels of these zeolite materials new paths open for reactions between NO⁺ and H₂O, and NO₂ and H₂O, resulting in significant changes in the adsorbed ionic species observed. These combined spectroscopic investigations afforded the understanding of the interactions between water and NO₂ on these zeolite catalysts.     

反式二氯二L-苯丙氨酸乙酯合铂分子结构和晶体结构

反式二氯二L-苯丙氨酸乙酯合铂[Pt(C₁₁H₁₅NO₂)₂Cl₂]属单斜晶系,空间群为P2₁,α=13.555(6)?,b=6.487(3)?,c=15.588(5)?,β=109.42(3)°,Z=2。该化合物晶体结构由重原子法求解,用块矩阵最小二乘方法修正,R=0.0617,R_w=0.0575。Pt—N 2.065(14)?,2.084(14)?;Pt—Cl 2.285(7)?,2.312(8)?。结构由以N—H……O氢键联结的分子层交错堆积组成。 关键词：     

A molecular dynamics study of uranyl hydration

Molecular dynamics calculations were carried out in order to investigate the hydration structure of uranyl in aqueous solution. The CF1 model of flexible water molecules is used. This model allows one to investigate a hydrolysis reaction for water molecules in the first uranyl hydration shell. Charge redistribution effects on hydrolysis products are also taken into account. We found five ligands in uranyl hydration shell, which is of bipyramidal pentacoordinated structure. The charge redistribution effects resulted in ligands of four water molecules and one hydroxyl, which was found closer to uranium than the other ligands.     

Electrostatic interaction of a spherical particle in the vicinity of a circular orifice

The electrostatic interaction of a charged spherical particle in the vicinity of an orifice plane has been investigated in this paper.The particle can creep along the axis of the orifice and is immersed in a bulk electrolyte.By solving the Poisson-Boltzmann problem,we have obtained the effective electrostatic interaction for several values of reduced orifice radius h,including the cases of h > 1,h = 1 and h < 1.Two kinds of boundary conditions of the orifice plane are considered.One is the constant potential model corresponding to a conducting plane,the other is the constant charge model.In the constant potential model,there is an electrostatic attraction between the particle and the orifice plane when they get close to each other,while there is a pure electrostatic repulsion in the constant charge model.The interactions in both boundary models are sensitive to the parameters of the reduced orifice radius,the reduced particle-orifice distance,surface charge densities of the particle and orifice plane,and the reduced Debye screen constant corresponding to the salt-ion concentration and ion valence.