四臂星型聚电解质刷在外加三价盐离子和电场下的塌缩

本文采用Langevin动力学模拟的方法,研究存在三价盐离子时,接枝在带相反电荷的极板上的部分带电的四个臂星型链呈现出的塌缩现象. 结果表明,在电场作用下,接枝星型链的平均带电分数和盐浓度在带电单体和三价盐离子的竞争性吸附中起关键作用. 对于接枝在带相反电荷的极板上的带电分数较高的星型链,刷子会塌缩到接枝极板上,并会产生极板表面电荷的过度补偿现象. 当带电分数较低时,如果星型链所带电荷数与三价盐离子电荷数相同,即使在很低的盐浓度下,极板对三价盐离子的吸引能力也高于对星型链中的带电单体的吸引. 结果表明,星型链在带电分数较低的情况下,三价盐离子的加入不会导致接枝电极表面电荷的过度补偿. 此外,本文还研究了三价盐离子对电场作用下星型刷的拉伸的影响.     

四臂星型聚电解质刷在外加三价盐离子和电场下的塌缩（英文）

本文采用Langevin动力学模拟的方法,研究存在三价盐离子时,接枝在带相反电荷的极板上的部分带电的四个臂星型链呈现出的塌缩现象.结果表明,在电场作用下,接枝星型链的平均带电分数和盐浓度在带电单体和三价盐离子的竞争性吸附中起关键作用.对于接枝在带相反电荷的极板上的带电分数较高的星型链,刷子会塌缩到接枝极板上,并会产生极板表面电荷的过度补偿现象.当带电分数较低时,如果星型链所带电荷数与三价盐离子电荷数相同,即使在很低的盐浓度下,极板对三价盐离子的吸引能力也高于对星型链中的带电单体的吸引.结果表明,星型链在带电分数较低的情况下,三价盐离子的加入不会导致接枝电极表面电荷的过度补偿.此外,本文还研究了三价盐离子对电场作用下星型刷的拉伸的影响.     

离子配对动力学不一定遵循Eigen-Tamm机理

Eigen-Tamm模型认为水溶液中的离子对从单水分子桥链离子对到紧密离子对是离子对溶剂化平衡的动力学控制性步骤,两态之间自由能垒最高,相互转化速率最慢. 设计了两类带有单位电荷的离子对模型(2.0:x和x:2.0,固定离子对中的阳离子或阴离子的半径为2 ?,另一个为不同半径的阴阳离子),通过计算离子对不同距离的平均力势来获取自由能曲线,发现2.0:x系列离子对由于溶剂水的作用,从单水分子桥链离子对到紧密离子对转化的自由能垒有明显减低,并不是离子成对动力学平衡中的最慢步骤,与Eigen-Tamm 模型描述存在偏差.     

NH_3退火热氮化SiO_2薄膜及其与Si界面特性的研究

采用不同方法研究了NH_3中高温退火所形成的氮化SiO_2薄膜及其界面特性,发现不同的退火条件对样品的组份、折射率、电子陷阱特性、表面电子迁移率、固定正电荷及界面态密度等有较大的影响。探讨了氮化机理及其对界面特性等的影响。分析了抗氧化机构。     

微通道内电解质溶液离子分布动电学效应模拟

动电学效应对微通道内流体流动特性影响很大,其对通道内粒子分布特性的影响使得通道近壁面流体流动特性极不稳定。本文采用分子动力学方法模拟了二维矩形微通道内NaCl稀电解质溶液的流动特性,考虑存在于不同粒子间的Lennard-Jones势能、静电力、以及带电离子与水分子间的相互作用,得到了粒子在通道内的分布特征。结果显示在动电学效应主要作用于通道壁面附近,而主流区域影响极小。Na~+离子在无量纲通道高度达到0.08和0.91时其浓度达到最大值,沿远离壁面其浓度逐渐降低,与壁面电性相反的Cl~-离子则在无量纲通道高度达到0.15和0.84附近浓度最高。其结果与基于连续介质解理论的Boltzamnn统计分布一致。水分子的浓度在壁面附近也较通道中心处高。     

电解质的加入对Au@Ag纳米粒子SERS效应的影响

通过先采用Frens法制备粒径约为12nm的Au NPs,以此为基础通过以抗坏血酸为还原剂,采用种子生长法成功制得Au@Ag纳米粒子,通过UV-Vis表征发现具有很好的稳定性。接着以4-巯基吡啶(4-MPy)分子为探针,考察了加入电解质的量、加入顺序、电解质的阳离子、电解质的阴离子对纳米粒子SERS活性的影响,并结合UV-Vis光谱进行了分析。结果显示加入电解质的量一般会有一个最佳值,加入阳离子种类以及加入顺序对纳米粒子SERS活性影响不是很明显。不同阴离子的加入对纳米粒子影响不同,这主要是由于阴离子的加入使溶胶发生聚集以及阴离子与Au@Ag纳米粒子银表面相互作用的结果。     

胶束体系中荧光素与四溴荧光素间能量转移条件及模型研究

研究了阳离子表面活性剂(CSAA)在水溶液中与阴离子酸性染料四溴荧光素(TBF)的荧光反应,发现当CSAA单体与TBF形成离子缔合物时,TBF的荧光发生猝灭,而CSAA胶束与TBF作用又会产生一个新的、更强的荧光。进而研究了阳离子表面活性剂CTMAB及CPB胶束体系中酸性阴离子荧光染料荧光素与四溴荧光素间的能量转移条件。表明只有在带相反电荷的CSAA形成的胶束中,阴离子染料间的能量转移才可能发生,在2/3临界胶束浓度(CMC)时能量转移效率达到最大。并推测了胶束体系中染料间能量转移模型及染料间能量转移的一般规律。     

影响聚合物离子导体电导率的一些因素

本文研究了极性基团浓度、碱金属盐阳离子和阴离子尺寸对均聚物聚环氧氯丙烷(PECH)和共聚物聚环氧氯丙烷-聚环氧乙烷(PECH-PEO)电导率的影响。对锂盐络合物,极性基团浓度增高,电导率降低。钠盐络合物则正好相反,极性基团浓度越高,电导率越高。碱金属盐阳离子和阴离子尺寸对聚合物离子导体电导率都有明显影响。所研究的聚环氧氯丙烷与三种碱金属盐络合物PECH-MI(M=Li,Na,K)的电导率数据表明,钠盐络合物的电导率最高,锂盐和钾盐络合物的电导率较低。碱金属盐阴离子越大,PECH络合物的电导率越低。此外,还 关键词：     

晶体中的库仑静电势

计算固体的结合能、晶体势以及电子能带结构时,都会遇到库仑(Coulomb)静电势问题.在离子晶体中,这种静电势问题最明显的例子是马德隆(Madelung)常数的计算.这是固体物理学中的一个基本问题,在计算技巧上也有着独特的地方[1].关于马德隆常数的计算,一般的固体物理教科书中都有介绍[2-4].本文采用离子球赝电荷方法计算晶体中的库仑静电势,并用来计算一些离子晶体的马德隆常数.本文方法与已有的厄瓦耳(Ewald)方法比较,有一些明显的优点。 一、静电势的计算 为便于比较,先简单地回顾一下计算离子晶体静电势的厄瓦耳方法[3-5].对于离子晶体,在…     

NH3退火热氮化SiO2薄膜及其与Si界面特性的研究

采用不同方法研究了NH₃中高温退火所形成的氮化SiO₂薄膜及其界面特性,发现不同的退火条件对样品的组份、折射率、电子陷阱特性、表面电子迁移率、固定正电荷及界面态密度等有较大的影响。探讨了氮化机理及其对界面特性等的影响。分析了抗氧化机构。 关键词：     

Reentrant condensation of proteins in solution induced by multivalent counterions

Negatively charged globular proteins in solution undergo a condensation upon adding trivalent counterions between two critical concentrations C and C, C 相似文献   

Static polarizability effects on counterion distributions near charged dielectric surfaces: A coarse-grained Molecular Dynamics study employing the Drude model

Coarse-grained implicit solvent Molecular Dynamics (MD) simulations have been used to investigate the structure of the vicinal layer of polarizable counterions close to a charged interface. The classical Drude oscillator model was implemented to describe the static excess polarizability of the ions. The electrostatic layer correction with image charges (ELCIC) method was used to include the effects of the dielectric discontinuity between the aqueous solution and the bounding interfaces for the calculation of the electrostatic interactions. Cases with one or two charged bounding interfaces were investigated. The counterion density profile in the vicinity of the interfaces with different surface charge values was found to depend on the ionic polarizability. Ionic polarization effects are found to be relevant for ions with high excess polarizability near surfaces with high surface charge.     

Binding of oppositely charged membranes and membrane reorganization

We consider the electrostatic interaction between two rigid membranes, with different surface charge densities of opposite sign, across an aqueous solution without added salt. Exact solutions to the nonlinear Poisson-Boltzmann equation are obtained and their physical meaning discussed. We also calculate the electrostatic contribution to the free energy and discuss the renormalization of the area per head group of the charged lipids arising from the Coulomb interaction. Received 13 October 1998     

Effective Electrostatic Interactions Between Two Overall Neutral Surfaces with Quenched Charge Heterogeneity Over Atomic Length Scale

Using Monte Carlo results as a reference, a classical density functional theory (CDFT) is shown to reliably predict the forces between two heterogeneously charged surfaces immersed in an electrolyte solution, whereas the Poisson–Boltzmann (PB) theory is demonstrated to deteriorate obviously for the same system even if the system parameters considered fall within the validity range of the PB theory in the homogeneously charged surfaces. By applying the tested CDFT, we study the effective electrostatic potential of mean force (EPMF) between two face–face planar and hard surfaces of zero net charge on which positive and negative charges are separated and considered to present as discontinuous spots on the inside edges of the two surfaces. Main conclusions are summarized as follows: (i) strength of the EPMF in the surface charge separation case is very sensitively and positively correlated with the surface charge separation level and valency of the salt ion. Particularly, the charge separation level and the salt ion valency have a synergistic effect, which makes high limit of the EPMF strength in the surface charge separation case significantly go beyond that of the ideal homogeneously charged surface counterpart at average surface charge density similar to the average surface positive or negative charge density in the charge separation case. (ii) The surface charge distribution patterns mainly influence sign of the EPMF: symmetrical and asymmetrical patterns induce repulsive and attractive (at small distances) EPMF, respectively; but with low valency salt ions and low charge separation level the opposite may be the case. With simultaneous presence of both higher valency cation and anion, the EPMF can be repulsive at intermediate distances for asymmetrical patterns. (iii) Salt ion size has a significant impact, which makes the EPMF tend to become more and more repulsive with the ion diameter regardless of the surface charge distribution patterns and the valency of the salt ion; whereas if the 1:1 type electrolyte and the symmetrical patterns are considered, then the opposite may be the case. All of these findings can be explained self-consistently from several perspectives: an excess adsorption of the salt ions (induced by the surface charge separation) serving to raise the osmotic pressure between the plates, configuration fine-tuning in the thinner ion adsorption layer driven by the energy decrease principle, direct Coulombic interactions operating between charged objects on the two face-to-face plates involved, and net charge strength in the ion adsorption layer responsible for the net electrostatic repulsion.     

Protein Binding on the Surface of Magnetic Nanoparticles

Magnetic nanoparticles (MNPs) are widely used in the areas of biology and biomedicine. The interaction between MNPs and proteins plays a crucial role in the bioapplication of MNPs, and the binding affinity of protein–MNPs is the manifestation of this interaction. The binding affinity of some proteins with MNPs modified in various ways is determined by fluorescence quenching. The results show that the binding affinity depends on the properties of both the MNPs and the proteins. The higher the surface curvature of MNPs, the larger the MNP, and the higher the binding affinity. No significant difference is found in binding affinity between MNPs with different modification methods. For proteins, the binding affinity depends on the properties of individual proteins, such as the amino acid sequence, the native protein conformation in solution, the isoelectric point, and surface potential. In general, the binding affinity is higher for proteins with cysteine residues on the surface. In addition, pH affects the binding affinity between proteins and MNPs; positively charged proteins and lower pH are more suitable for MNP binding due to electrostatic forces.     

Towards a microscopic theory of wetting by ionic solutions. I. Surface properties of the semi-primitive model

As a first step towards a density functional theory (DFT) of wetting by ionic solutions we examine the density profiles of ions and solvent molecules confined near a charged wall, or between two walls, and the corresponding interfacial properties, including adsorption, surface tension, solvation force and electrostatic properties, within the semi-primitive model (SPM) of solutions made up of hard sphere solvent particles and charged hard spheres. Both monovalent and divalent cations with species-dependent diameters are considered. The density functional includes the best available Rosenfeld hard-sphere functional, as well as mean-field and Coulomb correlation contributions. The simpler mean-field functional is found to be adequate, at least for monovalent ions. The size differences lead to an interesting ‘fine structure’ of the density and charge density profiles. Cohesive interactions between all species are shown to lead to significant changes in the density profiles.     

Structure and switching of single-stranded DNA tethered to a charged nanoparticle surface

Using a molecular theory, we investigate the temperature-dependent self-assembly of single-stranded DNA(ss DNA)tethered to a charged nanoparticle surface. Here the size, conformations, and charge properties of ss DNA are taken into account. The main results are as follows: i) when the temperature is lower than the critical switching temperature, the ss DNA will collapse due to the existence of electrostatic interaction between ss DNA and charged nanoparticle surface; ii)for the short ss DNA chains with the number of bases less than 10, the switching of ss DNA cannot happen, and the critical temperature does not exist; iii) when the temperature increases, the electrostatic attractive interaction between ss DNA and charged nanoparticle surface becomes weak dramatically, and ss DNA chains will stretch if the electrostatic attractive interaction is insufficient to overcome the elastic energy of ss DNA and the electrostatic repulsion energy. These findings accord well with the experimental observations. It is predicted that the switching of ss DNA will not happen if the grafting densities are too high.     

The origin of the attraction between like charged hydrophobic and hydrophilic walls confining a near-critical binary aqueous mixture with ions

The effect of ionic solute on a near-critical binary aqueous mixture confined between charged walls with different adsorption preferences is considered within a simple density functional theory. For the near-critical system containing small amounts of ions, a Landau-type functional is derived on the basis of the assumption that the correlation, ξ, and the Debye screening length, κ(-1), are both much larger than the molecular size. The corresponding approximate Euler-Lagrange equations are solved analytically for ions insoluble in the organic solvent. A nontrivial concentration profile of the solvent is found near the charged hydrophobic wall as a result of the competition between the short-range attraction of the organic solvent and the electrostatic attraction of the hydrated ions. An excess of water may be present near the hydrophobic surface for some range of the surface charge and ξκ. As a result, the effective potential between the hydrophilic and the hydrophobic surface can be repulsive far from the critical point, then attractive and again repulsive when the critical temperature is approached, in agreement with a recent experiment (Nellen et al 2011 Soft Matter 7 5360).     

Evaluation on performance of MM/PBSA in nucleic acid-protein systems

The molecular mechanics/Poisson-Boltzmann surface area (MM/PBSA) method has been widely used in predicting the binding affinity among ligands, proteins, and nucleic acids. However, the accuracy of the predicted binding energy by the standard MM/PBSA is not always good, especially in highly charged systems. In this work, we take the protein-nucleic acid complexes as an example, and showed that the use of screening electrostatic energy (instead of Coulomb electrostatic energy) in molecular mechanics can greatly improve the performance of MM/PBSA. In particular, the Pearson correlation coefficient of dataset II in the modified MM/PBSA (i.e., screening MM/PBSA) is about 0.52, much better than that (< 0.33) in the standard MM/PBSA. Further, we also evaluate the effect of solute dielectric constant and salt concentration on the performance of the screening MM/PBSA. The present study highlights the potential power of the screening MM/PBSA for predicting the binding energy in highly charged bio-systems.     

Mathematical simulation of interactions of protein molecules and prediction of their reactivity

A physical model of interactions of protein molecules has been developed. The regularities of their reactivity have been studied using electrostatics methods for two histone dimers H2A–H2B and H3–H4 assembled from monomers. The formation of histone dimers from different monomers has been simulated and their ability to the formation of stable compounds has been investigated by analyzing the potential energy matrix using the condition number. The results of a simulation of the electrostatic interaction in the formation of dimers from complete amino acid sequences of selected proteins and their truncated analogs have been considered. The calculations have been performed taking into account the screening of the electrostatic charge of charged amino acids for different concentrations of the monovalent salt using the Gouy–Chapman theory.