熔融ZnCl2结构的分子动力学模拟研究

熔融ZnCl2作为一种离子性共价性参半的典型熔盐, 其近邻结构在实验测量和分子动力学模拟方面均作过一些研究。本文依据新近EXAFS实验结果, 比较了不同的有效势下模拟得到的径向分布函数,表明KDR势可作为一种实用势。并进一步在KDR势模拟产生的瞬态构型基础上, 使用键序参数方法研究了晶态和熔融态ZnCl2中的近邻结构。结果表明, 和晶态ZnCl2一样, 在熔融ZnCl2中存在稳定的Zn/Cl正四面体结构, 但熔态和晶态Zn/Cl近邻结构热波方差σ不同。计算表明300K晶态σ=5.0℃, 613K熔融态σ=12.2℃。也对熔融ZnCl2的网络状结构和宏观输运性质进行了讨论。     

ZnCI~2-KCI系溶液的分子动力学模拟

用Busing离子间势,对ZnCI~2-KCI 系熔盐液的结构作分子动力学计算机模拟研究,模拟结果与中子衍射,X射线衍射,Raman光谱和红外光谱的若干结构相符.     

ZnCI~2-KCI系溶液的分子动力学模拟

用Busing离子间势,对ZnCI~2-KCI 系熔盐液的结构作分子动力学计算机模拟研究,模拟结果与中子衍射,X射线衍射,Raman光谱和红外光谱的若干结构相符.     

NaCl-NaBr系熔盐溶液的分子动力学研究

近年来，用计算机模拟馆公的结构和性质的研究已有较大进展[1，2]．但研究工作多集中在有阴离子相同、阳离子不同的盐组成的“同阴离子系”（commonanionsystems），而对由阳离子相同、阴离子不同的盐组成的“同阳离子系”（commoncationsystems）熔盐溶液则甚少研究．鉴于自然界和生产中同阳离子系也不乏实例，建立同阳离子系熔盐溶液的理论屯有必要．为止匕我们先选择NaCI－NaBr系熔盐溶液（同阳离子系的一个最简单的典型）为对象，开展分子动力学方法计算机模拟研究．1模型和计算方法采用标准文献中的计算模拟和方法，离子间劳用Fumi-…     

YCl3熔盐的分子动力学模拟研究

用Ｂｕｓｉｎｇ离子间势对ＹＣｌ３熔盐作分子动力学计算机模拟，得到的偏径向分布函数与中子衍射实验测量结果大致符合。Ｃｌ－Ｙ－Ｃｌ的角度分布表明熔体中存在ＹＣｌ＾３＋５类似正八面体结构或其“碎片”。     

基于机器学习势函数的熔盐体系分子动力学研究进展

熔盐是一类具有重要应用价值的熔融态材料,然而其微观结构与宏观性质之间的关系尚未完全探明,因此开展针对熔盐体系的分子动力学研究具有重要意义.针对高温熔盐体系的分子动力学研究以往主要依赖于传统分子动力学中力场的开发和第一性原理分子动力学的发展.近年来得益于机器学习和神经网络的加速发展,针对熔盐体系的机器学习势函数的开发工作取得了显著进展,其在探索熔盐配位化学和预测物理性质方面表现优异.本文首先梳理了熔盐领域内常用的分子动力学方法,重点介绍了机器学习势函数的发展现状;然后总结了机器学习势函数在熔盐研究方面的应用进展;最后展望了机器学习势函数在该领域的应用前景,并对可能存在的问题给出了建议.     

熔融NaCaF3、Na2CaF4和Na3CaF5的分子动力学模拟

通过分子动力学模拟，研究了熔盐溶液NaCaF_3、Na_2CaF_4和Na_4CaF_5体系，模拟表明，三种二元混合系的径向分布函数十分接近．由模拟所得到的摩尔混合焓很好地与实验值一致．混合焓与Na~+离子势阱深度之间表现出很好的线性关系．模拟表明，在Na_2CaF_4体系中，即NaF-CaF_2二元系处于低共熔混合组分比NaF:CaF_2＝2:1时，Na~+，Ca~(2+)和F~-离子的自扩散系数出现很大的反常．     

1-丁基-3-甲基咪唑氯化锌离子液体的合成、表征及催化性能

本文合成了1-丁基-3-甲基咪唑氯化锌([BMIM][Zn2Cl5])离子液体,通过红外光谱、TGA、DSC以及1H-NMR等方法对[BMIM][Zn2Cl5]进行了结构表征,实现了对于[BMIM][Zn2Cl5]的定性分析。以尿素醇解合成碳酸二乙酯反应为探针,考查了[BMIM][Zn2Cl5]离子液体的催化性能,结果显示,[BMIM][Zn2Cl5]表现出较好的催化活性及重复利用性能,碳酸二乙酯的收率接近30%。     

柱撑化合物Zn2Al-PW11Z的结构模型及酯化活性

杂多化合物是性能优异的酸型和氧化型或双功能催化剂[1－4]，而通式为的阴离子粘土通常具有减催化或还原催化性能[5，6]．因此，从在分子及原子水平上设计催化剂，调控催化性能观点出发，人们期望将体积较大的杂多阴离子嵌入阴离子粘土层间，合成大层间距的新型柱撑微孔材料．1988年Pinnavaia等人[7]首次报导了Zn2Al－V10O28是具有2．0nm孔径分布的中微孔材料．最近，笔者将单取代型Keggin结构杂多阴离子GeW11O39Z（H2O）6－（其中Z＝Ni2 和Cu2 ）和缺位Keggin结构的GeW11O嵌入Zn2Al－NO3层间，合成了通道高度为0．9nm的新型柱撑…     

超临界NaCl水溶液的分子动力学模拟

采用分子动力学模拟的方法对超临界NaCl水溶液的微观结构进行了研究.模拟发现在所研究超临界条件下,密度的变化比温度的变化对超临界NaCl水溶液的微观结构影响更大.温度及密度对Cl－ H2O径向分布函数的影响比对Na＋ H2O径向分布函数的影响要大.超临界条件下,各gNa＋－Cl－在0.261 nm处出现峰值,表明Na＋、Cl－之间发生了离子的缔合.超临界条件下,随温度增加,缔合作用增强；随密度增加,缔合作用减弱.本文工作为建立可适用于超临界条件下的电解质热力学模型提供了依据.     

Analysis of metastable defocusing spectra of lycoctonine bases having 7,8-methylenedioxy groups

The parameters of the MD spectra of the fragmentary ions of 21 lycoctonine alkaloids with 7,8-MDOGs have been investigated. On this basis, the monotypicity of the main fragmentation processes characteristic for the individual groups of compounds have been confirmed. A decrease in the number of common group characteristics of the MD spectra of the ions arising as the result of multistage breakdown processes is caused by alternative methods for their formation. This is not shown only by the doublet nature of the fragmentary ions. The results of a comparison of the MD spectra with the structures of the molecules have confirmed the hypothesis expressed previously concerning the 7,8-MDOG as the center of localization of the charge, competing with the nitrogen atom and facilitating the elimination of various substituents from the diterpene skeleton. A comparison has been made of two methods of evaluating the common nature of the fragmentation reaction: from the energies of the metastable transitions and from the relative intensities of the metastable peaks. The two methods give mutually supplementary information concerning the nature of the fragmentation processes.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 397–407, May–June, 1987.     

Coupling between lysozyme and glycerol dynamics: microscopic insights from molecular-dynamics simulations

We explore possible molecular mechanisms behind the coupling of protein and solvent dynamics using atomistic molecular-dynamics simulations. For this purpose, we analyze the model protein lysozyme in glycerol, a well-known protein-preserving agent. We find that the dynamics of the hydrogen bond network between the solvent molecules in the first shell and the surface residues of the protein controls the structural relaxation (dynamics) of the whole protein. Specifically, we find a power-law relationship between the relaxation time of the aforementioned hydrogen bond network and the structural relaxation time of the protein obtained from the incoherent intermediate scattering function. We demonstrate that the relationship between the dynamics of the hydrogen bonds and the dynamics of the protein appears also in the dynamic transition temperature of the protein. A study of the dynamics of glycerol as a function of the distance from the surface of the protein indicates that the viscosity seen by the protein is not the one of the bulk solvent. The presence of the protein suppresses the dynamics of the surrounding solvent. This implies that the protein sees an effective viscosity higher than the one of the bulk solvent. We also found significant differences in the dynamics of surface and core residues of the protein. The former is found to follow the dynamics of the solvent more closely than the latter. These results allowed us to propose a molecular mechanism for the coupling of the solvent-protein dynamics.     

Effect of the Dopant Nature on the Response of Sensor Arrays Based on Polypyrrole

The effect of the nature of the dopant on the response of a sensor array based on films of polypyrrole under the influence of the vapor of various organic solvents was studied. It was found the electric conductivity of the polymer can both increase and decrease during the action of analytes on electropolymerized films of polypyrrole. It is suggested that the main factors determining the response of polypyrrole are the morphology of the films and the type of charge carriers in the polymer, which depend on the nature of the dopant anion, and also the polarity and nucleophilicity/electrophilicity of the analyte. The responses of polypyrrole and polyaniline are compared, and the effect of the nature of the conducting polymer on them is analyzed. __________ Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 41, No. 5, pp. 265–271, September–October, 2005.     

Mode-coupling study on the dynamics of hydrophobic hydration II: Aqueous solutions of benzene and rare gases

The dynamic properties of both the solute and solvent of the aqueous solution of benzene, xenon and neon are calculated by the mode-coupling theory for molecular liquids based on the interaction-site model. The B-coefficients of the reorientational relaxation and the translational diffusion of the solvent are evaluated from their dependence on the concentration of the solute, and the reorientational relaxation time of water within the hydration shell is estimated based on the two-state model. The reorientational relaxation times of water in the bulk and within the hydration shell, that of solute, and the translational diffusion coefficients of solute and solvent, are calculated at 0-30 degrees C. The temperature dependence of these dynamic properties is in qualitative agreement with that of NMR experiment reported by Nakahara et al. (M. Nakahara, C. Wakai, Y. Yoshimoto and N. Matubayasi, J. Phys. Chem., 1996, 100, 1345-1349, ref. 36), although the agreement of the absolute values is not so good. The B-coefficients of the reorientational relaxation times for benzene, xenon and neon solution are correlated with the hydration number and the partial molar volume of the solute. The proportionality with the latter is better than that with the former. These results support the mechanism that the retardation of the mobility of water is caused by the cavity formation of the solute, as previously suggested by us (T. Yamaguchi, T. Matsuoka and S. Koda, J. Chem. Phys., 2004, 120, 7590-7601, ref. 34), rather than the conventional one that the rigid hydration structure formed around the hydrophobic solute reduces the mobility of water.     

Liesegang pattern formation in kappa-carrageenan gel

We report a new class of the spatial pattern formation process in which the gel plays essential roles. The system studied here is the solution of kappa-carrageenan in which potassium chloride is diffused. The solution transforms into the gel state with the diffusion of potassium chloride. Then the stripe pattern, which is perpendicular to the direction of the diffusion of potassium chloride, appears within the gel. The pattern thus formed in the gel is studied as a function of the concentration of the solution of potassium chloride. We find that the dense region of the stripe pattern consists of the liquid crystalline gel, whereas the dilute region is the amorphous gel. The transition from the amorphous gel to the liquid crystalline gel, hence, occurs in the gel state of kappa-carrageenan. The gel behaves as a pattern-forming substance as well as the supporting medium of the pattern in this system. The period and the thickness of the layers of liquid crystalline gel are analyzed. Both the period and the thickness of the layers are found to depend strongly on the concentration of the solution of potassium chloride.     

脉冲激光溅射下固液界面生长的碳纳米管及其机理初探

以脉冲激光束直接溅射浸在水中的单质碳样品，发现在固液界面也能产生的碳纳米管，实验还发现碳纳米管的形成与样品的结构有密切的关联：石墨的层状结构越完整，碳纳米管的形成越容易，而且石墨层面相对于激光束的取向也会显著地影响碳的生成。     

Electrothermal atomization—the way toward absolute methods of atomic absorption analysis

Considering the currently prevailing opinion that electrothermal atomizers are very susceptible to matrix interferences, an opinion which is contradictory to the optimistic forecasts of the first publications, the general status of the problem to date has been investigated.The first part of the paper deals with the ideal models of the two basic types of electrothermal atomizers, viz., those of the semi-enclosed and those of open type. The graphite cuvette and the Massmann furnace have been selected for discussion in their two commercial versions—the HGA and the CRA—of the first type of atomizers; the West filament and the combined atomizers—rod-in-flame and capsule-in-flame—of the second type. The models describing the distribution of atoms in the absorbing zone have been compared and the data obtained have been used to interpret the experimentally observed differences in the sensitivity of real atomizers.The second section of the paper discusses the conformity of real atomizers relative to ideal models and to the requirement of correctly recording the absorption by means of integrating the pulses. A marked time and space non-isothermality of the commercial atomizers has been established which makes it impossible to measure the integral absorption correctly. The graphite cuvette and the combined atomizers best meet the requirements of the ideal models. On the basis of the data obtained, the possible ways of bringing the semi-enclosed atomizers closer to ideal models have been explored. In this connection, the possibility of using a graphite platform for vaporizing samples in tube furnaces as well as using the temperature-controlled furnace and the pulse heated graphite furnace with a capacitance power supply has been examined. The application of the last method ensures time and space isothermality of the absorbing layer and reduces by 10–100 times the electric power input.The third section of the paper examines the thermochemical laws governing the possible chemical effects arising from the interaction between the analytes, on the one hand, and the furnace walls, the gaseous atmosphere and the matrix, on the other. A critical review has been carried out of the results of some recent publications on investigation of sample vaporization in graphite furnaces, which reveals the fact that the temperature of absorption appearance is rarely connected with the heat of vaporization of the free element. In most instances it is determined by the sum of the heat of decomposition of the non-volatile carbide and the heat of vaporization of the free element. Thermochemical examination of the stability of the compounds formed in the gaseous phase revealed the fact that besides forming monoxides, there is the possibility of forming monocyanides. In addition, the presence of large quantities of halogens causes partial binding of the analyte as gaseous monohalides, mainly monochlorides. In order to eliminate the latter effect, it has been suggested to employ higher atomization temperatures or to bind chlorine in a stable lithium monochloride. The efficiency of the proposed methods has been tested by experiment.Our research has shown that the main reasons for the unsatisfactory status of the problem concerning the matrix effects, are connected with the use of the amplitude (peak) method of recording the absorption, with the time and space non-isothermality of the absorbing layer of the commercial atomizers, and with the formation of gaseous monohalides. All these problems may be eliminated on the basis of theoretically proved and tested methods, some of which are discussed in this paper.     

Role of angular momentum conservation in unimolecular translational energy release: validity of the orbiting transition state theory

The translational kinetic energy release distribution (KERD) for the halogen loss reaction of the bromobenzene and iodobenzene cations has been reinvestigated on the microsecond time scale. Two necessary conditions of validity of the orbiting transition state theory (OTST) for the calculation of kinetic energy release distributions (KERDs) have been formulated. One of them examines the central ion-induced dipole potential approximation. As a second criterion, an adiabatic parameter is derived. The lower the released translational energy and the total angular momentum, the larger the reduced mass, the rotational constant of the molecular fragment, and the polarizability of the released atom, the more valid is the OTST. Only the low-energy dissociation of the iodobenzene ion (E approximately 0.45 eV, where E is the internal energy above the reaction threshold) is found to fulfill the criteria of validity of the OTST. The constraints that act on the dissociation dynamics have been studied by the maximum entropy method. Calculations of entropy deficiencies (which measure the deviation from a microcanonical distribution) show that the pair of fragments does not sample the whole of the phase space that is compatible with the mere specification of the internal energy. The major constraint that results from conservation of angular momentum is related to a reduction of the dimensionality of the dynamics of the translational motion to a two-dimensional space. A second and minor constraint that affects the KERD leads to a suppression of small translational releases, i.e., accounts for threshold behavior. At high internal energies, the effects of curvature of the reaction path and of angular momentum conservation are intricately intermeddled and it is not possible to specify the share of each effect.     

Orientation and distance dependent chiral discrimination in the first step of the aminoacylation reaction: Integrated molecular orbital and semi-empirical method (ONIOM) based calculation

Aminoacylation is a vital step in natural biosynthesis process of peptide and is the key step in correlating the realm of protein with the RNA world. Incorrect aminoacylation might lead to misacylation of d-amino acid in the tRNA which might cause synthesis of a hetero-peptide rather than natural homopeptide leading to the altered functionality of the peptide. However, the accuracy of this process is remarkable and leads to the attachment of the correct enantiomer of the amino acid with their cognate tRNA. Thus, the chiral discrimination is stringent. In the present work, we presented a combined ONIOM (ab initio/semi-empirical) study of the chiral discrimination in the first step of aminoacylation reaction based on a model of crystal structure of the oligomeric complex of histidyl-tRNA synthetase (HisRS) from Escherichia coli complexed with ATP and histidinol and histidyl-adenylate. The study reveals that the molecular mechanism of the chiral discrimination involves the amino acid, ATP as well as surrounding residues of the synthetase. Several factors are noted to be responsible for discrimination and explain the high level of stereospecificity of the process. The chirality of the amino acid of the substrate and its (principally) electrostatic interaction with the ATP is important for discrimination. The distance and orientational changes involved in the approach of the d-His towards the ATP is energetically unfavorable. The charge distributions on the His and ATP are important for the discrimination. Removal of the charges in the model drastically reduces the discrimination. Restricted nature of the mutual orientation within the cavity of the active site where the His and ATP are located during the change in orientation for the approach to form the adenylate makes the resultant interaction profile as different for l-His and d-His also influences chiral discrimination. The analysis of the transition state structure revealed that alteration of the chirality of the His destabilize the transition state by removing the favorable electrostatic interaction between the Glu-83 and NH₃⁺ group of the His substrate. The proximity of the surrounding residues as present in the active site of the synthetase with the His and ATP (the separation is of nanometer range) has influence of discrimination. The study provides a molecular mechanism of the retention of biological homochirality.     

On the contact conditions for the charge profile in the theory of the electrical double layer for nonsymmetrical electrolytes

In this paper, we generalize a recently derived expression of the contact value of the charge profile for the case of nonsymmetrical electrolytes. For the electrolytes with a single type of cation and anion, this relation can be presented as the sum of three contributions. One of them is the normal component of the Maxwell electrostatic stress tensor. The second one is the surface electrostatic property, which is defined as the integral of the product of the gradient of the electrical potential and the density distribution function of coions. The third term is the bulk contribution, which is defined by the sum for anions and for cations of the product of their charge and their partial pressure. For noncharged surfaces, only the last two terms are present and have the same sign in the case of size asymmetry. In the case of charge asymmetry, the contact value of the charge profile is the result of the competitions of bulk and surface terms in which the bulk term is dominant. Using both the contact theorems for the density and the charge profiles, the exact expressions for the contact values of the profiles of coions and counterions are obtained and some related properties are discussed. A semiempirical expression of the contact value of the charge profile is discussed in relation to our exact result.