甲酰胺水溶液的分子动力学模拟

为了解重要的生化模型甲酰胺在水溶液中的微观结构, 采用全原子力场在全浓度范围内对甲酰胺溶液进行了分子动力学模拟, 得到了溶液的径向分布函数, 分析计算了溶质和溶剂分子间的相互作用, 对甲酰胺和水分子的氢键缔合情况进行了分析. 研究发现羰基侧的H原子与水分子能形成C—H…O弱相互作用. 在作者早期的研究中发现, 此相互作用对于阻碍甲酰胺的异构化具有重要意义, 特别是当甲酰胺在溶液中含量增大时, 此相互作用更加不能忽视. 全浓度溶液的模拟表明, 甲酰胺在稀浓度区可以促进水局部结构的增强, 随FM浓度增加, 由水的自身缔合转变为水与FM的交叉缔合, 在FM高浓度区, 两者的交叉缔合将逐渐被甲酰胺自身的线状缔合代替.     

聚丙烯酰胺稀溶液的分子模拟

聚丙烯酰胺(PAM)是一类重要的线性水溶性聚合物,具有"百业助剂"之称,因此对其溶液性质的研究意义重大.在溶液质量浓度约为1g·mL-1的基础上,分别构建了含有不同水分子数的溶液模型.采用分子动力学(MD)方法模拟分析了不同温度下非离子型的聚丙烯酰胺(PAM-H)和阴离子型的聚丙烯酰胺(HPAM)在纯水溶液及含不同质量分数NaCl的水溶液中的回旋半径(Rg).结果发现,不同温度下PAM-H和HPAM的抗盐性能的模拟结果与实验数据基本吻合,水分子数不同的溶液模型所得模拟结果趋势没有明显变化,为了提高模拟效率,选取含有2000个水分子的溶液模型分析HPAM链中氧负离子及氧原子的径向分布函数,从微观结构模拟说明了HPAM水溶液粘度随NaCl质量分数增加而减小,且HPAM比PAM-H具有较好的增粘效果及较差的抗盐性能的原因.     

混合电解质的电导测定

电导测定为研究离子与离子之间的缔合效应、离子与溶剂的相互作用及溶剂结构提供了一个有效手段 .目前 ,电解质水溶液、电解质非水溶剂体系的电导数据却很缺乏 ,而混合电解质体系的电导测定在理论及应用方面都很重要 .作为全面系统地考察金属氯化物的混合电解质的电导性质变化规律 ,前文已测定了 Na Cl- KCl- H2 O体系 [1] 、 Na Cl- Rb Cl- H2 O体系及 KCl- Rb Cl- H2 O体系的电导值 [2 ] ,本文用自行设计的电导池测定了 Ca Cl2 - H2 O,Ca Cl2 - Na Cl- H2 O,Ca Cl2 - KCl- H2 O体系在 2 98.1 5 K时的低浓度电导数据 ,探讨了…     

碱性水溶液中4Na2SO4·2H2O2·NaCl的分解动力学

以低浓度(30(wt)%)的双氧水制备了硫酸钠-过氧化氢-氯化钠加合物,各组分的含量均接近于理论值,其纯度为99.3%;在323K和333K下,研究了4Na2SO4*2H2O2*NaCl于碱性水溶液中的分解动力学.结果表明,在不同条件下,其分解均为一级反应;随着温度和pH的增加,其分解速率加快.置信水平为95%时k和C0的联合置信域均为椭圆形且面积较小,求得的参数精确度较高;优化出的模型能较准确地描述4Na2SO4*2H2O2*NaCl于碱性水溶液中的分解过程.     

特殊缔合体系TFE水溶液分子动力学模拟

三氟乙醇(TFE)水溶液是一类特殊的缔合体系. 采用分子动力学模拟方法结合核磁共振化学位移研究了TFE水溶液体系全浓度范围的氢键网络, 并对动力学模拟结果和核磁共振化学位移进行了比较. 从径向分布函数(RDF)发现, TFE水溶液中存在着强氢键, 而体系中的C—H…O弱相互作用较为明显, 也不能忽略. 氢键网络分析发现TFE 水溶液体系的氢键大致分为以下三个区域: 在水富集区域, 水分子倾向于自身缔合形成稳定的簇结构, 随着TFE 浓度的增加, 水的有序结构受到破坏, 水分子和TFE分子发生交叉缔合作用形成氢键; 在TFE富集区域, 水分子较少, TFE分子自身通过氢键形成多缔体结构. 此外, 分子动力学统计的平均氢键数的变化和文献报导的核磁共振化学位移变化趋势相同, 实验和理论的结果吻合较好.     

超临界正己烷—甲醇溶液体系的Monte Carlo模拟：浓度对溶液构型？…

用Ｍｏｎｔｅ Ｃａｒｌｏ分子模拟方法对正己烷－甲醇溶液体系处于临界状态时微观结构随浓度变化的情况进行了研究。模拟采用随机边界条件，得到了不同浓度条件下体系各基团的径向分布函数。结果表明，在溶液临界状态，正己烷分子有较强的聚集行为，随着溶液中甲醇浓度的变大，正己烷分子的聚集程度逐渐下降；甲醇分子周围正己烷分子的分布有一个最佳的浓度范围，在甲醇浓度为２２．５％时，配位数达到最大；超临界正己烷－甲醇溶液     

不同浓度下NaCl水溶液的分子动力学模拟

采用分子动力学模拟的方法在298K时对1.33mol/L,2.71mol/L,4.14mol/L和5.12mol/L的NaCl水溶液的微观结构进行了研究。模拟发现浓度对离了近程水化结构的影响不大,浓溶液中Na^+,Cl^-之间有两种缔合方式,接触缔合离子对和溶剂分隔的缔合离子对。这表明在建立可适用于高浓度条件下的电解质溶液热力学模型时应考虑离子缔合的贡献。     

不同浓度下NaCl水溶液的分子动力学模拟

采用分子动力学模拟的方法在298K时对1.33mol/L,2.71mol/L,4.14mol/L和5.12mol/L的NaCl水溶液的微观结构进行了研究。模拟发现浓度对离了近程水化结构的影响不大,浓溶液中Na^+,Cl^-之间有两种缔合方式,接触缔合离子对和溶剂分隔的缔合离子对。这表明在建立可适用于高浓度条件下的电解质溶液热力学模型时应考虑离子缔合的贡献。     

剪应力下弱作用势胶体颗粒聚团的特点

探讨了不同剪应力下，具有Ｌｅｎｎａｒｄ－Ｊｏｎｅｓ势的胶体颗粒聚团的结构特性，包括簇团的大小分布，径向分布函数，分形维数和原子配位数。研究表明，在弱作用力下，胶体簇团的分布随剪应力的增加而趋向小簇团一边；径向分布函数曲线随剪应力的增加而降低，胡在近程距离内降低得最多；分形维数随剪应力的增加表现为先增加后减小的趋势，其值随模拟条件的不同而在１．９－２．４之间变动。剪应力“场”对分形维数的大小没有太大     

磷酸二氢铵水溶液构型能删和径向分布函数的分子动力学模拟

采用分子动力学模拟对不同温度下磷酸二氢铵水溶液的构型能和径向分布函数进行了研究．磷酸二氢根被看作七节点模型,铵离子被看作五节点模型,而水分子则被看作简单点电荷模型．在饱和温度附近,体系局域粒子数密度有波动．373-400K的溶液势能增长缓慢表明磷酸二氧铵部分分解．磷酸二氢根中的氧原子与铵离子中氢原子的径向分布函数在三种不同温度下呈现明显不同,表明溶液中平均氢键数目随温度的变化明显改变．温度对磷酸二氢根中的氧原子和氧原子的结合有一定的影响,而在饱和溶液中有更多的生长基无产生．     

Hydration of NaCl on glassy, supercooled-liquid, and crystalline water

Interactions of sodium chloride with amorphous and crystalline water films, leading to the possible formation of a dilute NaCl solution, were investigated using time-of-flight secondary ion mass spectrometry as a function of temperature. A monolayer of NaCl tends to remain on the surface or in subsurface sites of thick amorphous solid water films (200 monolayers); the Na+ ion is hydrated preferentially, whereas the Cl- ion is segregated at the surface. The hydration structure of NaCl is fundamentally unchanged for viscous liquid water that appears at temperatures higher than 136 K. The solubility of NaCl increases abruptly at 160 K because of the evolution of supercooled liquid water, which can hydrate the Cl- ion efficiently. However, the diffusion of the ions toward the bulk of supercooled liquid water is interrupted by crystallization; therefore, the dilute NaCl solution that is characterized by completely separated Na+-Cl- pairs may not be formed. When NaCl is deposited on the crystalline ice film, hydration of NaCl is enhanced above 160 K as well, indicating that a liquidlike phase coexists with crystals.     

The features of structurization of the dilute aqueous solution of lithium chloride at the near-critical and supercritical conditions

Method of integral equations in the RISM approximation was used for the study of the structural properties of the dilute aqueous solution of lithium chloride in the near-critical and supercritical state. The following general trends of structural changes in the solution at its transition from the standard conditions to the supercritical conditions were revealed: destruction of the solvent tetrahedral lattice, thermal dehydration of the cation and anion, and an increase in the contact association. We found that the effect of temperature on the decrease in the fraction of the hydrogen-bonded solvent molecules and the value of the thermal dehydration of the ions is comparable with the influence of the density on the same characteristics. The process of ion association is affected predominantly by temperature, the effect is maximal in the subcritical region.     

超临界水中碳酸钠团簇成核与生长分子动力学模拟

应用分子动力学方法研究了碳酸钠颗粒在超临界水中的成核与生长过程. 计算了温度为700-1100 K、压力在23-30 MPa下碳酸钠的团聚过程, 计算时间为1 ns. 对体系结合能与径向分布函数的分析表明, 碳酸钠成核过程主要受静电作用的影响. 在超临界态下, 水分子与Na⁺和CO₃^2- 之间的静电作用降低, Na⁺与CO₃^2- 能够很容易碰撞形成Na₂CO₃小团簇. 在Na₂CO₃整个成核过程中, 单个离子的碰撞在前50 ps 内完成, 同时离子碰撞速率达到10³⁰ cm^-3·s^-1. 另外, 在成核阶段温度的影响比压力更加明显, 温度越高, 离子碰撞速率越快, 形成的初始团簇越多. 而压力对Na₂CO₃团簇的进一步生长影响较大.     

电化学石英晶体微天平研究高氯酸钠水溶液中活性炭电极的离子存储行为

以电化学石英晶体微天平(EQCM)为主要测试手段,在不同浓度的高氯酸钠(NaClO4)水溶液中研究了水合离子吸附到活性炭电极孔隙过程中电极的质量变化.对于每种电解液,根据Raman光谱和EQCM数据分别计算了本体溶液中和电极/溶液界面上Na+的水合数.通过比对这两组Na+水合数,探讨了Na+存储到活性炭负极过程中的去溶剂化效应.     

Miscibility of sodium chloride and decyl methyl sulfoxide in the adsorbed film and micelle

The surface tension of aqueous solutions of a sodium chloride (NaCl)-decyl methyl sulfoxide (DeMS) mixture was measured as a function of the total molality of the mixture and the mole fraction of DeMS in the mixture at 298.15 K under atmospheric pressure. The total surface density of the mixture and the mole fraction of DeMS in the adsorbed film and micelle were numerically evaluated by applying the thermodynamic treatment of surfactant mixture to the NaCl-DeMS mixture. Miscibility of NaCl and DeMS in the adsorbed film and micelle was clarified by use of the phase diagram of adsorption and micelle formation. Positive adsorption of NaCl was observed in the presence of DeMS and attributed to attractive interaction between the polar head group of DeMS molecule and Na+ or Cl- ions in the adsorbed film and micelle. The results were compared with those of NaCl-octyl methyl sulfoxide and NaCl-decyldimethylphosphine oxide mixtures to elucidate the structure effect of nonionic surfactant on the miscibility.     

Solvation of sodium chloride in the 1-butyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide ionic liquid: a molecular dynamics study

We report molecular dynamics studies on the solvation of sodium chloride in the 1-butyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide ionic liquid ([BMI][Tf2N] IL). We first consider the potential of mean force for dissociating a single Na+Cl- ion pair, showing that the latter prefers to be undissociated rather than dissociated (by ca. 9 kcal/mol), with a free energy barrier of ca. 5 kcal/mol (at d approximately 5.2 A) for the association process. The preference for Na+Cl- association is also observed from a 100 ns molecular dynamics simulation of a concentrated solution, where the Na+Cl- ions tend to form oligomers and microcrystals in the IL. Conversely, the simulation of Na13Cl14- and Na14Cl13+ cubic microcrystals (with, respectively, Cl- and Na+ at the vertices) does not lead to dissolution in the IL. Among these, Na14Cl13+ is found to be better solvated than Na13Cl14-, mainly due to the stronger Na+...Tf2N- interactions as compared to the Cl-...BMI+ interactions at the vertices of the cube. We finally consider the solid/liquid interface between the 100 face of NaCl and the IL, revealing that, in spite of its polar nature, the crystal surface is solvated by the less polar IL components (CF3(Tf2N) and butyl(BMI) groups) rather than by the polar ones (O(Tf2N) and imidazolium(BMI) ring). Specific ordering at the interface is described for both Tf2N- anions and BMI+ cations. In the first IL layer, the ions are rather parallel to the surface, whereas in the second "layer" they are more perpendicular. A similar IL structure is found at the surface of the all-neutral Na0Cl0 solid analogue, confirming that the solvation of the crystal is rather "apolar", due to the mismatch between the IL and the crystal ions. Several comparisons with water, methanol, or different BMI+-based ILs as solvents are presented, allowing us to better understand the specificity of the ionic liquid-NaCl interactions.     

Mechanism of OH radical hydration: a comparative computational study of liquid and supercritical solvent

Flexible models of the radical and water molecules including short-range interaction of hydrogen atoms have been employed in molecular dynamic simulation to understand mechanism of (●)OH hydration in aqueous systems of technological importance. A key role of H-bond connectivity patterns of water molecules has been identified. The behavior of (●)OH(aq) strongly depends on water density and correlates with topological changes in the hydrogen-bonded structure of water driven by thermodynamic conditions. Liquid and supercritical water above the critical density exhibit the radical localization in cavities existing in the solvent structure. A change of mechanism has been found at supercritical conditions below the critical density. Instead of cavity localization, we have identified accumulation of water molecules around (●)OH associated with the formation of a strong H-donor bond and diminution of non-homogeneity in the solvent structure. For all the systems investigated, the computed hydration number and the internal energy of hydration Δ(h)U showed approximately linear decrease with decreasing density of the solvent but a degree of radical-water hydrogen bonding exhibited non-monotonic dependence on density. The increase in the number of radical-water H-acceptor bonds is associated with diminution of extended nets of four-bonded water molecules in compressed solution at ~473 K. Up to 473 K, the isobaric heat of hydration in compressed liquid water remains constant and equal to -40 ± 1 kJ mol(-1).     

Isopiestic Study of Water + Mannitol(sat) + Sodium Chloride + Ammonium Chloride + Barium Chloride at <Emphasis Type="Italic">T</Emphasis> = 298.15 K and Comparison with the Ideal-Like Solution Model

Isopiestic measurements have been carried out at the temperature 298.15 K for the quinary system (water + mannitol(sat) + sodium chloride + ammonium chloride + barium chloride) saturated with mannitol and its ternary sub-systems (water + mannitol(sat) + sodium chloride), (water + mannitol(sat) + ammonium chloride) and (water + mannitol(sat) + barium chloride). Taking aqueous sodium chloride as reference solutions, osmotic coefficients of the other aqueous solutions were determined. The experimental results show that the isopiestic activities of the quinary system in relation to its ternary sub-systems are in excellent agreement with the ideal-like solution model.     

Thermodynamic linkage of ion binding and hydration in myofibrillar protein solutions determined from multinuclear spin relaxation studies

The mechanisms for the anionic and cationic interactions with myofibrillar proteins in aqueous solutions were investigated by nuclear magnetic resonance over a wide range of salt concentration. Markedly nonlinear dependeces of the ¹⁷O and ²³Na NMR transverse relaxation rates on salt concentration were analyzed with a thermodynamic linkage model of salt-dependent solubility and hydration (ligand-induced association model), according to Wyman's theory of linked functions. Nonlinear regression analysis of both ¹⁷O and ²³Na NMR data suggested cooperative, reversible binding of hydrated ions to myofibrillar proteins. Both ions and water were found to exchange fast, on the NMR timescale, between the binding sites of the myofibrillar proteins and the aqueous solution. At sodium chloride concentrations higher than about 0.1 grams salt/gram water, ion activities have marked effects upon the NMR relaxation rates of both ions and water. A salt activity model allowed quantitative fitting of the NMR data at high salt concentrations. The effect of neglecting the ion activity in solutions of myofibrillar proteins was also estimated and compared with the ligand-induced, cooperative association model for myofibrillar proteins. The comparison between the ¹⁷O and ²³Na results strongly suggests that water is exchanged as the hydrated ion species between the myofibrillar protein binding sites and the bulk, aqueous solution.