Water Dynamics in Highly Concentrated Salt Solutions: A Multi-Nuclear NMR Approach

Living cells often contain compartments with high concentration of charged biomolecules. A key question pertinent to the function of biomolecules is how water dynamics are affected by interaction with charged molecules. Here, we study the dynamical behavior of water in an extreme condition, that is, in saturated salt solutions, where nearly all water molecules are located within the first hydration layer of ions. To facilitate disentangling the effects of cations and anions, our study is focused on alkali chloride solutions. Following a multi-nuclear NMR approach enabling direct monitoring of protons and the quadrupolar nuclei ⁷Li, ¹⁷O, ²³Na, ³⁵Cl, ⁸⁷Rb and ¹³³Cs, we investigate how the translational and rotational mobility of water molecules, chloride anion and corresponding cations are affected within the constrained environment of saturated solutions. Our results indicate that water molecules preserve a large level of mobility within saturated alkali chloride solutions that is significantly independent of adjacent ions.     

电解质水溶液结构研究进展及前景*

叙述盐湖中主要离子Li⁺ 、Na⁺ 、K⁺ 、Mg²⁺ 、Ca²⁺ 、Cl^- 、SO^2-₄ 、NO^-₃ 的水溶液和纯水的结构, 简单介绍了主要的研究方法, 分析讨论了溶液结构研究的现状和发展前景。     

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．     

熔盐中熟化处理提高BiFeO3的可见光催化活性

研究发现, 通过熔盐中熟化处理可以显著地提高BiFeO3的可见光催化活性.     

Fluorescence Probe Studies of Ionic Micelles in Concentrated Salt Solutions

We have investigated the effect of salt concentration and temperature on the average aggregation number and micro-polarity of the interior of micelles of sodium dodecyl sulfate (SDS). sodium tetradecyl sulfate (STDS) and lithium dodecyl sulfate (LiDS). The transient fluorescence decay of micelle-solubilized pyrene has been measured and analyzed. An exponent weighted average aggregation number <n>_e was obtained by this technique. For SDS and STDS in NaCl solution, <n>_e increases as the temperature is lowered or salt concentration is increased <n>_e increased from ～ 50 to ～ 250 over [NaCl] = 0 to 0.8 M. Due to the strong counterion binding of lithium in the micellar solution, the LiDS micelle is much, smaller and does not increase appreciabily even at [LiCl] =0.8 M. From the fluorescence spectrum fine structure of pyrene and the fluorescence decay of the monomer and excimer, we can understand the local polarity and the water penetration to the interior of the micelle upon addition of salts and with changing temperature. The interior of the micelle becomes more nonpolar as the salt concentration is increased and the temperature is lowered. A complete kinetic analysis of the time–dependence of the fluorescence is given. The kinetic analysis is in agreement with the results reached by fluorescence spectral analysis.     

熔盐电化学创新研究——武汉大学电化学研究中心熔盐电化学研究工作简介

简要介绍近3年武汉大学电化学研究中心在熔盐电化学方面的若干研究进展:1)熔盐电解固态化合物制备单质硅及其合金以及无机功能材料;2)适于高温熔盐的全密封长寿命Ag/AgCl参比电极和可负载微量粉末的金属腔(坑)工作电极新技术;3)“三相界线电化学”新概念以及描述三相界线在薄层固态化合物电解还原过程中扩展变化的薄层模型.     

采用稀释成盐法从富硼浓缩盐卤中合成的镁硼酸盐化合物及其结构与性质

通过稀释成盐法在富硼浓缩盐卤体系Na-K-Mg-Cl-SO₄中合成了一种新的六硼酸镁Mg[B₆O₇(OH)₆]·5H₂O化合物。根据X射线粉末衍射数据对其晶体结构进行了精修,并采用红外及拉曼光谱法对其结构进行了表征,分析了其光谱及结构特征。结果表明,该化合物由1个Mg原子、1个B₆O₇(OH)₆基团和5个H₂O分子构成,Mg原子以六配位形式与氧结合形成畸变MgO₆八面体构型;热重分析表明,高温分解过程该化合物脱水转化为四硼酸镁MgB₄O₇;通过紫外可见漫反射法求得其禁带宽度为4.44 eV。     

Imperfections in the aqueous lattice of clathrates,as detected by electron trapping

X-ray analysis has been used to elucidate the structure of hydrates, especially of aqueous clathrates, but it has not given information on imperfections occuring in crystals. Other methods, sensitive to the disturbance of structural periodicity, have to be applied to detect and identify the defects. Pulse radiolysis shows identical, intense transient spectra in a group of hydrates which exhibit certain common features. The spectrum ( _max = 620 nm) is tentatively ascribed to the electron trapped in a single water molecule vacancy in the aqueous moiety of the crystal. The pre-existing specific defect is formed during the crystallization process. The optical absorption spectrum is similar to the hydrated electron spectrum in liquid water or aqueous solutions. The nature of the traps is deduced from the known structure of clathrates, in which small anions substitute for one water molecule and may be displaced. Among investigated salt hydrates, amine hydrates and true clathrate hydrates, not all compounds show the ability to trap electrons. The present paper discusses the conditions for the occurrence of water molecule vacancies in the aqueous moiety of the clathrate and the general aspects of the observed phenomenon. A need to investigate imperfections by other methods is also stressed, although such alternatives are not yet available.     

The Study of Water Structure in Aqueous Solutions of Butoxyethanol by Enthalpy of Mixing Measurements

In order to confirm the existence of regions I and II in aqueous solutions of butoxyethanol(BE), the concentration and temperature dependences of enthalpies of mixing of aqueous BE solutions with some organic solvents were measured. It has been found that the increments of apparent enthalpies of mixing per mole of water with respect to the mole fraction of BE change irregularly at a certain concentration. This concentration nearly corresponds to the reported boundary between regions I and II. Although similar behavior has also been observed in aqueous solutions of iso-butoxyethanol, aqueous solutions oftert-butoxyethanol have shown no anomalous behaviors. This revised version was published online in July 2006 with corrections to the Cover Date.     

熔盐电化学还原二氧化碳制备碳材料研究进展北大核心CSCD

二氧化碳浓度持续升高导致的温室效应已在全球范围内引发极端天气、冰川融化等一系列生态环境问题。为降低二氧化碳含量,改善气候变暖带来的恶劣影响,研发高效、绿色、安全的二氧化碳处理技术,促进碳资源循环可持续发展刻不容缓。熔盐离子液体作为一种良好的电化学转化介质,为二氧化碳还原提供了一条极具应用前景的技术路线。综述了国内外近几年高温熔盐中二氧化碳的捕获与电化学还原的研究,简述了熔盐电沉积碳的电化学机理和热力学机制,对不同形貌高附加值碳材料:无定形碳、碳球和碳纳米管的制备进行了总结,最后对未来发展方向做出展望。     

Low Temperature Molten Salt Synthesis of Perovskite-type ACeO3(A=Sr,Ba) in Eutectic NaCl-KCl

A molten salt method was developed for the synthesis of ACeO₃(A=Sr, Ba) with perovskite structure at 750 ℃(SrCeO₃) and 850 ℃(BaCeO₃) in the eutectic NaCl-KCl. The synthetic temperature was much lower than that of the conventional method(generally>1000 ℃). The structure and morphology of the product were characterized by means of X^-ray diffraction(XRD), field emission scanning electron microscopy(FESEM) and transmission electron microscopy(TEM). The results show that the synthesized octahedral SrCeO₃ crystallizes in the orthorhombic system with the unit cell parameters of a=0.85855 nm, b=0.61523 nm, c=0.60059 nm, and the synthesized cuboid BaCeO₃ crystallizes in the cubic system with the unit cell parameter of a=0.43962 nm. The result of X^-ray photoelectron spectroscopy(XPS) analysis indicates that both Ce⁴⁺ and Ce³⁺ exist in the two structures, and the Ce⁴⁺/Ce³⁺ peak area ratios for SrCeO₃ and BaCeO₃ are 1.93 and 2.12, respectively. Meanwhile, the adsorbed/lattice oxygen ratios(1.87 for SrCeO₃ and 3.04 for BaCeO₃) indicate the existence of a lot of oxygen vacancies in the structures of SrCeO₃ and BaCeO₃, which indicates a far-reaching significance to study the corresponding physicochemistry performance.     

Structure of MgSO_4 in Concentrated Aqueous Solutions by X-Ray Diffraction

Detailed time-and-space-averaged structure of MgSO4 in the concentrated aqueous solutions was investigated via X-ray diffraction with an X’pert Pro θ-θ diffractometer at 298 K, yielding structural function and radial distribution function(RDF). The developed KURVLR program was employed for the theoretical investigation in consideration of the ionic hydration and ion association. Multi-peaks Gaussian fitting method was applied to deconvolving the overlapping bands of Differential radial distribution function...     

The Measurement of Heat Capacity Differences Due to the Change of Water Structure in Aqueous Solutions of Organic Compounds

In order to observe more directly the structural organization of water molecules around a non-polar molecule in an aqueous solution, heat capacity differences between two kinds of solutions (solution I and II) of quaternary ammonium salts were measured. In the solution I stable water structure was retained as much as possible and in the solution II water structure was destroyed either by heating to high temperatures or by irradiating with ultrasonic waves. It was found that the heat capacity differences ((C_p)_II-(C_p)_I) were slightly positive and its maximum values corresponded to 7-8 percent of the heat capacity of pure water itself. This revised version was published online in August 2006 with corrections to the Cover Date.     

Cerium Salt Promoted Homocoupling Reaction of Dialkylanilines in Water

Highly regioselective homocoupling of N,N-dialkylanilines can be achieved in water with cerium reagents, in which various N,N,N′,N′-tetraalkylbenzidines are obtained from N,N-dialkylanilines either by direct oxidation by cerium（Ⅳ）reagents or by cerium（Ⅲ） reagents in the presence of hydroperoxide.     

强酸性环境中氧氟沙星的质子化模型研究

利用核磁共振波谱技术研究了不同浓度硫酸溶液中氧氟沙星(OFL)的1H,19F和13C核磁共振谱,对不同硫酸浓度引起的δH,δF,δC和JFC耦合常数的变化进行比较分析,由此推测其结构状态.综合1H,19F和13C核磁共振谱特点及其变化,提出OFL分子在强酸性环境中N1'被进一步质子化的结构模型.在浓硫酸溶液中,N1'被进一步质子化,并与F9形成氢键(N1'—H+┈F9),该结构使分子的共轭程度大幅降低,导致其荧光发射波长、荧光激发波长及紫外吸收波长均发生蓝移.硫酸溶液中氧氟酸和甲基氧氟沙星的荧光光谱行为进一步证明了OFL分子在浓硫酸溶液中质子化模型的合理性.     

二元弱酸酸式盐溶液中微粒浓度大小的比较*

利用热力学计算软件HSC Chemistry动态探究了二元弱酸酸式盐溶液的稀释过程,通过图示法研究了NaHCO₃,NaHS,NaHSO₃,NaHC₂O₄等2类典型的二元弱酸酸式盐溶液浓度与各微粒浓度之间的关系及变化规律,方便快捷地比较了不同浓度范围内溶液中各微粒浓度大小的排序,有利于厘清二元弱酸酸式盐溶液的电离平衡过程。     

氯化物熔盐体系中Gd的电化学行为及提取效率的评估

研究了773 K时GdCl₃在LiCl-KCl熔盐体系中在Mo和Al 电极上的电化学行为和热力学特性. 利用开路计时电位曲线得到了Gd(III)/Gd(0)体系在723-873 K温度范围的平衡电极电位和表观电极电位. 结果表明: 平衡电极电位和表观电极电位随着温度的升高而变正. 通过吉布斯自由能变进一步计算得到了GdCl₃在LiCl-KCl熔盐体系中不同温度下的活度系数. 结合稳态极化曲线, 求得去极化值, 并通过热力学计算, 求得773 K时Gd的理论提取效率. 在773 K时, 在LiCl-KCl-GdCl₃体系中, 以Al 为工作电极在-1.5 V左右通过恒电位电解提取Gd, 电解20 h后实际电解提取效率为94.22%. 对电解沉积物进行X射线衍射(XRD)分析, 检测到了Al₃Gd合金相.     

Allylation of Carbonyl Compounds Mediated by Aluminum/Fluoride Salts in Water

A novel mediator (Al/KF) has been developed and employed in the Barbier‐type alkylations of various aldehydes and ketones with alkyl halide in water. The carbonyl compounds could be effectively converted into corresponding homoallylic alcohol in good yields only when allyl bromides or substituted allyl bromides were used as halides. Aromatic aldehydes could afford homoallylic alcohols in high yields, unfortunately, the allylation of aromatic aldehyde substituted by nitro‐ or amino‐group could not proceed smoothly, and the allylation yields of ketones and aliphatic carbonyl compounds were lower under the same condition. The diastereoselectivity and regioseletivity of the reaction have also been studied, the predominant products preferred the erythro‐ or anti‐isomer in dominant γ‐adduct by using Al/KF mediated allylation of benzaldehydes with cinnamyl bromide and ethyl 4‐bromo‐2‐butenoate in water.     

On the Structure of the Arginine-carboxylate Salt Bridge: A Density Functional Theory Study

The arginine-carboxylate salt bridge, which represents about 40% of the pairs of ionic groups within proteins, plays a crucial role in determining the structures and functions of proteins1. Numerous experimental evidences have indicated that this type of salt bridge, which usually includes the arginine-glutamate pair and the arginine-aspartate pair, should stay in a zwitterionic state rather than in a neutral one2. This viewpoint has been widely accepted and in usual it is directly used in the…     

毛细管气相色谱法测定水溶液中榄香烯哌啶盐的含量

 建立了一种准确测定水溶液中榄香烯哌啶盐含量的方法。样品水溶液经碳酸钠中和 ,并用含正十八烷(内标 )的正庚烷溶液萃取后 ,采用毛细管气相色谱法进行分析。方法的线性范围为 1 0 g/L～ 1 0 0 g/L ,精密度小于 2 % ,平均回收率为 99 96% ,RSD为 0 46% (n =5)。