L-丝氨酸在正丙醇-水混合溶剂中的体积性质

应用精密数字密度计测定了298.15 K时不同组成的L-丝氨酸-正丙醇-水体系的密度, 计算丝氨酸的表观摩尔体积、极限偏摩尔体积、迁移偏摩尔体积和水化数. 根据结构水合作用模型讨论了迁移偏摩尔体积和水化数的变化规律. 结果表明, 丝氨酸两性离子部分和亲水侧链与正丙醇羟基间的相互作用对其迁移体积有正贡献, 且占主导地位. 丝氨酸在正丙醇-水混合溶剂中的迁移偏摩尔体积为正值, 且随醇浓度的增大而增大. 丝氨酸在正丙醇-水混合溶剂中的水化数随溶液中醇浓度的增加而减小.     

醇/水混合溶剂中碱性聚合物电解质独特的溶解行为

Self-aggregated quaternary ammonium polysulfone (aQAPS) is a high-performance alkaline polymer electrolyte that has been applied in alkaline polymer electrolyte fuel cells (APEFCs). For a long time, N, N-dimethyl formamide (DMF) has been considered the best solvent to dissolve aQAPS, but the high boiling point of DMF makes it hard to remove from the electrodes, which potentially poisons the electrocatalysts. Our recent experiments have shown that although aQAPS is unable to dissolve in ethanol, n-propanol, or water, it can dissolve in the mixture of these alcohols and water. This peculiar dissolution behavior significantly facilitates the fabrication of the membrane electrode assembly (MEA) for APEFCs, even though it has not been understood. In this work, atomistic molecular dynamics (MD) simulations were employed to study the dissolution behavior of aQAPS in different solvents, including water, methanol, ethanol, n-propanol, DMF, and the mixture of these non-aqueous solvents and water. The conformation of the aQAPS chain in pure solvents agreed well with the dissolution behavior observed in the experiments, even though in the water-containing mixed solvents, the aQAPS chain tended to be in a more contracted state. The simulations further revealed that the water component in the mixed solvents played dual roles. On one hand, the hydrocarbon chain of aQAPS was compressed to a contracted state upon the addition of water, because of the hydrophobic effect. On the other hand, water can drive the dissociation of the counterion (Cl^{–­ ­ ­} ), which led to an enhancement in the solute-solvent interaction energy and thus facilitated the dissolution of aQAPS. In most mixed solvents, the compensation of these two interactions resulted in a general increase in the total solute-solvent interaction energy; therefore, the addition of water was energetically favorable for the dissolution of aQAPS. This study not only furthers our fundamental understanding of the dissolution behavior of polyelectrolytes but also is technologically significant for the development of better APEFCs.     

水-乙醇混合溶剂中弱酸电离的溶剂效应

本文用LKB2277Bioactivity monitor微量流动热量计测定卤代乙酸. 脂肪酸在水-乙醇混合溶剂中的标准电离焓,计算了热力学函数.结合文献数据,计算各酸根离子从水迁移到混合溶剂的迁移自由能,并讨论溶剂效应对弱酸电离的影响1.     

在N,N-二甲基甲酰胺/水混合溶剂中制备偶氮聚电解质自组装膜

利用静电吸附逐层自组装方法在有机溶剂N,N二甲基甲酰胺(DMF)和H2O的混合介质中制备非水溶性偶氮聚电解质自组装多层膜.研究了DMF和H2O的配比对自组装膜生长、结构与表面形态的影响.结果表明,DMFH2O的混合溶剂是非水溶性偶氮聚电解质自组装的理想介质,二者之间的配比对自组装膜的生长速度,膜的结构以及表面形态均有显著影响.随着混合溶液中DMF含量的升高,自组装膜的生长速度逐渐下降但线形生长关系越来越好,所得自组装膜中偶氮生色团的H聚集程度逐渐下降,而且自组装膜的表面越来越平整.     

氨基酸在甲醇-水混合溶剂中粘度的研究

报导了在293.15及298.15 K下, 氨基乙酸和DL-氨基丙酸在甲醇-水混合溶剂中的密度及粘度数据; 计算了在无限稀释条件下, 这些体系中氨基酸的粘度B系数及偏摩尔体积。实验结果表明: 在甲醇-水的质量比值(W_B)分别约为0.15及0.25处, 两种氨基酸的B系数均出现极小值。讨论了氨基酸的引入对溶剂结构的影响; 并应用流动过渡状态理论计算了两种氨基酸在甲醇水溶液中的流动活化参数。     

正丙醇-碘化钾-水体系析相萃取分离铱

利用无毒、易溶于水的小分子醇类作为萃取溶剂进行均相萃取、异相分离的快速萃取体系,可以克服异相萃取分离技术中的一些缺点而受到重视,但对铱的均相萃取研究未见报道。本工作以正丙醇为萃取溶剂进行均相萃取,以异相分离铱进行试验。     

电解质在非水混合溶剂中的溶解度和溶剂化数的研究-盐-甲醇-非电介质体系

本文测定了KClO3, NaNO3, NaNO2 三种盐在甲醇-苯, 甲醇-环己烷, 甲醇-四氯化碳和甲醇-二氧六环以及KCl 在甲醇-苯和甲醇-甲苯中的溶解度.它们与非电解质的摩尔分数Xne 的关系符合经验公式计算得到各种盐的甲醇化数: KClO3 为7.1 , NaNO3 为6.4 , NaNO2 为5.8 . 从单骀溶剂化模化模型出发,应用改进的Born 公式, 推导出第二介质参数k'的理论计算公式. 计算的k'和实验的k 数值相近, k'对k 有一定的预示.     

丝氨酸在葡萄糖-水和蔗糖-水混合溶剂中的体积性质

利用精密数字密度计测定了丝氨酸与不同组成的葡萄糖-水、蔗糖-水混合溶剂构成的三元系溶液的密度，计算了丝氨酸的表观摩尔体积、极限偏摩尔体积和理论水化数.根据结构水合作用模型讨论了迁移偏摩尔体积的变化规律，并与乙二醇-水和丙三醇-水等多羟基体系作了比较.结果表明，丝氨酸分子在多羟基化合物-水体系中增体积效应的大小与多羟基化合物所含OH基数目的多少有关.     

L-丝氨酸在乙醇-水混合溶剂中的稀释焓

氨基酸是重要的生物活性物质,是组成蛋白质的基本结构单位．氨基酸的稀释焓是氨基酸溶液热力学性质研究的一个重要方面［１,２］,即溶质 溶质相互作用．目前氨基酸的稀释焓研究大多集中在纯水溶液中．然而,大多数蛋白质的天然环境并不是单纯的水溶液,而是含有许多有机物质的复杂环境．有机溶剂对蛋白质的溶解度、变性行为、解缔成次一级结构和酶的活性等都有很大影响［３］,蛋白质在非水介质环境条件下的热力学性质与其在水溶液环境条件下的性质是大不相同的．由混合溶剂中稀释焓的研究可以获得溶剂介入的溶质分子间的相互作用信息．…     

KBr-水-正丙醇体系中析相萃取分离富集Hg(Ⅱ)

研究了KBr-水-正丙醇析相萃取Hg(Ⅱ)的行为及与一些金属离子分离的条件.结果表明,( NH4)2SO4能使正丙醇的水溶液分成两相,在分相过程中,Hg(Ⅱ)与KBr生成的HgBr42 -与质子化正丙醇(C3H7OH2+)形成的缔合物[HgBr42-] [C3H7OH2+]2能被正丙醇相完全萃取.当溶液中KBr、( N...     

Enthalpies of Transfer of Tetraalkylammonium Bromides and CsBr from water to Aqueous DMF at 298.15 K

Enthalpies of transfer of tetraalkylammonium bromides and CsBr from water to aqueous DMF mixtures are reported and analyzed in terms of a new solvation theory. It was found that a previous equation could not reproduce these data over the whole range of solvent compositions. Using a new solvation theory to model the enthalpies of transfer shows excellent agreement between experimental and calculated values over the entire range of solvent compositions. The analyses show that tetrapropylammonium bromide, Pr₄NBr, and tetrapentylammonium bromide, Pen₄NBr, are preferentially solvated by water; in contrast tetrabutylammonium bromide, Bu₄NBr, is preferentially solvated by DMF. The solvation of tetramethylammonium bromide, Me₄NBr, and cesium bromide, CsBr, is random. The extent to which the tetraalkylammonium bromides disrupt solvent–solvent bonds increases systematically in going from Me₄NBr to Pen₄NBr.     

Ionic Solvation in Aqueous and Nonaqueous Solutions

Summary.  The history of studies on ionic solvation is briefly reviewed, and structural and dynamic properties of solvated ions in aqueous and nonaqueous solutions are discussed. An emphasis is placed on ionic solvation in nonaqueous mixed solvents in which preferential solvation of ions takes place. A new parameter for expressing the degree of preferential solvation of an ion is proposed. Received January 16, 2001. Accepted January 31, 2001     

丝氨酸在醇-水溶液中的溶解焓

用RD-496III双热流精密微热量计测量了L-丝氨酸在纯水以及异丙醇、1,2-丙二醇和丙三醇水溶液中的溶解焓, 并计算了从水到醇-水溶液中的迁移焓. 实验发现, L-丝氨酸在水及醇-水溶液中的溶解焓都是正值, 它从水到醇-水溶液中的迁移焓也都是正值, 并且基本上随着醇浓度的增加而增加, 说明在溶解过程中, 溶质与混合溶剂分子的部分去水化吸热过程占主要地位. 另外, 实验还发现L-丝氨酸从水到异丙醇水溶液中的迁移焓大于在1,2-丙二醇水溶液中的, 更大于在丙三醇水溶液中的, 这是由于羟基的减少导致了疏水-亲水作用的增加和亲水-亲水作用的减弱.     

D-山梨醇在纯水和卤化钠水溶液中293.15K～318.15K的稀释焓

应用流动式等温精密微量热技术测定4个温度(293.15、303.15、308.15和318.15 K)下D-山梨醇在纯水和卤化钠水溶液中的稀释焓.根据改进的McMillan-Mayer理论对所测数据进行关联,得到了表观摩尔稀释焓对浓度变化的经验方程和各阶焓相互作用系数(h2,h3和h4)和二阶熵相互作用系数(s2),根...     

Solvation of Tetraethyl- and Tetrabutylammonium Bromides in Aqueous Acetone and Aqueous Hexamethyl Phosphoric Triamide Mixtures in the Water-Rich Region

The enthalpies of solutions of tetraethylammonium and tetrabutylammonium bromides in the water-rich region of the water–acetone and water–hexamethyl phosphoric triamide mixed solvents have been measured at 25°C using a precise calorimetry system. The enthalpies of electrolyte solutions at infinite dilution were calculated using the Debye–Hückel theory. The enthalpies of solute transfer from water to the mixtures with acetone and hexamethyl phosphoric triamide were calculated. The enthalpy coefficients of solute–pair interactions with hexamethyl phosphoric triamide and acetone in aqueous solution were obtained using the McMillan–Mayer formalism. The values obtained were compared with those for other organic cosolvents. It was found that in aqueous solution the solutes show a strong tendency for hydrophobic interaction with cosolvent molecules, particularly in the water–hexamethyl phosphoric triamide system.     

The Standard Partial Molar Volumes of Ions in Solution. Part 3. Volumes in Solvent Mixtures Where Preferential Solvation Takes Place

Standard partial molar volumes of 1:1 salts in aqueous mixtures of ethanol (EtOH), dimethyl sulfoxide (DMSO) and acetonitrile (MeCN) at 298.15 K were obtained from the literature. In such mixtures there is evidence that preferential solvation occurs in the solvent shell around the ion where electrostriction takes place. Specifically, the anions are better solvated by the water whereas the cations are generally solvated by both the water and the nonaqueous component of the mixtures to various extents. There are no clear-cut criteria for how the measured volumes are to be apportioned between the ions in such mixtures. Various solvation models were used to estimate the volumes of the salts by calculation of the electrostriction around the ions. Only the taking into account of the preferential solvation of the ions in the solvation shell yielded calculated results of the standard partial molar volumes of the salts in agreement with the experimental data.     

Enthalpies of dilution of electrolyte solutions by flow microcalorimetry

The enthalpies of dilution of NaCl, Me₄NBr, andn-Bu₄NBr were measured in water at 25°C with a new flow microcalorimeter. The data were analyzed with a polynomial equation, and the derived relative apparent molal enthalpies _L are in good agreement with literature values. Provided care is taken that mixing is complete, flow calorimeters are as reliable and much less time-consuming than cell-type instruments for enthalpies of dilution measurements.     

D-甘露醇与D-山梨醇在氯化钠水溶液中的稀释焓

应用等温流动微量热法测定了298.15 K时互为旋光异构体的D-甘露醇与D-山梨醇在不同浓度的氯化钠水溶液中的稀释焓, 利用 McMillan-Mayer 理论计算了D-甘露醇与D-山梨醇在不同浓度的氯化钠水溶液中的焓对相互作用系数. 结果表明, D-甘露醇和D-山梨醇在氯化钠水溶液中的焓对相互作用系数h2均为正值, h2的值随着氯化钠浓度的增加皆逐渐增大, 但D-山梨醇的焓对相互作用系数h2增大的速率[dh2 /dm(NaCl)]比 D-甘露醇的要大. 根据两多元醇分子构象结构的差异， 溶质-溶质相互作用和溶质-溶剂相互作用对结果进行了解释.     

The Enthalpies of Solution and Solvation of L-Serine in Aqueous Alcoholic Solutions at 298.15 K

The integral enthalpies of solution (Δ_sol H ^m ) of L-serine in water-alcohol (ethanol, n-propanol, isopropanol) mixtures were measured over the range of alcohol concentrations up to 0.32 mole fractions. The standard enthalpy of solution (Δ_sol H°), enthalpy of transfer of L-serine from water into a mixed solvent (Δ_tr H°), and enthalpy of solvation (Δ_solv H°) were calculated. The dependences of Δ_sol H°, Δ_solv H°, and Δ_tr H° on the composition of mixtures had extrema. The calculated enthalpy coefficients of the pair interactions of L-serine with alcohol molecules were positive and increased along the series ethanol, n-propanol, isopropanol. The data obtained were interpreted in terms of different types of interactions in solutions and the influence of the nature of amino acid residues on the thermochemical solution characteristics. Original Russian Text ? I.N. Mezhevoi, V.G. Badelin, 2008, published in Zhurnal Fizicheskoi Khimii, 2008, Vol. 82, No. 4, pp. 789–791.