Hydrophobic hydration and hydrophobic interaction in tetraalkylammonium salt solutions: The cation size effect

The heats of solution of tetrahexylammonium and tetraheptylammonium bromides in water and aqueous solutions of formamide and hexamethylphosphoric triamide have been measured at 318 and 338 K. The standard enthalpies and heat capacities of solution and the enthalpic and heart capacity parameters of amide-electrolyte pair interaction have been determined. It has been confirmed that the standard heat capacities of solution and the amide-electrolyte interaction parameters as a function of the cation size pass through an extremum. The hydrophobic hydration effect is weaker for large tetraalkylammonium cations.     

Thermodynamic properties of aqueous solutions of tetraalkylammonium salts: Dependence of the hydrophobic hydration effect on the cation size

The heats of solution of tetrahexylammonium and tetraheptylammonium bromides in water were measured at 318.15 and 328.15 K. The standard enthalpies and specific heats of solution and the temperature changes in the free energy and entropy of solution were calculated. A comparison of the thermodynamic properties of solutions for the homologous series of tetraalkylammonium salts demonstrated that the enthalpic, entropic, and specific heat characteristics of solution are positive and increase almost linearly up to tetrapentylammonium bromide. On passing to larger homologues, these parameters decrease, suggesting that the hydrophobic hydration effect is substantially weaker in solutions of tetraalkylammonium salts with larger cations. Original Russian Text ? A.V. Kustov, 2009, published in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 2, pp. 368–373.     

五种含氧酸盐对L-丙氨酸迁移焓的影响

本文以带疏水侧链的丙氨酸为研究对象, 在298.15 K下测定其在LiNO3, NaNO3, KNO3, NaClO4及Na2SO4水溶液中的溶解焓, 探讨了不同种类的阳离子和阴离子对迁移焓的影响, 为揭示蛋白质与含氧酸盐水溶液的相互作用提供了有用信息.     

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.     

Combined study of thermochemical properties of nitroform and its salts

A combined method for determination of the standard enthalpies of formation of nitroform and its salts was proposed. The enthalpies of dissolution of nitroform and its ammonium, hydrazinium, guanidinium, and potassium salts in water were measured. The enthalpy of combustion of hydrazinium salt of nitroform was determined by a combustion calorimetry, and its standard enthalpy of formation was calculated. The enthalpy of formation of trinitromethyl anion in indefinitely diluted aqueous solution −24.94±0.79 kJ mol⁻¹, was calculated on the basic of the data obtained for enthalpies of formation and dissolution of ammonium and hydrazinium salts of nitroform. Standard enthalpies of formation of nitroform and its salts were calculated. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2451–2454, December, 1998.     

Thermochemistry of complex salts of transition metal perchlorates with tetrazole ligands

The combined use of combustion and solution calorimetry was proposed as a method for determining the standard enthalpy of formation of the complex salts of transition metals, viz., cobalt(II), nickel(II), and zinc, with the organic ligand (5-aminotetrazol-1-yl)acethydrazide. The enthalpies of solution in water and in a 0.1 M solution of hydrochloric acid were measured for the complex salts and ligand. The enthalpy of combustion of the ligand was determined by the combustion calorimetry method, and its standard enthalpy of formation was calculated. The thermochemical cycle was developed for determining the standard enthalpy of formation of the complex salts. The reliable values of the enthalpies of formation of the salts in the standard states were obtained, and the enthalpies of formation of the earlier unknown complex ions were determined.     

Thermochemistry of complex salts of transition metal perchlorates with tetrazole ligands

Standard enthalpies of formation of transition metal (cobalt, nickel, and zinc) complex salts with an organic ligand 5-aminotetrazol-2-ylacetohydrazide (ATH-2) were obtained by combustion and solution calorimetry. The enthalpy of combustion of the ligand was determined using combustion calorimetry and the standard enthalpy of formation of the ligand was calculated. For calculations by reaction calorimetry, a thermochemical cycle was developed that allows determination of the standard enthalpy of formation of complex salts. The enthalpies of solution of the ligand and transition metal complex salts in water and in 0.1 M hydrochloric acid were determined. The data obtained allow calculations of the enthalpies of salts formation and the enthalpies of three new complex ions. The enthalpies of position isomerization in different compounds were analyzed.     

甘氨酸从水到有机物水溶液的迁移焓研究

蛋白质是各种生物形态结构和生命活动所依赖的物质基础,在水溶液中蛋白质天然结构的稳定性归结于氨基酸残基之间以及与溶液中其它组分的相互作用．天然环境中存在的众多物质对蛋白质的溶解度、变性行为和解缔等都有很大的影响．为深入了解蛋白质折叠与解折叠过程中的物理化学现象,以氨基酸、肽、酰胺及其衍生物作为蛋白质模型分子的热力学研究引起了广泛重视．     

Thermodynamic characteristics of Cu<Superscript>2+</Superscript> complexation processes with L-phenylalanine in an aqueous solution

The heats of interaction of Cu²⁺ ions with L-phenylalanine in aqueous solution were determined by calorimetry at ionic strengths of 0.50, 0.75, 1.00 (KNO₃) and a temperature of 298.15 K. The results of thermochemical study were interpreted taken into account complexation reactions, protolytic processes, and complexation with the competing ligand (OH^?) taking place in parallel. The effect of supporting electrolyte concentration on the heats of Cu²⁺ complexation with the amino acid was considered. The standard enthalpies of complexation were found by extrapolation to zero ionic strength. The standard enthalpies of formation of complex species in an aqueous solution were calculated.     

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.     

Effect of intramolecular hydrogen bond in unsaturated dicarboxylic acid molecules on the formation of cobalt(II) and nickel(II) carboxylates

The energies of formation of intramolecular hydrogen bonds (IHB) in unsaturated dicarboxylic acid molecules in aqueous solutions were calculated by the DFT method (B3LYP hybrid functional, 6-31G** basis set) using the GAMESS software, Version 1, May 2013 (R1). The medium effect was taken into account in terms of the Polarized Continuum Model (PCM). In the case of allylmalonic, itaconic, and maleic acids, fairly weak IHB with an energy of 5.8–13.9 kJ/mol were found to form. The enthalpies of formation of acid and normal cobalt and nickel salts of carboxylic acids in aqueous solutions were calculated by the semiempirical PM3 method using the HyperChem 8.0.8 software (Hypercube Inc.). The results indicate that in aqueous solutions, the formation of cobalt and nickel acid salts of allylmalonic, itaconic, and cis,cis-muconic acids is energetically more favorable than the formation of normal carboxylates, which is consistent with experimental data.     

Enthalpies of the urea-tert-butanol-water system at 25°C

The enthalpies of solution of urea (U) in water (W)-tert-butanol (TBA) mixtures and of TBA in W-U mixtures, the enthalpies of dilution of TBA in W, and the enthalpies of mixing of U and TBA aqueous solutions were measured with a solution calorimeter and a flow microcalorimeter. Enthalpies of transfer of U and TBA to the mixed solvents were derived. Also, pair and triplet interaction parameters between the various solutes were derived from the mixing and dilution experiments. The enthalpic pair parameter h_U-TBA is positive, suggesting that the main contribution to this parameter is the decrease in hydrophobic hydration of TBA in the presence of U.     

乙酸、卤代乙酸在水溶液中电离焓的测量和热力学过程的研究

本文用LKB-2277BioActivityMonitor以5℃的间隔测量了20-45℃温度区间乙酸、氯乙酸、溴乙酸和碘乙酸在水溶液中的电离焓。通过每一温度下测量五个不同浓度酸的热效应并外推至酸浓度无限稀,得到了电离焓ΔH~i^ⅲ。实验结果表明,在实验温度范围内,ΔH~i^ⅲ为:乙酸>氯乙酸>溴乙酸>碘乙酸;上述各个酸的ΔH~i^ⅲ跟温度呈线性变化的关系。本文用溶液中溶质与溶剂的相互作用及"内部-环境"模型较圆满地解释了取代基和温度对乙酸、氯乙酸、溴乙酸和碘乙酸的电离焓和电离熵的影响。     

盐湖盐类水溶液298.15K时稀释热和表观摩尔焓的研究

有关溶稀释热方面的研究报导很多,例如等溶液的稀释热均已有文献值．但全是采用分批式量热法研究部分间断浓度范围内的稀释热，数据设有连续性，很不全面．在稀释热理论估算方面，Pitier的半经验溶液理论能比较满意的解决一般浓溶液的稀释热估算问题，但文献只给出了某些多数，没有计算出具体的稀释热数据[6-9]，也没有将实验测定值与理论估算值相比较．基于Debye－Hckel理论推导出的烙极限公式[10-12]在溶液表观摩尔烂的研究中已得到广泛应用．但迄今没有一篇论文比较全面地将实验测定与Pitier理论和Debye－Hhdel极限公式相结合来研究溶…     

Enthalpies of solution and solvation of amides in N,N-dimethylformamide: Application of the random contact point approach

Calorimetrically determined molar enthalpies of solution at infinite dilution in N,N-dimethylformamide and densities of several amides at 25°C are reported. Some of the enthalpies are combined with literature data for enthalpies of vaporization to obtain molar enthalpies of solvation. Relations are found between the enthalpies of solution and the size, and between these enthalpies and the enthalpic pair interaction coefficients of the solute molecules. These relations are quantified by an extension of the random contact point approach. This additivity scheme is also applied to enthalpies of solvation, vaporization and cavity formation. With this approach thermodynamic quantities of solution, solvation, vaporization, and pair interaction of different solutes and solvents are correlated with a single consistent set of group interaction parameters. In addition, the random contact point model provides a simple method to calculate thermodynamics of cavity formation which appear to be as reliable as those of the much more complicated scaled particle theory.     

Enthalpies and heat capacities of transfer of sodium carboxylates and sodium dodecylsulfate from water to aqueoustert-butyl alcohol solutions

Integral enthalpies of solution at very low concentrations of sodium carboxylates and sodium dodecylsulfate in aqueous tert-butyl alcohol solutions at 25°C and 35°C were measured with an isoperibol submarine calorimeter. The enthalpies and heat capacities of transfer of these surfactants from water to aqueous tertbutyl alcohol solutions were derived from integral enthalpies of solution. The results are explained in terms of the structural alteration effect of the constituent hydrophobic and hydrophilic groups of the solute.     

甲酰胺与肌醇在氯化钠水溶液中的焓相互作用

应用等温流动微量热法测定298.15 K时甲酰胺与肌醇分子在不同浓度氯化钠水溶液中的混合过程焓变及其稀释焓, 根据McMillan-Mayer理论关联得到各级异系焓相互作用系数(h_xy, h_xxy及h_xyy). 结果表明, 甲酰胺与肌醇分子在氯化钠水溶液中的异系焓对相互作用系数h_xy均为负值, 并且随着氯化钠浓度的增加, h_xy的绝对值逐渐减小.     

Thermochemical study of equilibria in the Cu<Superscript>2+</Superscript>-D,L-threonine system in an aqueous solution

The heats of interaction of Cu²⁺ ions with D,L-threonine in an aqueous solution were determined by direct calorimetry at ionic strengths of 0.50, 0.75, 1.00 (KNO₃) and temperatures of 288.15, 298.15, and 308.15 K and the corresponding heats of dilution were found. In calculation of the equilibrium composition of the system, side protolytic processes were taken into account along with the complexation reactions. The standard heats of formation of the CuThr⁺ and CuThr₂ species were found. The results were analyzed on the basis of Gurney views. The standard enthalpies of formation of complex species in the hypothetical undissociated state in an aqueous solution were calculated.     

Thermochemistry of Binding of Lead(II) and Cadmium(II) by Saccharides in Aqueous Solution

Solution calorimetry was used to determine enthalpies and stability constants for binding of lead(II) or cadmium(II) by galacturonic acid and several monosaccharides in aqueous solution. New values for enthalpies of solution in water are reported for galacturonic acid and maltose monohydrate. The interaction of water solvent with the reactants is the largest factor in the binding process.     

Enthalpies of interaction of glycine with some amides in aqueous solutions at 298.15 K

The dissolution enthalpies of glycine in aqueous solutions of acetamide, N-methylacetamide, N,N-dimethylacetamide, N-ethylformamide, N,N-diethylformamide and N,N-diethylacetamide were measured at 298.15 K. The enthalpic pair interaction coefficients of glycine zwitterion-amide molecules were determined by using standard solution enthalpies of glycine in water and aqueous solutions of amides. The additivity of groups concept of Savage and Wood was used to estimate the contribution of each of the functional groups of the studied amides.