Freezing temperatures of aqueous solutions of mixtures of amides and polyols. Gibbs energy of interaction of the amide group with the hydroxyl group in aqueous solution

Freezing temperatures of dilute aqueous mixtures of: formamide with myo-inositol, d-mannitol, and cyclohexanol; N,N-dimethylformamide with inositol, mannitol, and cyclohexanol; and acetamide with inositol and mannitol have been measured. These data have been analyzed to yield the pairwise molecular Gibbs energies of interaction between the molecules in an aqueous solution. Using the group additivity principle, the results yield the pairwise functional group Gibbs energies of interaction of the amide group with the hydroxyl group, G _OH,CONH =–31 J-kg-mol^–2.     

Freezing temperatures of aqueous solutions of hexamethylenetetramine with polyols,amides, and ethers

Freezing temperatures of dilute aqueous solutions of hexamethylenetetramine and mixtures of hexamethylenetetramine with myo-inositol, d-mannitol, cyclohexanol, formamide, acetamide, 1,4-dioxane, and 1,3,5-trioxane have been measured. These data yield pairwise molecular Gibbs energies of interaction between the molecules in an aqueous solution. Using the additivity principle, the results also yield the pairwise functional group Gibbs energies of interaction in an aqueous solution for the amine nitrogen with itself and with the hydroxyl, amide, ether, and methylene groups.     

Freezing temperatures of aqueous solutions of methyl formate and ethyl acetate with a variety of nonelectrolytes. Gibbs energy of interaction of the ester group with other functional groups

Freezing temperatures of dilute aqueous solutions of ethyl acetate and mixtures with myo-inositol, D-mannitol, formamide, 1,3,5-trioxane, 1,4-dioxane, acetamide, hexamethylenetetramine, and methyl formate have been measured. In addition, freezing temperatures of dilute aqueous solutions of methyl formate and mixtures with the above solutes have been measured. From these data, the pairwise molecular Gibbs energies of interaction between the molecules were calculated. Using the additivity principle, the pairwise functional group Gibbs energies of interaction were calculated for ester group interactions with a variety of other functional groups.     

Freezing temperatures and enthalpies of dilution of aqueous solutions of amides. Gibbs energies and enthalpies of interaction of the N,N-dimethylamide group in aqueous solutions

Enthalpies of dilution, freezing temperatures, and densities of aqueous solutions of N,N-dimethylacetamide and N,N-dimethylpropionamide have been measured. Freezing temperatures of dilute aqueous solutions of formamide and N,N-dimethylformamide have also been measured. These data yield the pairwise molecular Gibbs energies and enthalpies of interaction: these have been treated according to a group additivity principle to give pairwise functional group Gibbs energies and enthalpies of interaction. The results indicate that substitution on the amide nitrogen may increase the Gibbs energy and enthalpy of interaction of the amide group with itself in an aqueous environment but the effect if present is small.     

Gibbs energies of interaction of the CH2 and CHOH groups from freezing point data for aqueous binary mixtures of D-mannitol,myo-inositol,and cyclohexanol

Freezing temperatures of dilute aqueous solutions of D-mannitol, myo-inositol, D-mannitol + myo-inositol, D-mannitol + cyclohexanol, and myo-inositol + cyclohexanol have been measured over the concentration range 0.1 to 1.0 mol-kg^–1. These data yield pairwise molecular Gibbs energies of interaction which have been corrected to 25°C and treated according to the Savage-Wood additivity principle to give pairwise functional group Gibbs energies of interaction for CH₂/CH₂, CH₂/COOH, and CHOH/CHOH. Anomalous behavior of some systems is discussed in terms of the interactions.     

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.     

甲酰胺溶剂中溶质间的过量Gibbs自由能相互作用参数

利用气液色谱方法测定了２９８．１５Ｋ时若干非电解质溶质在甲酰胺－乙酰胺、甲酰胺－尿素、甲酰胺－高氯酸钠固定液中的保留参数，采用ＭｃＭｉｌａａｎ－Ｍａｙｅｒ理论，将溶液热力学过量性质与溶液中粒子的对相互作用，参相互作用参数相联系，利用热力学方法求得了溶质的保留参数与Ｇｉｂｌｓ自由能相互作用参数的关系，并就溶质－溶质间的相互作用及溶剂性质的影响进行了讨论。     

Enthalpy of dilution of aqueous systems containing S-trioxane and some amides. Analysis of the interaction of saccharides with amides in aqueous media

Enthalpies of dilution of aqueous systems of trioxane+formamide and trioxane+dimethylformamide have been determined at 25°C. The data have been treated in terms of the Savage-Wood additivity principle, and a first estimate of the pairwise group interaction enthalpy for-O-/CONH is presented. Systems of saccharides and amides are not amenable to the Savage-Wood treatment used in recent works. However, when treated in conjunction with all available data to yield a different set of group interaction parameters, saccharides behave more predictably. Implications of this state of affairs are considered.     

肌醇在纯水和卤化钠水溶液中稀释过程的热力学性质

应用微量热法测定了298.15 K时肌醇在纯水和卤化钠水溶液中的稀释焓, 根据McMillan-Mayer理论, 计算了肌醇在溶液中的二到四阶焓相互作用系数. 结果表明, 肌醇在卤化钠溶液中的焓对相互作用系数h2均为负值, 并且随着卤素阴离子半径的增大, h2的绝对值呈增大趋势.     

Thermochemical Study of Solvation of Aliphatic Carboxamides in Aqueous Formamide Solutions

The entahlpies of solution of formamide, acetamide, and propionamide in aqueous formamide solutions (formamide concentration 8 mol kg^-1) at 298.15 K were measured. The entahlpies of transfer of amides from water to the mixed aqueous-organic solvent were calculated and compared with published data on the enthalpies of transfer of amides into aqueous urea solutions. The opposite trend in variation of the enthalpies of transfer of amides in these systems with increasing concentration of the nonaqueous component is due to different proton-donor power of formamide and urea relative to water. The enthalpy coefficients of pair interaction of amides with formamide in ternary aqueous solutions were calculated. Their positive values are due to endothermic interaction with formamide of the alkyl groups of amide molecules. The relative hydrophobicity of amides with different degrees of substitution of the amide group was estimated.     

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．     

甘氨酸从水到酰胺衍生物水溶液中的迁移焓

用RD496-Ⅱ型微量热量计测定了298.15 K甘氨酸在N-甲基甲酰胺（NMF）,N, N-二甲基甲酰胺（DMF）,N-甲基乙酰胺（NMA）,N, N-二甲基乙酰胺（DMA）水溶液中的溶解焓,计算了甘氨酸从水到四种酰胺衍生物水溶液中的迁移焓（ΔtrH）。根据结构水合作用模型讨论了酰胺的结构对甘氨酸迁移焓的影响。实验结果表明：甘氨酸在酰胺衍生物水溶液中的迁移焓均为正值,并且随着溶液浓度增大而增大。比较甘氨酸在甲酰胺（FA）和乙酰胺（AD）水溶液中的迁移焓,发现在不同酰胺水溶液中迁移焓大小为：DMA>NMA>DMF>NMF>AD>FA。甘氨酸与甲酰胺之间以亲水-亲水相互作用为主,与其它酰胺之间以亲水-疏水作用为主。     

Enthalpies of dilution of aqueous systems containing hexamethylenetetramine and other nonelectrolytes

Enthalpies of dilution of aqueous systems containing hexamethylenetetramine, alone and in ternary system with each of mannitol, myoinositol, cyclohexanol, formamide, dimethylformamide, and trioxane have been determined. The data have been treated in terms of the Savage-Wood additivity principle and first estimates for the pairwise groups interaction enthalpies of N/N, CH₂/N, CHOH/N, COHN/N and –O–/N have been made. The results are discussed in light of all other known group interaction enthalpies. The limitations and utilities of the Savage-Wood principle are reviewed.     

Thermodynamics of solvation and solvophobic effect in formamide

Using semi-adiabatic calorimetry, we measured the enthalpies of solution for various low-polar compounds including alkanes, aromatic hydrocarbons and their halogenated derivatives in formamide at temperature of 298 K. For the same compounds, the values of limiting activity coefficients in formamide were determined using GC headspace analysis at 298 K, and Gibbs free energies of solution and solvation were calculated. Based on these data and the available literature values of the Gibbs free energy of solvation in formamide for a number of other low-polar solutes, a study of the solvophobic effect in this solvent is performed, and its resemblance to the hydrophobic effect in aqueous solutions is demonstrated. It is shown that the contribution of the solvophobic effect into the solvation Gibbs free energy in formamide is much higher than that in aliphatic alcohols, but lower than that in water. Like in water, the magnitude of this contribution for different solutes linearly increases with the solute molecular volume. Solvophobic effect also significantly affects the enthalpies of dissolution in formamide, causing them to be more negative in the case of alkanes and more positive in the case of arenes.     

肌醇在碱金属氯化物溶液中的体积性质

使用精密数字密度计测定了298.15和308.15 K肌醇在不同浓度的LiCl-H2O、NaCl-H2O或KCl-H2O溶液中的密度, 计算了肌醇的表观摩尔体积Vφ和极限偏摩尔体积Vθφ , 得到了其由纯水溶剂转移至混合溶剂中的迁移偏摩尔体积⊿trsVθ椎 .结果表明, LiCl, NaCl和KCl在溶液中对肌醇的体积性质影响显著, 极限偏摩尔体积Vθφ和极限迁移偏摩尔体积⊿trsVθφ都随盐浓度的增大而增加;温度对肌醇的极限偏摩尔体积和极限迁移偏摩尔体积只有轻微影响. 从分子-离子间的相互作用角度对实验结果进行了讨论.     

AM1 and PM3 Study of Tautomerism of Hypoxanthine in the Gas and Aqueous Phases

Heats of formation, entropies, Gibbs free energies, relative tautomerisation energies, tautomeric equilibrium constants, dipole moments, and ionization potentials for the eight possible tautomers of hypoxanthine have been studied using semiempirical AM1 and PM3 quantum-chemical calculations at the SCF level in the gas and aqueous phases, with full geometry optimization. The COSMO solvation model was employed for aqueous solution calculations. The calculations show that the two keto tautomers H17 and H19 are the predominant species at room temperature in the gas and aqueous phase. However, the tautomer H17 is the more dominant species in gas phase, while the H19 tautomer is the more dominant species in the aqueous phase. Comparison with available experimental data provides support for the results derived from theoretical computations. The entropy effect on the Gibbs free energy of hypoxanthine is very small and there is little significance for the tautomeric equilibria of the base. The enthalpic term is dominant in the determination of the equilibrium constant.     

Thermodynamic properties, intermolecular interaction parameters, and structure of aqueous amide solutions of ammonium and tetraalakylammonium bromides

The thermal effects of dissolution of ammonium bromide in water and its mixtures with formamide (FA) at 277–328 K were studied by the calorimetry method in the region of small additions of the nonaqueous component. The standard values of enthalpy and heat capacity of solution, as well as the temperature changes in the solution entropy and reduced dimensionless Gibbs energy, were calculated. The parameters of electrolyte-amide pair interactions were calculated using the McMillan-Mayer formalism. The contributions of the cation and anion to the pair interaction parameters were determined by the group additivity method. The results are compared with the data obtained previously for solutions of tetrabutyl-and tetraethylammonium bromides in aqueous solutions of FA and hexamethylphoshotriamide (HMPT). At elevated temperatures the system becomes less structured in amide solutions of tetraalkylammonium bromides (except solutions of Et₄NBr in aqueous HMPT) but more structured in solutions of ammonium bromide and in aqueous FA and HMPT.     

Thermodynamic Parameters of Solvation and Complexing of Copper(II) Nitrate and Nickel(II) Nitrate in Water + Acetamide Mixtures at 298.15 K

The heats of mixing of aqueous solutions of copper(II) or nickel(II) nitrate in water + acetamide (AA) mixtures in the existing range of amide concentrations have been studied. A rise in the amide concentration enhances solvation more strongly in copper(II) salt solutions. Data are analyzed with reference to previous results on the enthalpies of transfer of the salts studied in water + formamide (FA) and water + N,N-dimethylformamide (DMF) mixtures. Electronic absorbance spectra have been recorded at a fixed electrolyte concentration for all thermochemically studied systems, and a linear correlation has been found between the enthalpy of transfer of Cu(NO₃)₂ and the optical density of the solution. The enhanced solvation of copper(II) nitrate in aqueous acetamide is due to inner-sphere interactions between the cation and acetamide; that of nickel(II) nitrate is more due to outer-sphere interactions.     

Electron transfer reaction with amide—one electron oxidant system in solution

The kinetics of reduction of Mn(III) by acetamide, formamide (F), N-methylformamide (NMF), and N,N-dimethylformamide (DMF) have been measured spectrophotometrically at 50°C in aqueous acid perchlorate media. Four moles of Mn(III) are consumed for formamides and two moles of Mn(III) are consumed per mole of acetamide, leading in each case to the formation of the respective amines. All rates were first order in each reactant and were independent of [Mn²⁺] and [NaClO₄]. The reciprocals of observed rate constants are inversely dependent on acidity. A free radical mechanism consistent with these results has been proposed for the reactions. Activation energies and entropies are calculated for each reaction.     

Hydrogen bonding between nucleic acid constituents and amino acid amide group

The formation of hydrogen-bonded complexes between 9-ethyladenine and acetamide in chloroform solution has been studied by infrared spectroscopy. Comparison of the mixed solution spectra with the sum of the spectra of the separate monomers in solution shows that cyclic heterodimers are formed when acetamide binds to adenine base. Information is also obtained about the atomic arrangement of these heterodimers, where acetamide is bound to adenine base predominantly through the pyrimidine ring. Hydrogen bonds of this nature have been also observed for concentrated aqueous solutions of adenosine 5′-monophosphate in the presence of acetamide using Raman spectroscopy.