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.     

The thermodynamic characteristics of dissolution of tetraethylammonium bromide and interparticle interactions in the water-formamide-Et4NBr and methanol-formamide-Et4NBr systems

The heat effects of dissolution of tetraethylammonium bromide in water-formamide (FA) and methanol-formamide mixtures were measured at 298.15 and 313.15 K. The second approximation of the Debye-Hückel theory was used to calculate the standard enthalpies of solution Δ_sol H ^o. The mean standard heat capacities of solution ΔC _p ^o and temperature-induced changes in the standard entropies of solution were determined over the temperature range studied. The electrolyte-FA pair interaction parameters in water and methanol were calculated. In the region of low FA concentrations in water and methanol, the Δ_sol H ^o = f(x ₂) and ΔC _p ^o = f(x ₂) dependences were substantially different in character. Some common features of the behavior of tetraethylammonium bromide were only observed in the region of high FA contents, where the intrinsic structure of water virtually disappeared.     

The standard enthalpies of formation of crystalline N-(carboxymethyl)aspartic acid and its aqueous solutions

The energy of combustion of N-(carboxymethyl)aspartic acid (CMAA) was determined by bomb calorimetry in oxygen. The standard enthalpies of combustion and formation of crystalline N-(carboxymethyl)aspartic acid were calculated. The heat effects of solution of crystalline CMAA in water and a solution of sodium hydroxide were measured at 298.15 K by direct calorimetry. The standard enthalpies of formation of CMAA and its dissociation products in aqueous solution were determined.     

The Standard Enthalpies of Formation of Crystalline Diethylenetriamino-N,N,N′,N″,N″-pentaacetic Acid and Its Dissociation Products

The heat effects of solution of diethylenetriamino-N,N,N′,N″,N″-pentaacetic acid (H₅dtpa) in water and solutions of potassium hydroxide were determined at 298.15 K by direct calorimetry. The standard enthalpies of formation of H₅dtpa and its dissociation products were calculated.     

Effect of intramolecular cyclization on the enthalpy of dissolution (solvation) of N,N’-dimethylurea in water and methanol at 298.15 K

The heat effects of dissolution of ethyleneurea (2-imidazolidinone) in water and methanol were measured (with an error not higher than 0.2%) at 298.15 K by using a hermetic isothermal calorimeter. The limiting (standard) molar solution enthalpies of the specified cyclic compound in different solvents were determined. Considerable weakening of the solvation of the solute was established in the case of both cyclization of dimethylurea molecules and replacement of the aqueous medium by a methanolic solution.     

甲酰胺与正负离子表面活性剂有序溶液的研究

对羧酸钠与烷基三甲基溴化铵1：1混合体系的研究表明：常温下各体系在不同比例甲酰胺（FA）／水混合溶剂中，表面张力随浓度变化均有明显的转折点，显示了混合体系中胶团的存在．实验中发现随混合溶剂中FA比例增加，各体系的临界胶团浓度（cmc）增大．在较高温度下发现在甲酰胺中亦存在着因胶团形成而产生的表面张力-浓度对数（γ－logc）曲线的转折点，利用相分离模型对体系胶团热力学参数进行了计算．并探讨了FA对正负离子表面活性剂囊泡的影响．     

Influence of high-volume electric furnace nickel slag and phosphorous slag on the properties of massive concrete

This study applied high-volume electric furnace nickel slag (FS), phosphorous slag (PS) and a mixture of the two (FP) to massive concrete, and using fly ash (FA) as the control admixture, investigated the effects of FS and PS on the hydration and hardening process of the cementitious materials, the mechanical properties and the durability of the concrete. Two curing conditions were set, namely the standard curing condition and temperature-matched curing condition (or constant 25 and 50 °C). The hydration heat, hydration products, pore size distribution, mechanical properties and ability of the concrete to resist chloride ion penetration were tested. The results show that the activity of PS and FP is higher than that of FA, while that of FS is lower than that of FA; the improvement of FP on the pore structure of the hardened paste is close to that of FA at late ages under the standard curing condition but better than that of FA at all ages under the temperature-matched curing condition; high-volume FP concrete shows similar or even superior mechanical properties and permeability to chloride ions of concrete to high-volume FA concrete at late ages under both curing conditions.     

The standard enthalpies of formation of succinic acid and the products of its dissociation in aqueous solution

Direct calorimetric measurements of the heat effects of solution of crystalline succinic acid in water and solutions of potassium hydroxide were performed at 298.15 K. The standard enthalpies of formation of succinic acid and the products of its dissociation in aqueous solution were calculated.     

The standard enthalpies of formation of citric and tartaric acids and their dissociation products in aqueous solutions

The energies of combustion of citric and tartaric acids in oxygen were determined by bomb calorimetry. The standard enthalpies of combustion and formation of crystalline citric and tartaric acids were calculated. The heat effects of solution of crystalline acids in water and aqueous potassium hydroxide were determined by direct calorimetry at 298.15 K. The standard enthalpies of formation of acids and their dissociation products in aqueous solution were calculated.     

Thermal properties of tetraalkylammonium bromides in several solvents

The enthalpies of solution of tetraethyl- and tetra-n-hexylammonium bromides have been measured in mixtures of formamide with ethylene glycol at 298.15 and 313.15 K in the whole mole fraction range by the calorimetric method. The standard enthalpies of solution in binary mixtures have been calculated with Redlich–Rosenfeld–Meyer type equation. The enthalpy and heat capacity parameters of pair interaction of organic electrolytes with EG in FA and with FA in EG have been computed and discussed. The enthalpy interaction parameters of single ions with EG in FA medium have been evaluated and compared with those for ion–water and ion–MeOH interaction in FA. The standard heat capacities of solution have been evaluated. The excess enthalpies of solution, Δ_sol H ^E, of Et₄NBr, Bu₄NBr, and Hex₄NBr have been determined. The Δ_sol H ^E values are positive for Et₄NBr and negative for Bu₄NBr and Hex₄NBr and become more negative from Bu₄NBr to Hex₄NBr.     

Thermal properties of <Emphasis Type="Italic">n</Emphasis>-R<Subscript>4</Subscript>NBr solutions in binary solvents containing formamide

The enthalpies of solution of tetraethyl- and tetra-n-hexylammonium bromides have been measured in mixtures of formamide with ethylene glycol at 298.15 and 313.15 K in the whole mole fraction range by the calorimetric method. The standard enthalpies of solution in binary mixtures have been calculated with Redlich–Rosenfeld–Meyer type equation. The enthalpy and heat capacity parameters of pair interaction of organic electrolytes with EG in FA and with FA in EG have been computed and discussed. The enthalpy interaction parameters of single ions with EG in FA medium have been evaluated and compared with those for ion–water and ion–MeOH interaction in FA. The standard heat capacities of solution have been evaluated. The excess enthalpies of solution, Δ_sol H ^E, of Et₄NBr, Bu₄NBr, and Hex₄NBr have been determined. The Δ_sol H ^E values are positive for Et₄NBr and negative for Bu₄NBr and Hex₄NBr and become more negative from Bu₄NBr to Hex₄NBr.     

The thermodynamic characteristics of complex formation in the zinc(II) ion-threonine system in aqueous solution

The heat effects of complex formation between D,L-threonine and zinc(II) ions at 288.15, 298.15, and 308.15 K and ionic strengths of 0.25, 0.50, and 0.75 were determined calorimetrically against the background of potassium nitrate. The thermochemical results were processed taking step equilibria into account. Along with complex formation, side protolytic processes were considered. The standard heat effects of complex formation in the system studied were determined by extrapolation to zero ionic strength with the use of an equation with one individual parameter. The heats of solution of D,L-threonine in water and aqueous alkali were used to calculate the standard enthalpies of formation of the complexes.     

Surface Tension, Heat Capacity, and Volume of Amphiphilic Compounds in Formamide Solutions

Density measurements of sodium dodecyl sulfate (SDS), sodium decyl sulfate (SDeS), sodium octyl sulfate(SOS), and sodium hexyl sulfate(SHS) in formamide (FA) as functions of the surfactant concentrations were carried out at 25°C. For SDS in FA, additional density measurements at 35 and 60°C and surface tension and specific heat capacity measurements at 25°C were also performed. From density and specific heat capacity data, the apparent molar volume and heat capacity of the surfactants as functions of concentration were calculated. The surface excess of SDS at the solution–air interface was also determined from the surface tension measurements using the Gibbs adsorption equation. Under our experimental conditions, none of the experimental results evidence micelle formation. In addition, volumetric studies of the hexanol–SDS–FA ternary system at 25°C evidence only interactions between the dispersed surfactant and alcohol.     

Trace humic and fulvic acid determination in natural water by cloud point extraction/preconcentration using non-ionic and cationic surfactants with FI-UV detection

A preconcentration and determination method for humic and fulvic acids at trace levels in natural water samples was developed. Cloud point extraction was successfully employed for the preconcentration of humic acid (HA) and fulvic acid (FA) prior to the determination by using a flow injection (FI) system coupled to a spectrophotometric UV-Vis detector. The quantitative extraction of HA and FA within the pH range 1-12 was obtained by neutralization of the anionic charge on the humic substances with a cationic surfactant, hexadecyltrimethylammonium bromide (CTAB). This generated a hydrophobic species that was subsequently incorporated (solubilized) into the micelles of a non-ionic surfactant polyethylene glycol, tert-octylphenyl ether (Triton X-114). The FI method for HA and FA determination was developed by injection of 100 microl of the extracted surfactant-rich phase using an HPLC pump with spectrophotometric detection at 350 nm. A 50 ml sample solution preconcentration allowed an enrichment factor of 167. The limit of detection (LOD) obtained under the optimal conditions was 5 microg l(-1). The precision for ten replicate determinations at 0.2 mg l(-1) HA was 3.1% relative standard deviation (RSD), calculated from the peak heights. The calibration using the preconcentration system for HA and FA was linear with a correlation coefficient (r2) of 0.9997 at levels near the detection limits up to at least 1 mg l(-1). The method was successfully applied to the determination of HA and FA in natural water samples (river water).     

The thermodynamic parameters of solution of L-phenylalanine in water

The heat effects of solution of L-phenylalanine in water were measured over wide concentration and temperature ranges. The enthalpies of solution of L-phenylalanine were found to be independent of the content of the amino acid in solution over the concentration range studied. The standard enthalpies, heat capacities, and entropies of solution of the amino acid and the solubility of L-phenylalanine over the temperature range studied were calculated.     

A new strategy for quality control and qualitative analysis of Yinhuang preparations by HPLC-DAD-MS/MS

A combinative method using fingerprint analysis (FA) and multi-ingredients quantification (MIQ) was developed and validated for the quality control of Yinhuang (YH) preparations including granule, capsule, and lozenge by high-performance liquid chromatography coupled with diode array detection (HPLC-DAD). Common peaks with or without standard references in FA were confirmed or identified by electrospray ionization tandem mass spectrometry (ESI-MS/MS). The chromatographic separations were achieved on a Sepax GP-C(18) column (250?mm?×?4.6?mm i.d., 5?μm) with a gradient elution using a mixture of 0.1?% formic acid methanol solution and 0.1?% formic acid water solution. In quantitative analysis, nine bioactive constituents (chlorogenic acid, caffeic acid, luteoloside, baicalin, luteolin, wogonoside, baicalein, wogonin, and oroxylin A) were simultaneously determined. The detection wavelength was set at 275?nm, 320?nm, and 350?nm according to the absorption properties of the nine quantified compounds. The linearity, recovery, intraday and interday precision, accuracy, limit of detection (LOD) and quantification (LOQ), repeatability and stability were all tested and good results were obtained. In the FA, 320?nm was selected. The correlation coefficients of similarity were determined on the basis of the relative retention time (RRT) and relative peak area (RPA) of 20 common peaks in chromatographic fingerprints. Results indicated that both the RRT and RPA of 20 common peaks shared a close similarity. From the 20 common peaks, 18 compounds, including the nine quantified compounds, were identified or tentatively characterized by comparing their retention times, UV spectra, and MS spectra with those of standard compounds or literature data. The study not only presents a powerful and reliable analytical tool for the quality control of YH preparations, but also provides the chemical evidence for revealing the material basis of their therapeutic effects.     

The thermodynamic characteristics of formation of cobalt(II) ion complexes with D,L-threonine in aqueous solution

The heat effects of interaction of cobalt(II) ions with D,L-threonine in aqueous solution and the corresponding heats of dilution were determined by direct calorimetry at 288.15, 298.15, and 308.15 K and ionic strength values of 0.25, 0.50, and 0.75 (against the background of potassium nitrate). The standard heat effects of formation of CoThr⁺, CoThr₂, and CoThr ₃ ^? complexes were determined by extrapolation to zero ionic strength according to the equation with one individual parameter. The standard enthalpies of formation of complex particles in the hypothetical nondissociated state in aqueous solution were calculated.     

The heat effects of dissociation of N,N-bis-(carboxymethyl)aspartic acid

The heat effects of dissociation of N,N-bis-(carboxymethyl)aspartic acid were measured calorimetrically at 298.15 K and various solution ionic strengths. The standard thermodynamic characteristics of dissociation of the complexone studied were calculated at fixed and zero ionic strength values.     

Catalytic effect of water,ammonia, formic acid,or sulfuric acid on the HCN + H2O reaction in the aqueous solution

Structural Chemistry - The effect of water (W), ammonia (AM), formic acid (FA), or sulfuric acid (SA) on the HCN + H2O reaction in the aqueous solution has been investigated at the...     

Thermodynamics of stepwise dissociation of D,L-tryptophan in aqueous solution

The heat effects of the reaction of a solution of D,L-tryptophan with solutions of KOH and HNO₃ were measured by calorimetry at temperatures of 288.15, 298.15, and 308.15 K and ionic strength values of 0.25, 0.5, and 0.75 (KNO₃). The effect of the temperature and concentration of the background electrolyte on the heats of dissociation of amino acid was considered. The standard heat effects of ionization of D,L-tryptophan were determined by extrapolation to zero ionic strength. The standard thermodynamical characteristics of the stepwise dissociation of D,L-tryptophan were calculated.