Surface Tension Measurements for Binary Mixtures of Chlorobenzene or Chlorocyclohexane + Tetrahydrofuran at 298.15 K

Surface tensions (σ) for the binary mixtures chlorocyclohexane + tetrahydrofuran and chlorobenzene + tetrahydrofuran at 298.15 K and 1.013 bar have been determined as a function of the mole fraction. In order to analyze the surface tension behavior, the extended Langmuir (EL) and Shereshefsky models were used and parameters of the models were obtained for these mixtures. The standard Gibbs energy of adsorption (\( - \Delta G^{\circ} \)) was calculated using both models. The Gibbs energy change for replacing 1 mol of solute with 1 mol of solvent in the surface region (?G _S), and the excess number of molecular layers of solute in the surface region, were calculated using Shereshefsky’s model. The magnitudes of ?G _S and \( - \Delta G^{\circ} \) are discussed in terms of the nature and type of intermolecular interactions in the binary mixtures.     

Determination of Protonation Constants of O-Phospho-<Emphasis Type="SmallCaps">l</Emphasis>-serine in Aqueous Solution: Potentiometry,Microcalorimetry, NMR Spectroscopy and Quantum Chemical Calculations

O-Phospho-l-serine is one of the naturally occurring phosphorylated amino acids, having important pharmacological activity and bioactivity. The protonation constants of O-phospho-l-serine were determined by means of potentiometric titrations at 25 °C and ionic strength of 0.5 mol·L^?1 (NaCl). The heat effects of the protonation reaction of the O-phospho-l-serine were measured by direct calorimetry. NMR spectroscopy has demonstrated that the first protonation site occurs at the nitrogen atom in the amino group, followed by one of the oxygen atoms in the phosphono group, and finally the carboxyl oxygen atom. This trend is in good agreement with the enthalpy of protonation and quantum chemical calculations. These data will help to predict the speciation of O-phospho-l-serine in physiological systems.     

Solution Chemistry of Arsenic Anions in the Presence of Metal Cations

The interaction of arsenic(V) and arsenic(III) oxyanions with metal cations was investigated by potentiometry under temperature and ionic strength conditions approaching those prevailing in natural waters. The selection includes the major metal cations and some other ions of high environmental relevance. Ionic pairs [M(As^VO₄)]^?, [M(HAs^VO₄)] and [M(H₂As^IIIO₃)]⁺ formation is suggested for all +2 metal cations, based on the potentiometric results. These ion-pairs between arsenic anions and other metal cations are hardly ever mentioned or taken into account when arsenic speciation in natural waters is considered. These results provide the basis for studying arsenic speciation in natural aquatic systems, on which environmental fate, bioavailability and toxicity of the element depend. Some extrapolations to the conditions of the natural waters are presented as well as some insights into the adsorption process onto hydrous oxides.     

Cystine as Ligand of Calcium(II) and Magnesium(II) in Two Ionic Media and at Two Different Temperatures (25 and 37 °C)

Cystine plays an important role in human physiology, it is the precursor of cysteine. Cystine is the molecular form preferred by the immunity cellules system, included macrophages. Although slightly soluble, it can be a ligand towards cations because it is a sulfur-containing amino acid. Because of the physiological importance of calcium(II) and magnesium(II), complex formation between these cations and cystine was studied potentiometrically by employing electrochemical cells involving glass electrodes. The investigation was performed at two temperatures (25 and 37) °C and in two ionic media (1.00 and 0.15 mol·dm^?3 NaCl). In both ionic media, the adoption of a constant ionic medium allows extension of the investigation to a large range of reagent concentration. As the formation of weak complexes was foreseen, the low solubility of cystine is an advantage. Experimental data can be explained in any case by assuming the formation of mononuclear complexes in the presence of both calcium(II) and magnesium(II). The relative stability constants were determined.     

Comments on “Thermodynamic Models for Correlation of Solubility of Hexaquocobalt(II) Bis(<Emphasis Type="Italic">p</Emphasis>-toluenesulfonate) in Liquid Mixtures of Water and Ethanol from 288.15 to 333.15 K”

Mathematical representations reported by Yu et al. for the CNIBS/R–K model and a hybrid model are carefully examined in regards to the model’s ability to predict the solubility of hexaquocobalt(II) bis(p-toluenesulfonate). The equation coefficients reported by Yu et al. were found to give calculated mole fraction solubilities in ethanol that exceed unity for both models.     

Ionization Constants of DL-2-Aminobutyric Acid and DL-Norvaline Under Hydrothermal Conditions by UV–Visible Spectroscopy

The first and second ionization constants for the amino acids DL-2-aminobutyric acid (DL-2-aminobutanoic acid) and DL-norvaline (DL-2-aminopentanoic acid) were determined under hydrothermal conditions, from 175 to 275 °C at 10 MPa, using thermally-stable colorimetric pH indicators (acridine, 4-nitrophenol and 2-naphthoic acid). The measurements were carried out by UV–visible spectroscopy using a high-temperature, high-pressure platinum flow cell with sapphire windows, which minimized the effects of thermal decomposition. The results were combined with literature values from titration calorimetry at 25–130 °C to yield an extended van’t Hoff model for the temperature dependence of the ionization constants for the carboxylic acid and ammonium groups, \( K_{\text{a,COOH}} \) and \( K_{{{\text{a,NH}}_{3}^{ + } }} \), over the entire temperature range. The experimental results for the second ionization constant \( K_{{{\text{a,NH}}_{3}^{ + } }} \) at elevated temperatures are consistent with the predictions from the Yezdimer–Sedlbauer–Wood functional group additivity model, but for the first ionization constant \( K_{\text{a,COOH}} \) are not. This suggests that the group contribution parameters for the standard partial molar heat capacity of the carboxylic acid group are in error, or that nearest neighbor interactions between the –COOH and \( - {\text{NH}}_{3}^{ + } \) groups cause a breakdown in the functional group additivity relationship.     

Determination of the Distribution of Cupric Chloro-Complexes in Hydrochloric Acid Solutions at 298 K

The distribution of metal-chloro complexes in hydrochloric acid solutions is a fundamental aspect of anion exchange reactions that allows ultrahigh purification during hydrometallurgical processes. However, these exchange reactions are not yet understood in detail. To clarify and improve anion exchange separation so as to obtain a more sophisticated purification process, it is necessary to accurately determine the distribution of metal-chloro complexes. In the present work, cupric-chloro complexes were investigated because copper is one of the most important base metals in modern society. The absorption spectra of solutions of these complexes were acquired at 298 K and analyzed by multivariate curve resolution–alternating least squares method (MCR–ALS), a factor analysis technique widely used in chemometrics. The resulting cupric-chloro complex distributions were fitted with a thermodynamic model using appropriate activity coefficients extended to the concentrated solutions. These calculations employed a modified Debye–Hückel model because the distributions acquired through the model-free MCR–ALS analysis were less meaningful, both physically and chemically. It was concluded that five [Cu^IICl _n ]^2?n species, where n = 0–4, are present in the hydrochloric acid solutions. In addition, cumulative formation constants and pure molar attenuation coefficients were obtained.     

Thorium(IV) and neptunium(V) uptake from carbonate containing aqueous solutions by HDTMA-modified natural zeolites

The ²³²Th-uptake ([Th(IV)]° = 9.7 × 10^?5 M) from carbonate solutions ([CO ₃ ² ]_tot = 0.25 M, 9.0 < pH_c < 10.8) by raw and HDTMA-modified HEU-type zeolitic-, chabazitic- and phillipsitic-tuffs was investigated. The strong uptake by the HDTMA-tuffs at pH_c≈9 was assigned to the Th(CO₃) ₅ ^6? and ThOH(CO₃) ₄ ^5? predominance. The sorption coefficients (R _d) decreased with increasing pH_c indicating carbonate competition. Enhanced R _d values for pH_c > 10.5 are likely due to ThO₂(am)-precipitation. The ²³⁷Np-uptake ([Np(V)]° = 2.6 × 10^?5 M) from carbonate solutions ([CO ₃ ² ]_tot = 0.25 and 3.0 × 10^?4 M) by raw and HDTMA-modified HEU-type zeolitic tuff and pulverized pure heulandite crystals was studied under Ar-atmosphere at 6 < pH_c < 11. The R _d values for both elements indicated the modified tuffs potential to remove tetravalent- and pentavalent actinides from environmental matrices.     

Plutonium concentration and <Superscript>240</Superscript>Pu/<Superscript>239</Superscript>Pu isotopic ratio in the surface soils from the Jiuquan region in northwestern China

Surface soil samples collected in the Jiuquan region in the downwind area of the Chinese nuclear test site (CNTs) were analyzed for Pu isotopes. The ^239+240Pu activities ranged from 0.025 ± 0.009 to 0.89 ± 0.16 mBq g^?1, varying significantly with different sampling sites. The Dunhuang city that is located in the southwestern part of the Jiuquan region received the heaviest Pu deposition (^239+240Pu activities, 0.23–0.89 mBq g^?1). Most of the ²⁴⁰Pu/²³⁹Pu isotopic ratios were similar with that of the global fallout. However, the low values (0.080–0.147) observed in three sampling sites further supported the finding of Pu originated from CNTs in that region.     

A novel method for separating Cs<Superscript>+</Superscript> from liquid radioactive waste using ionic liquids and a selective extractant

Selective separation of Cs ⁺ from liquid radioactive waste by “precipitation” was observed in a hydrophobic ionic liquid containing the Cs ⁺ -selective extractant dicyclohexano-18-crown-6. The precipitate was formed by the cation exchange mechanism, which simplified the treatment of Cs ⁺ after extraction. Solid–liquid extraction is a more economical extraction system than liquid–liquid extraction because it uses smaller quantities of ionic liquids. This work showed the possibility of developing a new method for removing Cs ⁺ from liquid radioactive waste using solid–liquid phase separation instead of the conventional liquid–liquid separation in an ionic liquid extraction system.