Isotope exchange study of the dissociation of metal —humic substance complexes

Isotope exchange was employed to study dissociation of metal cations from their complexes with humic substances (HS). Dissociation of cation from HS controls the rate of isotope exchange between two identical metal-HS solutions (but for the presence of a radiotracer) divided by a dialysis membrane. The rate of isotope exchange of Eu/¹⁵²Eu and Co/⁶⁰Co in the systems with various HS was monitored as a function of pH, ionic strength, and the degree of HS loading with metal. The apparent rate of Eu-HS dissociation was found to be enhanced by decreasing pH, increasing ionic strength, and increasing metal loading. Co-HS dissociation was too fast to be followed by the method. For interpretation of the experimental kinetic data, the multiple first order law has been applied. Based on the results, a concept of HS as a mixture of two types of binding sites is discussed.     

Surface charge and adsorption properties of polyethylene in aqueous solutions of inorganic electrolytes

Summary The streaming potentials of several sorts of polyethylene were determined as a function of p_H and composition of aqueous solutions and the electrokinetic (zeta) potentials were calculated. The results were compared with the electrokinetic properties of glass and polystyrene. It has been found that H⁺ and OH^– ions are potential-determining on polyethylene. The surface of polyethylene is charged negatively above p_H 2.5, probably due to dissociation of carboxyl groups, contained on polyethylene as a result of its oxidation during its polymerization and/or further processing. The zeta potentials depend in a rather complicated way on the concentration of various 11 inorganic electrolytes. The probable interpretation of this dependence has been given and conclusion was derived about the absence of compact adhered layer of water molecules at the surface of polyethylene. The results of the present work may be of some importance for elucidating the adsorption properties of polyethylene.

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Zusammenfassung Die Strömungspotentiale verschiedener Arten von Polyäthylen wurden als Funktion des p_H-Wertes und der Zusammensetzung wäßriger Lösungen bestimmt und aus diesen die elektrokinetischen Potentiale (Zeta) berechnet. Die Ergebnisse wurden mit den elektrokinetischen Eigenschaften von Glas und Polystyrol verglichen. Es zeigt sich, daß H⁺- und OH^–-Ionen auf Polyäthylen potentialbestimmend sind. Die Oberfläche des Polyäthylen ist oberhalb p_H 2,5 negativ geladen, vermutlich entsprechend der Dissoziation von Carboxylgruppen, die als Ergebnis der Oxydation während der Polymerisation und/oder weiterer Verarbeitungsprozesse im Polyäthylen enthalten sind. Die Zeta-Potentiale hängen in ziemlich komplizierter Weise von der Konzentration verschiedener ein-einwertiger anorganischer Elektrolyte ab. Die wahrscheinlichste Interpretation dieser Abhängigkeit wurde gegeben und Schlüsse über die Abwesenheit kompakter adsorbierter Schichten von Wassermolekülen auf der Oberfläche des Polyäthylens gezogen.Die Ergebnisse der vorliegenden Arbeit mögen von einiger Bedeutung für die Erkenntnisse der Adsorptionseigenschaften von Polyäthylen sein.

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The authors are indebted to Dr.P. Skivan for helpful discussion of the streaming potential method and to Dr.J. Hradil for kindly supplying the polyethylene samples.     

Extraction of microamounts of caesium into different organic solvents in the presence of sodium dipicrylaminate

A study has been made of the extraction of microamounts of caesium from the aqueous phase into 28 organic solvents in the presence of sodium dipicrylaminate and nitrate, and the extraction of macroamounts of ceasium and rubidium dipicrylaminates from nitrobenzene and nitromethane into some other organic solvents. The equilibrium constants of the reaction Cs _a ⁺ +Na _O ⁺ =Cs _O ⁺ +Na _a ⁺ were determined and a correlation with the water content of the organic phase has been discussed.     

Effect of natural clay components on sorption of Cs, Pu and Am by the clay

Sorption of Cs, Pu and Am on natural clay of complex composition was studied to better understand the sorption mechanisms. It was found that cesium sorption to natural clay was affected by its coatings and by the ionic strength of solution. The sorption of Pu and Am on the clay was compared with that on synthetic goethite, hematite and magnetite, representing components of the clay coatings. The sorption was quantitatively interpreted using models assuming ion exchange and/or complex formation on the “layer sites” and “edge sites” of the clay and its coatings. Constants characterizing properties of the sites and sorption equilibria were determined.     

Thermodynamic evaluation of the (LiF + NaF + BeF2 + PuF3) system: An actinide burner fuel

In this work the LiF–BeF₂, NaF–BeF₂, and BeF₂–PuF₃ binary phase diagrams have been thermodynamically assessed. The first two systems have been optimized based on the known experimental data, whereas the last one has been treated ideally. To describe the excess Gibbs parameters of the liquid solution the modified quasi chemical model based on the quadruplet approximation has been used. The results obtained together with the data of the (LiF + PuF₃), (NaF + PuF₃), and (LiF + NaF) systems, which have been assessed in previous studies, were used to extrapolate the (LiF + NaF + BeF₂ + PuF₃) quaternary system. The calculated (LiF + NaF + BeF₂) ternary subsystem has been compared with the experimental results published in literature. The nuclear fuel properties such as the melting behaviour, the vapour pressure, or the solubility of PuF₃ in the matrix of LiF–NaF–BeF₂ have been derived based on our assessment and compared with measurements in literature.     

Methods for determination of all binding parameters in systems with simultaneous borate and cyclodextrin complexation

Two novel methods for determination of binding constants in the systems with borate and cyclodextrin complexation were developed. The methods enable to determine all binding parameters in these systems and even the binding constants of interaction of a neutral analyte with a neutral cyclodextrin. The first method is based on nonlinear fitting of experimental data and further evaluation of fitting parameters. The second method requires a multiple regression. The methods provide identical results with low experimental error. Only one set of measurements is required for both methods. Thus the binding parameters can be mutually compared. The binding parameters for neutral analytes ((R,R)-(+)-hydrobenzoin and (S,S)-(-)-hydrobenzoin) and neutral cyclodextrin (heptakis(2,6-di-O-methyl)-β-cyclodextrin) were evaluated and the effect of individual types of interaction was revealed. The interaction of the analytes with cyclodextrin governs the chiral recognition, while the complexation of analyte with borate is responsible for electromigration. Very low values of the binding constants of mixed analyte-cyclodextrin-borate complexes indicate that this type of complexation has negligible effect on enantioseparation.     

Complexes H2CO:PXH2 and HCO2H : PXH2 for X=NC,F, Cl,CN, OH,CCH, CH3, and H: Pnicogen Bonds and Hydrogen Bonds

Ab initio MP2/aug’-cc-pVTZ calculations have been carried out to investigate H₂CO : PXH₂ pnicogen-bonded complexes and HCO₂H : PXH₂ complexes that are stabilized by pnicogen bonds and hydrogen bonds, with X=NC, F, Cl, CN, OH, CCH, CH₃, and H. The binding energies of these complexes exhibit a second-order dependence on the O−P distance. DFT-SAPT binding energies correlate linearly with MP2 binding energies. The HCO₂H : PXH₂ complexes are stabilized by both a pnicogen bond and a hydrogen bond, resulting in greater binding energies for the HCO₂H : PXH₂ complexes compared to H₂CO : PXH₂. Neither the O−P distance across the pnicogen bond nor the O−P distance across the hydrogen bond correlates with the binding energies of these complexes. The nonlinearity of the hydrogen bonds suggests that they are relatively weak bonds, except for complexes in which the substituent X is either CH₃ or H. The pnicogen bond is the more important stabilizing interaction in the HCO₂H : PXH₂ complexes except when the substituent X is a more electropositive group. EOM-CCSD spin-spin coupling constants ^1pJ(O−P) across pnicogen bonds in H₂CO:PXH₂ and HCO₂H : PXH₂ complexes increase as the O−P distance decreases, and exhibit a second order dependence on that distance. There is no correlation between ^2hJ(O−P) and the O−P distance across the hydrogen bond in the HCO₂H : PXH₂ complexes. ^2hJ(O−P) coupling constants for complexes with X=CH₃ and H have much greater absolute values than anticipated from their O−P distances.