Actinide(III) carbonate complexation

The following equations have been developed to estimate trivalent actinide and lanthanide carbonate stability constants: log B₁⁰ = −6.128+35.206R−21.557R²; log B₂⁰ = 14.797+7.945R−10.304R², where B₁⁰ = aMCO₃⁺/(aM³⁺aCO₃²⁻, B₂⁰ = aM(CO₃)₂⁻(aM³⁺(aCO₃²⁻), aX is the activity of ion X, M indicates a metal ion and R is the effective ionic radius of the metal ion in six-fold coordination. These equations describe carbonate stability constants for cerium, europium and ytterbium at zero ionic strength. Constants at zero ionic strength were estimated from experimental determinations made in 0.68 molal NaClO₄ by accounting for medium effects.     

氮对位取代基对联吡啶与Eu(Ⅲ)络合的影响

采用吸收光谱法测定了在CH3CN溶剂中,4,4'-二甲基[2,2']联吡啶、4,4'-二己基[2,2']联吡啶、4,4'-二壬基[2,2']联吡啶、[2,2']联吡啶-4,4'-二羧酸甲酯等氮原子对位含不同电性能取代基的联吡啶与Eu(Ⅲ)的络合物稳定常数。在实验条件下,含烷基取代基(-CH3,-C6H13,-C9H19)的配体观察到1∶3和1∶2两种络合物,而含吸电基(-COOCH3)的仅观察到一种1∶3络合物。以1∶3络合物生成反应为模型反应,采用密度泛函方法计算了络合反应的自由能变化,证实不同电性能对位取代基对络合反应的影响,络合反应自由能变化与取代基的供电性强弱顺序相一致。     

The nature of europium ion in carbonate solution and polarographic determination of micro amounts of europium

The nature of the complex europium carbonate ion in concentrated carbonate solution was studied polarographically. A polarographic method for the determination of micro amounts of europium ion in the presence of diverse ions (and especially lanthanides) was developed.     

Selective complexation and transport of europium ions at the interface of vesicles

The aim of the present work was to design functionalized lipidic membranes that can selectively interact with lanthanide ions at the interface and to exploit the interaction between membranes induced by this molecular-recognition process with a view to building up self-assembled vesicles or controlling the permeability of the membrane to lanthanide ions. Amphiphilic molecules bearing a beta-diketone unit as head group were synthesized and incorporated into phospholipidic vesicles. Binding of Eu(III) ions to the amphiphilic ligand can lead to formation of a complex involving ligands of the same vesicle membrane (intravesicular complex) or of two different vesicles (intervesicular complex). The effect of Eu(III) ions on vesicle behavior was studied by complementary techniques such as fluorimetry, light scattering, and electron microscopy. The formation of an intravesicular luminescent Eu/beta-diketone ligand (1/2) complex was demonstrated. The linear increase in the binding constant with increasing concentration of ligands in the membrane revealed a cooperative effect of the ligands distributed in the vesicle membrane. The luminescence of this complex can be exploited to monitor the kinetics of complexation at the interface of the vesicles, as well as ion transport across the membrane. By encapsulation of 2,6-dipicolinic acid (DPA) as a competing ligand which forms a luminescent Eu/DPA complex, the kinetics of ion transport across the membrane could be followed. These functional vesicles were shown to be an efficient system for the selective transport of Eu(III) ions across a membrane with assistance by beta-diketone ligands.     

Spectrophotofluorometric determination of terbium and europium in potassium carbonate solution

The conditions for the spectrophotofluorometric determination of terbium and europium, in solutions of potassium carbonate, have been established. The apparent excitation and fluorescence wavelengths used, respectively, are 245 mmu and 550 mmu for terbium and 400 mmu and 620 mmu for europium. The fluorescence varies linearly with the concentration of terbium and europium in the range 0.3-70 mug, of terbium/ml and 4-800 mug of europium/ml. Large amounts of gadolinium, lutetium and yttrium do not interfere. Cerium(IV) interferes seriously.     

Spectroscopic investigation on europium complexation with humic acid and its model compounds

Time resolved fluorescence spectroscopy (TRFS) of Eu(III) (an analogue of trivalent actinides) complexation with humic acid (HA) and its model compounds, namely phthalic acid (PA), mandelic acid (MA) and succinic acid (SA) has been carried out at varying concentration ratios of ligand to metal ion. The emission spectra were recorded in the range of 550–650 nm by exciting at an appropriate wavelength. The intensity of the 616 nm peak of Eu(III) was found to be sensitive to complexation. The ratio of the intensities of 616 and 592 nm peaks was used to determine the stability constants of Eu-phthalate, Eu-mandelate and Eu-succinate complexes. In the case of model compounds, the life-time was found to increase with increasing ligand to metal ratio (L/M) indicating the decrease in quenching of the fluorescence by coordinated water molecules with increasing complexation. On the other hand in the case of HA, the life-time was found to be constant at least up to L/M of 5, indicating the formation of outer sphere complex. Beyond L/M = 5 the life-time value was found to increase which can be attributed to the binding of the metal ion to the higher affinity sites in the HA macromolecule.     

Determination of trace europium by adsorptive cathodic stripping voltammetry after complexation with cupferron

This article describes the determination of Eu by adsorptive cathodic stripping voltammetry after complexation with N-nitroso-N-phenylhydroxylamine (cupferron). The accumulation of the complex at the HMDE was performed at 0.0 V and the subsequent potential scan was made in the square wave mode. The analyte signal occurred at −0.88 V. The detection limit is 0.06 nmol dm⁻³. The effect of instrumental and chemical parameters on the peak height and potential was investigated. The same technique can be used for the determination of ytterbium and of the other rare earth elements (REEs) after separation.     

Temperature dependence of the rate constants for reactions of the carbonate radical with organic and inorganic reductants

Rate constants have been measured by pulse radiolysis for the reactions of the carbonate radical, CO₃^·?, with a number of organic and inorganic reactants as a function of temperature, generally over the range 5 to 80°C. The reactants include the substitution-inert cyano complexes of Fe^II, Mo^IV, and W^IV, the simple inorganic anions SO₃^2?, ClO₂^?, NO₂^?, I^?, and SCN^?, several phenolates, ascorbate, tryptophan, cysteine, cystine, methionine, triethylamine, and allyl alcohol. The measured rate constants ranged from less than 10⁵ to 3 × 10⁹ M^?1 s^?1, the activation energies ranged from ?11.4 to 18.8 kJ mol^?1, and the pre-exponential factors ranged from log A = 6.4 to 10.7. The activation energies for the metal complexes and inorganic anions generally decrease with increasing driving force for the reaction, as expected for an outer sphere electron transfer. For highly exothermic reactions, however, the activation energy appears to increase, probably reflecting the temperature dependence of diffusion. For many of the organic reactants, the activation energies were low and independent of driving force, suggesting that the oxidation is via an inner sphere mechanism.     

Temperature dependence of metal-organic heteroepitaxy

The nucleation and growth of 2D layers of tetraphenyl porphyrin molecules on Ag(111) are studied with variable-temperature scanning tunneling microscopy. The organic/metal heteroepitaxy occurs by strict analogy to established principles for metal heteroepitaxy. A hierarchy of energy barriers for diffusion on terraces and along edges and around corners of adislands is established. The temperature is key to activating these barriers selectively, thus determining the shape of the organic aggregates, from a fractal shape at lower temperatures to a compact shape at higher temperatures. The energy barriers for the terrace diffusion of porpyrins and the molecule-molecule binding energy were determined to be 30 meV < E(terrace) < 60 and 130 meV < E(diss) < 160 meV, respectively, from measurements of island sizes as a function of temperature. This study provides an experimental verification of the validity of current models of epitaxy for the heteroepitaxy of organics and is thus expected to help establish design principles for complex metal-organic hybrid structures.     

Characterization of europium(III) carbonate complexes in simulated groundwater by solvent extraction

The complex formation of Eu(III) by bicarbonate/carbonate ions has been studied at 0.1 M ionic strength and 25°C using synergistic solvent extraction system of 1-nitroso-2-naphthol and 1,10-phenanthroline in chloroform. Concentrations of bicarbonate (5·10^–3 to 1·10^–1 M) and carbonate (5·10^–4 to 1·10^–2 M) ions in the aqueous phase have been varied in the pH range of 8.0 to 9.1 to simulate ground and natural water compositions. Under these conditions, the following species have been identified: Eu(HCO₃)²⁺, Eu(HCO₃)₂ ⁺, Eu(CO₃)⁺ and Eu(CO₃)₂ ^–. Their conditional formation constants (log ) have been calculated as 4.77, 6.74, 6.92 and 10.42, respectively. These values suggest that the carbonate complexes of Eu(III) are highly stable.     

Temperature dependence of sorptive deformation

A study has been made of the temperature dependence of deformation of CaA, CaX, and LaX zeolites when krypton or xenon is adsorbed, and also the deformation of activated carbon when dimethyl ether is adsorbed. It has been shown that the volume compressibility and the standard chemical potential of the adsorbate in a vacancy solution, within the interval of temperatures and pressures that were investigated, can be considered as linear functions of temperature. In this case, knowledge of the temperature dependence of sorptive deformation offers a means for calculating sorptive deformation curves for other temperatures.Institute of Physical Chemistry, Russian Academy of Sciences, 117915 Moscow. Institute of Petrochemical Synthesis, Russian Academy of Sciences. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 23–28, January, 1992.     

Temperature dependence of mucin adsorption

The kinetics of adsorption and desorption on a silica-like surface of the large glycoprotein mucin have been measured across a range of temperatures from 25 to 60 degrees C. The area occupied per molecule diminishes with increasing temperature both in the bulk and adsorbed states, implying that the glycoprotein belongs to the "natively open" conformational class. Due to the conformational rearrangement, the specific interaction energy governing desorption greatly increases with temperature, resulting in an impressively regulated temperature-invariant dynamic surface coating.     

A direct carbon-13 and nitrogen-15 NMR study of europium(III) complexation-nitrate and europium(III)-isothiocyanate complexation in aqueous solvent mixtures

A direct, low-temperature nuclear magnetic resonance spectroscopic study of europium(III)-nitrate contact ion-pairing has been completed, and preliminary results for europium(III)-isothiocyanate have been obtained. In water-acetone-Freon mixtures, at –110°C to –120°C, four¹⁵N NMR signals are observed for coordinated nitrate ion. Area evaluations of the signals and their concentration dependence indicate the formation of Eu(NO₃)²⁺, Eu(NO₃) ₂ ¹⁺ , and two higher complexes, possibly the tetra-, with either the penta-or hexanitrato. This correlates well with similar¹⁵N NMR results obtained for Ce(III), Pr(III), Nd(III), and Sm(III). As a result of a higher dielectric constant, complex formation is significantly less in water-methanol mixtures, wheein only three complexes form with Eu(NO₃) ₂ ¹⁺ dominating at the highest anion concentrations. Competitive complexing experiments in water-methanol also were made by³⁵Cl NMR chemical shift and linewidth measurements, as well as¹⁵N NMR. Initial experiments with the Eu³⁺-NCS^– system show four coordinated anion signals, displaced from the bulk anion peak by about –250 ppm and –2,500 ppm in the¹³C and¹⁵N NMR spectra, respectively. Area evaluations are consistent with the presence of Eu(NCS)²⁺ through Eu(NCS) ₄ ^1- in these solutions. A consideration of the chemical shifts identified the nitrogen atom as the site of binding in the NCS^–. A discussion of these preliminary results, as well as those for several other metal-ions, will be presented.     

Temperature dependence of negative ion lifetimes

The autodetachment lifetimes of SF6-* and C6F6-* ions formed by charge transfer in K(np)/SF6, C6F6 collisions are measured as a function of target temperature over the range of approximately 300-600 K with the aid of time-of-flight techniques and a Penning ion trap. At room temperature only formation of long-lived SF6 -* ions with lifetimes tau >or similar to 1 ms is seen. As the temperature is increased the lifetime of these long-lived ions is reduced, some having lifetimes as short as approximately 0.4 ms. The appearance of a short-lived, tau 相似文献   

Temperature dependence of self-diffusion in adamantane

Radiotracer experiments show that self-diffusion in the rotator crystalline phase of adamantane proceeds by a vacancy mechanism. The results are in good agreement with those determined from NMR experiments.     

Surface complexation of carbonate on goethite: IR spectroscopy, structure and charge distribution

The adsorption of carbonate on goethite has been evaluated, focussing on the relation between the structure of the surface complex and corresponding adsorption characteristics, like pH dependency and proton co-adsorption. The surface structure of adsorbed CO3(-2) has been assessed with (1) a reinterpretation of IR spectroscopy data, (2) determination of the charge distribution within the carbonate complex using surface complexation modeling, and (3) evaluation of the proton co-adsorption of various oxyanions, including carbonate, in relation with structural differences. Carbonate adsorption leads to a degeneration of the nu3 IR vibration. Currently, the magnitude of the Deltanu3 band splitting is used as a criterion for metal coordination. However, the interpretation is not unambiguous, since the magnitude of Deltanu3 is influenced by polarization and additional field effects, due to, e.g., H bonding. Our evaluation shows that for goethite the magnitude of band splitting Deltanu3 falls within the range of values that is representative for bidentate complex formation, despite contrarily assignments made in literature. Determination of the charge distribution (CD), derived by modeling available carbonate adsorption data, shows that a very large part (2/3) of the carbonate charge resides in the surface. Interpretation of this result with a bond valence and a ligand charge analysis strongly favors the bidentate surface complexation option for adsorbed carbonate. This option is also supported by the proton co-adsorption of carbonate. The H co-adsorption is very high, which corresponds closely to an oxyanion surface complex in which 2/3 of the ligands are common with the surface. The high H co-adsorption is in conflict with the monodentate option for adsorbed CO3(-2). The study shows that the H co-adsorption of CO3(-2) is almost equal to the experimental H co-adsorption obtained for SeO3(-2) adsorption, which can be rationalized supposing for both XO3(-2) complexes the same ligand distribution in the interface, i.e., bidentate complex formation.     

Temperature and composition dependence of viscosity. II. Temperature dependence of viscosity of propylene carbonate-dimethoxyethane mixtures

The application of the currently used equations for the reproduction of the temperature dependence of viscosity η of binary solvent mixtures of propylene carbonate (PC) and dimethoxyethane (DME) favors the choice of the Vogel-Fulcher-Tammann (VFT) equation using the ideal glass transition point as the reference temperature T_o for the estimation of free and blocked (inaccessible) volumes. Reduced plots show that the free volumes as obtained from the VFT equation mainly determine the viscosities of the liquid mixtures; the blocked volumes V_x(T_o)≡V_o (x: mole fraction of PC) show ideal behavior. The effect of negative excess volumes V ^E on viscosity, studied in the preceding paper, is examined in comparison with the effect of a temperature decrease. The equal signs of η ^E and V ^E can be explained by referring the viscosities to the reference temperature T_o.     

Cation dependence of chloride ion complexation by open-chained receptor molecules in chloroform solution

Seventeen peptides, most having the sequence GGGPGGG, but differing in the C- and N-terminal ends, have been studied as anion-complexing agents. These relatively simple, open-chained peptide systems interact with both chloride and the associated cation. Changes in the N- and C-terminal side chains appear to make little difference in the efficacy of binding. NMR studies suggest that the primary interactions involve amide NH contacts with the chloride anion, and CD spectral analyses suggest a concomitant conformational change upon binding. Changes in binding constants, which are expected in different solvents, also suggest selective solvent interactions with the unbound host that helps to preorganize the open-chained peptide system. Significant differences are apparent in complexation strengths when the heptapeptide chain is shortened or lengthened or when the relative position of proline within the heptapeptide is varied.     

Temperature dependence of the permittivity of water

In a previous work the temperature dependence of the permittivity of some pure normal alcohols was analyzed. The experimental values were fitted to a modification of Onsager’s equation. In this work, the static permittivity of water at different temperatures was measured and its values were fitted to the same equation used for alcohols. One parameter of the fittings agrees with the tendency observed for the alcohols and the other tends to the square of the refractive index. A good agreement was obtained between the experimental values and the fittings, this fact showing that water behaves, under this point of view, like an alcohol.