NUCLEAR SIZE AND SHAPE EFFECTS IN CHEMICAL ISOTOPE ENRICHMENT OF NEODYMIUM USING A CROWN ETHER

ABSTRACT

Neodymium was extracted and isotopically fractionated in the liquid-liquid extraction using a crown ether of dicyclohexano-18-crown-6. The maximum value in isotope enrichment factor was observed on the isotope pair ¹⁴²Nd-₁₅₀Nd, and was ε_142,150 = 0.00084±0.00009: this was 0.00011±0,00001 in terms of the unit mass enrichment factor The isotope enrichment factors showed breakdown of the conventional mass-dependent theory. We presented the advanced theory by use of the nuclear size and shape effect and the nuclear spin effect. The field shift effect was proved to give larger contribution than the nuclear mass effect. The predominance of the field shift effect in this study agreed with our previous studies on samarium and gadolinium.     

Separation of Zinc Isotopes by Liquid-Liquid Extraction Using a Crown Ether

Abstract

The zinc isotope effect in a liquid-liquid extraction system using dicyclohexano-18-crown-6 was investigated. The enrichment factor for a unit difference of mass number was ?_u = 0.018 as a maximum, which is greater than that for magnesium isotopes. The enrichment factor to eliminate ⁶⁴Zn from ⁶⁶Zn, ⁶⁷Zn, ⁶⁸Zn, or ⁷⁰Zn is over 0.036. The isotope with an odd mass number, ⁶⁷Zn, behaved differently from those with even mass numbers. This odd/even isotope effect was ?_O/E = 0.056. From the values of ?_u and ?_O/E, it was found that the crown ether separated the zinc isotopes more effectively on the basis of an odd or an even mass number than of mass difference. The separation factors vary with the concentrations of salt and/or conjugated acid in the initial aqueous phases of extraction. The optimal concentration necessary to obtain the largest separation factor had components of 2.0 M ZnCl₂ and 1.0 M HCl. The large value of ?_u for the high atomic number zinc and the notable ?_O/E make it clear that the vibration frequencies of the intramolecular bonds should have an isotope shift which is recognized in the orbital energy of the atoms.     

NUCLEAR SIZE AND SHAPE EFFECT IN CHEMICAL ISOTOPE EFFECT OF GADOLINIUM USING DICYCLOHEXANO-18-CROWN-6

ABSTRACT

Gadolinium isotopes were fractionated in a liquid-liquid extraction system using dicyclohexano-18-crown-6. The isotope enrichment factors showed breakdowns of the conventional Bigeleisen-Mayer approximation for every condition of the initial phases; the concentrations of gadolinium and hydrochloric acid and the type of organic solvents. The nuclear mass effect and the field shift effect were estimated by use of the isotope pairs ¹⁵²Gd-¹⁶⁰Gd and ¹⁵⁴Gd-¹⁶⁰Gd. Since both isotopes, ¹⁵²Gd and ¹⁵⁴Gd, have the unique characteristics of the nuclear charge radii, <r²>'s, the unusual isotope effects due to the field shifts took place, while the mass effects of the other isotopes canceled the field shift effects. The maximum isotope effect was observed to be ε_160,152 =0·0252 ± 0·0024 whose initial aqueous phase was 0·023 M GdCl₃ in 12 M HC1, and its organic phase was 0·2 M DC18C6 in chloroform: this was 0·00315 ± 0·00030 in terms of the enrichment factor for unit mass.     

GOLD ADSORPTION FROM ALKALINE AUROCYANIDE SOLUTION BY NEUTRAL POLYMERIC ADSORBENTS

ABSTRACT

Isotope effects were investigated for strontium and barium complexes of dicyclohexano-18-crown-6. The isotopes of odd mass number behaved differently than those of even mass number. A value of ε_0/E which represents the difference between the isotope of odd mass number and that of even mass number, was -0.0017 for ⁸⁷Sr,-0.011 for ¹³⁵Ba,and -0.009 for ¹³⁷Ba. The unit mass enrichment factors were ε_u = -0.0009 for strontium and ε_u = 0.004 for barium. The direction of enrichment was opposite for strontium and barium, and the absolute value of the enrichment factor of barium was larger than that of strontium isotopes. This phenomenon was attributed to the difference in the predominant form of the strontium and barium ions in the aqueous solution. That is, the population of aquo-complexes is larger than that of anionic complexes for strontium, while the reverse is the case for barium.     

Contributions of Nuclear Size and Shape,Nuclear Mass,and Nuclear Spin to Enrichment Factors of Zinc Isotopes in a Chemical Exchange Reaction by a Cryptand

ABSTRACT

The isotope effect of zinc in the chemical exchange reaction using a macrocyclic ligand was not found to be ruled by the Bigeleisen-Mayer approximation, which suggested that the enrichment factor is proportional to the mass difference and is inversely proportional to the product of the masses of the isotopes. The separation factors of zinc isotopes in the chemical exchange reaction using cryptand(2_B,2,l) polymer were precisely measured by means of an ICP mass spectrometer equipped with nine collectors as ion detectors. The liquid chromatography of a column packed with the cryptand polymer was used for the separation of the zinc isotopes. The enrichment factor ε_67,66 for ⁶⁷Zn to ⁶⁶Zn was ?3.3329(3) × l0^?4.That for ⁶⁸Zn to ⁶⁶Zn was 1.846(1) × 10 ^?4 and that for ⁷⁰Zn to ⁶⁸Zn was 7.19(2) × 10^?4.They were not scaled with δm/mm′, where δm is the mass difference between the isotope pairs, and m and m′ represent the masses of the isotopes. The isotope effect of zinc is implicated with the isotope shift, and the hyperfine structure shift in the isotopomer of the zinc isotopes. The sum contribution of the vibrational energy shift from one isotope to the other and the nuclear mass shift to the enrichment factor of ⁶⁷Zn was ? 1.05 × 10^?3, and the contribution of the field shift caused by the nuclear size and shape of the isotope was 5.26 × 10^?4. The contribution of the nuclear spin or the hyperfine structure shift to the enrichment factor of ⁶⁷Zn was small: 1.94 × 10 ^?4     

Secondary Isotope Effects Part IV Complex Formation Between Aromatic Hydrocarbons and HCl,

The isotope effects on complex formation between HCl and variously deuterated benzenes and toluenes have been measured at ?80°C, using a differential solubility technique. Both methyl and nuclear deuteration increase the basicity of the hydrocarbon, the two effects being additive in toluene. All the results can be fit with values of: δ F_M^° = ?3.1₅^? cal / g. atom D for methyl deuteration of toluene, and δ F_N^° = ?3.5₆^? cal/g. atom D for nuclear deuteration of either benzene or toluene. The implications of these results for the theory of secondary isotope effects are discussed.     

Solvent Effect in Isotope Exchange Reaction of Strontium by Liquid Chromatography using a Cryptand (2B,2,2) Polymer

Abstract

Strontium isotopes were fractionated using liquid chromatography with a cryptand (2_B,2,2) polymer as a stationary phase. In this study, we observed that the single stage isotope enrichment factor of ⁸⁴Sr shows the following order, water[6.4×10^?3]>MeOH[4.9×10^?3]>DMF[1.1×10^?3]. The enrichment factors observed in this study did not show a mass‐dependent profile, indicating that the mass‐independent isotope effect affects isotope enrichment phenomena. The mass‐dependent and the mass‐independent isotope effects that influence the enrichment factor of ⁸⁴Sr are related to the donor number linearly, implying that the solvation strongly affects the isotope effect.     

Dimethylsulfoxide Augmented Calcium Isotope Effect with Polymer-Bound 18-Crown-6 in a Chromatographic Chemical Exchange System

Abstract

The enrichment of calcium isotopes with polymer-bound 18-crown-6 proceeds according to the following chemical exchange reaction: ⁴⁰Ca²⁺ _(fluid) + ⁴⁴CaL²⁺ _(solid) ? ⁴⁴Ca²⁺ _(fluid) + ⁴⁰CaL²⁺ _(solid) where L_(solid) represents 18-crown-6 bound to a polystyrene solid support. The separation coefficient, ε, for this exchange was found to be larger when dimethylsulfoxide (DMSO) was added to the fluid phase. When a fluid phase of 70% methanol and 30% chloroform (volume) is used as stock solution, ε=0.0035±0.0003 (for the ⁴⁰Ca-⁴⁴Ca isotope pair) after DMSO is added. DMSO was added to the extent of two and five volume percent. This compared to ε=0.0025±0.0002 without DMSO. The difference in the isotope effect is attributed to a change in the coordination sphere of the calcium solvate in the fluid phase.

The stability of the calcium-crown complex was reduced when DMSO was added. The binding constant of the calcium-crown complexation-decomplexation reaction was smallest when the higher concentration of DMSO was used. This was attributed to the formation of a calcium complex with DMSO in the fluid phase.     

Kinetics measurements on a stationary disk electrode in a uniformly rotating fluid (SDERF). II. The electron transfer reaction in the Fe(CN)4−6/Fe(CN)3−6-system

The operation of the SDERF-cell in the study of the electron transfer kinetics of the Fe(CN)^4?₆/Fe(CN)^3?₆-system in 1 M KCl and 1 M KNO₃-solutions at a stationary Pt-disk electrode is reported. The experimental current—overpotential curves are recorded by linear sweep voltammetry and analysed by two different methods using the theoretical relationship derived for a stationary disk electrode placed in a free rotating fluid. Both methods give the same value for the experimental rate constant k*. The effects of the temperature (0° to 40°C) and of the ratio of the rotor radius (r_r) to the electrode radius (r_e)(r_r/r_e = 0.50 to 0.81) have been studied. The activation energy for the redox process in 1 M KCl and 1 M KNO₃ are: E_a = 3.4 ± 0.6 kcal/mol and E_a = 3.7 ± 0.7 kcal/mol respectively, while the k*-values at 25°C are: k* = (5.67 ± 0.41) × 10^?3 cm.s^?1 and k* = (4.53 ± 0.29) × 10^?3 cm.s^?1 respectively. The difference from the standard rate constant k₀ ? 0.100 cm.s^?1 is explained by the effect of the cell-geometry characterized by the G-factor, so that k° = Gk*, where G ? 19 for our cell.     

A DSC study of the polymerization of 2-Vinylpyridine in dimethylformamide

The polymerization of 2-vinylpyridine (2VP) in dimethylformamide (DMF) with azobisisobutyronitrile (AIBN) as initiator was studied with a differential scanning calorimeter. By taking an appropriate amount of AIBN and after correction for its decomposition, the following values could be obtained: Heat of polymerization ΔH_p,o = ?68 ± 4 kJ/mol; overall Arrhenius activation parameters E_a = 90.0 ± 4 kJ/mol and ln A = 24 ± 1.0 (A = 2.6 × 10¹⁰ dm^3/2/mol^1/2. s).     

Separation of Gallium and Indium Isotopes by Cation and Anion Exchange Chromatography

Ion exchange chromatography was applied to study chemical isotope effects of gallium and indium in ligand exchange reactions. A strongly acidic cation and a strongly basic anion exchange resin were used as a solid phase, and aqueous HCl as a liquid phase. On the cation exchanger, the light isotope ⁶⁹Ga was enriched at the front part of the elution band and the heavy isotope ⁷¹Ga at the end part. Instead, the light ¹¹³In isotope was enriched at the end part, and the heavy isotope ¹¹⁵In at the front part. The isotope separation factor ? is equal to 3.3?×?10^–5 for gallium and 2.0?×?10^–4 for indium. On the anion exchanger, the heavy gallium isotope was enriched at the front part, whereas the heavy indium isotope at the end part of the band, with ? equal to ～10^–3 and 1.7?×?10^–4, respectively. This pattern of enrichment is caused by stronger Ga³⁺–OH₂ than Ga³⁺–Cl^? bond, and by inverse order of bond strength for indium. In the displacement method, gallium and indium on anion exchanger also show opposite enrichment of their isotopes, but the ? values (1.5?×?10^–2 for gallium and 5?×?10^–3 for indium) are greater than those found in the elution method, probably due to much higher concentrations of the metals.     

Isothermal and nonisothermal melt‐crystallization kinetics of syndiotactic polystyrene

Analyses of the isothermal and nonisothermal melt kinetics for syndiotactic polystyrene have been performed with differential scanning calorimetry, and several kinetic analyses have been used to describe the crystallization process. The regime II→III transition, at a crystallization temperature of 239°, is found. The values of the nucleation parameter K_g for regimes II and III are estimated. The lateral‐surface free energy, σ = 3.24 erg cm^?2, the fold‐surface free energy, σ_e = 52.3 ± 4.2 erg cm^?2, and the average work of chain folding, q = 4.49 ± 0.38 kcal/mol, are determined with the (040) plane assumed to be the growth plane. The observed crystallization characteristics of syndiotactic polystyrene are compared with those of isotactic polystyrene. The activation energies of isothermal and nonisothermal melt crystallization are determined to be ΔE = ?830.7 kJ/mol and ΔE = ?315.9 kJ/mol, respectively. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2528–2538, 2002     

Thermal and physical properties of allyl PPO and its composite

The thermal behavior of allyl PPO and its cured resin were investigated. In the allyl PPO curing process, the specific temperatures were T_gel = 173.6°C, T_cure = 225.4°C, and T_treat = 237.7°C, and the activation energy (E_a) was 122 kJ/mol. The average number of PPO molecular units between two crosslinking points was about 20. In the degradation process of cured allyl PPO resin, the temperature at which mass loss equaled 1% was much higher than 300°C. The E_a for degradation was calculated as 125 kJ/mol, with a degradation fraction (α) in the range of 0.15–0.65, or 117 kJ/mol with an α of 0.10–0.90. The most probable mechanism function of decomposition of the cured allyl PPO resin was f(α) = 2(1 ? α)^3/2 or g(α) = (1 ? α)^?1/2 ? 1. The thermocompressed laminate of the allyl PPO blending with an additive resin (made from BDM and DP) exhibited the desired properties. ©2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4111–4115, 2006     

Multiplicity of photoluminescence in Raman spectroscopy and defect chemistry of (Ba1−xRx)(Ti1−xHox)O3 (R = La,Pr, Nd,Sm) dielectric ceramics

(Ba_1?xR_x)(Ti_1?xHo_x)O₃ (R = La, Pr, Nd, Sm; x ≥ 0.04) (BRTH) ceramics were prepared using a mixed oxides method. The solubility limits in BRTH with R = La, Pr, Nd, Sm were determined by XRD to be x = 0.11, 0.12, 0.06, and 0.14, respectively. The ionic radius of R at Ti-site plays a decisive role in the solubility limit in BRTH. Only BRTH with R = La satisfied Vegard's law. The multiplicity of photoluminescence (PL) signals of Nd³⁺/Ho³⁺ and Sm³⁺/Ho³⁺ in Raman scattering under 532-nm excitation laser and the high-permittivity abnormality for the denser BRTH with R = Sm and at x = 0.07 were reported. The PL provided the evidence of a small number of Ho³⁺ at Ba-site in BRTH and it was determined that the number of Ba-site Ho³⁺ ions increased from 0.05 at% at R = La to 0.19 at% at R = Sm with increasing atomic number of light rare earth. BRTH exhibited a much broadened dielectric-temperature characteristics, marked by ×5 T, ×6 T, ×7 T, and ×8 S dielectric specifications for BRTH with R = La, Pr, Nd, Sm and at x = 0.06, respectively, and they exhibited lower dielectric loss (tan δ < 0.015) at room temperature. The dielectric-peak temperature (T_m) of BRTH decreased linearly at a rate of less than ?21 °C/%(R/Ho). The defect chemistry, solubility limit, lower dielectric loss, and dielectric abnormality are discussed.     

Iron and hydrogen electrodes in liquid ammonia

Equilibrium potentials of the iron(II)—iron electrode vs TlTlCl; 0.1 M NH₄Cl in liquid ammonia are determined from intersections of Tafel lines for iron deposition and dissolution. The hydrogen electrode is shown to behave reversibly at palladium hydride, but not at platinum with respect to the dependence of hydrogen pressure. The standard potential of iron at 293 K is estimated at E° = ?0,356 (±0,010)V in 0.1 M NH₄NO₃. Standard potentials of other electrodes are reevaluated and shown to be consistent with earlier measurements except for the standard potential of lead. Steady state and transient polarization curves indicate in simple mechanism of the iron electrode involving transfer of iron(II) in one step. The temperature-independent anodic transfer coefficient is α₊ = 0.41 (±0.02), the cathodic transfer coefficient α_? = 0.61 (±0.03). The standard exchange current density at E° is j°_° = 7.10^?7 Acm^?2 for 293 K. Exchange current densities of the hydrogen electrode are j_° = 1.6·10^?9 Acm^?2 at platinized platinum in 0.1 M NH₄Cl both for 293 K.     

Mechanistic studies of ruthenium(III)-catalyzed oxidation of DL-methionine by hexacyanoferrate(III) in an alkaline medium

The kinetics and mechanism of ruthenium(III) catalyzed oxidation of dl-methionine by alkaline hexacyanoferrate(III) (HCF(III)) in an alkaline medium were studied spectrophotometrically at 30±0.1°C. The reaction was first-order-dependent each on [HCF(III)] and [ruthenium(III)] and fractional-order-dependent on [alkali]. The rate of the reaction was found to be decreased with the increase in [methionine]. The main product of oxidation was methionine sulfone nitrile (3-(methylsulfonyl)propanenitrile) and it was identified and confirmed by FT-IR and mass spectral studies. Further, no effect of added reaction product was observed. A plausible mechanism was proposed involving complexation between methionine and ruthenium(III) species, [Ru(H₂O)₅OH]²⁺. Thermodynamic parameters for the reaction, E _a and Δ S ^#, were computed using linear least squares method and are found to be 65.83±1.03 kJ/mol and?249.58±3.35 J/K mol, respectively.

     

Two-electron tin centers with a negative correlation energy in lead sulfide

The valence and coordination states of the impurity tin centers in the lead sulfide crystal lattice were determined by emission Mössbauer spectroscopy. Tin atoms that replace lead atoms are two-electron donors with negative correlation energy. The correlation energy U = ?0.072 ± 0.004 eV, as well as the positions of the first (E _V + E ₁ = 0.079 ± 0.002 eV) and second (E _V + E ₂ = 0.151 ± 0.004 eV) ionization energies, were determined (E _V is the energy of the top of valence band).     

Use of gas chromatography/isotope ratio-mass spectrometry to study triglyceride metabolism in humans

The study of triglyceride (TG) metabolism using stable isotope tracers would be facilitated by being able to detect low¹³C enrichment. To meet this goal, we developed a gas chromatography/isotope ratio-mass spectrometry technique to measure the enrichment of palmitate in nonesterified fatty acids (NEFA) and TG as its methyl derivative. This method allows accurate and reproducible measurements of enrichment as low as 0.009 mole percent excess (MPE), in a range between 0–0.65 MPE. The usefulness of this method is shown by two studies of lipid metabolism in human beings. First, we studied the metabolic fate of an oral TG load labeled with [1,1,1-¹³C₃]tripalmitin. Labeled palmitate appeared concurrently in plasma NEFA and TG, and four hours after the load, the labeling was higher in NEFA than in TG (MPE NEFA: 1.53±0.31 vs. MPE TG: 0.78±0.06,P<0.05). In a second study, the hepatic reesterification of NEFA was estimated by measuring the appearance of infused [1-¹³C]palmitate in circulating TG. The estimated contribution of plasma NEFA to circulating TG increased to a maximum of 22%. Thus, gas chromatography/isotope ratio-mass spectrometry appears to be a useful tool for future studies of lipid metabolism in humans.     

A novel economical grain boundary engineered ultra-high performance ZnO varistor with lesser dopants

A varistor having ultra-high performance was developed from doped ZnO nanopowders using a novel composition consisting of only three (Bi, Ca and Co oxides) dopants. Improved varistor properties were obtained (breakdown field (E_b) 27.5?±?5?kVcm^?1, coefficient of nonlinearity (α) 72?±?3 and leakage current density (L_c) 1.5?±?0.06?μAcm^?2) which are attributed to the small grain size and grain boundary engineering by phases such as Ca₄Bi₆O₁₃ and Ca_0.89Bi_3.11O_5.56 along with Co⁺² doping in the ZnO lattice. Complex impedance data indicated three relaxations at 25?°C and two relaxations at high temperature (>100?°C). The complex impedance data were fitted into two parallel RC model to extract electrical properties. Two stages of activation energy for DC conductivity were observed in these varistor samples where region I (<150?°C) is found to be due to shallow traps and region II (<225?°C) is due to deep traps. The novel composition is useful for commercial exploitation in wide range of surge protection applications.     

Lanthanide(II) amide complexes: Efficient initiators for the living polymerization of methyl methacrylate

Lanthanide(II) complexes supported by amido ligands, [(C₆H₅)(Me₃Si)N]₂Ln(DME)₂ [Ln = Sm ( 1 ) or Yb ( 2 ); DME = 1,2‐dimethoxyethane] and [(C₆H₃? ⁱPr₂‐2,6)(Me₃Si)N]₂Ln(THF)₂ [Ln = Sm ( 3 ) or Yb ( 4 ); THF = tetrahydrofuran], were found to initiate the polymerization of methyl methacrylate (MMA) as efficient single‐component initiators (in toluene for 3 and 4 and in toluene with a small amount of THF for 1 and 2 ) to produce syndiotactic polymers. The catalytic behavior was highly dependent on both the amido ligand and the polymerization temperature. Initiators 3 and 4 initiated MMA polymerization over a wide range of temperatures (20°C to ?40°C), whereas the polymerization with 1 and 2 proceeded smoothly only at low temperatures (≤0°C). The kinetic behavior and some features of the polymerizations of MMA initiated by 3 and 4 were studied at ?40°C. The polymerization rate was first‐order with the monomer concentration. The molar masses of the polymers increased linearly with the increase in the polymer yields, whereas the molar mass distributions remained narrow and unchanged throughout the polymerization; this indicated that these systems had living character. A polymerization mechanism initiated by bimetallic bisenolate formed in situ was proposed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009