Sorption and diffusion of HTO and cesium in crushed granite compacted to different lengths

In this study, batch and through-diffusion experiments have been performed in order to determine the distribution coefficients (K _d ), apparent diffusion coefficients (D _a ) and retardation factor (Rf), respectively. Both apparent and effective diffusion coefficient (D _a and D _e ) of Cs were obtained by accumulative concentration method developed by Crank (1975). In addition, a non-reactive radionuclide, HTO, was initially conducted in through-diffusion experiment for assessing the ability of radionuclide retardation. The distribution coefficients (K _d ) obtained by batch tests in 14 days under aerobic and anaerobic systems were 2.06 and 3.52 ml/g. Moreover, it is found in through-diffusion test that Rf = 4.12 and 4.40 and K _d = 0.97 and 1.06 of Cs did not have an obvious discrepancy in a length/diameter/ (L/D) ratio of 0.44 and 1.78. However, Rf and K _d revealed a larger difference in an L/D ratio closing to 1 due to the geometric change of one-dimension diffusive hypothesis. Therefore, it demonstrates that Rf and K _d obtained by through-diffusion experiments only could be achieved at a lower or larger L/D ratio and would be reliable for long-term performance assessment.     

Determination of sorption and diffusion parameters of <Superscript>99</Superscript>Tc in crushed granite using through-diffusion experiments

Diffusion and sorption are important processes associated with radionuclides migration in crystalline rock. These processes are studied in the laboratory using borehole core samples. In this study, we obtained distribution coefficients (K _d), apparent diffusion coefficients (D _a) and retardation factor (R _f) using batch and through-diffusion experiments. The \( R_{\text{f}}^{\text{H/Tc}} \) and \( K_{\text{d}}^{\text{H/Tc}} \) values obtained using the accumulative concentration method were lower than those derived in the batch experiments. These findings demonstrate that reliable R _f and K _d values of ⁹⁹Tc can be obtained using through-diffusion experiments with a non-reactive radiotracer, thereby bolstering confidence in the assessment of the long-term performance of disposal repositories.     

Thermal and kinetic studies of epoxidized natural rubber in lithium salts-epoxidized natural rubber polymer electrolytes

The thermal and kinetic studies of epoxidized natural rubber (ENR) and its polymer electrolytes, LiX/ENR PEs, (where X = ClO ₄ ^? , CF₃SO ₃ ^? , COOCF ₃ ^? , I^?, and BF ₄ ^? ) were carried out using thermogravimetric analysis at different heating rates. The thermal behaviors for LiX/ENR PEs are closely related to the morphology and interactions between the LiX and ENR chains. The LiCF₃SO₃, LiCOOCF₃, and LiI form pseudo-crosslinking within the ENR; their thermal behavior resembled purified ENR. The LiClO₄ tends to form aggregates within the ENR. This phenomenon has promoted a much earlier decomposition of epoxide in the ENR. The occurrence of ring-opening and complexation or cross-linking reactions in and between the ENR chains in the LiBF₄/ENR has produced a thermally stable macrostructure. The activation energy for the thermal degradation (E _d) of purified ENR was 239.8 and 239.9 kJ mol^?1 using Kissinger and FWO methods, respectively. According to the Coats–Redfern method, the degradation mechanism of purified ENR follows the F₁ type model, while the Criado method revealed that the degradation starts with F₁ followed by D₃ type models. The E _d for LiX/ENR (X = COOCF ₃ ^? , CF₃SO ₃ ^? , I^?, and BF ₄ ^? ) PE’s obtained via the Kissinger method are 258.5, 257.0, 251.0, and 198.9 kJ mol^?1, respectively, and the corresponding E _d values obtained by FWO are 236.0, 223.6, 349.7, and 206.6 kJ mol^?1, respectively. The degradation of ENR in these PEs followed the D₃ type model. However, for LiClO₄/ENR, the presence of two distinct degradations of ENR gave two E _d values. These are 174.5 and 234.7 kJ mol^?1 using Kissinger and 117.8 and 293.6 kJ mol^?1 using FWO method. The degradation mechanism of ENR in the LiClO₄/ENR PE was similar to purified ENR that is F₁ followed by D₃ type models.     

Lifetime measurements of the 2p 3d 3 D 1, 2, 3 0 and 2p 3d 1 P 1 0 levels in NII by beam-foil-laser spectroscopy

Accurate lifetimes measured by means of the cascade-free method based on laser excitation of a fast ion beam preexcited in a carbon foil are reported for four 2p 3d levels in NII. The lifetime results are: τ(2p 3d ³ D ₁ ⁰ )=0.209±0.007 ns, τ(2p 3d ³ D ₂ ⁰ )=0.219±0.007 ns, τ(2p 3d ³ D ₃ ⁰ )=0.217±0.005 ns, and τ(2p 3d ¹ P ₁ ⁰ )=0.410±0.017 ns. These results are compared to theoretical and experimental lifetimes reported previously.     

Diffusion of cesium and selenium in crushed mudrock

In this study, the diffusion behavior of cesium and selenium with 10⁻⁴M concentration in mudrock was studied by trough-diffusion tests and summarized in order to provide confidence on long-term performance assessment of nuclear waste repositories. The diffusion process of Cs and Se reached equilibrium after 60 and 500 days, respectively. Besides, it also displays that the distribution coefficients (K _d ) of Se in through-diffusion tests is higher than that of Cs in agreement with that obtained from the batch method. The K _d value (15.14±1.99 mL/g) of Cs by diffusion techniques is equivalent to that of batch method (15.10±0.40 mL/g) because sorption of Cs was assumed to fast sorption step. However, the K _d value of Se (137.58±12.20 mL/g) derived from the diffusion technique is higher than that from batch tests (76.72±2.96) and showed an obvious variation with K _d of Cs. The difference of K _d between diffusion and batch methods resulted from the fact that 14 days were not long enough to reach equilibrium or stable state in the batch method.     

Determination of sorption and diffusion parameters of Se(IV) on crushed granite

Sorption and diffusion are important processes for the transport of radionuclides through geomedia from a radioactive disposal facility. In this study, batch tests and through-diffusion experiments were performed to investigate the sorption and diffusion of Se(IV) in crushed granite. Different column lengths of 2, 4 and 8, were employed in the through-diffusion experiments to study the effect of the column length on the apparent diffusion coefficients. Synthetic groundwater (GW) and synthetic seawater (SW) were the liquid phases in these experiments. A two-site kinetic linear model and the Freundlich isotherm were applied to match the sorption/desorption batch data quite closely for both of GW and SW conditions. The retardation factors (R _f ) were estimated by comparing the breakthrough curve of Se(IV) with that of HTO. Experimental results indicated that whether in GM or SW solution, the column lengths did not significantly affected D _a or R _f of Se in crushed granite.     

Hyperfine structure measurements in Kr II

The fast ion beam laser technique has been utilized to study the hyperfine structure in the transitions 4d ⁴ D _7/2-5p ⁴ D ₇ ^2/0 at 6420 Å and 4d ⁴ D _7/2-5p ⁴ D ₅ ^2/0 at 6303 Å in singly-charged krypton. The magnetic dipole and electric quadrupole hyperfine constants have been extracted for the upper levels of the transitions.     

Velocity cross correlations in binary mixtures of simple fluids

The velocity cross correlation integrals $$D_{{\text{ab}}}^{\text{J}} = (N/3)\mathop \smallint \limits_{\text{o}}^\infty< {\text{v}}_{{\text{1a}}} ({\text{t}}) \cdot {\text{v}}_{{\text{2b}}} (0) > {\text{dt,}} {\text{a}} {\text{ = }} {\text{1,2;}} {\text{b}} {\text{ = }} {\text{1,2}}$$ can be estimated from the intradiffusion coefficients D ₁ ^° and D ₂ ^° at each mole fraction x₁ of component 1 on the basis of the exact relations among the Onsager phenomenological coefficients together with an assumed equation relating the joint diffusion coefficients D _ab ^J . The results from several such equations are compared with experimental data and with similar results derived by Hertz in a different way to represent the behavior of f _ab ≡D _ab ^J x _b in ideal reference systems. In some cases the agreement with experimental data for relatively ideal systems is even better than given by Hertz's results. For greater accuracy in predicting the D _ab ^J from D _a ^dg data one would need a prediction of the limiting value of D _aa ^J at x_a=0 for a=1,2. Presently known theory does not give a basis for estimating this limit reliably.     

Low-temperature thermodynamic properties of L- and DL-valines

Heat capacities C _p(T) of L-valine and DL-valine were measured in the temperature range 6–300 K with an adiabatic calorimeter; thermodynamic functions were calculated based on these measurements. At 298.15 K, the values of heat capacity, C _p; entropy, S _m ⁰ (T) ? S _m ⁰ (0); enthalpy, H _m ⁰ (T) ? H _m ⁰ (0) of L-valine are equal, respectively, to 167.9 ± 0.3 J K^?1 mol^?1; 178.5 ± 0.4 J K^?1 mol^?1; and 27510 ± 60 J mol^?1. For DL-valine, these values are equal, respectively, to 167.3 ± 0.3 J K^?1 mol^?1, 174.4 ± 0.3 J K^?1 mol^?1, and 27000 ± 50 J mol^?1. The difference between the heat capacities of enantiomer and racemate has been calculated and compared with the similar data for serines, cysteines, and phenylglycines.     

The influence of pH on diffusion of 75Se(IV) in Beishan granite

The through-diffusion method and batch sorption experiments were used to explore the influence of pH on the diffusion behavior of ⁷⁵Se(IV) in matrix Beishan granite (BsG). In the pH range of 2.0–8.5, the D_e values of ⁷⁵Se(IV) in BsG decreased first and then increased with pH increasing, while the changing trend of K_d was nearly opposite. It was speculated that the influence of pH on the diffusion of ⁷⁵Se(IV) in BsG was due to the joint effects of different species distribution of Se, change in surface charge of BsG and change in ionic strength at various pH values.

     

An Improved and Validated LC Method for Resolution of Panthenol

An improved LC method was developed and validated for determination of enantiomeric purity of panthenol in bulk drugs. The method is based on derivatization of panthenol with 3,5-dinitrobenzoyl chloride. Baseline separation with resolution >2.7 was achieved within 20 min on Kromasil CHI-DMB (250 × 4.6 mm) column using n-hexane:ethanol (95:5 v/v) as mobile phase at a flow rate of 1.5 mL min^?1. The analytes were detected by their UV absorbance at 265 nm. The effects of ethanol, 2-propanol and temperature on enantioselectivity and resolution of enantiomers were evaluated. The method was extensively validated and proved to be robust. The recoveries were between 98.3 and 101.4% with <1.6% relative standard deviation. The regression equations for the derivatives of d-panthenol and l-panthenol were y ₁ = 18.01x ₁ ? 32.56 (r ₁ ²  = 0.9984) and y ₂ = 17.855x ₂ ? 28.16 (r ₂ ²  = 0.9990), respectively. The LOD and LOQ for the derivative of d-panthenol were 10.6 and 37.4 μg mL^?1 and for the derivative of l-panthenol were 12.1 and 40 μg mL^?1, respectively. The improved method was found to be simple, rapid, and sensitive for the determination of enantiomeric purity of panthenol in bulk drugs.     

Carbohydrate recognition of symmetrical tripodal receptor type tris(2-aminoethyl)amine derivatives

Carbohydrate recognition of some bioactive symmetrical tripodal receptor type tris(2-aminoethyl)amine (TAEA) derivatives was investigated. In calorimetric experiments, the highest binding constant (Ka) of compound C (C₃₅H₄₉N₅O₄S) with methyl α-d-mannopyranoside was Ka = 858 M^?1 with 1:1 stoichiometry. Formation of hydrogen bonds in binding between symmetrical tripodal receptor type compound C and sugars was suggested by the large negative values of ?H° (=?34 to ?511 kJ mol^?1). In a comparison of each set of α- and β-anomers of some monosaccharides (methyl α/β-d-galactopyranoside, methyl α/β-d-glucopyranoside, and methyl α/β-l-fucopyranoside), compound C showed that the binding constant of β-anomer was larger than that of the corresponding α-anomer, indicating higher β-anomer selectivity. The calculated energy-minimized structure of the complex of compound C with guest methyl α-d-mannopyranoside is also presented. The experimental results obtained from this work indicated that symmetrical tripodal receptor type TAEA derivative C has a lectin-like carbohydrate recognition property.     

Theoretical Investigation on the Interaction of C2H Radical with Small Gold Clusters Au n 0/− (n = 1–4)

A density-functional theory investigation on the interactions between C₂H radical and small gold clusters Au _n ^0/? (n = 1–4) has been performed. The calculated results predict that C₂H radical inclines to interact with small gold clusters Au _n ^0/? (n = 1–4) as an integrity in the most stable structures of C₂HAu _n ^0/? (n = 1–4). The Au _n ^0/? (n = 1–4) clusters retain their structural integrity as units in the ground states of C₂HAu _n ^0/? (n = 1–4). The stretching vibrational frequencies of C≡C and C–H in the ground states of C₂HAu _n ^? (n = 1–4) are decreased compared with those of the C₂H radical due to the interaction between the Au _n ^0/? clusters and C₂H radical. Smaller red shifts in the C≡C and C–H stretching bands of C₂HAu _n ^? occur with an increase in n. The photoelectron spectra of the most stable structures of C₂HAu _n ^? (n = 1–4) have been simulated to aid their future experimental characterizations. The current study provides further insight into the interaction between C₂H radicals and gold clusters, which may lead to exploitation of the high activity of gold nanocrystals.     

Group VB transition metal oxide clusters M4O n −/0 (M = Nb, Ta; n = 8–11): structural evolution and chemical bonding

The structural and electronic properties of two series of Group VB transition metal oxide clusters, M₄O _n ^? and M₄O _n (M = Nb, Ta; n = 8–11), are investigated using density functional theory calculations. Generalized Koopmans’ theorem is applied to predict the vertical detachment energies and simulate the photoelectron spectra. Large highest occupied molecular orbital–lowest unoccupied molecular orbital gaps are observed for these two stoichiometric M₄O₁₀ clusters and estimated to be 3.98 and 4.38 eV for M = Nb and Ta, respectively. The M₄O ₁₀ ^?/0 (M = Nb, Ta) clusters are polyhedral cage structures with high symmetry (T _d for the neutral and D _2d for the anion) in which each metal atom joints three bridging and one terminal O atoms. For the Nb oxide species, Nb₄O ₈ ^?/0 and Nb₄O ₉ ^?/0 can be viewed as removing two and one terminal O atoms from Nb₄O ₁₀ ^?/0 , respectively. The Ta species follow the same rule to the Nb species, except that the anionic Ta₄O₈ ^? is formed by removing one terminal and one bridging O atoms from Ta₄O₁₀ ^?. The Ta₄O₉ containing a localized Ta³⁺ site can readily react with O₂ to form the Ta₄O₁₁ which can also be viewed as replacing a terminal oxygen atom in Ta₄O₁₀ by a peroxo O₂ unit, whereas the added oxygen atom is found to be a bridging one in the O-rich clusters Nb₄O ₁₁ ^?/0 and the anionic Ta₄O₁₁ ^?. Molecular orbital analyses are performed to analyze the chemical bonding in the tetra-nuclear metal oxide clusters and to elucidate their structural and electronic evolution.     

Pressure and isotope effects on the proton jump of the hydroxide ion at 25°C

The limiting molar conductances Λ⁰ of potassium deuteroxide KOD in D₂O and potassium hydroxide KOH in H₂O were determined at 25°C as a function of pressure to disclose the difference in the proton-jump mechanism between an OH^? (OD^?) and a H₃O⁺ (D₃O⁺) ion. The excess conductance of the OD^? ion in D₂O λ _E ^O (OD ^-), as estimated by the equation $$\lambda _E^O (OD^ - ) = \Lambda ^O (KOD/D_2 O) - \Lambda ^O (KCl/D_2 O)$$ increases a little with pressure as well as the excess conductance of the OH^? ion in H₂O $$\lambda _E^O (OH^ - ) = \Lambda ^O (KOH/H_2 O) - \Lambda ^O (KCl/H_2 O)$$ However, their rates of increase with pressure are much smaller than those of the excess deuteron and proton conductances, λ _E ^O (D ⁺) and λ _E ^O (H ⁺). With respect to the isotope effect on the excess conductance, λ _E ^O (OH ^-)/λ _E ^O (D ⁺) decreases with presure as in the case of λ _E ^O (H ⁺)/λ _E ^O (D ⁺), but the value of λ _E ^O (OH ^-)/λ _E ^O (OD ^-) itself is much larger than that of λ _E ^O (H ⁺)/λ _E ^O (D ⁺) at each pressure. These results are ascribed to the difference in the pre-rotation of water molecules, which is brought about by the difference in the intial orientation of the rotating water molecule adjacent to the OH^? (OD^?) or the H₃O⁺ (D₃O⁺) ion.     

β-d-Xylosidase from Selenomonas ruminantium: Thermodynamics of Enzyme-Catalyzed and Noncatalyzed Reactions

β-d-Xylosidase/α-l-arabinofuranosidase from Selenomonas ruminantium is the most active enzyme known for catalyzing hydrolysis of 1,4-β-d-xylooligosaccharides to d-xylose. Temperature dependence for hydrolysis of 4-nitrophenyl-β-d-xylopyranoside (4NPX), 4-nitrophenyl-α-l-arabinofuranoside (4NPA), and 1,4-β-d-xylobiose (X2) was determined on and off (k _non) the enzyme at pH 5.3, which lies in the pH-independent region for k _cat and k _non. Rate enhancements (k _cat/k _non) for 4NPX, 4NPA, and X2 are 4.3?×?10¹¹, 2.4?×?10⁹, and 3.7?×?10¹², respectively, at 25 °C and increase with decreasing temperature. Relative parameters k _cat ^4NPX/k _cat ^4NPA, k _cat ^4NPX/k _cat ^X2, and (k _cat/K _m)^4NPX/(k _cat/K _m)^X2 increase and (k _cat/K _m)^4NPX/(k _cat/K _m)^4NPA, (1/K _m)^4NPX/(1/K _m)^4NPA, and (1/K _m)^4NPX/(1/K _m)^X2 decrease with increasing temperature.     

Anionic charge effects on the crystal structures of Re6 octahedral cluster based compounds: The structure of the cubic bromide K2Re6S6Br8

The title compound synthesized by solid state reaction crystallizes in the cubic system (Pn-3) witha=13.433 Å. The structure has been determined by singlecrystal X-ray diffraction and shows that the compound is based on isolated |(Re₆S ₆ ⁱ Br ₂ ⁱ )Br ₆ ^a |^2? units. The K⁺ cations occupy two different sites. Steric effects lead to the switching from the cubic symmetry present in KRe₆Se₅Cl₉ to the monoclinic one in the case of KRe₆S₅Br₉ and again the former cubic symmetry in the new compound K₂Re₆S₆Br₈.     

Ab initio MRD-CI study of neutral and charged Ga2, Ga3 and Ga4 clusters and comparison with corresponding boron and aluminum clusters

MRD-CI calculations were performed on Ga, Ga₂, Ga₃, Ga₄ and on the corresponding positive and negative ions. In general, pseudopotentials were used, and 4s4p/2s2p basis sets withs andp diffuse functions and one or twod functions. For Ga₂, all-electron calculations were also performed. For Ga ₂ ^(±) , potential functions for ground and low-lying excited states are given. For Ga ₃ ^(±) , geometries were optimized both inC _2v andD _∞h symmetry. The lowest state of Ga ₃ ⁺ is found to be¹Σ _g ⁺ , of Ga₃ ⁴ A ₂, and of Ga ₃ ^{? 1} A ₁ (D _3h ). Ionization potentials and electron affinities of Ga₃ were evaluated. Many low-lying excited states of Ga ₃ ^(±) were found. Rhombic (D _2h , including squareD _4h ), tetrahedral (T _d ), T-shaped (C _2v ) and linear structures (D _∞h) were investigated in the search for the lowest state of Ga₄. A square-planar arrangement of the nuclei, withR _e = 5.30 a₀, was found to have the lowest energy. The other geometries lie about 0.5 eV higher. InD _2h symmetry, low-lying excited states of Ga₄, as well as ground and excited states of Ga ₄ ⁺ and Ga ₄ ^? were studied. Geometries, ionization potentials, electron affinities, atomization and fragmentation energies of Ga _n are compared with corresponding data for B _n and Al _n . Typical changes in going from first-row to third-row atoms are observed.     

Analytical photoion spectroscopy applied to dissociative single and double photoionization of diatomic molecules (H2, N2, O2, CO,and NO)

This work reports the principle, advantage, and limitations of analytical photoion spectroscopy which has been applied to dissociative photoionization processes for diatomic molecules such as H₂, N₂, CO, and NO. Characteristic features observed in the differential photoion spectra are summarized with a focus on (pre)dissociation of(i) multielectron excitation states commonly observed in the inner valence regions,(ii) shape resonances, and(iii) doubly charged parent ions. Possible origins for negative peaks in the differential spectra are discussed. This spectroscopy is applied to the reported photoion branching ratios for D₂ (and H₂ at high energies). The main findings are as follows: (1) The direct dissociation of theX ²Σ _g ⁺ (1sσ _g ) state of D ₂ ⁺ , the two-electron excited state¹Σ _u ⁺ (2pσ _u 2sσ _g ) of D₂, and the²Σ _u ⁺ (2pσ _u ) state of D ₂ ⁺ appear clearly in the differential spectrum, as previously observed for H₂. (2) Decay of H ₂ ⁺ (D ₂ ⁺ ) to H⁺ (D⁺) above 38 eV is due to the direct dissociation of highly excited states of H ₂ ⁺ (D ₂ ⁺ ) such as the²Σ _g ⁺ (2sσ _g ) and high-lying Rydberg states converging on H ₂ ²⁺ (D ₂ ²⁺ ). (3) In the ionization continuum of H ₂ ²⁺ (D ₂ ²⁺ ) peculiar dissociation pathways are observed. The differential photoion spectra for O₂ derived from the reported photoion branching ratios are also presented. The (pre)dissociation of theb ⁴Σ _g ^? ,B ²Σ _g ^? , III²Π _u ,²Σ _u ^? , and^2,4Σ _g ^? states of O ₂ ⁺ appears as the corresponding positive values in the spectra in accord with previous observations. Some other dissociation pathways possibly contributing to the spectra are discussed including dissociative double ionization.