Diffusion coefficients of ions through ion excange membrane in Donnan dialysis using ions of different valence

Donnan dialysis with an ion exchange membrane was investigated for ions of different valence. The effective diffusion coefficients (D_e) of various kinds of ions in the membrane were obtained by fitting of the equation derived from the Nernst–Planck equation to three or more sets of experimental data for Donnan dialysis. It became apparent that the value of D_e/D_s of monovalent ions (e.g., K⁺ or Na⁺ ions) at z_A=1 and z_B=2 (feed ions are monovalent ones and driving ions are bivalent ones) remained constant at ca. 1/210 and that of bivalent ions (e.g., Ca²⁺, Cu²⁺, or Mg²⁺ ions) remained constant at ca. 1/526 where D_s denotes the diffusion coefficient of ions at infinite dilution in water calculated from the Nernst–Einstein equation, and z_A and z_B represent the valences of the feed and driving ions, respectively. D_e/D_s of monovalent ions (e.g., H⁺, K⁺, or Na⁺ ions) at z_A=2 and z_B=1 (feed ions are bivalent ones and driving ions are monovalent ones) was constant at ca. 1/23.3 and that of bivalent ions remained constant at ca. 1/58.4. It was proved that D_e/D using D_e at z_A=1 and z_B=2 was constant at 1/3.0 and that at z_A=2 and z_B=1 remained constant at 3.0 where D represents the diffusion coefficient of ions in the membrane at z_A=z_B (the valences of both feed and driving ions are equal). Therefore, it was found that a large flux of ions could be obtained using the monovalent driving ions in Donnan dialysis. On the other hand, the small flux can be obtained using bi- or higher-valent driving ions.     

Application of ring study: water toxicity determinations by bioluminescence assay with Vibrio fischeri

Acceptance of toxicity bioassays as effective analytical tools in environmental areas needs guarantees of standardization but also validation. Ten European laboratories took part in an inter-laboratory study using different commercial devices based on bioluminescence inhibition of bacteria Vibrio fischeri. Reproducibility and stability by short toxicity endpoints, effective concentration that gives 10%, 50% and 80% of inhibition (EC₁₀, EC₅₀ and EC₈₀) is evaluated. Parametric and non-parametric statistic is applied and performance of participant laboratories is addressed by z-scores calculated by non-parametric statistic. z-Score classification was based on harmonised protocol for proficiency testing of analytical laboratories (satisfactory |z| ≤ 2; questionable 2 < |z| ≤ 3; unsatisfactory |z| > 3). Tested samples were phenol, 3,5-dichlorophenol and influent wastewater. Based on z-score classification, more than 70% of the laboratories showed a satisfactory performance for phenol, 3,5-dichlorophenol and influent wastewater (86%, 90% and 70%, respectively). Reproducibility and stability was observed in toxicant references and in wastewater samples. EC₈₀ determination appears to be more robust that EC₁₀ and EC₅₀. EC determinations can be considered favorable at 5 and 15 min of exposition, in particular for EC₈₀. The use of different commercial devices can not be considered an additional source of variation.     

Thermodynamic properties of the intermediate phases of the Ag-Sb-Se system

The emf (?) dependence of C|Ag|AgI|glass Ag₂GeS₃|D|C galvanic elements on temperature is studied in the range of 470 to 575 K (C represents current electrodes, D denotes equilibrium three-phase alloys of individual Ag-Sb-Se systems, and AgI|glass Ag₂GeS₃ is a bilayer membrane with purely ionic (Ag⁺) electroconductivity). Analytical equations ? = ?(T) are used to calculate the thermodynamic functions of saturated solid solutions of the AgSbSe₂, Sb₂Se₃, and Ag₂Se phases of the Ag-Sb-Se system in the standard state.     

The structure of low temperature triplet energy traps in organic solids from pmdr spectroscopy 11. 1,3,5-Trichloro and hexachlorobenzenes

The new technique of polarized microwave PMDR spectroscopy is used to determine the structure of the low temperature (1.6 – 4.2°K) triplet energy traps. The structure of 1.3,5-trichlorobenzene (Tri-CB) and hexachlorobenzene (HCB) molecules in hexamethylbenzene (HMB) host as well as in their own neat crystals (present as x-traps) is determined from the linear polarization characteristics of their optically detected microwave zerofield (zf) transitions as well as from the analysis of their phosphorescence emission. The former technique gives the direction of the principal magnetic axes of these trap molecules in the crystal as well as the relative order of their zf levels.ln HMB host, deviation from trigonal symmetry is found to be only slight for HCB and absent for Tri-CB. ln the neat crystals, large deviations from trigonal symmetry are observed for the traps of both HCB and Tri-CB. In HCB x- traps, the HCB molecule is found to be slightly contracted along the CCl axis near parallel to the c′ crystal axes. Deviation From planarity is also strongly suggested by the large value of the zf parameter D. ln addition, the principal magnetic axis of the 2|E| moment for HCB x-traps is found to lie only 5° off the molecular N axis. The |D| + |E| and |D| — |E| moments, however, are 15° away from the A and B molecular axis, respectively.In Tri-CB neat crystal. two traps are observed optically with their phosphorescence origins 10 cm^?1 apart. The zf parameter E is found to have a non-zero value and is opposite in sign for the two traps. If the distortion is to be blamed on pseudo-Jahn-Teller forces, the results lead to the conclusion that the x-(shallow) trap is contracted while the y- (deep) trap is expanded along an in-plane axis going through the CCl bonds near parallel to the a axis of the Tri-CB crystal. The plane containing the |D| + |E| and |D| — |E| moments of the x-trap suffers a rotation around the N-molecular axis, which is almost parallel to the 2|E| moment. Th |D| + |E| moment is 10° off the A axis and the |D| — |E| moment is 10° off the B axis. The 2|E| transition moment of the y-trap lies off the molecular N axis and the plane containing the |D| + |E| and |D| — |E| moments moves upward from theThe results of these and other studies suggest that low temperature trapping in neat crystals of this type results from crystal induced geometrical and orientational changes in the molecules at point defects. The observed traps are those molecules for which the crystal field induced deformation leads to a lowering in their singlet-triplet transition energy as compared with that for the host lattice.     

X-traps in isotopically mixed benzene crystals: phosphorescence spectrum and zero-field splitting of the lowest triplet state

We have observed temperature-dependent X-trap phosphorescence in C₆H₆ crystals doped with C₆D₆. The observed X-trap is identified as C₆H₆ which is perturbed by the presence of C₆D₆ in a nearest-neighbor crystal site. Zero-field optical-microwave double resonance measurements on the X-traps give for the zero-field anisotropy parameter |E| a value of 20 ± 5 MHz. This is an order of magnitude smaller than that observed for C₆H₆ in C₆D₆ and indicates for the X-traps a nearly hexagonal distribution of spin density in the ³B_1u state. This difference shows that the electronic structure of the ³B_1u state is sensitive to subtle changes in its environment.     

Diffusion in polyacrylate aqueous systems at 25°C. Role of reference frame choice in interpreting diffusion coefficient data

Diffusion coefficients have been measured for the binary systems sodium polyacrylate-water and polyacrylic acid-water at 25°C as a function of concentration. Diffusion coefficients have been also measured for the ternary system sodium chloride-sodium polyacrylate-water at constant NaCl concentration and varying polyacrylate concentration. The experimental results have been compared with some limit expressions, available in literature, for the four D _ik diffusion coefficients of systems containing two electrolytes with a common ion. The ternary system shows strong interaction between flows: as the polyelectrolyte concentration, C₂, approaches zero, the main diffusion coefficient D₂₂ and the cross coefficient D₂₁ approach zero, while the cross coefficient D₁₂ reach quite high values. The water motion during the diffusion process is also discussed.     

The minimal energy conformations of o-benzosemiquinone anion radicals in the solvents containing the alkali metals and the alkali earth metals

The minimal energy conformations of o-benzosemiquinone anion radicals in the solvents containing the alkali metals and the alkali earth metals were calculated by using the INDO method and the molecular geometry adjusting method. Our previous calculations of o-benzosemiquinone anion radical in the lithium ion solution showed that the total energy of the minimal energy conformation in the case of the assignment |A₃| > |A₄| were lower by approximately 320 kcal/mol than that in the case of the assignment |A₃| > |A₄|. Therefore, the calculations of the minimal energy conformations of o-benzosemiquinone anion radicals in the metal ion solutions were carried out in the cases of the assignment |A₃| > |A₄|. The conformations in both assignments A₃ < A₄ < 0 and (A₃ < 0 < A₄ and |A₃| > |A₄|) were calculated. Although the metal ions were not explicitly contained in the molecular geometries, the minimal energy conformations are considered to be close to the real minimal energy conformations of o-benzosemiquinone anion radicals in the metal ion solutions. The C? O bond lengths has a good positive rank correlation with the stabilities of o-benzosemiquinone radicals in the divalent metal ion solutions and the bond angles ∠C₃C₄H₄ had a good negative rank correlation with those stabilities.     

Expansion of potential 1/r12 of c‐spherical harmonics

The expansion coefficient C^D_|L| of Coulomb potential 1/r₁₂ of atomic system in hyper‐spherical harmonics is derived and the explicit expression is given.     

The influence of an electric field on the wetting of an SiO2 film by ionic liquids

The electrowetting of a dielectric SiO₂ film 100 nm thick by drops (D = 2–3 mm) of [C₄mIm][PF₆], [C₆mIm][PF₆], and [C₆mIm][BTI] ionic liquids was studied at |U| ≤ 60 V in a ～10^?8 mbar vacuum. Electrocapillary curves of the dependence of the wetting angle on electric field potential were constructed with an accuracy of ±1 deg. In conformity with the Young-Lippman equation, the wetting angle θ° decreased by the parabolic law from 51° to 43° for [C₄mIm][PF₆], from 48° to 38° for [C₆mIm][PF₆], and from 35° to 27° for [C₆mIm][BTI] as |U| increased at 298 K. The electrocapillary curve branches were situated symmetrically in the (θ°, U) coordinates with respect to the line passing through the point U = 0; that is, zero-charge potential is zero for the electrowetting of the dielectric film by the ionic liquids. The capacitance of the double electrical layer at the ionic liquid-dielectric interface was determined. This value was found to be 4.65, 2.93, and 1.73 μF/m² for the electrowetting of the SiO₂ film at 298 K by the ionic liquids specified, respectively.     

Optical activity of oriented molecules III. The absorption process and the vibrational coupling effects for the tensor of rotation

Equations for the rotation and the ellipticity of samples exhibiting linear and circular birefringence and dichroism (i.e. for small elliptical birefringence and dichroism) are given. By this a second presentation of the frequency dependence for linear and circular birefringence of anisotropic solutions is developed. The absorption coefficients of anisotropic solutions for linearly polarized light are calculated from the H-matrix of Gō. For a special type of orientational distribution function the absorption behaviour is analysed. Within the adiabatic approximation and by neglecting the variation of the electronic transition moments with the nuclear distances, the structure of a circular dichroism band is independent of the orientational distribution function. Empirically, this is not the case for α, β-unsaturated keto steroids. By including this variation in the adiabatic approximation the coordinates of the tensor of rotation R^NnKk_ij are altered by different amounts due to the coupling by vibrations of the involved states with other electronic states of the system (Herzberg-Teller method). As a consequence of this coupling electric dipole and magnetic dipole/electric quadrupole transition moments not belonging to the observed transition |K⁰> ← |N⁰> are added to the zeroth order tensor of rotation R^NK_ij. Le., first order tensor of rotation R^LM/PR_ij = $\text{1}\text{4}$ <μ_k>_LM|ε_kli <C_tj>_PR + ε_klj<C_lj>_PR}, multiplied by a mixing parameter depending on the type of vibration have to be added to R^NK_ij. As a consequence, the structure of the CD band will depend on the orientational distribution function. The model developed is demonstrated for molecules with symmetry D₂.     

Theoretical study of the electronic transition moment for the d 3IIga 3IIu band system of the C2 molecule

Large scale ab initio SCF and CI calculations are employed to study the potential curves for the d ³II_g, a ³II_u and X¹Σ⁺_g states of the C₂ radical. The electronic transition moment R_e′e″ for the Swan bands (d ³II_ga ³II_u) is calculated in various AO and MO basis sets as a function of the internuclear CC distance. The form of the Σ|R_e′e″|² curve is in very good agreement with that obtained recently from measurements of Danylewych and Nicholls and Tatarczyk et al.; the calculated value for Σ|R_e′e″² at 2.44 bohr is found to be 5.2 au² compared to the most recent experimental values of |R_e(r_oo)|² = 3.57 au² of Tatarczyk et al.     

Covalence reduction factors of four-coordinated pseudo-tetrahedral paramagnetic compounds inD 2d symmetry

Theoretical expressions for the covalence reduction factors of orbital angular momentum and spin-orbit coupling in pseudo-tetrahedral four-coordinated paramagnetic complexes withD _2d symmetry, denoted ask's andR's respectively, have been derived. p ]The mixing coefficients in the antibonding MO's for the CuCl ₄ ^2- ion in three complexes are estimated using suitable approximations. It is shown thatk's must be less thanR's in Tinkham's approximation. Certain misconceptions existing in the literature regarding the value of the integral 〈p _u |???u|s〉 have been clarified.     

Raman study of ratational diffusion in methyl iodide

The usefulness of Raman and NMR spin relaxation spectroscopic methods in probing the details of molecular motions in liquids is demonstrated in a study of methyl iodide. Analysis of the lineshape of the ν₃ Raman band of methyl iodide as a function of temperature yields values of the perpendicular component D_⊥ of the diffusion tensor D_i and an activation energy of reorientation perpendicular to the C₃ axis of the molecule of 2.1 kcal/mole. Coupling the Raman data with ²D NMR spin relaxation data yields values of D_| and an activation energy for reorientation about the C₃ axis of 0.4 kcal/mole indicating quasi-free rotation for this motion. Thus the reorientational motions of methyl iodide are shown to be highly anisotropic in the liquid state.     

Standard pH values for potassium hydrogenphthalate reference buffer solutions in 10, 30 and 50% (w/w) 1,4-dioxane/water mixed solvents at temperatures from 288.15 to 318.15 K

Standard pH(S) values for 0.05 mol kg^?1 potassium hydrogenphthalate (KHpH) reference buffer solutions in 10, 30 and 50% (w/w) 1,4-dioxane/water solvent mixtures within the temperature range 288.15–318.15 K are determined from e.m.f. measurements of the cell without transference Pt|H₂|KHPh + KCl|AgCl|Ag|Pt. The consistency of the results is analysed by a recently described method of multilinear regression of the quantity p(a_Hγ_Cl) as a function of both solution composition and temperature. The standard pH(S) determined can be reproduced to within ±0.01 by the equation pH(S) - 4.004 + 3.309w + 0.408z + 1.037w³ - 14.95zw² + 27.1zw³, where w is the weight fraction of dioxane in the solvent mixture,z = (T –θ)/θ, and θ - 298.15 K. Values of the first ionization constant of phthalic acid (H₂Ph; benzene-1,2-dicarboxylic acid) in the above solvent mixtures are also determined from e.m.f. measurements of the cell without transference Pt|H₂|H₂Ph + KHPh + KCl|AgCl|Ag|Pt.     

Determination of binding constants of multiple charged cyclodextrin complexes by ACE using uncorrected and ionic strength corrected actual mobilities of the species involved

In this study, the apparent binding constants and limiting mobilities of the multiply charged complexes of the Δ− and Λ−enantiomers of Ru(II)- and Fe(II)-polypyridyl associates ([Ru(2,2′-bipyridine)₃]²⁺, [Ru(1,10-phenanthroline)₃]²⁺, and [Fe(1,10-phenanthroline)₃]²⁺) with single-isomer 2,3-diacetylated-6-sulfated-cyclodextrins (CDs) (12Ac-6S-α-CD, 14Ac-7S-β-CD, and 16Ac-8S-γ-CD) were determined by ACE using uncorrected and ionic strength corrected actual mobilities of the species involved. Two limiting models were tested for the ionic strength correction of the actual mobilities based on an empirical relation for the ionic strength correction of multivalent ionic species. In model 1, the nominal values of the charge numbers (z_S,nom) and analytical concentrations (c_S,nom) of the above CD selectors in the BGEs were applied for calculation of the BGE ionic strength, as usual. In model 2, the CD selectors were considered as singly charged species (z_S = −1) with |z_S,nom|-times higher concentrations in the BGE than their analytical concentrations (c_S = |z_S,nom| × c_S,nom) in the calculation of the BGE ionic strength. In all three cases–with uncorrected actual mobilities as well as with actual mobilities corrected according to the two limiting models–the measured effective mobilities of the above enantiomers fit well the theoretical curves of their mobility dependences on the CD selectors concentrations in the BGE, with high average coefficients of determination (R² = 0.9890–0.9995). Nevertheless, the best physico-chemically meaningful values of the apparent binding constants and the limiting mobilities of the enantiomer-CDs complexes with low RSDs were obtained using the actual mobilities of the species involved corrected according to model 2.     

Effect of long-range hydrodynamic and direct intermacromolecular forces on translational diffusion

Within the framework of recently formulated microscopic theories of macromolecular diffusion it is shown that hydrodynamic forces act always to diminish the influence of direct forces, but never to reverse the sign of the correction term due to direct forces alone. Although the correction term D(k) to the intrinsic diffusion coefficient may vary with scattering vector |k|, it is shown that a reversal in sigh of the correction term with increasing |k|, if it occurs, must be associated with an amplitude of less than 10% of the correction term at |k| = 0. At |k| = 0 direct repulsive forces are predicted to always increase the apparent diffusion constant, even after accounting for hydrodynamic interactions. Although experiments on polylysine (1 mg/ml) at salt concentrations above 0.01 M are in qualitative accord with the theory, below 10^?3 M salt the apparent diffusion coefficient is reduced by a factor of about 20, concomitant with a much reduced intensity of scattered light. The strong contradiction of the theory implied by this observation is attributed to a dramatic rise in Stokes friction arising from long-range interionic forces in the low-salt solutions.     

Microwave spectrum,barrier to internal rotation and dipole moment in 5-methyl-pyrimidine

The microwave rotational spectrum of 5-methyl-pyrimidine has been investigated in the region from 8 to 27 GHz, the three types of lines to be expected for a molecule of this symmetry and with a very low sixfold barrier hindering internal rotation of the methyl top have been found: m = 0; |m| ≠ 0,3; |m| = 3n. From the m = 0 (a-type transitions) the rotational constants A′ (less methyl top) = 6108.41, B = 2642.198, C = 1844.196 MHz and the dipole moment μ = 2.881D have been determined. From the wide splitting of the lines |m| = 3, |k| = 1 the potential barrier has been derived as V₆ = 11.73 cal/mole.     

Diffusing probe measurements in Newtonian and elastic solutions

The diffusion coefficients of polystyrene latex spheres and hematite particles in both Newtonian and elastic liquids have been measured using dynamic light scattering. The diffusion coefficients of the latex particles measured in glycerol/water (Newtonian) solutions obey Stokes–Einstein behaviour over a range of solvent viscosities and temperatures. Two apparent diffusion coefficients for the particles are measured in visco-elastic polyacrylamide and polyacrylate solutions and are designated D_fast and D_slow. The apparent fast diffusion coefficients measured in the elastic solutions show an increase to a maximum, above that measured in the solvent water, with increasing polyelectrolyte concentration. At higher polyelectrolyte concentrations the observed D_fast values decrease below the value obtained in the solvent water. D_fast increases with the scattering vector squared (q²) while D_slow, is independent of q².     

Relation of gas-transport parameters of amorphous glassy polymers to their free volume: Positron annihilation study

Correlations of transport parameters (diffusion coefficients D and permeabilities P of gases) and thermodynamic parameters (solubility coefficients S and parameters C′ _H of sorption isotherms) with the sizes of free-volume elements, v _h, as estimated via positron annihilation lifetime spectroscopy are analyzed for the first time on the basis of the data array obtained for glassy polymers. Correlations of logD and logP with 1/v _h that agree with the free-volume model under the condition of a weak change in the concentration of free-volume elements in different polymers are ascertained. Certain deviations from linear correlations with 1/v _h for polymers with high free volumes are interpreted as evidence that the connectivity (openness) of pores increases with the sizes of free-volume elements. For solubility coefficients and Langmuir parameters of sorption capacity C′ _H , good linear correlations with the value of v _h are demonstrated.     

IR and Raman study of rotational relaxation of furan and thiophene. I. Bandwidths. Comparison of the rotations about the principal axes of inertia

IR absorption and Raman scattering bandwidths of some fundamental modes of A₁, B₁ and B₂ species of furan and thiophene and their temperature dependence have been studied. This analysis has been carried out on the pure liquid phase. Rotational A, bandwidths are directly obtained. Rotational B₁ and B₂ bandwidths are deduced by using the Rakov model. The same activation energy U accounts for all the results concerning the reorientations around the three principal axes of inertia. The rotational diffusion coefficients D_x,D_y and D_z are then deduced from the rotational IR bandwidths. The results allow us to conclude that quasi isotropic molecular rotations occur in the liquid phase.