Chronoammetric Determination of the Lithium Transfer Rate in Carbon Electrodes

The diffusion processes, which proceed in an Li _x C₆ electrode under potentiostatic conditions (when a potential step is applied), are considered. The passive film, which continuously exists on the surface of the electrode, has a pronounced effect on the current–time plot and quantitative diffusion parameters, which are determined chronoammetrically. An analytical solution of the diffusion problem is obtained for small deviations from equilibrium. Experimental current–time plots for thin lithium–carbon electrodes are well described by the theoretical equations; simultaneously, the passive-layer resistance, the diffusion coefficient for lithium in carbon, and the derivative of the electrode potential with respect to its composition, , are determined.     

The effects of aqueous solvent structure on the mutarotation kinetics of glucose

The mutarotation rates of glucose in aqueous mixtures of tetrahydrofuran andtert-butanol in the mole fraction (x_i) range 0i<0.2 have been measured at 5° intervals in the range 5–35°C. The kinetic deuterium isotope effects have been determined for the same solvent compositions at 25 and 35°C. A statistical analysis of the Arrhenius plots indicates that the experimental errors, although small, are too large for the establishment of any compensation behavior between H and S which has often been claimed for reactions in mixed aqueous solvents. Nevertheless, it appears that H exhibits a complex solvent composition dependence, and the solvent effects on the measured rate constants differ markedly from those found for aqueous solutions ofN,N-dimethyl-formamide and dimethyl sulfoxide. There is a deuterium isotope rate effect for solvent mixtures in which 0i<0.1, over and above the usually observed kinetic isotope effect. This additional effect decreases with rising temperature. The results are discussed in terms of competing water ordering effects in ternary mixtures containing water, a hydrophilic solute, and a hydrophobic solute.     

Taylor dispersion measurements at low electrolyte concentrations. I. Tetraalkylammonium perchlorate aqueous solutions

An equipment for the determination of mutual diffusion coefficients using the Taylor's dispersion technique is described. The radius of the capillary was determined with the help of various calibration methods. Diffusion coefficients of aqueous tetraalkylammonium perchlorates, Me₄NClO₄, and Et₄NClO₄, were measured at 25°C in the concentration range 10^–3 to 5×10^–2 mol-dm^–3, and the slightly soluble Pr₄NClO₄ up to 1×10^–2 mol-dm^–3. The slope of linear plots ofD vs. is in agreement with theory, in contrast to the limiting valuesD ₀, which all deviate by about –5% from the Nernst-Hartley values.     

Studium der Röntgen-Kleinwinkelstreuung von Nylon-6 unter Verwendung der absoluten Intensitätsmessung

Zusammenfassung Das Ziel der vorliegenden Untersuchung ist vor allem die Ermittlung des kristallinen und amorphen Anteils der untersuchten Proben aus dem mittleren Schwankungsquadrat der Elektronendichte, die aus der Absolutintensität der Röntgenkleinwinkelstreuung hergeleitet werden kann. Es sollen ferner die mittleren Dimensionen der kristallinen Anteile aus der Intensität des Auslaufes der Streukurven berechnet werden.

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The mean square electron density fluctuations of three Nylon-6 samples (untreated, stretched, stretched and tempered) were obtained from the scattering curves. The degree of crystallinity of each sample was calculated from and from the densities of the crystalline and amorphous phases,d _c =1.23 andd _a =1.10, which were available from the literature. Crystallinities thus obtained were found to be as much as 50% less than those calculated from measured sample densitiesd. The discrepancy was ascribed to a small uncertainty ind _a , the amorphous density: the calculated crystallinities are very sensitive to small changes in this parameter. If one sets the crystalline volume fractions obtained from equal to those obtained fromd, an equation ford _a in terms of andd results, and is solved to yieldd _a -values only about 1% higher than the literature value and of course consistent with both X-ray and density determinations. The volume fractions of the crystalline phases range from 20 to 30%. The possibility that the samples contained small amounts of air-filled holes may be excluded, since thed _a -values (based on andd) calculated on the assumption of a volume fraction of as little as 0.3% for such holes are already much too high.The specific inner surface and an average dimension of the regions of the two phases were also determined. The crystalline regions are roughly 30 Å in size, the amorphous ones three to four times as large, and largest for the tempered sample.

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Mit 3 Abbildungen     

The graphical representation of equilibrium for the isothermal and isobaric reactions of ideal gases

The equilibrium for the isothermal and isobaric reactions of ideal gases is investigated in virtue of the intuitionistic figure. The curve is similar to the curve of tangential function which has one inflection and two vertical asymptotes. The equation only has one root ξ _e and it is suitable to find ξ _e by dichotomy. For non-inert substance, when or x_i^0 $$" align="middle" border="0"> , to increase substance i will make an equilibrium shift in the direction to deplete substance i; when {\nu_i} \mathord{\left/ {\vphantom {{\nu_i} {\sum_i {\nu _i}}}} \right. \kern-\nulldelimiterspace} {\sum _i {\nu _i}}> 0$$" align="middle" border="0"> , to increase substance i will make an equilibrium shift in the direction to produce more substance i.     

Dissociation Constants for Citric Acid in NaCl and KCl Solutions and their Mixtures at 25 °C

The constants for the dissociation of citric acid (H₃C) have been determined from potentiometric titrations in aqueous NaCl and KCl solutions and their mixtures as a function of ionic strength (0.05–4.5 mol-dm^–3) at 25 °C. The stoichiometric dissociation constants (K_i^*)

Über die Definition der Nachweisgrenze

Zusammenfassung Um die Nachweisgrenze zu bewerten, benützt man den Begriff des Entscheidungsniveausy _k , eine Größe, die man mit Hilfe eines zweistufigen Modells bewertet, indem man das Neyman-Pearsonsche Kriterium aus der statistischen Theorie der Signalidentifizierung benutzt. Zu diesem Zweck stellt man eine falsche IdentifizierungswahrscheinlichkeitP ₁₀ fest, so daß , worin den Mittelwert des Blindsignals mit der Standardabweichung _k , und z_k die normierte Abweichung bedeuten, die man aus dem Wert der Laplaceschen Funktion z _k =0,5–P ₁₀ erhält. Das der Nachweisgrenze entsprechende analytische Signal: , worink=z _k –z _i das Verhältnis Signal-Störpegel darstellt und man z_i ebenso aus dem Wert der Laplaceschen Funktion (z _i )=P ₁₁–0,5 erhält (z _i ist negativ). WennP ₁₀=10^–3 undP ₁₁=0,998, erhält mank=6, und die Nachweisgrenze wird: .Die frequentometrisch definierte Nachweisgrenze⁶ hat genau dieselbe Bedeutung, wie jene, die den Begriff des Entscheidungsniveaus bzw. das zweistufige Modell und das Neyman-Pearsonsche Kriterium benutzt.

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On the definition of the detection limit

Summary In order to estimate the detection limit, the notion of decision levely _k is used, a magnitude which is estimated with the help of a two-stage model, using the Neyman-Pearson criterion from the statistical theory of signals detection. For this reason a fals identification probability P₁₀ is fixed, so that: , where is the mean value of the background fluctuations with the standard deviation _y ,z _k is the normalized deviation obtained from the value of the Laplace function (z _k )=0.5–P ₁₀. The analytical signal corresponding to the detection limit: , wherek=z _k +Z _i , represents the signal-noise ratio andz _i is also obtained from the value of the Laplace function(z_i)=P ₁₁–0.5 (z _i is negative). If one considersP ₁₀=10^–3 andP ₁₁=0.998,k=6 and the detection limit will be: .The detection limit defined frequentometrically⁶ is shown to have just the same significance as that, which uses the notion of decision level or the two-stage model and the Neyman-Pearson criterion respectively.

     

Solubilities of the Silver Halides in Aqueous Mixtures of Methanol,Acetonitrile, and Dimethylsulfoxide

Summary.  The solubilities of the silver halides in three non-aqueous solvents: methanol, acetonitrile, and dimethylsulfoxide, and in their aqueous mixtures, are reviewed. Values for the solubility product, K _SO , the enthalpies of solution, Δ _sol H ^o , and the equilibrium products for AgX ⁽ⁱ⁻¹⁾⁻ _i silver halide complexes, β _i , are listed and, where possible, compared. The solvent systems provide examples for three types of mixed aqueous solvent system: aqueous alcohol mixtures and aqueous mixtures with dipolar aprotic solvents that are weakly or strongly basic. The experimental data are discussed in terms of the solvation of the silver and halide ions in the mixed solvents. E-mail: Earle.Waghorne@ucd.ie Received September 30, 2002; accepted October 29, 2002 Published online April 7, 2003 RID="a" ID="a" Dedicated to Prof. Heinz Gamsj?ger on the occasion of his seventieth birthday     

Characterization of Potassium Chloride as an Equitransferent “Intersolvental” Salt Bridge

The electromotive forces (emf) E _A and E _C of the following concentration cells with transference: respectively, together with the emfs E _MAX of the corresponding double cell without transference: have been measured at KCl molalities m (m ₁ fixed and m ₂ varied, with m ₂>m ₁) approximately up to the KCl solubility limit in 12 solvent mixtures for the three aqueous–organic solvent systems (ethylene glycol+water), (acetonitrile + water), and (1,4-dioxane + water) up to 0.8 mass fraction of organic component. For all the cases explored, the E _A vs. E _MAX relation is linear over the whole KCl molality range. The ionic transference numbers t of KCl determined therefrom show a curvilinear dependence on the mass fraction of the organic component of the relevant solvent mixture and are found to fall in the range 0.52–0.48, viz., within ±4% of exact equitransference (t ₊ = t _– = 0.5). In particular, KCl becomes exactly equitransferent (i.e., an ideal salt bridge) in aqueous mixtures with the following mass fractions of organic component: 0.4 ethylene glycol and 0.09 acetonitrile, as well as 0.12 methanol, and 0.08 and 0.34 ethanol from our recent work. Even if use of KCl as a salt bridge would be somewhat restricted by its limited solubility in high mass fractions of dioxane and acetonitrile and pending extension of investigation to other mixed-solvent systems, the above figures characterize KCl as a fairly good intersolvental salt bridge in electrochemistry, electroanalysis, and corrosion science.     

Über die Berechnung der Elektronenenergie eines Moleküls aus dem Erwartungswert der kinetischen Energie

Knowing the mean value of the electronic kinetic energy T(X _i ) of a molecule as a function of the nuclear coordinates X _i , it is shown that the electronic energy can be uniquely determined by the virial theorem . The result is .

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Herrn Prof. R. G. Parr danke ich für die Fragestellung und Diskussionen. Herrn Prof. G. Weber und Herrn Dr. R. Güther möchte ich ebenfalls für Diskussionen danken.     

Kinetics of the oxidation of [N-(2-hydroxyethyl)-ethylene-diamine-N,N′,N′-triacetato]cobalt(II) by N-bromosuccinimide

The kinetics of the oxidation of [N-(2-hydroxyethyl)-ethylene-diamine-N,N,N-triacetato] cobalt(II), [Co^II-(HEDTA)]^–, by N-bromosuccinimide, NBS, have been studied in aqueous solutions and water-methanol solvent mixtures under various conditions. The reaction stoichiometry indicates that one mole of NBS reacts with one mole of [Co^II(HEDTA)]^–. In aqueous solutions the reaction obeys the following rate law:

Heuristic lipophilicity potential for computer-aided rational drug design: Optimizations of screening functions and parameters

In this research we test and compare three possible atom-basedscreening functions used in the heuristic molecular lipophilicity potential(HMLP). Screening function 1 is a power distance-dependent function, b , screening function 2is an exponential distance-dependent function, b_iexp( , and screening function 3 is aweighted distance-dependent function, For every screening function, the parameters ( ,d₀, and are optimized using 41 common organic molecules of 4 types of compounds:aliphatic alcohols, aliphatic carboxylic acids, aliphatic amines, andaliphatic alkanes. The results of calculations show that screening function3 cannot give chemically reasonable results, however, both the powerscreening function and the exponential screening function give chemicallysatisfactory results. There are two notable differences between screeningfunctions 1 and 2. First, the exponential screening function has largervalues in the short distance than the power screening function, thereforemore influence from the nearest neighbors is involved using screeningfunction 2 than screening function 1. Second, the power screening functionhas larger values in the long distance than the exponential screeningfunction, therefore screening function 1 is effected by atoms at longdistance more than screening function 2. For screening function 1, thesuitable range of parameter d₀ is 1.5 < d₀ < 3.0, and d₀ = 2.0 is recommended. HMLP developed in this researchprovides a potential tool for computer-aided three-dimensional drugdesign.     

Dielectric properties of solutions of tetra-iso-pentylammonium nitrate in dioxane-water mixtures

Dielectric properties of solutions of tetra-iso-pentylammonium nitrate, i-Pen ₄ NNO ₃ . in various dioxane-water mixtures have been studied using dielectric time domain spectroscopy (TDS). The static permittivity of the solutions _s increases for low concentrations of solute but levels off to asymptotic values at higher concentrations. The limiting sloped_s dc, and the asymptotic value depend on the static permittivity of the solvent mixture. The relaxation time due to the solute varies with solute concentration and depends on the solvent mixture. In the solvent mixtures of lowest permittivity the plots of relaxation time vs. concentration go through a maximum, while in the mixtures of highest permittivity the relaxation time initially decreases and then levels off to an asymptotic value. The concentration dependence of the dielectric parameters is discussed in relation to ion association.     

A rigorous theory of ring tensiometry: Addendum on the wall effect

Summary As a supplement to our theoretical calculations for the ring method of measuring surface and interfacial tensions of liquids, the effect of the finite size of the liquid container on the measurement has been studied employing (i) an exact analysis for the case of an infinite straight cylinder midway between two parallel walls and (ii) an approximate analysis for a ring in a circular container. The parameters which can cause errors are identified, and their magnitude is estimated and compared with the experimental results for surface tension of water in air. It is shown that conditions can be readily adjusted to produce negligrors.Nomenclature a radius of cylinder or ring wire; - C ₂₃ (₂ –₃)g/ ₂₃ D=semi-gap width between parallel walls, or radius of liquid container; - f Harkins-Jordan (1) factor - F, E elliptic integrals of the first and second kind (k = modulus) - F equilibrium capillary force on ring or per unit length of a straight cylinder; - F _D,F maximumF for finiteD andD = - g gravity - r _i,z _i r- andz-coordinates of the inner (i =1) and outer (i = 2) contact line circles on ring; - z _c vertical coordinate of the contact line on cylinder; - Y23, YD interfacial tension (D= ; uncorrected interfacial tension measured in container of radiusD - _i density of thei phase - _i slope angle of the inner (i = 1) and outer (i = 2) menisci on ring - 180° - _c slope angle of cylindrical meniscus at the contact line - ₂ 180° – ₂ - Oo contact angle at container wall - (F _D -F )/F for cylinder; (YD - ₂₃)/Y23 for ring     

Throwing power of a dilute sulfuric acid copper plating electrolyte during intensive electrodeposition

A method of determination of the throwing power (TP) of electrolytes in conditions of forced convection in a Hull cell with a rotating cylindrical electrode is presented. The method is used to determine TP of a copper plating electrolyte containing 0.15–0.5 M CuSO₄ and 1 M H₂SO₄ at current densities of up to 75 mA cm^-2. The TP decreases with increasing current density at a constant i _av/i _d ratio, where i _av is the average working current density and i _d the limiting diffusion current density. With increasing the i _av/i _d ratio due to an increase in the cathodic polarizability conditions for an increase in TP may be achieved. In optimum (for uniform deposition) modes, i _av/i _d 0.4–0.5. The TP may increase upon diluting electrolyte with respect to its main component.Translated from Elektrokhimiya, Vol. 41, No. 1, 2005, pp. 91–96.Original Russian Text Copyright © 2005 by Dikusar, Bobanova, Yushchenko, Yakovets.To the Centennial of B.N. Kabanov.     

Excess molar volumes of 2-methylethylbenzene with benzene,methylbenzene or ethylbenzene at various temperatures

Excess molar volumes of benzene or methylbenzene + 2-methylethylbenzene at 25, 35 and 45°C and of ethylbenzene + 2-methylethylbenzene at 25°C have been determined from density measurements using a vibrating tube densimeter. Experimental V _m ^E values have been compared with calculated values based on the Flory theory.List of Symbols p _i characteristic pressure of pure component - reduced temperature of pure component - V ^E excess molar volume - V _i ^* characteristic volume of pure component - reduced volume of mixture - reduced volume of pure component i - X ₁₂ interaction parameter in Flory's theory - site fraction of component 2 - segment fraction of component 2     

Mechanism of the catalyzed by cysteine electroreduction of the insoluble in water cobalt(II) salt as a component of carbon paste electrode

The mechanism of the Co(II) catalytic electroreduction of water insoluble CoR₂ salt in the presence of cysteine was developed. CoR₂ = cobalt(II) cyclohexylbutyrate is the component of a carbon paste electrode. Electrode surface consecutive reactions are: (a) fast (equilibrium) reaction of the complex formation, (b) rate-determining reversible reaction of the promoting process of CoR(Ac⁺) complex formation, (c) rate-determining irreversible reaction of the electroactive complex formation with ligand-induced adsorption, and (d) fast irreversible reaction of the electroreduction. Reactions (a,b) connected with CoR₂ dissolution and reactions (c,d) connected with CoR₂ electroreduction are catalyzed by . Regeneration of (reactions “b,d”) and accumulation of atomic Co(0) (reaction “d”) take place. Experimental data [Sugawara et al., Bioelectrochem Bioenergetics 26:469, 1991]: i _a vs E (i _a is anodic peak, E is cathodic accumulation potential), i _a vs , and i _a vs pH have been quantitatively explained.     

Darstellung und Eigenschaften von Heteropolykationenverbindungen,IV: Darstellung und Struktur von Natriumdodekaaluminogalliumsulfat-Ikosihydrat,Na[GaO4Al12(OH)24(H2O)12](SO4)4 ·xH2O mitx∼20

Summary A chemical analyses of Na[GaO₄(Al₁₂(OH)₂₄(H₂O)₁₂](SO₄)₄ ·xH₂O withx20 [a=17.861 (4) Å; F 3 m-T _d ² ;Z=4] in connection with a crystal structure investigation confirmed the tetrahedral coordination of the gallium atom by oxygen atoms, as well as the far extending statistical distribution of the crystal water in the structure. The syntheses was done by neutralization of a satured aqueous aluminium chloride solution, mixed with metallic gallium and sodium sulfate, by an aqueous sodiumhydroxide solution.

     

Apparent molal volumes of phosphonium halides at 15, 25 and 35°C

The densities of aqueous solutions of the phosphonium halides, Bu _4-n Ph _n PX(n=0–4), some of which were synthesized from the phosphines, were measured at 15, 25 and 35°C. Partial molal volumes at infinite dilution, , and B _v coefficients for the apparent molal volumes were determined at each temperature. For the first four cations varies little with n. For all salts B _v are negative but become less negative with increasing n. The temperature dependence of B _v is positive for butyl-rich salts (n<2) but negative for phenyl-rich salts (n>1). Also it appears that is relatively large for phenyl-rich cations in comparison with that for butyl-rich cations.