Ionic strength dependence of formation constants. Part II: potentiometric study of the copper(II)-malonate-glycinate system in the range 0.01≤I≤1.0

Summary The ternary copper(II)-malonate-glycinate system has been investigated by potentiometric measurements using a glass electrode, at 37° and at different ionic strengths (0.01I1.0 mol dm^–3), with KNO₃ as background salt. Complex formation between K⁺ and malonate has also been taken into account, and the parameters for the dependence on ionic strength have been obtained for each formation constant. A general equation, valid for all the complexes formed in this system, for the dependence, log K=f(I), is also proposed. The stabilization parameters of the ternary complex are also analyzed as a function of the ionic strength.     

Ionic strength dependence of formation constants. Part 4. Potentiometric study of the system Cu2+-Ni2+-citrate

Summary The ternary Cu²⁺-Ni²⁺-citrate (cit^3–) system was investigated potentiometrically in aqueous solution, at different temperatures, 10t45°C, and ionic strengths, 0.03I0.8 mol dm^–3, using potassium nitrate or tetraethylammonium bromide as background salt. Since the citrate anion forms weak complexes with potassium, the stability constants here reported differ according to whether the potassium association is considered or not. In the presence of both Cu²⁺ and Ni²⁺, the mixed metal species, [CuNi(cit)₂H_–2]^4– is formed with citrate in solution, in addition to the various binary complexes. We have obtained the dependence for all the formation constants on ionic strength and temperature. The previous suggestions concerning a general equation for describing the dependence, log =f(I), are confirmed; from the study of log =f(T) we have obtained the values of thermodynamic parameters. The dependence of H on ionic strength is discussed.     

Hydrolysis of Protactinium(V). III. Determination of Standard Thermodynamic Data

Hydrolysis constants of protactinium(V) at tracer scale were deduced from the variations of partition coefficient of Pa(V) in the system: TTA/toluene/Pa(V)/H₂O/H⁺/Na⁺/ClO^– ₄, as a function of TTA and proton concentrations, ionic strength (0.1 3 M), and temperature (10 60°C). Extrapolations of theses constants to zero ionic strength were performed using the SIT model. Standard thermodynamic data (under atmospheric pressure) related to the two hydrolysis equilibria involved, were derived from the temperature dependence of the hydrolysis constants at infinite dilution.     

Mechanism of the oxidation of L-ascorbic acid by the bis(pyridine-2,6-dicarboxylate)cobaltate(III) ion in aqueous solution

A detailed investigation of the oxidation of L-ascorbic acid (H₂A) by the title complex has been carried out using conventional spectrophotometry at 510 nm, over the ranges: 0.010 [ascorbate] _T 0.045 mol dm^–3, 3.62 pH 5.34, and 12.0 30.0 °C, 0.50 I 1.00 mol dm^–3, and at ionic strength 0.60 mol dm^–3 (NaClO₄). The main reaction products are the bis(pyridine-2,6-dicarboxylate)cobaltate(II) ion and l-dehydroascorbic acid. The reaction rate is dependent on pH and the total ascorbate concentration in a complex manner, i.e., k _obs = (k ₁ K ₁)[ascorbate] _T /(K ₁ + [H⁺]). The second order rate constant, k ₁ [rate constant for the reaction of the cobalt(III) complex and HA^–] at 25.0 °C is 2.31 ± 0.13 mol^–1 dm³ s^–1. H = 30 ± 4 kJ mol^–1 and S = –138 ± 13 J mol^–1 K^–1. K ₁, the dissociation constant for H₂A, was determined as 1.58 × 10^–4 mol dm^–3 at an ionic strength of 0.60 mol dm^–3, while the self exchange rate constant, k ₁₁ for the title complex, was determined as 1.28 × 10^–5 dm³ mol^–1 s^–1. An outer-sphere electron transfer mechanism has been proposed.     

Kinetics and mechanism of the reaction of aquachromium(III) with l-ascorbic acid in aqueous media

The kinetics of the reaction of l-ascorbic acid (H2A) with aquachromium(III) has been studied over the range 0.04 [H2A]T 0.16 mol dm–3, 3.5 pH 6.0, 25.0 t 50.0C, 0.03 I 1.0 mol dm–3 (KNO3) and 0% [MeOH] 20% (v/v). The reaction takes place via an outer-sphere association between Cr3+/CrOH2+ and H2A, followed by transformation of the outer- into an inner-sphere complex by slow interchange. The anation rate constants for Cr3+ and CrOH2+ species (k1 and k2) at 25C and I=1.0moldm–3 (KNO3) are 1.68×10–4 and 2.14×10–4s–1, respectively. H and S for the k1 and k2 paths are 27.0±2kJmol–1, –227±5J K–1mol–1 and 57.2± 4kJmol–1, –123±14JK–1mol–1, respectively. Anation of Cr(H2O)3+6 and Cr(H2O)5OH2+ follow an Ia path.     

Thermodynamic parameters for the protonation of carboxylic acids in aqueous tetraethylammonium iodide solutions

The protonation constants of 21 carboxylic acids (formic, acetic, propionic, benzoic, phenoxyacetic, salicylic, oxalic, malonic, succinic, itaconic, malic, tartaric, oxydiacetic, thiodiacetic, thiodipropionic, phthalic, maleic, citric, 1,2,3-tricarboxylic, 1,2,4-tricarboxylic and 1,2,4,5-tetracarboxylic), have been determined potentiometrically, by pH-metric measurements, at several temperatures and ionic strengths, 5T55°C, 0<11 mol-dm^–3, using tetraethylammonium iodide as background salt. General equations for the dependence on ionic strength of thermodynamic parameters have been found. The statistical significance of results and the possibility of using a simple model for the thermodynamics of carboxylic acids protonation, is discussed.     

A new catalyst for hydrodesulfurization of heavy residue

Catalytic hydrodesulfurization plays an important role in the conversion of sulfur laden residual oils. Cobalt molybdate catalysts are more commonly used for this process. In the present study, a precipitation technique at constant pH value was used to prepare alumina support. This material has very narrow pore size distribution centered around the pore diameter of about 8 nm. It also has a large surface area and pore volume and, therefore, can be used as a support for CoMo RDS catalysts. The results of temperature-programmed desorption of ammonia indicated that this catalyst has higher surface acidity than the conventional catalysts. The high surface acidity could enhance the cracking ability of the catalyst. The RDS reaction results showed that the samples prepared by precipitation are more active and more stable than the conventional catalysts, at least in the first 72 h. The results can be attributed to its unique pore structure and high surface acidity.

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. . pH. 8 . CoMo . , , . , , , , , - 72 . .

     

Conformation of a chain polyelectrolyte in solution with low molecular weight salt: small angle neutron scattering measurements

Small angle neutron scattering measurements have been carried out on the tetramethylammonium salt of the polystyrenesulfonic acid withDP _w =310 and 1060 in water solution with tetramethylammonium chloride with ionic strength between 0.02 M and 1.0 M. The scattering curves in the scattering vector range 0.05 nm^–1Q1.8nm^–1 have been fitted using the form factor of a worm-like chain of finite thickness. The conformational parameters mean square radius of gyration, statistic chain element, mass per unit length and mean square radius of the cross-section have been determined experimentally and used for describing the conformation of the coils. By these molecular weights and ionic strengths, excluded volume is not necessary to explain the conformation changes depending on the salt content of the solutions; relatively short coil molecules can be described in their unperturbed dimensions even in a thermodynamically good solvent: a change in the stiffness of the chain according to Odijk's theory succeeds in describing the conformation of the polyions. Together with a slow decrease of the coil dimension by increasing salt content, a transition at ionic strength 0.1–0.5 M between two different conformations has been observed. The conformation at lower ionic strength is characterized by higher stiffness of the chain and lower mass per unit length than the form at higher salt concentration.     

Dissociation equilibrium between uncharged and charged local anesthetic lidocaine in a surface-adsorbed film

The dissociation equilibrium between uncharged local anesthetic lidocaine (LC) and charged local anesthetic LC (LCH⁺) in a surface-adsorbed film was investigated by measuring the surface tension and pH of aqueous solutions of a mixture of hydrochloric acid and LC. The surface tension values decreased slightly with increasing total molality m_t at 0X₂0.5, where X₂ is the mole fraction of LC in the mixture, while they decreased rapidly with increasing m_t at 0.5<X₂1. It was shown from the pH measurements that almost all LC molecules were changed into LCH⁺ ions by protonation at 0X₂0.5 and both forms coexisted only at 0.5<X₂1. The quantities of the respective LC and LCH⁺ transferred from the aqueous solution to the adsorbed film, i.e., their surface densities, were calculated by applying the thermodynamic equations derived to the surface tension and pH data. A greater quantity of LC than LCH⁺ existed in the adsorbed film at the coexisting composition. The partitioning behavior of LC and LCH⁺ in the adsorbed film was characterized by three composition regions: (1) slight partitioning of low surface-active LCH⁺ in the region at 0X₂0.5, (2) preferential partitioning of LC at 0.5<X₂<around 0.7, and (3) negative partitioning of LCH⁺ at around 0.7X₂1. The present results clearly indicate that uncharged local anesthetics transfer into hydrophobic environments such as cell membranes more than charged ones.     

Solid-Solute Phase Equilibria in Aqueous Solution. XI. Aqueous Solubility and Standard Gibbs Energy of Cadmium Carbonate

The solubilities of CdCO₃ (otavite) in aqueous NaClO₄ solutions have been investigated as a function of ionic strength (0.15 I/mol-kg^–1 5.35, 25°C) and temperature (25°C T 75°C, I = 1.00 mol-kg^–1). A new Chemsage optimization routine was employed to simultaneously evaluate solubility data from this work and other sources, as well as standard electrode potentials determined at different ionic strengths. With the Pitzer equations the solubility constants, , were extrapolated to infinite dilution resulting in log and the ternary ion-interaction parameters ^S_Na,Cd = 0.19 and at 25°C. In addition, the following set of thermodynamic quantities can be derived from the present solubility data for otavite: _f G = –674.2±0.6 kJ-mol^–1; _f H = –755.3±3.4 kJ-mol^–1; S = 93±10 J-mol^–1K^–1. However, the present solubility data are also consistent with a recent determination of the standard entropy of otavite which leads to a recommended set of thermodynamic quantities [_f G (CdCO₃) = –674.2±0.6; _f H (CdCO₃) = –752.1±0.6; S (CdCO₃) = 103.9±0.2].     

The effect of preparation conditions on the activity and stability of copreciptitated Ni/Al2O3 catalysts for the methanation of carbon monoxide

The activities and stabilities of coprecipitated Ni/Al₂O₃ methanation catalysts depend markedly on their preparation and pretreatment. The results are discussed in relation to the structure of the precipitate and to changes which occur during calcination and reduction.

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Ni/Al₂O₃ . , .

     

Metallreiche Phasen im ternären System Ni-Se-Te

Zusammenfassung Die metallreichen Phasen im System Ni-Se-Te wurden durch Röntgenaufnahmen bei Zimmertemp. und bei höheren Temperaturen sowie durchDTA untersucht. Bei Zimmertemp. wurden im pseudo-binären Schnitt Ni₃(Se_1-x , Te _x )₂ Phasen mit den folgenden Strukturen gefunden: rhomboedrischer Ni₃S₂-Typ fürx=0; tetragonaler (Ni,Fe)₁₁Se₈-Typ für 0,15x0,35; tetragonaler Rickardit-Typ für 0,50x0,80; Überstrukturen des Rickardit-Typs für 0,95x1. Bei höheren Temperaturen verbreitert sich das Homogenitätsgebiet der Phase mit der tetragonalen Rickardit-Struktur. Über 600–770°C tritt im ganzen Gebiet 0x1 eine kubisch.

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Metal-rich phases in the ternary system Ni-Se-Te

The metal-rich phases in the system Ni-Se-Te have been studied by X-ray diffraction at room temperature and elevated temperatures, and byDTA. At room temperature phases with the following structures were found in the pseudo-binary section Ni₃(Se_1-x , Te _x )₂: rhombohedral Ni₃S₂ type forx=0; tetragonal (Ni,Fe)₁₁Se₈ type for 0,15x0,35; tetragonal rickardite type for 0,50x0,80; superstructures of the rickardite type for 0,95x1. At higher temperatures the homogeneity range of the phase with the tetragonal rickardite structure broadens. Above 600–770°C a face-centered cubic phase exists in the whole range 0x1; a model for the structure of this phase is proposed. The compound Ni_2,6Te₂ is orthorhombic at room temperature; it becomes hexagonal at 720°C and disproportionates at 820°C; by partial substitution of Te by Se the hexagonal form is stabilized at room temperature. Similarly, the compound Ni₆Se₅ which is stable above 440°C only, is stabilized at room temperature by partial substitution of Se by Te. The phase Ni₆(Se_1-x , Te _x )₅ decomposes by a peritectoid reaction at 650° (x=0) to 590°C (x=0,3).

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Herrn Prof. Dr.H. Nowotny gewidmet.     

Zeta potential and surface charge density of polystyrene-latex; comparison with synaptic vesicle and brush border membrane vesicle

The electrophoretic mobility of polystyrene — latex (PSL) of diameter 870 Å was determined using a Laser Zee System 3000. This instrument enables automatic measurement of the electrophoretic mobility of fine particles. Effect of pH and ionic strengthI on the PSL mobility was analyzed. It was found that the mobility as a function of pH has a minimum around pH 3–4 atI=0.1, showing no isoelectric point, and that the mobility decreases with increasing ionic strength up toI=0.1 but is almost constant forI=0.1–0.2 at pH=7.34. From the mobility date, we estimated the zeta potential of PSL. We used an approximate mobility formula derived by Ohshima, Healy and White, which is considerably more accurate than Smolchowski's and Henry's formula and is applicable for fine particles with small a ( a10), where is the Debye-Hückel parameter anda is the particle radius. Further, we calculated the surface charge density of PSL using an approximate relationship. It was found that there are 2000–4000 negative charges on the PSL surface at pH=7.34. Comparison is made with the results on synaptic vesicles (SV) from brain cerebrum cortex and brush-border-membrane vesicles (BBMV) from the small intestine.     

Performance of Pt?Sn/Al2O3?Cl catalysts in isopropanol decomposition

Highly dispersed TiO₂-supported copper with strong interactions with the support has been prepared. After reduction at 770 K, H₂ chemisorption is suppressed. Two types of copper sites exist, one easily and reversibly oxidized by O₂ at room temperature, and another interacting with the support.

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, TiO₂, . 770 H₂ . , O₂ , - .

     

Low temperature crystal and molecular structure of nitrobenzene

The crystal and molecular structure of nitrobenzene was determined at 103 K by X-ray diffraction, yieldingR=0.034 and a highly precise geometry of the molecule (esds of bond lengths 0.001 Å and bond angles 0.1°). The bond angles in the ring agree very well with additive scheme based on angular substituent parameters. X-X electron density maps support the view that the C-N bond does not exhibit-character, and, hence, the nitro group interacts with the ring mostly by inductive effects.     

Kinematic Viscosities of Binary Liquid Mixtures of 2-Butanone with 1,2-Propanediol

Kinematic viscosities of the binary 2-butanone (1) + 1,2-propanediol (2) solvent system have been measured for mixtures covering the whole miscibility range expressed by 0 x _i 1, at 19 temperatures in the range –10 t/°C 80. The measured values have been used to test empirical equations that express the kinematic viscosities as functions of the composition and temperature. Excess kinematic viscosities (^E) have also been calculated. Sign and magnitude of these quantities are discussed in terms of type and nature of specific intermolecular interactions. Furthermore, derived quantities such as thermodynamic parameters of viscous flow (G, H and S), are analyzed on the basis of Eyring's model. All the investigated excess mixing properties indicate the probable existence of stable two-component adducts in this binary solvent system.     

The antiferromagnetic and ferrimagnetic properties of iron selenides with NiAs-type structure

The magnetic properties of the NiAs-type iron selenides have been investigated by susceptibility measurements between 100 and 450 K. Hexagonal -Fe_1-x Se exhibits both antiferromagnetism and ferrimagnetism depending on composition. For antiferromagnetic alloys with 0.02x0.10 (50.5 to 52.5 at % Se) the transition to the paramagnetic state is assumed to occur in the unstable range between room temperatur and about 573K. Ferrimagnetism is observed at compositions near Fe₇Se₈ (0.10x0.16; 52.5 to 54.3 at % Se) withCurie temperatures varying only slightly with composition. In Fe₇Se₈ the ferriparamagnetic transition is observable at 453 K. The characteristic discontinuities in the magnetization curves of Fe₇Se₈ in both superstructures (3c, 4c) are related to the rotation of the magnetic moments from a direction close to [001] into (001).The antiferromagnetism of Fe_0.89Se (52.8 at % Se) changes abruptly into ferrimagnetism when the temperature is raised above 160 K. The similar abrupt changes of the magnetic susceptibilities in the antiferromagnetic region are possibly associated with a crystallographic transformation. In the range of monoclinic -Fe_1-x Se with 0.24x0.36 (56.8 to 61.0 at % Se) only Fe₃Se₄ is ferrimagnetic above room temperature; alloys containing more selenium are ferrimagnetic far below room temperature. In Fe_0.69Se (59.1 at % Se) the transition from ferrimagnetism to paramagnetism was observed at 145 K. The saturation magnetization and the magnetic moments obtained from neutron diffraction are compared with values calculated from a simple ionic model.

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Die antiferromagnetischen und ferrimagnetischen Eigenschaften von Eisenseleniden mitNiAs-Struktur

Zusammenfassung Die magnetischen Eigenschaften von Eisenseleniden mit NiAs-Struktur wurden mittels Suszeptibilitätsmessungen zwischen 100 und 450 K untersucht. Hexagonales -Fe_1-xSe zeigt abhängig von der Konzentration sowohl Antiferromagnetismus als auch Ferrimagnetismus. In antiferromagnetischen Legierungen mit 0,02x0,10 (50,5 bis 52,5 At % Se) verläuft die Umwandlung in den paramagnetischen Zustand im nichfstabilen Bereich zwischen Raumtemperatur und 573 K. Ferrimagnetismus wurde in der Nähe von Fe₇Se₈ (0,10x0,16; 52,5 bis 54,3 At % Se) beobachtet mitCurietemperaturen, die sich nur wenig mit der Konzentration ändern. Fe₇Se₈ zeigt die ferri-paramagnetische Umwandlung bei 453 K. Die charakteristischen Diskontinuitäten der Magnetisierungskurven von Fe₇Se₈ in beiden Überstrukturen (3fache und 4fachec-Achse) hängen mit der Drehung der magnetischen Momente aus einer [001]-nahen Richtung in die (001)-Ebene zusammen. Der Antiferromagnetismus von Fe_0,89Se (52,8 At % Se) geht bei 160 K sprunghaft in Ferrimagnetismus über. Ähnliche sprunghafte Änderungen der magnetischen Suszeptibilitäten im antiferromagnetischen Bereich sind möglicherweise mit einer kristallographischen Umwandlung verbunden. Im Phasenbereich von monoklinem -Fe_1-x Se mit 0,24x0,36 (56,8 bis 61,0 At % Se) ist einzig Fe₃Se₄ oberhalb Raumtemperatur ferrimagnetisch; Legierungen mit mehr Selen sind weit unterhalb Raumtemperatur ferrimagnetisch. In Fe_0,69Se (59,1 At % Se) wurde der Übergang von Ferri- zu Paramagnetismus bei 145 K beobachtet. Die Sättigungsmagnetisierung und die magnetischen Momente aus Neutronenbeugungsexperimenten wurden mit Werten verglichen, die mit einem einfachen ionischen Modell berechnet wurden.

     

On the size variation of the primary solvation sphere of Nd3+ and Tm3+ in mixed system of methanol and water

The stability constants, ₁, of each monochloride complex of Nd(III) and Tm(III) have been determined in the mixed system of methanol and water with 1.0 mol·dm^–1 ionic strength using a solvent extraction technique. The values of ₁ of Nd(III) and Tm(III) increase as the mole fraction of methanol in the mixed solvent system (X _s) increases. However, the variation mode of ₁ againstX _s in the region of 0.00X _s0.40 differs from each other, a concave curve for the Nd(III) and a convex curve for the Tm(III). The LnCl²⁺ formed is present as a solvent-shared ion-pair. Since Cl^– is a structure breaking ion, it was assumed that the primary solvation sphere of Ln³⁺ directly contacted with Cl^–. Calculation of Ln³⁺–Cl^– distance using Bom-type equation revealed the followings: (1) for Tm³⁺ with coordination number 8, the estimated distance between Tm³⁺ and Cl^– increases linearly withX _s in 0.00X _s0.40. The results mean an increase of the primary solvation sphere size of Tm³⁺ withX _s. (2) For Nd³⁺, the distance between Nd³⁺ and Cl^– decreases linearly withX _s in 0.00X _s<0.13, where both coordination numbers of 9 and 8 coexist, while it increases withX _s in 0.13<X _s0.40. The results mean a decrease of the primary solvation-sphere size of Nd³⁺ withX _s in 0.00X _s<0.13 and an increase of that withX _s in 0.13<X _s0.40.     

Effect of Cation Nonstoichiometry on the Properties of Solid Electrolyte Ba x Ce0.97Nd0.03O3 - δ (0.90 ≤ x ≤ 1.10)

The effect of the cation nonstoichiometry on the electroconduction, electrotransfer, and stability in humid air of solid proton-conducting electrolyte Ba _x Ce_0.97Nd_0.03O_{3 -} (0.90 x 1.10) is studied. The electroconduction is found to decrease with decreasing content of BaO (x 1.0) and weakly depend on the BaO excess (x> 1.0). Ceramics of a stoichiometric composition (x = 1) and with lack of barium is stable when stored in humid air at room temperature, as opposed to the ceramics with barium excess, which rapidly decomposes in these conditions. The conduction of materials under study in oxidizing environment is ion-hole and in reducing media, ionic (proton + oxygen). The cation nonstoichiometry barely affects the nature of the ion transfer. An analysis of possible models for the formation of defects shows oxygen vacancies to be always present in Ba _x Ce_0.97Nd_0.03O_{3 -} , even at the CeO₂ excess exceeding the content of neodymium.     

Liquid Chromatographic Determination of Sulfamonomethoxine, Sulfadimethoxine, and their N 4-Acetyl Metabolites in Chicken Plasma

An environmentally-friendly method has been established for simultaneous determination of sulfamonomethoxine, sulfadimethoxine, and their N⁴-acetyl metabolites in chicken plasma. The sample is prepared by mixing with 4 mol L^–1 ammonium sulfate solution then centrifugation, and analysis is performed by high-performance liquid chromatography (HPLC) on a polyethylene glycol reversed-phase column with 0.001 mol L^–1 sodium acetate solution as mobile phase and photodiode-array detection. Average recoveries from samples spiked with 0.1, 0.5, and 1.0 g mL^–1 of each drug were >78% and relative standard deviations were within 4%. The practical quantitation limits were 0.09 g mL^–1. No organic solvents or hazardous reagents were used at any stage of the analysis.