Dielectric Relaxation of the β-Cyclodextrin Complexes with Tridecanoic Acid and 1,13-Tridecanedioic Acid

The frequency and temperature dependence of the real (') and imaginary (') parts of the dielectric permittivity of the polycrystalline complex-cyclodextrin-tridecanoic acid in two hydration forms (with 16.2 and 10.7 water molecules) and -cyclodextrin-1,13-tridecanedioic acid with 16.4 and 10.5 water molecules have been investigated, in the frequency range 0.1–100 kHz and temperature range 120–310 K. The dielectric behavior is described well by Debye-type relaxation dispersion. All systems except for the complex of partially dehydrated monocarboxylic acid, exhibit an additional -dispersion, at low frequencies (f < 1000 Hz). Only one-step was found in the ' vs. Tplots of both complexes in the two hydration forms, a fact indicating that the watermolecules cannot be divided into strongly bound and easily movable molecules. The'vs. T plots, at a fixed frequency (200 Hz), show the characteristic peakattributed to a transition between ordered and disordered -CD hydroxyl groupsand water molecules. The transition temperature was 202.7 K for all systems examinedexcept for the complex -CD-tridecanoic acid.16.2 H₂O (214.5 K). This means that the order to disorder transformation process was unaffected by the dehydration process in the case of the dicarboxylic acid complex, whereas in the case of the monocarboxylic acid, it was unexpectedly facilitated. The relaxation time varies with temperature, in a like curve (in the range 8–14 s), with maximum values located at the corresponding order-disorder transition temperatures. The activation energies of the fully hydrated complexes have absolute values of 5 kJ/mol in the range 1.98–3.82 K_{BT transition} which are higher than the corresponding values of :2 kJ/mol of the dehydrated complexes. A thermal hysteresis observed in all complexes is a result of the order-disorder transformation.     

Preparation of Polycrystalline Antimonic Acid Films by Electrophoretic Deposition

Cubic antimonic acid (Sb₂O₅·nH₂O) films were successfully prepared on stainless steel and Si(100) substrates by electrophoretic deposition (EPD) using two types of sols. The sols were prepared by reacting an H₂O₂ aqueous solution with Sb(O-i-C₃H₇)₃ or metallic Sb powder. The resulting films were found to consist of fine particles of cubic Sb₂O₅·nH₂O single crystals with uniform particle sizes of 30 nm and 150 nm. The weight of the Sb₂O₅·nH₂O deposit on the anode Si(100) substrate by EPD increased linearly with the current density in the range of 0–0.67 mA cm^–2, when the sol pH was over 7. The proton conductivity of the polycrystalline Sb₂O₅·nH₂O discs, formed from the two types of sols, was evaluated by an ac impedance method at room temperature under controlled levels of relative humidity.     

Insertion of 3d- and 4f-Elements into Silver Iodide

The interaction of manganese and some 4f-metals (M) with silver iodide is studied. The samples are obtained by sputtering M onto the surface of polycrystalline AgI films (0.2 m, 300 K) in a vacuum. Optical absorption in the samples is interpreted as the insertion of M ions into AgI with the formation of dopants AgI:M. A new phase with an optical bandgap of 3.7 eV emerges in the samples with elevated concentrations of La, Ce, Pr, Nd, Sm, or Dy (n _M/n _Ag 0.1). X-ray diffraction patterns for such samples with Sm correspond to structures with large interfacial distances, for example, 0.99, 0.87, 0.76, and 0.67 nm. In air, AgI forms in the samples with a new phase; this process is hindered by the sputtered protective coatings. According to optical absorption data, X-ray diffraction, and local microanalysis the Mn insertion into AgI is followed by the formation of a new phase (2Ag:Mn:4I), which may belong with solid electrolytes Ag₂MI₄, where nonmagnetic M are known (Zn, Cd, Sn, Hg, Pb).     

The influence of ionic surfactants on the acid-base properties and tautomeric equilibrium of 2-dimethylaminomethylphenol

Shifts in the acid-base and tautomeric equilibria have been observed in aqueous solutions of 2-dimethylaminomethylphenol (DAMP) containing surfactants. Cationic micelles of cetyltrimethylammonium bromide increase the dissociation constants of DAMP (pK₁ 0.3, pK₂ 0.5), and anionic micelles of sodium dodecyl sulfate reduce them (pK₁ 1.5, pK₂ 0.3). The constant of tautomeric equilibrium decreases when ionic surfactants are added. This is connected with the better solubilization of the neutral form by micelles.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1215–1218, July, 1994.     

Percolation Effects on the Surface of a Polyimide Film Modified with Aqueous Solutions of an Alkali and Acid

A cluster structure of the surface of a polypyromellitimide film was studied by the electron microscopy and ATR IR spectroscopy methods at different steps of consecutive treatment with aqueous solutions of an alkali and acid. The effective size and fractal dimension D of polyamidoacid clusters, as well as the degree _s of the filling of the surface with the latter were calculated from the data of the electron microscopy as a function of the degree of imide group conversion into amidoacid units on the film surface. The _s and D parameters were shown to increase with a rise in : _s = 0.1–0.3 and D = 1.3–1.4 at < _cr and _s 0.6 and D 1.7 at > _cr, where _cr is a critical degree of conversion, which corresponds to the formation of a continuous physical network of polyamidoacid macromolecules or a percolation cluster. In a region close to _cr (at < _cr), the correlation length land the concentration C of the clusters vary according to the laws of the percolation theory for two-dimensional lattices: l (_cr – )^– and C (_cr – ), where = 1.3 ± 0.1 and = 0.67 ± 0.05.     

Über einige Komplexboride von Übergangsmetallen

Zusammenfassung Dreistofflegierungen in dem Kombinationen {Mo, W}-{Fe, Co, Ni}-B; {V, Nb, Ta, Mo, W}-B-Al werden vornehmlich auf die Existenz von Komplexboriden hin untersucht. Die isotypen Phasen Mo₂CoB₂, Mo₂NiB₂, W₂FeB₂, W₂CoB₂ und W₂NiB₂ sind strukturell mit Mo₂FeB₂ verwandt, aber doch von dieser Phase verschieden. Gefunden werden außerdem die isotypen Phasen MoCoB und WCoB. Das Problem der -Phase wird diskutiert. In manchen Fällen tritt ein Zwischenzustand auf, der vermutlich durch Stapelfehler einer Unterzelle (c/3 in hexagonaler Aufstellung) hervorgerufen wird. Neben dem Auftreten ternärer Phasen bei Nb-B-Al und Ta-B-Al wird eine ausgeprägte Mischphasenbildung: (Nb, Al)B₂ und (Ta, Al)B₂ beobachtet. Der Dreistoff: Mo-B-Al ist durch die ternäre Phase MoBAl gekennzeichmet, ferner tritt der durch Al stabilisierte CrB-Typ auf (Mo_0,45B_0,50Al_0,05). Die Gleichgewichtsverhältnisse in denT-B-Al-Dreistoffen werden abgeschätzt.

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Alloys of the combinations {Mo, W}-{Fe, Co, Ni}-B, {V, Nb, Ta, Mo, W}-B-Al have been examined with respect to the existence of complex borides. The phases of the approximate formula Mo₂CoB₂, Mo₂NiB₂, W₂FeB₂, W₂CoB₂ and W₂NiB₂ have been found to be isotypic. They do however not correspond to Mo₂FeB₂ having U₃Si₂ structure. Two other complex borides of formula MoCoB and WCoB have been detected having the same crystal structure. The problem of the -phases which partially contain boron will be discussed considering the supposedly occurring stacking faults of a subcell unit (c=c/3 for hexagonal symmetry). Besides formation of ternary compounds for: Nb-B-Al and Ta-B-Al an extended solid solution (Nb, Al)B₂ and (Ta, Al)B₂ has been observed. The Mo-B-Al-system is characterized by the ternary phase of formula MoBAl. Mo-monoboride having CrB-type has been found to be stabilized by a small amount of Al, thus Mo_0,45B_0,50Al_0,05 being formed. The phase equilibria within the ternary systems have been established for the major part.

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Mit 4 Abbildungen     

Anodic Dissolution of Palladium in Sulfuric Acid: An Electrochemical Quartz Crystal Microbalance Study

Regularities of formation of a palladium oxide layer and its cathodic reduction in 0.5 M H₂SO₄ at 0.5–1.3 V (SHE) are studied by cyclic voltammetry, x-ray photoelectron spectroscopy, and electrochemical quartz crystal microbalance. A pure Pd plate and a 0.5-m-thick Pd coating on gold-sputtered quartz crystal is used for electrochemical and microgravimetric studies. It is shown that a Pd electrode dissolves electrochemically in 0.5 M H₂SO₄ when its potential is cycled between 0.5 and 1.3 V. In the case of 0.5-m-thick Pd coating on the gold substrate, the decrease in the electrode weight during one anodic–cathodic cycle is 1.0–1.5 g/cm². It is suggested that anodic process at 0.5–1.3 V (SHE) represents electrochemical oxidation of palladium, yielding a surface layer of poorly soluble Pd(OH)₂ and/or PdO phases, as expressed by the equation Pd + 2H₂O (Pd(OH)₂/PdO)_s + 2H⁺ + 2e. This surface layer, (Pd(OH)₂/PdO)_s, undergoes reduction during the cathodic process. About 5% of the total amount of ionized palladium dissolve in electrolyte.     

Neue τ-Boride

The following -borides have been synthesized: Cr₁₃Ir₁₀B₆, Mn₁₆Ir₇B₆, Fe_10–15.4Ir_13–7.6B₆, Co₁₅Ir₈B₆.

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Mit 1 Abbildung

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Herrn Prof. Dr.A. Knappwost in Freundschaft gewidmet.     

Flow-Injection Simultaneous Chemiluminescence Determination of Ascorbic Acid and L-Cysteine with Partial Least Squares Calibration

In this paper, a flow-injection chemiluminescence system is proposed for simultaneous determination of ascorbic acid and L-cysteine with partial least squares calibration. This method is based on the fact that both AA and Cys can quantitatively reduce Fe³⁺ to Fe²⁺, and that the reaction rates of AA and Cys with Fe³⁺ are different. The reduced product Fe²⁺ was detected with the luminol-Fe²⁺–O₂ CL system. The CL intensity was measured and recorded at different reaction times of Fe³⁺ with AA and Cys, and the obtained data was processed by the chemometric approach of partial least squares. The experimental calibration set was composed of 16 sample solutions using an orthogonal calibration design for two component mixtures. The calibration curve was linear over the concentration range of 0.066µgmL^–1 and 0.440µgmL^–1 for ascorbic acid and L-cysteine, respectively. The proposed method was successfully applied to the simultaneous determination of both analytes in pharmaceutical formulations and human urine samples.     

Sol-Gel Derived Nanocomposites and Nanoporous Oxide Powders and Related Coatings for the Reversible Chemisorption of Hydrogen Sulfide

Two types of nanocomposites and nanoporous powders and related coatings were prepared by the sol-gel route. These silica-based materials contain dispersed reactive oxides, ZnO and ZnCr₂O₄, respectively. Experiments evidenced their ability of reversible chemisorption of H₂S as ZnS. Their attractive porous characteristics (small pore size 2–2.5 nm, high specific surface area 900–1100 m²· g^–1, high porosity 50–60%) are not significantly modified during the successive treatments of H₂S chemisorption and oxide regeneration. These preliminary results encourage to pursue this study which aims at the preparation of nanofilters for the desulfurization of gas mixtures.     

A π-acceptor series for phosphines from51V N.M.R. data on [η5-CpV(CO)3L] complexes

Summary Qualitative molecular orbital considerations of the complexes [⁵-CPV(CO)₃ L] (L = substituted phosphane, SbPh₃, AsPh₃, CN^–) suggest that s' V chemical shift parameters () obtained for these compounds should correlate with the -acceptor abilities of L. Based on observed r-values, the ligands are arranged in sequence of their -acceptor ability, which lies in the order P(OR)₃ > CN^– > PR'₃3 SbPh₃ PPhF₂ > P(i-Bu)₃ P(NR ₂ )₃ > PPh₃ > AsPh₃ Nuclear spin-spin coupling constants J (⁵¹V-³¹ P), line widths H and i.r. data in the (CO) region are also presented.P(OR)₃ = P(OEt)₃, 4-Ethyl-l-phospha-2,6,7-trioxabicyclo[2.2.2]-octane; R = Me, n-Pr; R = Me, Et.     

Simple screening method for the fast determination of clenbuterol in animal feeds

Summary A simple method for the determination of clenbuterol is described. It is extracted from the sample at pH 3 and then at pH 11, followed by partitioning the analyte into water at pH 3 and reextraction into ethyl acetate at pH 9. Clenbuterol is oxidized with KMnO₄ to clenbuteron for GC-determination. Recoveries for 0.01– 1.0 mg/kg were between 70% and 110% (standard deviation ±14%, n = 18).

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Eine einfache Screening-Methode zur schnellen Bestimmung von Clenbuterol in tierischen Futtermitteln

     

Homogeneous Rhodium–Copper–Halide Catalytic Systems for the Oxidation and Oxidative Carbonylation of Methane

Homogeneous catalytic systems for the oxidation and oxidative carbonylation of methane in aqueous trifluoroacetic acid solutions were developed. The system included rhodium compounds and copper compounds as cocatalysts. Methanol, methyl trifluoroacetate, formic acid, and acetic acid were the reaction products. The process was accompanied by the intense oxidation of CO to CO₂. Regularities of the process were studied, optimum process parameters were determined, and conditions at which methyl trifluoroacetate was formed with 90% selectivity were found. Kinetic isotope effects with respect to the solvent were determined. For the formation of organic products, k _H/k _D was 1, whereas it was 1.6 for the oxidation of CO. Studies were also performed with the use of compounds containing the ¹⁸O isotope. Conceivable mechanistic models of this process are discussed.     

Crystal Structure Formation in Compounds with [Hg2]2+ Dimers

This paper describes the arrangement of cations in the structures of inorganic compounds HgVO₃, HgReO₄, Hg₂MoO₄ ( and , Hg₂Mo₂O₇, Hg₂Mo₅O₁₆, Hg₅Re₂O₁₀ (two modifications), Hg₂ReO₅, and Hg₂VO₄. To isolate crystal-forming planes and cation sublattices, it is preferable to consider the [Hg₂]²⁺ dumbbell pair as a single cation. Two types of mutual orientation of close-packed cation planes intersecting at an angle of 60° or 90° (45°) have been found. Details of three-dimensional ordering of cations and possible methods of structure modification in polymorphous transformations are discussed.     

Diastereoselectivity in theLewis acid mediated aldol reaction of chiral α, β-epoxyaldehydes with a ketene silyl acetal

Summary The Lewis acid mediated aldol reaction of chiral , -cis andtrans epoxyaldehydes1 and2 withtert-butyl ketene silyl acetal proceeds mainly withanti diastereofacial preference. The best results were obtained forcis epoxyaldehyde1 in the presence of catalytic amounts of BiCl₃·1.5 eq. ZnI₂ (anti:syn 13:1), whereas the poorest stereoselectivity was observed when an excess of LiClO₄ was used (anti:syn 1:1). The more stable epoxyaldehyde conformers were determined and the diastereofacial preference was found to be in agreement with a nucleophilic attack on the energetically more favoured conformers.

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Diastereoselektivität derLewis-Säure-katalysierten Aldolreaction zwischen chiralen , -Epoxyaldehyden und einem Ketensilylacetal

Zusammenfassung DieLewis-Säure-katalysierte Aldolreaktion der chiralen , -cis- und -trans-Epoxyaldehyde1 und2 mittert-Butylketensilylacetal verläuft stereoselektivanti. Die besten Ergebnisse wurden für dencis-Epoxyaldehyd1 in Gegenwart katalytischer Mengen BiCl3·1.5 eq. Znl₂ erhalten (anti:syn 13:1). Die geringste Stereoselektivität trat auf, wenn LiClO₄ im Überschuß eingesetzt wurde (anti:syn 1:1). Das beobachtete Verhalten steht mit einem nucleophilen Angriff am energetisch günstigeren Konformeren im Einklang.

     

Effect of H2S-uptake on the conversion of cyclohexene on Ru- and Pd-promoted molybdena-alumina catalysts

The effect of H₂S on the activity and selectivity of catalysts (Ru/Al₂O₃, Pd/Al₂O₃ and Ru and Pd promoted molydena-alumina) was different (on differnt catalysts and different conversions of cyclohexene). Ru-containing catalysts showed higher sulfur sensitivities than the Pd-containing ones. The sequence of catalysts by their H₂S uptake related to mass of catalyst was PdMo/Al₂O₃RuMo/Al₂O₃Mo/Al₂O₃>Pd/Al₂O₃Ru/Al₂O₃.     

Determination of solid state basicity of rare earth oxides by thermal analysis of their carbonates

Relative basicities of the rare earth oxides (M₂O₃) were determined from the measurement by TG - DTA of decomposition temperatures of the carbonates of Ce, Pr, Sm, Eu, Gd, Tb, Dy, Ho, Er and Yb. From the comparison of this data with that published by Head and Holley, a sequence of basicity has been proposed for the entire range of rare earth oxides. This sequence in decreasing basicities is: La > Pr ~ Nd > Sm > Gd ~ Eu > Tb ~ Ho ~ Er > Dy Tm Yb Lu > Ce. Basicity of rare earth oxides, therefore, does not decrease progressively with an increase in atomic number.

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Zusammenfassung Die relative Basizität der Seltenerdenoxide (M₂O₃) wurde mittels der durch TG-DTA-Untersuchungen festgestellten Zersetzungstemperaturen der Karbonate folgender Metalle bestimmt: Ce, Pr, Sm,Eu, Gd, Tb, Dy, Ho, Er und Yb. Aufgrund eines Vergleiches der hier ermittelten Daten mit denen von Head und Holley wird für die Basizität der Seltenerdenoxide folgende Reihenfolge aufgestellt: La > Pr Nd > Sm > Gd Eu > Tb Ho Er > Dy Tm Yb Lu > Ce. Wie ersichtlich nimmt die Basizität der Seltenerdenoxide mit ansteigender Ordnungszahl nicht progressiv ab.

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This research forms part of a larger nationally coordinated program on natural gas conversion conducted in collaboration with the Divisions of Materials Science & Technology and Fuel Technology, and with BHP Melbourne Research Laboratories.

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The author is grateful to Dr E. Patsalides of Sydney University for his generous donation of eight rare-earth oxides. The author wishes to thank the colleagues for their contribution to this work: Mr K. Riley and Mr W. Godbeer (chemical analysis), Dr P. F. Nelson and Mr R. Quezada (FTIR analysis), Mr A. Home (XRD analysis), Mr S. P. Chatfield (thermal analysis) and the project leader, Mr R. J. Tyler for his constant encouragement and valuable suggestions.     

Tail-end purification of americium from plutonium loading effluents using a mixture of octyl (phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide and tri-N-butyl phosphate

The tail-end purification of Am from Pu loading effluents in 7.5M HNO₃ containing 160 mg l^–1 Am and 1.2 mg l^–1 Pu has been carried out. With 0.2M CMPO+1.2M TBP in dodecane as the extractant and stripping by 0.04M HNO₃+0.05M NaNO₂, the Pu level is brought down to 31.2 g l^–1. When the acidity was reduced to 4.2M HNO₃, one contact with 20% TLA/dodecane and subsequent extraction by a mixture of CMPO and TBP and stripping with 0.04M HNO₃+0.05M NaNO₂ gave Am samples without any detectable amounts of Pu. The recovery of Am was 90% by the first procedure and 98% by the second one.     

On the use of a dead-time meter for pile-up corrections

Correction for pile-up losses in the amplifier is possible by the dead-time fraction indicator of the ADC in case of long-lived radionuclides. If the dead-time meter has been calibrated, an accuracy of 1.5% is feasible up to a dead-time fraction of 25%. The precision decreases from 1.5% at 10% dead-time fraction to 3% at a deadtime fraction of 30%.     

On-stream measurement of heavy water concentration by intermediate neutron moderation

A method of measuring heavy water concentration is described based on intermediate neutron moderation. With a 1.6 g²⁵²Cf neutron source and a BF₃ proportional counter, for 500 ml samples, accuracies of the measurements are within ±0.02 mol% in the concentration range of 0100 mol% with 210 minute counting. To evaluate the practical effectiveness of the method, a model apparatus was built for routine use in laboratory and on-stream measurements. It was successfully applied to observe the substitution process between light water and heavy water in an ion exchange resin tower at a nuclear power station.