bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electrochemical preparation of semipermeable polymer membranes on carbon fiber microelectrodes for selective amperometric detection of cations
Authors: Potje‐Kamloth Karin , Josowicz Mira 
Published: March 2014

AbstractAn electrochemical procedure is presented for in situ preparation and subsequent deposition of semipermeable membranes on ultramicroelectrodes. The membranes are based on a matrix of poly(oxyphenylene) bearing carboxyl and sulfonic groups, i.e. poly(1,2‐oxyphenylene‐4‐sulfonic acid) or poly(1,2‐oxyphenylene‐3‐carboxylic acid). These membranes exhibit a cation exchange behavior whereas the transport of anions is inhibited. The diffusion coefficients of Ru(NH3)6·3+ within the semipermeable membranes could be estimated by means of chronoamperometric and steady‐state measurements. The values obtained are in the range of 1.0–6.9 · 10−7 cm2/s. The permeability of the cation through the membranes is high. Therefore, no distortion of the voltammetric response due to the attached membrane is observed. It is shown that the transport rate can be modulated by copolymerization of the functionalized phenolic monomer with varying amounts of a cross‐linking agent. The ultramicroelectrodes modified with the above membranes can be used as amperometric sensors displaying a linear current/concentration relationship.
A high‐temperature study of defect‐induced optical absorption in nickel oxide, Ni1−δO
Authors: Becker K. D. , Rau F. 
Published: March 2014

AbstractUV‐VIS‐NIR absorption spectra of single crystalline nickel oxide, Ni1−δO, have been measured at high temperatures (up to 1200°C) as a function of oxygen partial pressure, pO2. The observed pO2‐dependence of the spectra is discussed in the context of the point defect chemistry of the compound. From its dependence on oxygen partial pressure and temperature, and from its spectral shape it is concluded that the pO2‐dependent contribution to absorption is due to singly charged cation vacancies, V'Ni. The microscopic model of the optical process is discussed in the framework of light‐induced charge transfer processes involving ions in the neighbourhood of the cation vacancy.
Solvent and isotope effects on addition of atomic hydrogen to benzene in aqueous solution
Authors: Roduner E. , Bartels D. M. 
Published: March 2014

AbstractPulsed ESR has been used to measure rate constants for the addition of hydrogen atoms to benzene as a function of temperature in aqueous solution. At 298 K we obtain kH(aq) = (1.1 ± 0.1) · 109 M−1 s−1. The average Arrhenius activation energy, Ea = 19.1(6) kJ · mol−1, is essentially the same in solution as in the gas phase, but the frequency factor, represented by log(A/M−1 s−1) = 12.34(9), is 54 times higher than in the gas. This may be explained in terms of solvation of reactants and transition state, with most of the enhancement attributed to H atom solvation. In a 90% D2O/10% H2O mix, H atoms react at the same rate, but deuterium atoms react more slowly than H atoms by a factor of 1.4. The much smaller solvent enhancement previously demonstrated for the light muonium isotope is tentatively attributed to incomplete hydration of the transition state in that case.
Dispersion of mean molecular dipole polarizability and second density virial coefficients of 1,3‐butadiene
Authors: Hohm Uwe , Trümper Ulf 
Published: March 2014

AbstractFor the first time, measurements of the gas‐phase refractive index of 1,3‐butadiene are performed in the ranges of temperature 295 K < T < 365 K, pressure 0 < p < 1.7 · 105 Pa, and wavelength 325 nm < λ < 633 nm, respectively. Precise values of the dispersion of the mean dipole polarizability α0(λ, T) with an uncertainty of Δα0/α0 < 0.25% are obtained. Moreover, second density virial coefficients B(T) are estimated with error bounds of 10cm3mol−1 from the interferometric measurements.
Thermal Diffusion in Crystalline Binary Compounds with Narrow Range of Homogeneity – II. Stationary Thermal Diffusion in β‐Ag2+δS
Authors: Janek J. , Korte C. 
Published: March 2014

AbstractThe experimental determination of the (reduced) heat of transport of silver, Q*Ag, in β‐Ag2+δS by the direct measurement of the silver flux in a given temperature gradient, under the condition of equal composition at the ends of the crystalline sample, is reported. The measurement is based on the application of galvanic cells for the simultaneous control and measurement of both the silver flux and composition. A set of data for the heat of transport of silver is determined for 210°C<T<270°C and 0.96·10−3<δ< 1.7·10−3.The measured values for the heat of transport, Q*Ag, are positive and nearly independent of the composition of β‐Ag2+δS. Thus, a flux of silver metal which is induced by a temperature gradient is directed towards the low temperature side of the crystal. In addition, a strong temperature dependence of Q*Ag was observed.
Surface Diffusion on Heterogeneous Surfaces: The Effect of Steps
Authors: Uebing Christian 
Published: March 2014

AbstractMonte Carlo modeling was utilized for determining the tracer and chemical surface diffusion coefficients of adsorbates. Simulations were carried out on a square array of 64×64 lattice sites applying periodic boundary conditions. In order to analyze the effects of steps on surface diffusion different atomistic models of steps were introduced. For the simplest model steps were assumed to affect the site energies of a single row of lattice sites located on the down‐side of the step. Another set of simulations was performed for steps affecting the site energies on the up‐side of the step as well. For attractive interactions between adsorbates and step sites surface diffusion is slowed down with respect to the noninteracting Langmuir gas on a plain surface. Steps cause diffusion to be anisotropic as crossing of steps costs an extra activation energy. Additional calculations are performed in order to analyze the effect of the saddle points of the periodic potential on surface diffusion.
Profiles of Voltage and of Channel Density in a Planar Membrane Cable on Micromachined Silicon
Authors: Klingler Jürgen , Fromherz Peter 
Published: March 2014

AbstractA lipid bilayer of glycerolmonoleate is spanned over a microscopic shallow groove etched into the 110 surface of a silicon wafer and insulated by thermal oxidation. The conductance of the bimolecular membrane is modulated by gramicidin. The voltage profile in the groove is recorded by a set of Ag/AgCl electrodes which are integrated into the bottom of the groove. It is used to determine the distribution of ion channels along the membrane on the basis of Kelvin's cable equation.
Relationship Between Phase Transition Temperature and Protonation Degree of Dipalmitoylphosphatidylcholine in Liposomes
Authors: Fernández Marta S. 
Published: March 2014

AbstractThe relationship between the gel‐liquid ctystal phase transition temperature (tm) of dipalmitoylphosphatidylcholine (DPPC) liposomes and the protonation degree of the lecithin phosphodiester moiety, has been studied. A linear function is obtained when the phase transition temperatures of liposomes determined by 90° light scattering variation at different bulk pH values, are plotted against the corresponding protonation degrees calculated either as described previously from the potentiality for tm elevation of DPPC liposomes using stearylamine as a probe [Ber. Bunsenges. Phys. Chem. 95, 1669 (1991)] or from combination of Boltzmann, Henderson‐Hasselbach and Gouy‐Chapman equations, by assuming an interfacial intrinsic pK of 4 for the phosphodiester group and an average cross section molecular area of 45 or 65 Å2 for the phospholipid. The approach described here, which supplements the above‐mentioned previous work, allows to predict that the tm of fully protonated DPPC in liposomes should be in the range from 59.2 to 62.9°C, the variation being dependent on the procedure used to calculate the protonation degree.
Thermodynamic Properties of Pd‐Nd Alloys
Authors: Hennemann K. , Schaller Hans‐Jürgen 
Published: March 2014

AbstractA complete set of thermodynamic functions was determined for the palladium‐rich solid solution and for the intermetallic compounds Pd5Nd, Pd3Nd, Pd2Nd, Pd4Nd3, and PdNd from electromotive force measurements between 700 and 800°C. A CaF2 single crystal was employed as the solid electrolyte. The activity of Nd in Pd‐rich alloys shows pronounced negative deviations from Raoult's law with a relative partial excess Gibbs energy of Nd at infinite dilution of −305 kJ/mol. Two effects are discussed to account for the non‐ideal properties of the solid solution: the transfer of the valence electrons of Nd to the electron gas of the alloy and the lattice distortion brought about by the size difference of the components. Remarkably exothermic values were obtained for the heats of formation of the intermetallic compounds. The results are compared with predictions of the Miedema model.
Investigation of the Redox Couple Benzophenone/Benzophenone Anion Radical in Acetonitrile and N,N‐Dimethylformamide by Electrochemical and Spectroelectrochemical Methods
Authors: Walczyk K.R. , Popkirov G.S. , Schindler R.N. 
Published: March 2014

AbstractDiffusion layer imaging (DLI), time‐resolved spectroelectrochemical methods and electrochemical impedance spectroscopy (EIS) were applied to determine the influence of the solvent and the supporting electrolyte on reaction parameters for the benzophenone/benzophenone radical anion redox couple (BP/BP*−) formed at a Hg‐covered Au wire in aprotic solvents.Results are reported for the solvents acetonitrile (AN) and N,N‐dimethylformamide (DMF) using two different tetraalkylammonium salts as supporting electrolytes. Heterogeneous rate constants for the electron transfer reaction and diffusion coefficients of the neutral BP and the radical anion BP*− obtained with the different methods are discussed and compared.
Study of Electrical Migration in Electrochemical Cells by the Network Method
Authors: Moya A.A. , Hayas A. , Horno J. 
Published: March 2014

AbstractNetwork approach has been used to analyse the electrical properties of a system consisting of three ionic species having different charges in contact with blocking electrodes. A network model for the electrodiffusion process taking place in such a system has been proposed. With this model and the electric circuit simulation program PSPICE, the transient response of the system to a step‐function applied potential difference and the small‐signal ac response of this system subject to a steady external voltage bias have been simulated. Nyquist plots for the electrochemical impedance, and the time evolution of the surface charge density stored in the electrical double layers at the electrode/electrolyte interfaces as well as the electric current density through the system, are given. The ionic concentration, the electric charge density, and the electric potential profiles across the cell were also obtained as a function of time.
Determination of Infinite Dilution Diffusion Coefficients of Polycyclic Aromatic Hydrocarbons in Heptane and in Octane
Authors: Fan Yiqun , Qian Renyuan , Cheng Mingxiao , Shi Meiren , Shi Jun 
Published: March 2014

AbstractThe diffusion coefficients of benzene, naphthalene, anthracene, phenanthrene, and diphenyl at infinite dilution in heptane and in octane in the temperature range 303.2 to 333.2 K were determined by the Taylor dispersion technique. Two empirical estimation methods for diffusion coefficient were tested against our experimental data and a free‐volume‐type expression was used to correlate the diffusion coefficients.
Application of Paramagnetic Relaxation Reagents in Characterization of Fullerene Derivatives
Authors: Kitaygorodskiy Alex , Lawson Glenn E. , Sun Ya‐Ping 
Published: March 2014

AbstractThe 13C spin‐lattice relaxation times of C60/C70 were measured in CS2 solutions containing different concentrations of Cr(acac)3. The coincidence of paramagnetic relaxation times for fullerenes and TMS shows that there is no specific intermolecular interaction between fullerenes and Cr(acac)3. The relaxation times were used to select optimal experimental parameters for accumulation of 13C NMR spectra of fullerenes. It was demonstrated that proper application of Cr(acac)3 overcomes unfavorable relaxation properties of fullerenes and leads to considerable (at least 5‐fold) improvement of signal‐to‐noise ratio in their 13C NMR spectra.
Chaos Control and Tracking of Periodic States in a Forced Thermokinetic Oscillator Model
Authors: Delgado E.J. , Münster A. F. , Schneider F. W. 
Published: March 2014

AbstractThe Sal'nikov thermokinetic oscillator model is investigated in a spherical reactor with a temperature‐dependent surface/volume ratio. If the temperature is driven sinusoidally, period doubling and chaos occurs. A typical chaotic state of the model is analyzed by various methods, like attractor reconstruction, dimensional analysis and computation of Lyapunov exponents. We demonstrate that unstable periodic orbits embedded in the strange attractor are stabilized by a continuous delay time method according to Pyragas. Two simple stabilized orbits are shown and discussed. We also use the continuous method of chaos control for the tracking of unstable orbits through a sequence of period doublings and chaos.
Pressure Dependence of the OH‐Stretch Raman Spectra of Supercooled Water
Authors: Karger N. , Lüdemann H.‐D. , Sceats M.G. 
Published: March 2014

AbstractRaman spectra of the OH‐stretching region of liquid H2O and 10% H in D2O have been obtained between −50 and + 100°C at pressures up to 240 MPa, extending into the deeply supercooled region. Application of pressure made it possible to study liquid water at temperatures 20 K lower than reported so far.The low‐frequency shoulder of the H2O‐spectra grows rapidly with falling temperature. The relative intensity of the collective band increases monotonically to the lowest temperatures studied.Supercooled water shows a number of thermodynamic and transport anomalies, which become apparent from the unusual p‐, T‐dependence of the compressibility and the molecular mobility in the pressure range between 0 and 200 MPa. The Raman spectra, however, do not change significanctly in this pressure region. At the lowest temperatures they are practically independent of pressure.This finding suggests that the intensity of the collective Raman band originates from short range correlations of the OH‐bond vibrations, that are not identical to the more extended density fluctuations responsible for the well known anomalies of supercooled water.
Firm Binding and Loose Attachment of Ru(II) Complexes to Colloidal Silica in Aqueous Solution. Evidence Based on Biphotonic Ionization and a Kinetic Salt Effect on the Reaction with Hydrated Electrons
Authors: Naik D.B. , Schnabel W. 
Published: March 2014

AbstractThe photoionization of tris‐2,2′‐bipyridyl Ru(II) complexes in dilute aqueous solution (pH = 9.8), yielding hydrated electrons, is enhanced by a factor of about 2.5 by colloidal silica. LiCl reduces the enhancement factor. The photoionization yield decreases with decreasing pH. Moreover, the presence of colloidal silica causes a drastic increase in the lifetime of the hydrated electrons. The results are interpreted in terms of firm binding and loose attachment of Ru(II) complexes to the negatively charged silica particles the extent of which is controlled by the silica concentration at fixed Ru(II) complex concentration. Firm binding causes a reduction in the ionization potential which results in higher photoionization yields. Loose attachment results in a kinetic salt effect on the rate constant of the reactions of hydrated electrons.
Ion Pairing in the Analysis of Voltammetric Data at the ITIES: RbTPB and RbTPBCl in 1,2‐dichloroethane
Authors: Kontturi A. K. , Kontturi K. , Manzanares J. A. , Mafé S. , Murtomäki L. 
Published: March 2014

AbstractThe association of rubidium‐tetraphenylborate (RbTPB) and rubidium‐tetrakis(‐chlorophenyl)borate (RbTPBCl) ion pairs in the organic solvent 1,2‐dichloroethane (DCE) have been obtained from condutivity and voltammetric data. Conductivity measurements given KRbJPBCl = 43100 M−1 and yield a lower bound for KRbTPB (KRbTPB > 70000 M−1). The latter association constant is at variance with the previously accepted value. A method for analysing voltammetric data which allows for the determination of the association constants is presented. The positive polarization limit where the transfer of Rb+ takes place is shifted by ca. 200 mV when changing the anion of the organic base electrolyte from TPB− to TPBCl−. If we interpret this shift in terms of the association constant, then KRbTPB = 7.4·107 M−1. The values of KRbTPB and KRbTPCl are discussed in terms of the classical theories by Bjerrum and Fuoss. Finally, we consider if the preferential solvation of p‐chlorophenyl rings of TPBl− could account for the observed difference between the values of the association constants.
UV/VIS‐absorption Spectra of HOBr and CH3OBr; Br(2P3/2) Atom Yields in the Photolysis of HOBr
Authors: Benter Th. , Feldmann Ch R. , Kirchner U. , Schmidt M. , Schmidt S. , Schindler R. N. 
Published: March 2014

AbstractGas phase UV/VIS‐absorption spectra are reported for HOBr and CH3OBr in the wavelength range (230 < λ < 400)nm. The quantum yield for Br(2P3/2) atom generation was determined to be ≥0.95 in the laser photolysis of HOBr at λ = 363 nm.
Strukturvorhersage von Kristallen aus binären Edelgasgemischen mit globalen und lokalen Optimierungsmethoden
Authors: Putz H. , Schön J. C. , Jansen M. 
Published: March 2014

AbstractUsing global optimization methods (Simulated Annealing, Quench, Gradient Descent) possible structures of crystals consisting of binary combinations of the four considered noble gases Ne, Ar, Kr and Xe have been investigated. The computer simulations showed that in all instances they should crystallize either in separate phases of the pure noble gases or in a shared close‐packed structure. No other structure types occurred among the optimal configurations. Phase separation was observed in all systems containing Ne and in the system Ar/Xc. Mixing Ar and Kr led to a random distribution of the two species on the sites of a close‐packed structure, i.e. to a solid solution. This corresponds to experimental observations.
Far Precritical Effect in 1,3‐Dimethoxybenzene‐Alkane Mixtures Studied by Nonlinear Dielectric Effect
Authors: Śliwinska‐Bartkowiak M. , Radojewska L. 
Published: March 2014

AbstractNonlinear dielectric effect (NDE) was measured in mixtures of 1,3‐dimethoxybenzene with n‐alkanes. The mixtures were found to exhibit an apparent critical point, concealed below the melting point of the mixture and manifesting itself by anomalous NDE behaviour in the vicinity of the critical concentrations in the stable liquid phase.
SERS Study of Acridine Adsorption on Copper Electrode
Authors: Niaura G. , Malinauskas A. 
Published: March 2014

AbstractIt was demonstrated that acridinium cation does not interact directly with copper electrode surface in acid sulfate solution. In the presence of chloride, acridinium cation adsorbed on the electrode as an ion pair with chloride anion. In the whole potential range investigated, from 0 V to a chloride desorption potential at about −0.6 V, acridinium did not undergo any redox‐process. By shifting a potential towards negative values acridinium tends to reorient to a position perpendicular to the electrode plane. The formation of the ion pair stabilized chloride adsorption on the electrode surface.
New Approach to Synthesis of Fractal Materials with a given Fractal Dimension. Synthesis and Some Properties of Amorphous Fractal Films of Copper Sulfide
Authors: Strizhak Peter E. 
Published: March 2014

AbstractA method of synthesis of fractal films of copper sulfide is proposed. Formation of fractal films is induced by spatial patterns formed in so‐called ‘oxygen’ oscillating chemical reaction – oxidation of ascorbic acid by air oxygen in the presence of hydrogen sulfide ions, methylene blue, and copper(II) coordination compound. The formation of the CuS film in this system is observed due to the slow reaction between copper(II) coordination compound and the hydrogen sulfide ions. A fractal dimension of CuS films correlates with the fractal dimension of chemical patterns. The electrical resistance of the fractal films and the sensitivity of Cu2+‐selective electrodes with the fractal CuS surface to Cu2+ ions were measured. These results are interpreted in terms of fractal dimension.
Differential Thermal Analysis of Long‐Chainn‐Alcohols under High Pressure
Authors: Reuter Jörg , Würflinger Albert 
Published: March 2014

AbstractDifferential thermal analysis (DTA) measurements under pressures up to 250 MPa and temperatures of about 300 to 370 K have been performed on long chainn‐alcohols CnH2n+1OH, including 1‐tetradecanol, 1‐pentadecanol, 1‐hexadecanol, 1‐heptadecanol and 1‐octadecanol. On heating, these alcohols change from a crystalline to a rotator phase a few degrees below their melting points. The rotational state of 1‐tetradecanol can only be reached by cooling from the melt. Thep‐T‐phase diagrams of these alcohols have been established. They demonstrate, that the coexistence region of the rotator phase is increased under pressure. In contrast to the high‐pressure phase behaviour of long chainn‐paraffins the phase transition lines ofn‐alcohols diverge upon increasing pressure and no triple point is observed. This different behaviour is connected with the enlarged enthalpy change at the transitions to the rotator phase that reduces the slope dT/dpof this phase transition line. Dielectric measurements were performed on 1‐pentadecanol which support the orientationally disordered state of the rotator phase.
Adsorption of Gases on Solid Surfaces
Authors: Freund Hans‐Joachim 
Published: March 2014

AbstractMetal surfaces have for a long time been and still are in the focus of experimental and theoretical activities in surface science. One has started to understand in some detail the interaction of gases with respect to structural and dynamical aspects. Non‐metallic substrates on the other hand have only recently received more attention and corresponding studies have been started. In view of the importance of compound surfaces in many fields, including catalysis, this development is not unexpected. We review our efforts in the field of surface science studies of oxide surfaces and emphasize in addition to clean oxide surfaces also metal modified surfaces as a model towards the study of complex systems which are typical for catalysts. In addition to studies of the geometric and electronic structure of compound surfaces we also cover investigations of adsorbate dynamics reporting on newly designed experiments on the basis of magnetic resonance as well as on laser‐induced desorption studies. In the latter investigations we have probed spatially resolved the time‐of‐flight distributions of molecules in individual quantum states as they leave the oxide surface.
Heterogeneous Catalysis at an Atomic Scale
Authors: Sachtler Wolfgang M.H. 
Published: March 2014

AbstractFor the overwhelming majority of processes in modern chemical and petrochemical industry, the presence of an active and selective catalyst is crucial. In the USA the total value of products from catalytic processes has been estimated to be roughly 9·1011 $ per year, corresponding to 17% of the GNP. An arsenal of modern methods enables the physical chemist to characterize active sites and chemisorption complexes; quantum chemical calculations increasingly lead to concrete predictions. The key issue remains, however, to unravel reaction mechanism and to use this knowledge for the design of superior catalysts.In the present paper some challenging problems are addressed:
How does a “promoter” in a Rh/NaY catalyst direct CO hydrogenation towards synthesis of ethanol and ethyl acetate?
How does NOx decompose over Cu/ZSM 5 catalysts and how is its reduction to N2 enhanced by O2?
How does the isomerization of butane to isobutane avoid primary carbenium ions over some acid catalysts, why are other catalysts with stronger acid sites less active?