bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermal Diffusion in Crystalline Binary Compounds with Narrow Ranges of Homogeneity: (III) Experimental Study of the Soret Effect in β‐Ag2+δS
Authors: Korte C. , Janek J. 
Published: July 2012

AbstractExperiments on thermal demixing of β‐Ag2+δS (high‐temperature phase) are reported. By means of a nonisothermal solid state galvanic cell, the redistribution of the metal excess δ in an external temperature gradient has been investigated in the temperature range 200°C <T<300°C and for metal excesses 8·10−4<δ<2·10−3. From the results of the demixing experiments and from additional determinations of the relative molar partial entropy of silver in β‐Ag2+δS, the (reduced) heat of transport, Q*Ag, of silver has been evaluated. Q*Ag increases strongly with increasing temperature, and at a temperature of approximately 205°C we observe a sign reversal of Q*Ag. The results support our previous conclusions from experiments on stationary thermal diffusion. A discussion of our experimental results for the heat of transport of the metal component, in respect to the properties of ions and electrons, is given.
Medium Effects on the Electron‐Transfer Reactions between cis‐Co(NH3)4(H2O)32+ and the Donors Fe(CN)4‐6 and Mo(CN)4‐8
Authors: Galan Manuel , Graciani Maria Del Mar , Jiménez Rafael , Luisa Moyá M. , Muñoz Ernestina , Rodriguez Amalia , Sánchez Francisco 
Published: July 2012

AbstractThe electron transfer reactions of the cis‐tetraamminediaquocobalt(III) complex with hexacyanoferrate(II) and octacyanomolibdate(IV) in four different water‐cosolvent binary mixtures have been investigated. ket and KIP values have been experimentally determined and discussed within the framework of current theories on electron transfer reactions and ionic association. For this purpose, the standard formal potentials of hexacyanoferrate(II) and octacyanomolibdate(IV) were also determined.Comparison of the second order rate constants (k12‐ ketKIP) to predictions of the Marcus Cross‐relation gives some indication of the adiabaticity of the processes investigated.
Formation of Fractal Clusters of Colloidal Copper Hydrous Oxides
Authors: Thies Michael , Hinze Ulrike , Paradies Henrich H. 
Published: July 2012

AbstractThe fractal dimensions of colloidal particles of copper hydrous oxides in the presence of natural occurring anionic exopolymers are reported from measurements using both small‐angle X‐ray‐ and static light scattering techniques. The power law decay of the structure factor [S(k) ∼ k −D] of colloidal copper hydrous oxides dispersions can be explained in terms of fractal geometry. D is found to be 2.15 ± 0.05 for Cu(OH)2, and for colloidal Cu2O·x H2O aggregates a value of 1.75 ± 0.07 was determined.
Proton‐Transfer Reactions between 7‐Hydroxycoumarin and Tertiary Amines. Formation of the Ground‐State Tautomer Anion
Authors: Sakurai Tadamitsu , Mizoguchi Hiroki , Yamada Satoshi , Inoue Hiroyasu 
Published: July 2012

AbstractThe UV absorption, fluorescence, and 13C NMR studies of proton‐transfer reactions between the title compound (7‐HC) and tertiary amines confirmed that the hydrogen‐bonded 7‐HC tautomer anion, being stable in the ground state at room temperature, is exclusively produced in acetonitrile containing 1,8‐diazabicyclo[5.4.0]undec‐7‐ene. In addition, 7‐HC in the ground state was found to give the hydrogen‐bonded complex and 7‐HC anion in the presence of the less basic amines, pyridine and triethylamine, respectively, but not to afford the 7‐HC tautomer anion formation of which is markedly enhanced in the excited singlet state.
The Reversible Redox Behaviour of Adsorbate Layers on Account of the Electrosorption Valency
Authors: Huck Horst 
Published: July 2012

AbstractThe electrosorption valencyγ[9–11] was introduced regarding acid‐base and redox equilibria at low surface concentrations at excess supporting electrolyte. A formula is given for the calculation of the apparent protolytic dissociation constant of an adsorbate (Eq. (10)) and a modified Nernst equation for adsorbates being to some extent immersed in a compact double layer (Eq. (17)). Neglecting the integral term another formula was obtained for the pH dependence of the half‐wave (peak) potentials of reversible surface redox reactions (Eq. (18)). Also modified equations for the peak current (Eq. (23)) and peak width (Eq. (24)) of cyclic voltammograms involving adsorbed species were deduced. Test substances were Pyocyanine, Nile blue and Neutral red adsorbed at graphite electrodes.
Analysis of chemical and physical relaxation processes of polyelectrolytes by electric field pulse methods: A comparison of critical comments with facts
Authors: Porschke Dietmar 
Published: July 2012

AbstractAccording to some statements in the literature, it is very hard or virtually impossible to get meaningful relaxation data for macromolecular systems by methods involving electric field pulses (electric field jump and Joule temperature jump), mainly because of perturbations resulting from field induced orientation effects. These statements have been presented until recently, in spite of the fact that the magic angle technique for suppression of such effects has been described in the literature quite some time ago. Apparently there is not sufficient knowledge on the existence/validity/practicability of this technique. More than 20 years experience with magic angle detection is summarized, including a recent detailed comparison of magic angle fluorescence T‐jump data with corresponding stopped flow data for the case of ethidium intercalation into DNA double helices. The results demonstrate that chemical relaxation induced by application of electric field pulses to macromolecular solutions can be measured without perturbations, provided that appropriate procedures are used. Moreover, techniques using electric field pulses proved to be the only practicable approach to analysis of many macromolecular reactions.It is not always necessary to suppress orientation effects; on the contrary, orientation effects can be very useful to follow reactions which cannot be detected by other procedures. A special case is demonstrated where reaction and orientation effects appear as a convolution product.
Enthalpies of dilution of some polycation solutions and exchange enthalpies of polycation counterions
Authors: Keller Markus , Lichtenthaler Rüdiger N. , Heintz A. 
Published: July 2012

AbstractExperimental data of the enthalpies of dilution of aqueous polycation solutions with water and with salt solutions are presented, as well as the exchange enthalpies of polycation counterions. Measurements were performed using a titration calorimeter. The procedure of obtaining the exchange enthalpies from the calorimetric data is described. The knowledge of these exchange enthalpies reveals information about the enthalpies of formation of (polycation‐polyanion) complexes which are the basic material for the preparation of so‐called “symplex” membranes employed in pervaporation. The data obtained are also of interest for paper manufacturing industries because of the interaction energies of polyelectrolytes with multiple‐charged electrolytes, e. g. lignin sulfonate. The experimental enthalpies of dilution and exchange enthalpies determined for the different counterions are discussed and can be explained by differences in molecular conformation and by different binding of the counterions, respectively.
Phase separation of a polycarboxylate at high ionic strength
Authors: Clegg S. M. , Hall D. G. , Robb I. D. , Williams P. A. 
Published: July 2012

AbstractThe phase separation of polycarboxylates in the presence of high concentrations of 1:1 and 1:2 electrolytes has been studied. Sodium polyacrylate remained in one phase at concentrations as high as 5 mol dm−3 sodium chloride whereas the fully ionised copolymer of acrylic acid and maleic anhydride (PAMA) phase separated at less than 1.0 mol dm−3. PAMA phase separated at polymer and electrolyte concentrations that had constant sodium ion activity, showing that the separation was essentially due to the common ion effect. Potassium salts did not produce any separation. In contrast to the 1:1 electrolytes, addition of 1:2 electrolytes (Na2SO4 and Na2CO3) produced no separation, indeed caused a two‐phase system, to revert to one phase. This initially surprising result was attributed to the increasing negative adsorption of the SO4−2 or CO3−2 from the polyion as the latter's concentration increased. This negative adsorption was expected to be greater for divalent than monovalent anions.
Static scattering from multicomponent polyelectrolyte solutions
Authors: Benmouna M. , Hakem F. I. , Vilgis T. A. 
Published: July 2012

AbstractThe theory developed originally by Benoit to study the static scattering properties of multicomponent neutral polymer mixtures is extended here to polyelectrolytes mixtures. Applications of this formalism to cases of practical interest are presented. The case of a ternary mixture made of a polyelectrolyte, a neutral polymer and a solvent is considered. The effects of the neutral polymer on the scattering peak of the polyelectrolyte are discussed. This formalism is also used to analyze the recent neutron scattering data from mixtures of polystyrenesulfonate and tetramethylammonium in aqueous solutions reported by Van der Maarel et al. A good agreement between the data and the theoretical predictions is obtained for the polyion‐polyion structure factor in the whole range of the wavevectors covered in these experiments.
Molecular mass and ionic strength dependence of electrochemical properties of flexible polyelectrolytes
Authors: Wandrey Christine 
Published: July 2012

AbstractConductometry and potentiometry have been employed to examine the influence of macromolecular parameters and chemical structure on the electrochemical behaviour of flexible polyelectrolytes with finite chain length in the concentration range 10−6<cp<10−2monomol·l−1. For polyelectrolytes with charge distances below the Bjerrum length at low ionic strength the equivalent conductivity increases strongly with decreasing polymer concentration. Correlating this behaviour with concentration regimes according to de Gennes and Odijk the strong and nearly linear increase is situated below the overlap concentration. In highly diluted polyelectrolyte solutions without and with addition of low molecular electrolyte the equivalent conductivity reaches a limit whose absolute high and position was found to have strong correlations with the molecular mass, the ionic strength, and the ratio of polyelectrolyte to salt concentration. The electrolytic conductivity results correspond with counterion activities in the concentration range cp > 10−4 monomol·l−1. The discussion of the findings in terms of existing theories point to defined changes of the interionic interactions.
Reversible swelling of polyanion/polycation multilayer films in solutions of different ionic strength
Authors: Sukhorukov Gleb B. , Schmitt Johannes , Decher Gero 
Published: July 2012

AbstractImmersion of consecutively adsorbed polyanion/polycation multilayer films in solutions of different ionic strength causes reversible thickness changes. Swelling of the films up to 18% was observed after soaking the films in aqueous solutions of NaCl at concentrations up to 1.0 mol/1. X‐ray reflectivity clearly shows that the thickness changes are reversible within experimental error and that the films seem to get smoother after several cycles of immersion in salt solutions and in pure water. The extent of swelling depends on the internal film structure, namely on the number of polyanion/polycation interfaces in a film of a given thickness. Interestingly, the swelling levels off at salt concentrations above 0.1 mol/1 and no additional changes were observed even at NaCl concentrations of 3.0 mol/1 over periods of several days. It is believed that Na+ and Cl− ions penetrate reversibly into the films and are responsible for the observed effects.
Peptides at lipid bilayers and at the air/water interface
Authors: Schwarz Gerhard 
Published: July 2012

AbstractThere is a multitude of amphiphilic peptides which interact with lipid bilayers and biological membranes. From a physical chemical point of view a fundamental issue in this respect concerns the quantitative analysis of the involved partitioning equilibrium between a hydrophobic interface (lipid/water or air/water) in structural and thermodynamic terms. In the present article some relevant theoretical and experimental approaches are discussed and illustrated by means of special examples. Regarding lipid bilayers this comprises various problems of pertinent evaluation of measured data when an aqueous solution is titrated with lipid vesicles. On the other hand, a novel method is presented that makes it possible to derive and interpret true surface concentrations at an air/water interface of a Langmuir trough with peptide or other surfactant material if only a comparably small part of the substance seeps away from the monolayer into the subphase.
Polyelectrolyte synthesis in a lamellar liquid crystal
Authors: Friberg Stig E. 
Published: July 2012

AbstractThe synthesis of polyelectrolytes is described of an unsaturated amphiphile with polar and non‐polar monomers in a lamellar liquid crystal using low angle x‐ray diffraction to obtain information about conformational changes and location of monomers in the lamellar structure. The results demonstrated the potential to use the synthesis in a lamellar liquid crystal to obtain comb copolymers with polar or non‐polar combs.
Interfacing neurons and silicon by electrical induction
Authors: Fromherz Peter 
Published: July 2012

AbstractDirect electrical coupling of a nerve cell and silicon microstructures is achieved by electrical induction without electrochemical current across the silicon/electrolyte interface. A field‐effect transistor with an insulated open gate detects the action potential of an attached neuron. A voltage step applied to a silicon microelectrode elicits an action potential through, an insulating film of silicon dioxide. The electrical aspects of the neuron‐silicon junctions are described by a representative circuit. Its capacitive and resistive components are determined by AC‐signals using patch‐clamp technique. A spatially resolved picture of a junction is obtained by placing an array of closely packed transistors beneath a single neuron. The cable theory is used to describe the extended region of adhesion. Aspects of a further development of the systems and of their application are considered.
A contribution to the study of the solubility of oxidic solids in water: The disolution kinetics of silica gel and its interpretation
Authors: Vogelsberger Wolfram , Mittelbach Thomas , Seidel Andreas 
Published: July 2012

AbstractThe dissolution process of silica gel in water is investigated in its dependence on dissolution time, pH (2 < pH < 10), and temperature (25°C, 45°C, 55°C). The dissolved amount of silica is depicted as a function of time and pH. A dissolution surface is formed. The saturation concentration at a certain temperature is relatively high at low pH‐levels. When the pH is increased, a minimum of solubility is found at pH about 4. A maximum seems to follow. Its position depends on the dissolution temperature. After this maximum a relatively constant region of amount of dissolved silica with a second small minimum is observed. If the pH‐value is as high as 10, the solubility increases drastically by the formation of an alkali silicate solution.A model is developed for the interpretation of the experimental results. The model consists of four reactions with proton transfer which are assumed to be in equilibrium. Furthermore, four elementary reactions of monosilicic acid addition or elimination are considered. The model allows for the determination of the equilibrium constants of the proton transfer reactions as well as the corresponding enthalpies and entropies. The rate constants of the elementary reactions, and the activation enthalpies and entropies are estimated.The expressions for the (overall) rate constants of dissolution and precipitation are derived, which are commonly used in the literature. They depend on the equilibrium constants of the proton transfer reactions, on the rate constants of the elementary reactions and on pH. Thus the course of the rate constant as a function of dissolution pH, as reported by several authors, could be established and interpreted.As far as appropriate data are available in the literature, a general good agreement of thermodynamic and kinetic quantities with the results obtained in this work could be observed. Therefore they could be a base for further investigations.
Proton NMR studies on the structure of water in ionic and nonionic water‐in‐oil microemulsions
Authors: Seoud Omar A. El , Okano Laura T. , Novaki Luzia P. , Barlow Graham K. 
Published: July 2012

AbstractThe structure of water present in water‐in‐oil microemulsions of anionic magnesium bis(2‐ethylhexyl) sulfosuccinate in C6D6, cationic cetyldimethylbenzylammonium chloride in C6D6, cetyldimethyl‐3‐phenylpropylammonium chloride in chlorobenzene, and nonionic polyoxyethylene (4) dodecyl ether in n‐heptane was probed by 1H NMR. Chemical shifts of solubilized H2O‐D2O, and of surfactant discrete protons were determined, at fixed [water]/[surfactant] ratios, as a function of the deuterium content of solubilized water. Chemical shift data were used to calculate the so called “fractionation factor”, φ, of the aggregate‐solubilized water. Calculated φ for the different systems are unity, showing that micellar water, although different from bulk water, does not seem to coexist in “layers” of different degrees of structure, as suggested, e.g., by the two‐state water solubilization model.
Methylviologen redox reactions at semiconductor single crystal electrodes
Authors: Schoenmakers G. H. , Waagenaar R. , Kelly J. J. 
Published: July 2012

AbstractThe mechanism of the two‐step reduction of the methylviologen cation radical (MV2+) was studied at CdS, GaAs and InP single crystal electrodes. In aqueous solution the second step (MV+• → MV0) gives rise to layer formation which is not observed in mixed ethanol/water solutions. This layer has interesting electrical properties. The reoxidation of MV0 occurs by electron injection into the conduction band of all three semiconductors. The reoxidation of MV+• at InP is also a conduction band reaction and electroluminescence is observed with the p‐type semiconductor. Electron injection from MV+• into the conduction band of GaAs is not observed while the kinetics of the reaction at CdS depend critically on the state of the electrode surface and on the nature of the electrolyte solution.
Solvent dependence of electron‐transfer sensitized photolysis of onium salts
Authors: Eckert Gerd , Goez Martin , Maiwald Beate , Müller Uwe 
Published: July 2012

AbstractThe photoreactions of 9,10‐diphenylanthracene with two iodonium salts and a sulfonium salt in different solvents were investigated by fluorescence quenching, flash photolysis with UV/vis detection, measurements of the quantum yields of sensitizer decomposition, and photo‐CIDNP spectroscopy. Energy‐transfer sensitization is precluded by thermodynamics in these systems. In a solvent of lower polarity such as dimethoxyethane, the quenching rate constant is still about a third of the value in acetonitrile; the quantum yields of formation of radical cations and the quantum yields of sensitizer decomposition are decreased by about the same factor. In contrast, dramatic effects occur in the CIDNP spectra of the iodonium salts, which derive from two consecutive radicals pairs, the first containing the radical cation DPA± of the sensitizer and the radical On• of the onium salt, the second comprising DPA± and a phenyl radical produced by fragmentation of On•: In less polar solvents, the polarizations from the first pair are strongly reduced, and the polarizations from the second pair are larger by an order of magnitude. From a kinetic analysis, this effect was attributed to a higher rate of transformation of the first radical pair into the second in the less polar solvent. For the sulfonium salt, this transformation is faster than in the case of iodonium salts, so even in acetonitrile all polarizations stem from the second radical pair. S‐T±‐type CIDNP, which had been proposed in the literature for analogous chemical systems, could be excluded unambiguously, and all CIDNP effects could be explained by radical pair theory (S‐T0‐type CIDNP).
Fluorescence quenching of meso‐substituted anthracene derivatives by molecular oxygen
Authors: Wirp Christoph , Güsten Hans , Brauer Hans‐Dieter 
Published: July 2012

AbstractRate constants of fluorescence quenching by molecular oxygen, kSq, of a series of meso‐substituted anthracene derivatives have been determined in toluene and acetonitrile at room temperature. They adopt values between 0.4 and 3.4 × 1010M−1 s−1 in toluene and values between 0.7 and 5.5 × 1010M−1 s−1 in acetonitrile. The ratio k(toluene)/k (acetonitrile) in all cases nearly equals the inverse ratio of the solvent viscosities η(acetonitrile)q/η(toluene) = 0.61. Additionally, singlet oxygen (1O2) efficiencies for quenching of the singlet state ϕ and the triplet state ϕ have been measured in both solvents. No significant decrease of the efficiencies of 1O2 formation in the polar solvent compared to the non‐polar solvent has been observed for the meso‐substituted anthracenes. In both solvents ϕ varies approximately linear with 1/kSq. The weak dependence of (1 ‐ ϕ)k = k(3O2) on the free enthalpy of electron transfer suggests the participation of charge transfer in the quenching process, but small and almost identical slopes of Hammett‐plots of the rate constants of fluorescence quenching in both solvents indicate that there is only little contribution of charge transfer interactions if the rate constant of fluorescence quenching is below the diffusion limit.
HF infrared chemiluminescence in the reactions of fluorine atoms with cis‐Butene‐2, trans‐butene‐2 and 2,3‐d2‐butene‐2
Authors: Dehe Katharina , Heydtmann Horst 
Published: July 2012

AbstractFor the reactions F+cis‐butene‐2 and F+trans‐butene‐2 identical vibrational distributions for the product molecule HF were determined: Nv=1 : Nv=2: Nv=3: Nv=4 = 0.26:0.33:0.26:0.15. Two reaction channels for each compound are responsible for this distribution. Isolated reaction channels were observed in the reaction system F+2,3‐d2‐butene‐2. The determined distributions for the latter reactions were N: N: N: N = 0.26:0.26:0.31:0.17 for HF and Nv=1, CD: Nv=2, CD: Nv=3, CD: Nv=4, CD = 0.23:0.38:0.31:0.08 for DF. For the latter system also rotational distributions are documented which indicate several microscopic channels. The comparison of F+d2‐butene‐2 with other F+RH reactions (RH = saturated hydrocarbon) shows a decrease in vibrational inversion due to the presence of a II‐bond system.
On the relative leaving group abilities of imidazole and the substituted phenoxide ions. The effect of the acyl group
Authors: Neuvonen Helmi 
Published: July 2012

AbstractRate coefficients for the imidazole‐catalysed hydrolysis of substituted phenyl acetates, chloroacetates and dichloroacetates have been determined in 40% (v/v) acetonitrile‐water. It is shown that the increasing electron‐withdrawal by the acyl group makes the general base‐catalysed nucleophilic reaction of imidazole detectable beside the uncatalysed nucleophilic attack of the amine. This is attributed to the acyl group‐induced change of the partitioning ratio of imidazole and the ester leaving group. A kinetic evidence is obtained of a change in the rate‐limiting step with increasing imidazole concentration for the imidazole‐catalysed reactions of 4‐chloro‐ and 4‐methoxyphenyl dichloroacetates.