bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spectroelectrochemical investigations of polyxylidines
Authors: Probst Matthias , Holze Rudolf 
Published: July 2012

AbstractAniline derivatives carrying two methyl substituents in different ring positions (2,3‐, 2,5‐ and 2,6‐xylidine) were polymerised electrochemically. The obtained polymers were characterised by cyclic voltammetry, in situ UV‐vis spectroscopy and in situ Resonance Raman spectroscopy. With poly(2,5‐xylidine) in situ conductivity measurements were performed. The polymers show various degrees of electrochromism. Vibrational spectra of poly(2,3‐xylidine) and poly(2,5‐xylidine) show a reversible change of the ring from a benzoid into a quinoid state depending upon the degree of oxidation. A structure analogous to the one proposed for polyaniline is suggested.
Networks of hydrogen bonds between pyridones ‐ structure breaking effects by organic solvents and sensor applications
Authors: Dickert F. L. , Keppler M. , Zwissler G. K. , Obermeier E. 
Published: July 2012

AbstractPyridone shows self‐assembling properties via hydrogen bonds as can be shown by IR‐spectroscopy. In this way networks are formed by intermolecular interaction of tris‐(2‐pyridone‐5‐carbonacid)‐glycerol ester, each molecule containing three units of pyridone. The structure breaking effect of organic solvents leads to a reduced ordering of this material and can be observed directly by hyperchromic changes of the UV‐absorbance. This process is traced by capacity measurements as the unpaired structures of pyridone possess a strong dipole moment. For this purpose the permittivity of an interdigital capacitor (IDC) coated with a thin solid film of the network‐forming material is measured in an atmosphere of organic solvent vapours.
Thermokinetics of reactions with liquid‐liquid phase separation
Authors: Baumann Christian , Becker† Friedrich 
Published: July 2012

AbstractIsothermal heat flow calorimetry with controlled thermoelectric cooling resp. heating is applied to study the critical slowing down of the kinetics of reactions with liquid‐liquid phase separation. Results (i) on the acid‐catalysed hydrolysis of chloromethyloxirane by water, and (ii) on the ring‐opening and esterification of bromomethyloxirane by dichloroacetic acid in the presence of cyclohexane as an inert solvent, both at 298.15 K, are presented. The heat production w(t) which is proportional to the reaction rate ∂ζ/∂t (where ζ is the reaction coordinate) exhibits a funnel‐like fall‐off when the reaction path intersects the binodal curve at the critical solution point CP. From the shape of this part of the w(t) curves an average value of the critical exponent φ = 0.72±0.003, which refers to the change of ζ with t at constant T and p, is calculated. This result is to be compared with the theoretical value of φ = 0.708 obtained from a modification of the Griffiths and Wheeler theory of critical points in multi‐component systems to chemically reacting systems far from equilibrium by introducing ζ as an additional extensive variable. This allows the critical slowing down of the reaction rates to be interpreted as resulting from the divergence of the correlation length ζ resp. from the convergence of the transport phenomena to zero at the CP.
Computer simulations of crystal structures and elastic properties of cellulose
Authors: Marhöfer Richard J. , Reiling Stephan , Brickmann Jürgen 
Published: July 2012

AbstractStructures and elastic properties (Young's moduli) of the different phases of cellulose I and II are studied on the basis of molecular dynamics (MD) simulations using a new force field for carbohydrates. The structural results for all phases as well as the Young's moduli for cellulose I and cellulose II with parallel chain arrangement are in very good agreement with experimental data whereas the calculated Young's modulus for cellulose II (with antiparallel chains) does not match the experimental error margin. Our results lead to the conclusion that cellulose II, as resulting from the mercerization, is arranged in parallel chains. Microscopically the transition from phase I to II can then easily be explained as a rearrangement of the exocyclic torsional angles.
Measuring the static dielectric constants of pure carbon dioxide and carbon dioxide mixed with ethanol and toluene at elevated pressures
Authors: Wesch A. , Dahmen N. , Ebert K. H. 
Published: July 2012

AbstractStatic dielectric constants (relative permittivities) of binary carbon dioxide/ethanol mixtures and carbon dioxide/toluene mixtures of various compositions at 10 MPa and 313 K, which were experimentally determined, are presented. In addition, the dielectric constant of pure carbon dioxide was measured at temperatures of 293, 313 and 336 K in the pressure range of up to 30 MPa. The measurements were conducted with a new type of sensor design. The dielectric constant of pure carbon dioxide shows a pronounced dependence on pressure close to the critical pressure. There is a nearly linear relationship between density and the dielectric constant. The dielectrical behavior of the mixtures of supercritical carbon dioxide with ethanol and toluene is qualitatively very similar to that of liquid benzene/ethanol and benzene/toluene mixtures at normal pressure.
Studying the energy hypersurface of multi‐minima systems — the threshold and the lid algorithm
Authors: Schön J. C. 
Published: July 2012

AbstractA method is presented that allows the detailed study of regions of multi‐minima energy landscapes close to some deep‐lying minimum. Two versions are described the “lid algorithm” and the “threshold algorithm” for discrete and continuous landscapes, respectively. Applications of these algorithms to the travelling salesman problem (TSP), a two‐dimensional layer of Ne atoms, and the system Mg2F4 are sketched.
Study of the extrusion induced changes in the Li2O·2SiO2 glass structure by the methods of optical spectroscopy and radiation influences
Authors: Arbuzov V. I. , Carl G. , Durschang B. , Rüssel C. 
Published: July 2012

AbstractThe objects of investigation were Li2O·2SiO2 glass samples cutted out of the initial and the extruded glasses along and across the extrusion axis. All the glasses contained iron microimpurities (∼80 ppm). Some glasses were doped with Tb3+ ions the luminescence characteristics of which depend on average distances Tb3+ ‐Tb3+. It has been shown that the rates of radiation color centers accumulation as well as the rates of their isothermal annealing, on one hand, the absorption spectra of iron microimpurities, on the other hand, and finally the spectroscopic properties of terbium ions have been changing regularly when passing from extruded longitudinal sample to initial and finally to extruded transverse ones. All these results convincingly show that, under the conditions of extrusion, glass structure becomes less dense in its direction and more dense in the perpendicular one.
High‐temperature study of multivalent elements in glass‐forming melts: The particular case of iron
Authors: Tilquin J.‐Y. , Duveiller P. , Glibert J. , Claes P. 
Published: July 2012

AbstractLinear sweep voltammograms and absorption spectra were recorded in Na2O·2.5 SiO2 containing about 1 wt% Fe at some temperatures ranging from 600°C to 1000°C. The reduction peaks which are observed in the melt at 600°C disappear at 1000°C. The absorption spectra obtained at high temperature are characteristic by a displacement of the charge transfer band and of the band related to octahedral Fe(II) towards higher wavelengths. No remarkable change in the Fe(III)‐Fe(II) redox equilibrium and in the coordination of the Fe(II) has been observed between 600°C and 1000°C.
Transport phenomena in oxidic glass‐forming melts
Authors: Pfeiffer Th. , Müller R. , Werner R. D. 
Published: July 2012

AbstractViscosities, electrical conductivities and Seebeck‐coefficients of a number of glass‐forming oxidic melts are presented and discussed. The data support the notion that glass melts do have a residual, temperature‐dependent structure that significantly determines mass, momentum and heat transport. It is shown that the use of Tg/T as reduced variable helps to develop a deeper insight in the underlying physics of these transport properties.
Solubility of gases in glass melts
Authors: Krämer Fritz W. 
Published: July 2012

AbstractA short overview on gas solubility and solubility mechanism in oxide melts in given. Many gases of practical importance in glass melting like oxygen, nitrogen, carbon dioxide and sulfur dioxide and others dissolve in a glass forming melt both chemically by a chemical controlled process and physically by occupying the holes in the network structure. The chemical solubility at conditioning temperatures is orders of magnitude higher than the physical solubility and decreases with increasing temperatures. An exception is water whose chemical solubility increases with increasing temperature, and that is why water cannot be used as a fining agent. The physical solubility on the other hand increases slightly with increasing temperatures. At measuring physical solubilities mistakes can be made because of the omnipresent chemical solubility or because of impurities. Therefore the known relationship between physical inert gas solubilities and the size of the dissolving atoms or molecules was used to calculate the physical solubility of a lot of non‐inert gases for soda‐lime silica melts, for fused silica and for molten boric oxide.
A new approach on the coordination of al in non‐crystalline gels and glasses of the system Al2O3‐SiO2
Authors: Schmücker M. , Schneider H. 
Published: July 2012

AbstractIn the present study the idea of five‐fold coordinated aluminium in Al2O3‐rich aluminiumsilicate gels and glasses with compositions near to that of mullite (≈72 wt.% Al2O3, 28 wt.% SiO2) is re‐aximated. Analyses of 27AlMAS NMR spectroscopy and pair correlation functions on the basis of X‐ray diffraction data together with a critical review of crystallization mechanisms provide evidence for short‐range‐order similarities of mullite and corresponding gels and glasses. The study provides evidence for an occurrence of (Al/Si)O4‐tetrahedra and of AlO6‐octahedra in the gels and glasses. The (Al/Si)O4 to AlO6 ratios of non‐crystalline aluminium silicates are similar to that of mullite and comparable tricluster units of tetrahedra may occur in both, mullite and its non‐crystalline counterparts. There is less evidence that 5‐fold coordinated Al exists in aluminium‐silicate gels and glasses as was reported frequently in the literature.
Dynamics of lithium ions in monoconducting polymer electrolytes: A 7Li spin‐lattice‐relaxation study
Authors: Chung S. H. , Heitjans P. , Winter R. , Bzducha W. , Florjańczyk Z. 
Published: July 2012

AbstractIn monoconducting gel electrolytes prepared from polymeric lithium salt, poly(ethylene glycol), dimethylsulfoxide or propylene carbonate 7Li(I= 3/2) NMR spin‐lattice relaxation times (T1) at two resonance frequencies (24.5 and 77.5 MHz) have been measured for various compositions of the above system over the temperature region 0.75 to 2 Tg, with the glass transition temperature T″g≈200 K. The T1 data as a function of inverse temperature exhibit a cationic diffusion‐induced minimum. Both the temperature and the frequency of T1, indicate a change in the dynamical process at about 1.3 Tg.
Structural investigation of ferrimagnetic particles formed by glass crystallization
Authors: Hoell A. , Kranold R. , Lembke U. , Brückner R. , Müller R. , Görnert P. , Schüppel W. 
Published: July 2012

AbstractBy means of a definite heat treatment magnetite crystals were formed dispersed in a silicate glass, which initially contains Fe2O3 as a glass component. The specific saturation magnetization of the glass ceramic manufactured turns out to be dependent on the heat treatment conditions and shows a significant maximum for a certain temperature and treatment duration. Small angle X‐ray scattering, transmission electron microscopy, and X‐ray diffraction were used to obtain structural parameters. The correlations between size and packing density of the magnetite crystals and the magnetic properties are discussed.
Investigation of borosilicate electrode glasses using 11B SATRAS MAS NMR, 29Si MAS NMR and REDOR
Authors: Herzog K. , Peters J. , Thomas B. , Jäger C. 
Published: July 2012

AbstractThe structure of various hydrated and untreated glasses of the system Na2O‐B2O3‐SiO2 was investigated using multinuclear NMR. Two different BO4 units have been detected by 11B SATRAS (Satellite Transition Spectroscopy) NMR. Comparing the spectra of the untreated and hydrated glasses it was found, that nearly all BO3, units and one of the BO4 units are removed during the reaction of the glasses with hydrous solution. Furthermore, 1H‐11B REDOR (Rotational Echo Double Resonance) has been used to investigate the incorporation of protons in the hydrated glasses. New aspects containing the structural role of protons are obtained.
2D exchange NMR investigations of phosphate glass ceramic
Authors: Hartmann P. , Vogel J. , Jäger C 
Published: July 2012

Abstract31P MAS and Exchange nuclear magnetic resonance (NMR) measurements were used to investigate the structure of P2O5‐CaO‐Na2O‐{Al2O3} glasses and glass ceramics. The progress of two‐dimensional (2D) Exchange NMR techniques is demonstrated.
The effect of alkyl groups on carbanion stability part II. Analysis of α‐ and β‐alkyl substitution on experimental and theoretical acidities
Authors: Balcioǧlu Nurettin , Sevin Fatma , Evin Özden (Özel) , Peynircioǧlu N. Bekir 
Published: July 2012

AbstractMultivariational analyses were performed to separate the contribution of electronic and steric effects of alkyl groups on the experimental hydrocarbon acidities of four different sets of compounds, consisting of hydrocarbons (SET‐I), acetophenone derivatives (SET‐II), and acetone CH3COCHR1R2 derivatives, where the acidity of the protons on the alkyl substituted site, (SET‐III), and the acidity of the methyl protons are both investigated (SET‐IV). Significant regression was obtained upon backward elimination for the first and last set. Due to the colinearity of the parameters in SETs‐II and ‐III the significance of the correlation is not so high. As expected, the gas phase acidity of the hydrocarbons in SET‐I is very sensitive to the polarizability and electronegativity of the alkyl substituents. The substituent have similar effects on the solution acidities of the ketone derivatives in SETs‐II, ‐III, though suppressed due to solvation, unlike the cases in SET‐II and SET‐III, the effects of the substituents in SET‐IV, where the substituents are relatively far away from the carbanion center generated are strongly reduced and reversed. This different behavior may be attributed to the domination of the solvent effects. Theoretical acidities of these compounds were calculated using the semiempirical methods such as MNDO, AM1 and PM3. The results are, quantitatively and qualitatively, unsatisfactory for the gas phase, as well as for the solution acidities. Multivariational analysis of substituent effects shows the insufficiency of the present parametrization to reflect the substituent effect properly. It seems that all these semiempirical methods are useless in prediction of carbon acidities, without reparametrization using carefully selected sets of compounds.
Reactions of sodium/antimony‐clusters with molecular chlorine in a flow‐tube‐reactor coupled to a time‐of‐flight mass spectrometer
Authors: Hartmann A. , Castleman A. W. , Weil K. G. 
Published: July 2012

AbstractA gas aggregation technique is used to produce NaxSby, clusters. After passing a flow‐tube reactor, the clusters are ionized with unfocused high fluence KrF‐excimer laser radiation and then mass analyzed in a time‐of‐flight mass spectrometer. Dramatic changes are observed in the cluster ion distribution upon adding high purity chlorine gas into the flow tube. As a result of reactions with Cl2, all NaxSby, clusters disappear while pure antimony cluster ions arise. The distribution patterns of the produced Sbx+ clusters are the same as those observed in experiments with pure antimony.
Role of electrolyte/polymer interface on the quantitative interpretation of in‐situ ellipsometry of electroactive polymer films
Authors: El‐Rahman H. A. Abd , Kudelka S. , Schultze J. W. 
Published: July 2012

AbstractA new in‐situ ellipsometric procedure has been used for determination of the optical properties and thickness of polyaniline films as a function of. the redox state in sulphuric and p‐toluenesulfonic acids. The results could be interpreted successfully only when the optical properties of the electrolyte/polymer was considered variable with the redox state. Most probably for the first time, the study shows, that the apparent refractive index of electrolyte varies with the redox state in a similar manner to the optical properties and thickness of the polymer film. In this case, for all calculations a one layer model was sufficient. The origin of such observation is attributed to the change in electrolyte composition at the polymer surface and heterogeneity of the film when oxidized.
Density functional theory: Structure and interfacial properties of binary mixtures
Authors: Wadewitz T. , Winkelmann J. 
Published: July 2012

AbstractBased on Density Functional Theory (DFT) of inhomogeneous fluid mixtures we model the liquid‐vapour interface of some binary mixtures. Attractive contributions to the Helmholtz free energy are treated by a mean‐field approximation (MF). The local density approximation (LDA) is applied to the repulsive reference system described by a hard sphere equation of state. A cut‐off and shifted Lennard‐Jones‐12‐6 potential divided according to the WCA‐prescription is used as interaction pair potential. Binary Lennard‐Jones parameter are introduced and fitted to experimental liquid‐vapour compositions to describe interactions between different species. The calculations give good results in the case of simple fluid mixtures like Ar‐N2 and CO‐N2. Similar results are obtained for the nonpolar mixture n‐heptane‐toluene. The predicted surface tensions γ agree very well with experimental data. Computed partial density profiles clearly show the enrichment of the component with the lower surface tension in the interphase. The relative Gibbs surface excess concentration is calculated from partial density profiles and compared with experimental values. The influence of activity coefficients on Gibbs adsorption is discussed.
Measurement and thermodynamic evaluation of phase equilibria in the Fe‐Ti‐O system
Authors: Eriksson Gunnar , Pelton Arthur D. , Woermann E. , Ender A. 
Published: July 2012

AbstractThe stability of pseudobrookite type solid solutions in the binary section FeTi2O5‐Ti3O5 is investigated in the temperature range 1060° to 1360°C by the quench method combined with chemical analysis and X‐ray diffractometry. These data are then combined with all other available phase equilibrium and thermodynamic data in order to obtain a set of optimized thermodynamic equations for the phases in the FeTiO3‐TiO2‐Ti2O3‐Fe system. Models for the ilmenite and pseudobrookite solutions are developed. The good agreement between the calculated phase equilibria and the measurements indicates the essential correctness of the thermodynamic data and the phase diagrams.
Primary reactions of oxygenic photosynthesis
Authors: Witt H. T. 
Published: July 2012

AbstractFunctional and structural aspects of the mechanism of oxygenic photosynthesis are described and documented by examples: (1) Coupling of two Photosystems I and II for the electron transfer from water to NADP+. (2) Vectorial electron transfer and transmembrane charge separation as the primary act of light energy conversion. (3) Functioning of the reaction centers I and II in the photosystems and the role of the pool of plastoquinones. (4) Proton translocation and use of the proton potential for ATP formation. (5) Approaches to the mechanism of water oxidation. (6) Organization of the proteins and their cofactors as well as the molecular structure of Photosystem I. (7) Light energy migration in the antenna system.
Comparison of electron paramagnetic resonance lineshape, orientation and power saturation of the TyrD radical from spinach and the green alga Scenedesmus obliquus
Authors: Schille Hilmar , Luzzolin Lucia , Dittme Jens , Dau Holger 
Published: July 2012

AbstractTyrD is a redox‐active amino acid of the Photosystem II (PS II) D2‐protein. Upon oxidation it forms an unusually stable neutral radical with characteristic EPR properties. We prepared highly active BBY particles of spinach and the green alga Scenedesmus obliquus. The X‐band EPR spectra are similar with a peak to trough linewidth of 19.3 G for spinach and 19.0 G for Scenedesmus. Power saturation experiments were performed at 20 K. For unknown reasons, the signal of spinach satures slightly faster than that of the alga. Partially oriented PS II membrane particles exhibit comparable orientation‐dependent four‐line spectra. This indicates that the orientation of TyrD with respect to the membrane normal is similar in both species.
The pH‐dependence of the photosystem II fluorescence: Cooperative transition to a quenching state
Authors: Heinze Ilona , Dau Holger 
Published: July 2012

AbstractThylakoid membranes were isolated from various cultures of the green alga Scenedesmus obliquus which differed in the extent of the observable‐high‐energy‐state quenching of chlorophyll fluorescence (qE). In uncoupled thylakoid membranes the pH‐dependence of the fluorescence parameters FM and F0 exhibits two distinct phases: (1) for pH‐values ranging from 6.5 to 5.7, acidification results in a pronounced decrease of FM and F0; (2) for pH‐values below 5.7, acidification results in a slight decrease of FM and a significant increase of F0. The extent of the first phase of F and F quenching corresponds to the extent of qE in intact cells; the variability of qE of intact cells is not explainable by a pK‐shift. Simulations on basis of the reversible radical pair model using pH‐dependent molecular rate constants indicate the occurrence of a cooperative transition to a state with an enhanced rate of non‐radiative decay of excited chlorophyll‐singlet states (Hill coefficient n1 ≥ 4, pK1 ≈︁ 6.1 for all cultures). For pH‐values below 5.7, a pH effect on Photosystem II electron transfer reactions is involved (n2 ≈︁ 1, pK2 ≥ 4.5).