bluuebunny/crossref_metadata_2025 huggingface dataset:
ESR‐Spectroscopic Investigation of the Homogeneous Electron Transfer Reactions between Substituted p‐Phenylenediamines and Quinonediimines, and the Validity of Marcus' Theory. I. Measurements at 293 K
Authors: Grampp Günter , Jaenicke Walther
Published: July 2012

The rate constants k1, and k2 of the self exchange reactions between the half oxidized and the totally oxidized or the reduced forms of some p‐phenylenediamine derivatives are investigated at 293 K by ESR line‐broadening in various aprotic solvents (dielectric constants ϵ between 4.7 and 49). The dimerization constants of the radicals at 183 K and the enthalpies of dimerization are measured, too. The results are discussed in terms of Marcus' theory. In k1, is found to depend linearly on γ = 1/n2 ‐ 1/ϵ (n = refractive index), the covered range being 0.27 < γ < 0.53. The distance parameter g is obtained from the slope and compared with values derived from different molecular models. The results are represented satisfactorily by ellipsoidal molecules with half axes obtained from crystallographic data, the distance in the activated complex being approximately the same as in the radical dimers. The inner reorganization energy is calculated by Hückel methods and compared with experimental values obtained from the intercept of the straight line ln k1 (γ). The deviations are considerable. The calculated Marcus activation free enthalpies are smaller then the measured ones. — The slow rate constant k2 of the second step can be computed, if the Coulomb forces between the radical cation and the dication of the quinone diimine are considered. The inner reorganization energy of the transformation between aromatic and quinoidic structures is negligible. The rate constants of different cross reactions with p‐phenylene diamines are calculated with Marcus' formula which, however, has to be extended by work terms. The symproportionation rate is nearly diffusion controlled. With some other reactions the conformity of measured and calculated rate constants is excellent.
The Redox‐Reaction [Fe(CN)6]3‐/4‐ on Electrodes Coated with Fixed Charge Polymer Films — Observation of Membrane Permeability Modulation by the Electrode Potential
Authors: Braun H. , Decker F. , Doblhofer K. , Sotobayashi H.
Published: July 2012

Thin films of anion exchangers were prepared from quaternized polyvinylpyridine on glassy carbon and Pt electrodes. To render the polymer insoluble in aqueous electrolytes it was cross‐linked chemically or by exposing the coated electrodes to synchrotron‐radiation. With these electrodes the redox system [Fe(CN)6]3‐/4‐ was investigated with electrochemical methods, including the rotated ring/disk technique. The high equilibrium concentration of [Fe(CN)6]3‐ in the polymer matrix leads to extensive cross‐linking and desolvation of the film rendering its permeability low. During cathodic reduction a large fraction of the produced [Fe(CN)6]4‐ leaves the polymer phase. Anions from the background electrolyte replace the redox‐system; the film swells. The electrochemical phenomena associated with this reversible film structure change are discussed, in particular, a remarkable electrochemical rectification effect.
Double Layer Simulation Studies in Ultrahigh Vacuum of Anion and Cation Hydration at Metal Surfaces
Authors: Sass J. K. , Bange K. , Döhl R. , Piltz E. , Unwin R.
Published: July 2012

Using low energy electron diffraction (LEED), thermal desorption spectroscopy (TDS) and measurements of work function changes (Δø), the coadsorption of water and ions on metal surfaces has been studied in ultrahigh vacuum. As an example of anion specific adsorption, the hydration of bromide on Cu(110) has been characterized with regards to inner layer composition, surface hydration number and the formation of long‐range order. Simulation of non‐specific adsorption of lithium ions has also been attempted. On Ag(110), a drastic reduction of the binding energy of lithium in the presence of water is attributed to this type of surface hydration. Such evidence is not observed on Cu(111), where substantial fragmentation of the water seems to occur. The electrochemical relevance of these results is discussed.
Dyes Adsorbed at Ag‐Colloids: Substitution of Fluorescence by Similarly Efficient Surface Fluorescence and Surface Raman Scattering
Authors: Pettinger B. , Gerolymatou A.
Published: July 2012

With the addition of Ag‐sol to extremely diluted rhodamine 6G solutions (ca. 10−10 M/l) the prevalent fluorescence can be replaced by surface fluorescence and surface enhanced resonance Raman scattering (SERRS) of similar intensity, however only in presence of coadsorbed anions such as chloride. For strong bands the Raman cross sections are as high as 10−19 cm2 sr−1 molecule−1. Referred to the extinction of the sol which is much larger than that of the dye solution, the mean quantum yield for the surface Raman scattering is estimated to 0.0004. In addition, SERRS consisting of a set of fundamental vibrations, overtones and combination modes and a broad continuum shows throughout the spectral range a significant, but identical polarisation (I(sp): I(ss) = 0.55), whereas the solution as well as surface fluorescence is completely depolarised.
Tracerdiffusion von64Cu in γ‐Kupferbromid im Vergleich mit Ergebnissen aus Leitfähigkeits‐ und Kernresonanzmessungen
Authors: Schäfgen H.‐P. , Richtering H.
Published: July 2012

In order to elucidate the mechanism of atomic transport of copper ions in γ‐CuBr the tracer diffusion coefficient of64Cu had been determined between 170 and 340°C. The ionic conductivity was measured for comparison. — The tracer diffusion coefficient is found to be larger than the diffusion coefficient calculated from ionic conductivity (by a factor 5 at 170°C and 2 at 340°C). The Arrhenius plots of both are curved. Their difference, however, is linear and coincides with the diffusion coefficient derived from nmr relaxation rates. — From the observed differences between the three diffusion coefficients it is concluded that atomic transport of Cu+in γ‐CuBr takes place to a considerable extent via associated pairs of interstitial Cu+‐ions and cation vacancies.
Millimeter Wave Spectrum and Structure of Isoselenocyanic Acid, HNCSe
Authors: Vogt Jürgen , Winnewisser Manfred
Published: July 2012

The rotational a‐type spectra of the five most abundant isotopomers of HNCSe were recorded in natural abundance. Using Watson's S‐reduced Hamiltonian the rotational and some centrifugal distortion constants could be determined for the ground vibrational state of the various isotopic species. With the aid of these constants the restructure of HNCSe could be refined and the parameter specifying the quasilinearity of the molecule could be estimated.
On the Mechanism of Formation of Formation of Positronium in Polar Solvents
Authors: Alfassi Zeev B.
Published: July 2012

In this paper it is shown that various results on the effect of solutes and temperature on the formation of positronium in polar solvents can be better explained by a hybrid model between the “Ore‐gap” model and the “spur” model, stating that both contribute to the formation of positronium but the inhibition in case of partial inhibitors as well as the enhancement is due only to the second model. Complete inhibition is explained as due to the removal of positronium by its oxidation rather than preventing its formation.
Electrical and Magnetic Properties of the Molten Ag – TlTe System
Authors: Uemura Osamu , Suzuki Kiyomi , Satow Tsuneo
Published: July 2012

The electrical conductivity, the magnetic susceptibility, and the thermoelectric power of the liquid Ag – TlTe system have been obtained, respectively, as a function of temperature and composition from near the liquidus temperature up to about 900°C. These mixtures exhibit a sharp decrease in electrical conductivity and a change in sign of thermoelectric power around the stoichiometric composition AgTlTe. Measurements of magnetic susceptibility also indicate a marked anomaly at this composition. These electronic properties for the molten Ag – TlTe system are discussed in the light of current transport theories employed in the amorphous and liquid semiconductors.
Radiative Lifetimes of Optically Excited Cu and Au Atoms in Rare Gas Matrices
Authors: Schrittenlacher W. , Kolb D. M.
Published: July 2012

The time dependence of the fluorescence decay for optically excited Cu and Au atoms in rare gas matrices was investigated. The metastable 2D3/2 and 2D5/2 states of these atoms exhibit lifetimes in the millisecond regime. For Cu in Ne, emission from the matrix‐relaxed Cu 4p‐level was also observed. For fluorescence from 2D states, a multiple decay was observed for Cu in all matrices despite careful annealing. This multiple decay is most likely due to metal atoms at slightly different matrix sites which cannot be distinguished energetically by their matrix shifts. Obviously lifetime measurements are extremely sensitive to the matrix environment. For matrix‐isolated Au atoms a transition between the spin‐orbit split 2D states was observed for the first time.
Investigation of a Rechargeable Electrochemical Cell with Polyacetylene Electrodes
Authors: Broich B. , Hocker J.
Published: July 2012

Electrochemical cells with polyacetylene, (CH)x, as active anode and cathode material have been built. The cells were of the type (CH)x/R4N+ClO4⊖/(CH)x. The cells with different electrode thicknesses and areas, respectively, showed all the same typical charging and discharging behaviour. From the experimental data the change of molar doping concentration during charge and discharge, charge capacity, energy – and power density are evaluated. – The cell performance is limited by internal losses and electrochemically induced irreversible processes, which also limit the rechargeability to a few cycles.
Ion‐Exchange Kinetics. A Qualitative Quasi‐Electrical Approach
Authors: Du Preez J. G. H. , Gerber T. I. A. , Wantenaar D. C.
Published: July 2012

One of the possible mechanisms operating in ion‐exchange kinetics is film‐diffusion. The typical rate law describing this process can also be derived by viewing the exchange system as an electrical circuit containing a seat of emf, a resistor and a capacitor. The loading of the ion exchanger can be likened to the charging of the capacitor, and a qualitative description is given of the influence of the chemical potential as the driving force for the ion exchange process.
Optical Activity of Oriented Molecules. 10.Analysis of the n‐π Transition of 4‐en‐3‐one Steroids and Comparison of the Order Parameters of Host and Guest in a Compensated Nematic Phase
Authors: Altschuh J. , Weiland R. , Kosack J. V. , Kuball H.‐G.
Published: July 2012

While different substitution in the 17β‐position of 4‐en‐3‐one steroids (testosterones, progesterones) does not influence the CD spectra, the CD of the anisotropic solutions (ACD) undergoes a drastic variation of the band shape connected with a change from negative to positive curves. From this variation and the wavelength dependence of the degree of polarization of the UV spectra results that at least two progressions of vibrations (v̄00 + nv̄1 and v̄00 + v̄x + nv̄1) are responsible for the band structure of the n‐π* transition of the 4‐en‐3‐one chromophore where the totally symmetric (v̄1) and the non‐totally symmetric vibration (v̄x) are about 1200 and 600 cm−1, respectively. Furthermore, this variation of the ACD spectra for constant temperature and solute (guest) to solvent (host: cholesteryl chloride/cholesteryl laurate) ratio is a consequence of a change of the order parameter of the guest and the host which have been determined in the same solution by ACD and AORD, respectively. Most variation of the guest order can be understood by the proportionality to the anisotropy of the polarizability 2α33‐α22‐α11 or the length to width ratio 2l3‐l2‐l1 if no hydroxy group is present. Here a very high order exists. For some compounds the high order of the guest is connected with a strong decrease of the host order. In general, the alteration of the host order is not a function of the order of the guest i.e. at least one molecular property responsible for the ordering of the guest should be different from those properties of the guest which alterate the order of the host.
Kinetics of Proton‐Transport‐Coupled ATP Synthesis in Chloroplasts. Activation of the ATPase by an Artificially Generated ΔpH and Δψ
Authors: Gräber Peter , Junesch Ulrike , Schatz Güther H.
Published: July 2012

The kinetics of proton transport coupled ATP synthesis at the chloroplast membrane was investigated upon energization of the membrane by an artificially generated ΔpH and an electric potential difference, Δψ. Using a rapid mixing system, rates of ATP synthesis were studied at short reaction times (<150 ms) where all relevant parameters (ΔpH, Δψ, substrate and product concentrations) remain practically constant at their initial values. Under these conditions it was found:

The maximal rate of ATP synthesis obtained under these artificial conditions is the same as that obtained by light‐induced ATP synthesis.

The turnover number of the ATPase is 410 s−1.

The rate of ATP synthesis depends in a sigmoidal way on the transmembrane electrochemical potential difference of protons, Δψ, regardless of the relative contributions by ΔpH and Δψ.

The functional dependence of the rate of ATP synthesis on Δμ does not reflect the kinetics of the catalytic events at the ATPase but the transformation of the ATPase from an inactive to a catalytically active state.

The binding of two protons to the ATPase from the inside of the membrane is necessary for activation.
Structural Phase Transition due to a Release of Bound Water in Phospholipid Bilayers at Temperatures below 0°C
Authors: Grünert M. , Börngen L. , Nimtz G.
Published: July 2012

Measurements of dielectric and calorimetric properties and of the lamellar repeat distance revealed a structural phase transition at temperatures below 0°C in hydrated phospholipid (DPPC) bilayers. The transition is marked 1. by a jump of the dielectric constant at microwave frequencies, 2. by a jump of the lamellar repeat distance, and 3. by an enthalpy of transition. These observations are interpretated by a change of the amount of bound water. Below the transition temperature only seven H2O molecules per lipid molecule are left bound as interlamellar water independent on the amount bound at higher temperatures. The observed loss of bound water at this subzero temperature phase transition may represent a physical process for irreversible freezing effects.
The Temperature Dependence of the Properties of Electrolyte Solutions. VI. Triple Ion Formation in Solvents of Low Permittivity Exemplified by LiBF4 Solutions in Dimethoxyethane
Authors: Barthel J. , Gerber R. , Gores H.‐J.
Published: July 2012

Investigations in the temperature range −45 ≤ θ/°C ≤ + 25 on LiBF4 solutions in dimethoxyethane from infinite dilution to saturation permit to exemplify the features of conductance in solvents of low permittivity. Conductance measurements on thoroughly purified materials with the help of a measuring equipment known to produce precise data yield a complete set of conductance curves from infinite dilution to saturation at all temperatures of the program. The conductance curves show a minimum and a maximum of equivalent conductance and the change from positive to negative and once more to positive temperature coefficients of conductance. Various methods both for the evaluation of the limiting conductances, Λ∞, and the formation constants of ion pairs, KA, triple ions, KT, are critically discussed and reliable data for the LiBF4 solutions in dimethoxyethane at all temperatures of the program are communicated.
Static Light Scattering Experiments with a Critical Isobutyric Acid (COOD)/Deuterium Oxide Mixture Above its Critical Solution Temperature
Authors: Oswald U. , Belkoura L. , Jungk M. , Woermann D.
Published: July 2012

Static light scattering experiments are carried out with an almost critical mixture of isobutyric acid (COOD) and D2O (mole fraction of isobutyric acid (COOD) xDA = 0.11; temperature of phase separation TP = 45.9°C) to determine the critical amplitude of local concentration fluctuation. The following results are obtained: critical amplitude of local concentration fluctuations ξ0 = (3.1 ± 0.2) · 10−8 cm; critical exponent of correlation length of local concentration fluctuations: ν = 0.63 ± 0.01; critical exponent of susceptibility: γ = 1.26 ± 0.01. The values of the critical exponents v and γ are in good agreement with theoretical values predicted for binary liquid mixtures. The system‐specific parameter (0 of the system isobutyric acid (COOD)/D2O is slightly smaller (about 10%) than the corresponding value of the system isobutyric acid (COOH)/H2O (xcHA = 0.11; Tc = 26.1°C) reflecting differences between the intermolecular forces in the two systems.
Excess Properties of Binary Mixtures Composed of a Polar Component and an Alkane
Authors: Fuchs Reiner , Krenzer Luise , Gaube Johann
Published: July 2012

Mixtures containing a polar component and an alkane show a transitional behaviour between non‐associated and associated mixtures. The excess enthalpy and the excess Gibbs energy can be described by the quasichemical approximation with a temperature dependent interchange parameter. The excess entropy is given by SE = SconfE + SINTE. The first term is due to the non‐randomness of the mixture. The second term is correlated to HE. Using this correlation GE, HE and TSE can be roughly predicted. — Excess enthalpies and vapor pressure data were measured in order to supplement excess property data.
Enthalpies of Formation at 1373 K of the Liquid Alloys Ag + Au, Ag + Sn, Au + Sn and Ag + Au + Sn
Authors: Rakotomavo J. , Gaune‐Escard M. , Bros J. P. , Gaune P.
Published: July 2012

The enthalpies of formation ΔHM of the liquid binary (Ag + Au, Ag + Sn and Au + Sn) and ternary alloys (Ag + Au + Sn) were measured at 1373 K by direct calorimetry on the whole concentration range. The ternary investigations were conducted along the sections XAg/XAu = 1/4, 1/1, 6.25/3.75 and 7/3 with XSn < 0.60 and XAg/XSn = 3/7, 1/1 and 7/3 with XAu < 0.60. The apparatus used was a very high temperature calorimeter with a sensing device consisting in 20 Pt + 6% Rh/Pt + 30% Rh thermocouples. The experimental uncertainty was quoted at 10%. The results obtained for the limiting binary systems were compared with those, numerous and contradictory, reported in literature. The enthalpies of formation of the ternary alloys Ag + Au + Sn can be represented using a modified Kohler's equation including a supplementary correction term to the binary contributions.
Optisches Verfahren zur Bestimmung der Geschwindigkeit einzelner suspendierter kolloider Teilchen
Authors: Busch D. , Haase G. , Zörgiebel F.
Published: July 2012

Using components of a standard electrophoresis equipment (Zytopherometer) a stroboscopic dark field method was developed to record colloidal particles moving in an electric field. An argon ion laser served as a strong illuminant, a TTL electronic equipment provided the synchronization of electric field pulses, illumination and camera shutter. With this method speeds of particles ‐ e.g. soot dispersed in cyclohexan – could be measured at field strengths from zero (Brownian movement) up to 3 · 105 V/m (beginning of turbulence).
The Application of Generalized Nernst‐Planck Equations to the Description of Ion Retention in the Hyperfiltration of Mixed Electrolyte Solutions through a Neutral Membrane
Authors: Vonk M. W. , Smit J. A. M.
Published: July 2012

Pseudo‐binary Nernst‐Planck equations have been employed to derive expressions for the ion retention in a neutral membrane as a function of the volume flux. The derivation requires an integration across the membrane. In case of a solution of two ion species this integration is exact. For solutions of three kinds of ions the desired result is only obtained along an approximative route and then still only in certain limiting cases.

Nevertheless anomalies in the retention observed in systems containing three types of ions are predicted by the developed theory.
Thermal, Conductivity, Density, Viscosity, and Prandtl‐Numbers of Ethylene Glycol‐Water Mixtures
Authors: Bohne D. , Fischer S. , Obermeier E.
Published: July 2012

Thermal conductivity, density, and viscosity of ethylene glycol – water mixtures have been measured. The measurements have been performed in the temperature range from ‐−20°C to 180°C for thermal conductivity, from ‐−10°C to 150°C for density, and from – 10°C to 100°C for viscosity. Prandtl‐Numbers calculated with the own experimental data and literature values of specific heat capacity are presented in dependence of temperature and concentration.
Acid Base Reactions Between Acridine Orange and Substituted Phenols in Benzonitrile Part I. Thermodynamics of Association and Ionic Equilibria
Authors: Süttinger Rudolf , Strohbusch Frank
Published: July 2012

Proton transfer reactions of the five substituted phenols 3‐Cl−4‐nitrophenol CNP, 4‐nitrophenol NP, 3‐methyl−4‐nitrophenol MNP, 4‐Cl−3,5‐dimethylphenol CMP, and 3,5‐dimethylphenol DMP with acridine orange, and the formation of hydrogen bonded complexes AHA− of the anions A− of CNP, NP, and MNP with the respective phenols AH in benzonitrile solution were investigated by means of absorption spectroscopy. Thermodynamic data for the formation of the complexes AHA− and of the ionic reactions (1) and (2) of CNP, NP, and MNP with the acridine orange base B magnified image and for the reactions (2) and (3) of CMP and DMP with B were determined. The reactions (1) ‐ (3) are exothermic. The absolute values of ΔH1 increase with the acidity of the phenols. The formation enthalpies of the hydrogen bonded anions AHA‐ are much larger than ΔH1, so that ΔH2 is mainly determined by this association. On the other hand there is no significant difference between ΔH2 and ΔH3; thus the hydrogen bond formed between a phenol and a complexed anion AHA‐ is very weak. Substituent effects on the acidity of phenols are about twice as large in benzonitrile as in aqueous solution.
Acid Base Reactions Between Acridine Orange and Substituted Phenols in Benzonitrile Part II. Kinetics: An Extended Eigen Mechanism of Proton Transfer
Authors: Süttinger Rudolf , Strohbusch Frank
Published: July 2012

The kinetics of proton transfer between five substituted phenols (AH) and the acridine orange base (B) are studied in benzonitrile solution using the temperature jump method. In the overall reactions (1)–(3)magnified imagethe formation and dissociation of an intermediate ion pair A‐.. HB+is rate determining. The rate constants of the bimolecular recombination of the ions to the ion pair arekb1,kb2, andkb3. Their values are in the range (0.18‐ 1.7) · 109M‐1s‐1(25 °C,I= 0.1 M).kb2andkb3do not depend on the pKof the phenol involved, although these rates are not diffusion controlled. The rate of proton transfer from the protonated acridine orange (BH+) to the free anions (A‐) does depend to some degree on the acidity of the corresponding phenol. In the case of the 3‐methyl‐ 4‐nitrophenolate ion this rate is diffusion controlled, as shown by the dependence ofkb1on the temperature and the ionic strength. Lower limits for the formation constants of the ion pairs are estimated from the rate data. The equilibria and the kinetics are discussed in terms of an extended Eigen scheme of proton transfer, and the separate steps of anion solvation by hydrogen bonding to phenol molecules shown to depend in different ways on the basicity of the anion.
A Mass Spectrometric Investigation of Iron(II)‐Iodide
Authors: Grade M. , Rosinger W.
Published: July 2012

A consistent set of thermodynamic data for solid FeI2and for molecules which constitute its equilibrium gas phase is provided, based on measurements by the high‐temperature mass spectrometry and electron impact techniques. Second‐ and third‐law heats of formation, atomization and reaction, as well as individual Fe‐I bond strengths, are reported for the species FeI2(g), Fe2I4(g), Fe2I2(g) and for solid FeI2. Partial and total pressure data are also given, as well as an up to date literature survey of thermochemical data for the FeI2system.
Phase Equilibria and Density Calculations for Mixtures in the Critical Range with Simple Equations of State (Invited Lecture)
Authors: Vidal J.
Published: July 2012

The “Supercritical solvency” is connected to the liquid‐like density of gases at high pressure, and to the high sensitivity of this density to temperature and pressure in the near critical range of the solvent. The dissolution of the supercritical solvent in the liquid phase may also lead to liquid liquid equilibria, whose continuity with vapour liquid equilibria has been shown. – Simple methods, like cubic equations of state give a qualitative representation of such properties. However new formulations of the equation of state should be used to obtain a satisfactory prediction of the pVT properties in the critical range, while maintaining the simplicity of the cubic equation of state. The classical mixing rules cannot take into account the intermolecular forces existing between the solutes and the solvent, which often greatly differ in size, shape and polarity, and our experience of the classical liquid‐liquid equilibria can help us in the formulation of new and effective methods, such as the “density dependant local composition” mixing rules. Such theories contain empirical binary parameters and their application needs experimental data. – However, prediction methods based on the concept of group contribution are being developed, and can help the selection of selective supercritical solvents.
Application of a Local Composition Equation of State to Supercritical Fluid Phase Equilibrium Problems
Authors: Brignole E. A. , Skjold‐Jørgensen S. , Fredenslund A. A.
Published: July 2012

The group contribution equation of state (GC‐EOS) is used for the prediction of phase equilibria related to supercritical extraction of ethanol from aqueous solutions. The calculations show that it is not possible to design an economically favourable alternative to distillation processes using CO2 as the supercritical solvent. This is in accordance with the available experimental evidence. – Further calculations indicate that the use of light hydrocarbons as supercritical or near‐critical solvents may be a very attractive alternative for the recovery of pure alcohol from dilute aqueous solutions.
Heats of Mixing of Water + Hydrocarbons at High Temperatures and Pressures (Invited Lecture)
Authors: Wormald C. J.
Published: July 2012

Measurements of the excess enthalpy HE of mixtures of water + hydrocarbon vapour in the region 363 to 698 K and at pressures up to 12 MPa are described. Results obtained at low temperatures and pressures yield values of the cross term second virial coefficient B12. Analysis of results on several mixtures containing steam show that in its interaction with n‐alkane water has effective Lennard‐Jones parameters ε/k = 285 K and σ = 0.27 nm. Combining rules for ε12 in the water + alkane interaction are established. For alkanes above n‐pentane the isothermal HE (x = 0.5), p curves show maxima at pressures well below saturation. Results for all mixtures can be fitted using a new association model. HE measurements on water + benzene show clear evidence of a specific interaction. The enthalpy of formation of the water + benzene complex is ΔH = −9 kJ mol−1.
Continuous Viscosity Measurements in Order to Observe the Solubility and Miscibility of Carbon Dioxide in a Crude Oil
Authors: Killesreiter Hermann
Published: July 2012

A spring‐bellows‐capillary viscometer is now semi‐automatically working and makes, thus, a continuous record of viscosity data possible. These very structure sensitive viscosity measurements have been used to observe the solubility of carbon dioxide in a crude oil, and to demonstrate under proper conditions the lack of miscibility between both compounds. Some measurements with other gases such as nitrogen, methane, and propane are shown for comparison.
Spectroscopic Determination of Caffeine Solubility in Supercritical Carbon Dioxide
Authors: Ebeling H. , Franck E. U.
Published: July 2012

The solubility of caffeine in supercritical carbon dioxide was measured from 50°C to 160°C and with CO2‐densities from 3 mol dm−3 to 15 mol dm−3 (5 MPa to 25 MPa). Gas phase concentrations were derived from the UV‐absorption of caffeine at 273 nm. The high pressure optical cell and additional equipment are described. Results are given as “Enhancement Factors”. Enhancement factors up to 106 were found. The factors increase with solvent density and decrease with temperature at isochoric conditions. Virial coefficients B12 are derived between 323 K and 433 K and also calculated assuming a square‐well interaction potential. In addition the sublimation pressure curve of pure caffeine was determined spectroscopically.
Phase Equilibria Related to Supercritical‐Fluid Solvent Extractions (Invited Lecture)
Authors: Paulaitis M. E. , Kander R. G. , Diandreth J. R.
Published: July 2012

Process concepts for supercritical‐fluid solvent extraction are discussed with emphasis on the fluid‐phase equilibria for ternary and multicomponent mixtures. Experimental data for well‐characterized model systems are presented to illustrate important equilibrium phase behavior. Several existing processes are described to demonstrate the utility of supercritical‐fluid solvents in separation and extraction processes.
Chemical Engineering Applications of Supercritical Solvents (Invited Lecture)
Authors: Peter S.
Published: July 2012

The process conditions of extraction with supercritical solvents are dicussed. Treated are a) extraction of substances from solid materials; b) counter‐current extraction for separating low volatile temperature sensitive substances in presence of an entrainer; c) separation of solids from viscous media under supercritical conditions with respect to all involved components. Also considered are some economical aspects of extraction with supercritical solvents.
Supercritical Fluid Extraction: A Film Demonstration (Invited Lecture)
Authors: Eisenbach Wilhelm
Published: July 2012

Some of the phenomena associated with supercritical fluid extraction are discussed and illustrated by a film. A number of isolation techniques to remove the dissolved product from the loaded supercritical phase are presented, special emphases is given to the effect of variation of the isolation techniques when mixtures of homologous compounds are to be fractionated. As an example the separation of eicosapentaenoic acid ethyl ester (C20‐−5) from a mixture of fatty acid ethyl esters from codfish oil which consists of saturated and unsaturated fatty acid ethyl esters from C14to C22containing up to 6 double bonds is discussed.
Applications of Atmospheric Gases in High Pressure Extraction
Authors: Jasper Gährs Hans
Published: July 2012

The paper presents results of solubility measurements as well as extraction experiments using CO2 and mixtures of CO2 with atmospheric gases like N2 or Ar as solvents under high pressures. Influences of additional components to a single component gaseous solvent are discussed with respect to solvent properties and possible new applications of the HPE‐process.
Utilization of Supercritical Fluid Solvent‐Effects in Heterogeneous Catalysis
Authors: Tiltscher H. , Wolf H. , Schelchshorn J.
Published: July 2012

Comparative studies on fixed‐bed catalytic isomerization of 1‐hexene and disproportionation of 1,4‐diisopropylbenzene were performed under liquid, gaseous or supercritical conditions. The kinetic measurements show that by variation of pressure in the different fluid states catalytic surface reactions as well as mass transfer effects between catalyst and fluid phase and/or transport processes inside porous catalysts can be influenced in a very sensitive way. Conclusions are drawn in view of new possibilities for the direction of yield and selectivity of multiple reactions, for the prolongation of catalyst lifetime, and the study of deactivation mechanisms on heterogeneous catalysts.
Photo‐Chemistry of Colloidal Metal Sulfides 8. Photo‐Physics of Extremely Small CdS Particles: Q‐State CdS and Magic Agglomeration Numbers
Authors: Fojtik A. , Weller H. , Koch U. , Henglein A.
Published: July 2012

Extremely small CdS particles were prepared in propanol−2 solution at − 78°C and in aqueous solution in the presence of sodium hexametaphosphate at room temperature. These colloids are colorless. Their UV absorption spectra exhibit several maxima. Aging of the colloids is accompanied by intensity variations in the absorption maxima and by a shift of the onset of absorption to longer wavelengths. These small CdS particles hardly possess semiconductor properties (Q‐state CdS). A semi‐classical treatment of the energies of an electron‐hole pair in these particles yielded the wavelengths of their absorption spectra. At the small particle sizes used, the first excited state was reached by photon‐absorption in the UV, and the second excited state was generally not reached at all. The various maxima in the absorption spectra are explained in terms of a size distribution of the colloids with preferential agglomeration numbers. Reasons for the formation of such a structured size distribution are given. The fluorescence and fluorescence excitation spectra of the small particles were also investigated. Particles below a certain size have only one broad fluorescence band at a much longer wavelengths than the onset of absorption. As the particle size increases, this band is shifted towards longer wavelengths, and finally an additional rather sharp band appears at the threshold of absorption. CdS colloids in the Q‐state can be made which fluoresce as desired anywhere between the red and the blue. Also reported are the first experiments in which the preparation of Q‐type CdS in the solid state is achieved by evaporating the solvent from the colloidal solutions.
Mean Polarizabilities and Second Virial Coefficients of the Gases Ar, CH4, C2H6, C3H8 and C(CH3)4
Authors: Kerl K. , Häusler H.
Published: July 2012

Mean polarizabilities α0(λ0, T) and second virial coefficients B(T) of the gases Ar, CH4, C2H8, C3H8 and C(CH3)4 are determined from refractive indices measured with an interferometer in the ranges 260 K ≤ T ≤ 366 K, 0 ≤ p ≤ 3 bar of temperature T and pressure p (λ0 = 546.266 nm). The following results are discussed:

α0 depends linearly on T.

For each gas B(T)/Vc respectively B(T)/AR can be fitted best versus (Tc/T)2 by two straight lines, which are different for the ranges Tc < T and Tc > T (Tc = critical temperature, Vc = molar critical volume, AR = 4 πNA α0/3).

In the range T > Tc the straight line is common to all gases, whereas in the range T < Tc the straight lines are different for all gases.

For all gases a linear correlation between α0 respectively AR and Vc exists.
Präzisionsmessungen des Viskositätskoeffizienten von Stickstoff und den Edelgasen zwischen Raumtemperatur und 650 K
Authors: Vogel E.
Published: July 2012

The viscosity coefficients of nitrogen and of the rare gases have been determined at atmospheric pressure and within the temperature range 300 – 650 K using an oscillating‐disk viscometer with small gaps completely made of quartz glass. The results have been compared with direct experimental data as well as some data correlations. At room temperature there are only deviations of ±0.1% between our results and experimental data obtained by Kestin et al. Above room temperature differences between our data and values reported by other workers have been found. Some of them exceed 0.5% or even 1.0% and are larger than the mutual uncertainties of different viscometers. Comparisons with values calculated for XC potentials of neon, argon, and krypton and with results calculated for the extended law of corresponding states of Kestin, Ro, and Wakeham have shown that the uncertainty of our data should be at 600 K ± 0.2 to ±0.3%.
Self‐Diffusion in Water‐Alcohol Mixtures Part II. Water‐Methanol Solutions of LiCl and NaCl
Authors: Hawlicka E.
Published: July 2012

Using radioactive tracers the self‐diffusion coefficients of methanol, DM, and water, Dw, in methanol solutions of LiCl and NaCl at 298.2 K have been measured in the whole range of solvent composition. A significant effect of electrolytes on water self‐diffusion coefficient has been observed. The interrelation between the viscosity of the solution and the component self‐diffusion coefficients in mixed solvent solutions of electrolytes is discussed. The important influence of the nature of anions on the disruption of the solvent structure is pointed out.
Exploring the combinatorial genomic space in Escherichia coli for ethanol tolerance
Authors: Nicolaou Sergios A. , Gaida Stefan M. , Papoutsakis Eleftherios T.
Published: July 2012

Strain tolerance to toxic chemicals is desirable for biologically producing biofuels and chemicals. Standard genomic libraries can be screened to identify genes imparting tolerance, but cannot capture interactions among proximal or distant loci. In search of ethanol tolerance determinants, we expanded the genomic space combinatorially by screening coexisting genomic libraries (CoGeLs) of fosmids (large inserts) and plasmids (smaller inserts) under increasing ethanol concentrations. Such screening led to identification of interacting genetic loci imparting ethanol tolerance. One pair of fragments ([galT, galE] and [recA, pncC, mltB]) increased survival under 50 g/L ethanol by 38% when coexpressed, but individually the fragments had no effect. Coexpression of two genomic fragments ([sfsB, murA, yrbA, mlaB, mlaC, mlaD, mlaE, mlaF, yrbG] and [yrbA, mlaB, mlaC]) enhanced Escherichia coli survival to 50 g/L ethanol by up to 115%. A 35‐kb fosmid fragment increased tolerance to 63 g/L ethanol by 160%. While the tolerance levels of these strains compare favorably to or exceed the performance of previously reported engineered strains, more significantly, this study demonstrates that combinatorial library screening and screening fosmid libraries offer new, previously unexplored tools for identifying genetic determinants of ethanol, and by extrapolation, other alcohol tolerance.
Hydride Ligands Make the Difference: Density Functional Study of the Mechanism of the Murai Reaction Catalyzed by [Ru(H)2(H2)2(PR3)2] (R=cyclohexyl)
Authors: Helmstedt Ulrike , Clot Eric
Published: July 2012

The catalytic cycle for the Murai reaction at room temperature between ethylene and acetophenone catalyzed by [Ru(H)2(H2)2(PMe3)2] has been studied computationally at the B3PW91 level. The active species is the ruthenium dihydride complex [Ru(H)2(PMe3)2]. Coordination of the ketone group to Ru induces very easy CH bond cleavage. Coordination of ethylene after ketone de‐coordination, followed by ethylene insertion into a RuH bond, creates the Ruethyl bond. Isomerization of the complex to a RuIVintermediate creates the geometry adapted to CC bond formation. Re‐coordination of the ketone before the CC coupling lowers the energy of the corresponding TS. The highest point on the potential energy surface (PES) is the TS for the isomerization to the RuIVintermediate, which prepares the catalyst geometry for the CC coupling step. Inclusion of dispersion corrections significantly lowers the height of the overall activation barrier. The actual bond cleavage and bond forming processes are associated to low activation barriers because of the presence of hydrogen atoms around the Ru center. They act as redox buffers through formation and breaking of HH bonds in the coordination sphere. This flexibility allows optimal repartition of the various ligands according to the change in stereoelectronic demands along the catalytic cycle.
Two‐Dimensional Oxides: Multifunctional Materials for Advanced Technologies
Authors: Pacchioni Gianfranco
Published: July 2012

The last decade has seen spectacular progress in the design, preparation, and characterization down to the atomic scale of oxide ultrathin films of few nanometers thickness grown on a different material. This has paved the way towards several sophisticated applications in advanced technologies. By playing around with the low‐dimensionality of the oxide layer, which sometimes leads to truly two‐dimensional systems, one can exploit new properties and functionalities that are not present in the corresponding bulk materials or thick films. In this review we provide some clues about the most recent advances in the design of these systems based on modern electronic structure theory and on their preparation and characterization with specifically developed growth techniques and analytical methods. We show how two‐dimensional oxides can be used in mature technologies by providing added value to existing materials, or in new technologies based on completely new paradigms. The fields in which two‐dimensional oxides are used are classified based on the properties that are exploited, chemical or physical. With respect to chemical properties we discuss use of oxide ultrathin films in catalysis, solid oxide fuel cells, gas sensors, corrosion protection, and biocompatible materials; regarding the physical properties we discuss metal‐oxide field effect transistors and memristors, spintronic devices, ferroelectrics and thermoelectrics, and solar energy materials.
Solution and Solid‐State Dynamics of Metal‐Coordinated White Phosphorus
Authors: Mirabello Vincenzo , Caporali Maria , Gallo Vito , Gonsalvi Luca , Gudat Dietrich , Frey Wolfgang , Ienco Andrea , Latronico Mario , Mastrorilli Piero , Peruzzini Maurizio
Published: July 2012

The dynamic behavior in solution of eight mono‐hapto tetraphosphorus transition metal‐complexes, trans‐[Ru(dppm)2(H)(η1‐P4)]BF4 ([1]BF4), trans‐[Ru(dppe)2(H)(η1‐P4)]BF4 ([2]BF4), [CpRu(PPh3)2(η1‐P4)]PF6 ([3]PF6), [CpOs(PPh3)2(η1‐P4)]PF6 ([4]PF6), [Cp*Ru(PPh3)2(η1‐P4)]PF6 ([5]PF6), [Cp*Ru(dppe)(η1‐P4)]PF6 ([6]PF6), [Cp*Fe(dppe)(η1‐P4)]PF6 ([7]PF6), [(triphos)Re(CO)2(η1‐P4)]OTf ([8]OTf), and of three bimetallic Ru(μ,η1:2‐P4)Pt species [{Ru(dppm)2(H)}(μ,η1:2‐P4){Pt(PPh3)2}]BF4 ([1‐Pt]BF4), [{Ru(dppe)2(H)}(μ,η1:2‐P4){Pt(PPh3)2}]BF4 ([2‐Pt]BF4), [{CpRu(PPh3)2)}(μ,η1:2‐P4){Pt(PPh3)2}]BF4 ([3‐Pt]BF4), [dppm=bis(diphenylphosphanyl)methane; dppe=1,2‐bis(diphenylphosphanyl)ethane; triphos=1,1,1‐tris(diphenylphosphanylmethyl)ethane; Cp=η5‐C5H5; Cp*=η5‐C5Me5] was studied by variable‐temperature (VT) NMR and 31P{1H} exchange spectroscopy (EXSY). For most of the mononuclear species, NMR spectroscopy allowed to ascertain that the metal‐coordinated P4 molecule experiences a dynamic process consisting, apart from the free rotation about the MP4 axis, in a tumbling movement of the P4 cage while remaining chemically coordinated to the central metal. EXSY and VT 31P NMR experiments showed that also the binuclear complex cations [1‐Pt]+–[3‐Pt]+ are subjected to molecular motions featured by the shift of each metal from one P to an adjacent one of the P4 moiety. The relative mobility of the metal fragments (Ru vs. Pt) was found to depend on the co‐ligands of the binuclear complexes. For complexes [2]BF4 and [3]PF6, MAS, 31P NMR experiments revealed that the dynamic processes observed in solution (i.e., rotation and tumbling) may take place also in the solid state. The activation parameters for the dynamic processes of complexes 1+, 2+, 3+, 4+, 6+, 8+ in solution, as well as the X‐ray structures of 2+, 3+, 5+, 6+ are also reported. The data collected suggest that metal‐coordinated P4 should not be considered as a static ligand in solution and in the solid state.
Innovative Surfaces to Reduce the Soiling in Food Industry
Authors: Bellmann Cornelia , Calvimontes Alfredo , Caspari Anja , Marx Sandra , Mauermann Marc
Published: July 2012

Es hat sich gezeigt, dass Foulingprozesse sehr komplexer Natur sind. Sie werden weitestgehend durch die Wechselwirkungskräfte zwischen der entsprechenden Festkörperoberfläche und den adhärierenden Molekülen bestimmt. In diesem Beitrag werden entsprechend der DLVO‐Theorie van‐der‐Waals‐ und elektrostatische Wechselwirkungen betrachtet, wobei auch die Oberflächentopographie der Festkörperoberfläche mit einbezogen wird. Es kann gezeigt werden, dass eine Vielzahl an Einflussgrößen das Adsorptionsverhalten bestimmt. Mithilfe dieser Ergebnisse können Anforderungen an eine Festkörperoberfläche gestellt werden, die eine Verunreinigung weitestgehend verhindern.
Wood‐Plastic Composites: Rheological Characterization and Filling Behavior during Injection Molding Process
Authors: Kirchhoff Nadine , Schröder Cathrin , Stute Daniel , Moritzer Elmar , Schmid Hans‐Joachim
Published: July 2012

Wood‐Plastic‐Composite (WPC) zeigen im Vergleich zu reinen Kunststoffen ein sehr unterschiedliches und überaus komplexes Material‐ und Fließverhalten. Letzteres ist für die Verarbeitung der Composite von entscheidender Bedeutung. Im Folgenden werden die Ergebnisse rheologischer Charakterisierungen sowie einiger Untersuchungen zum Füllverhalten im Spritzgießprozess dargestellt. Dabei werden auch auftretende Herausforderungen und mögliche Lösungsansätze diskutiert.
Increased Energy and Material Efficiency of Steelmaking in the Electric Arc Furnace
Authors: Kleimt Bernd , Dettmer Bernd , Haverkamp Vico , Deinet Thomas , Tassot Patrick
Published: July 2012

Der Elektrolichtbogenofen ist das wichtigste Verfahren zur Stahlerzeugung über das Recycling von Stahlschrott. Ein erheblicher Teil der Produktionskosten entsteht durch den Verbrauch an elektrischer und chemischer Energie sowie durch die Einsatzstoffe. Die Energie‐ und Materialeffizienz des Verfahrens kann durch eine Reduzierung der thermischen Verluste sowie eine dynamische Prozessführung basierend auf mathematischen Prozessmodellen und einer kontinuierlichen Abgasanalyse erhöht werden. Erste Ergebnisse hierzu werden vorgestellt.
Synthesis of Stable Genipin Derivatives and Studies of Their Neuroprotective Activity in PC12 Cells
Authors: Luo Jun , Wang Rikang , Huang Zhao , Yang Jian , Yao Xinsheng , Chen Heru , Zheng Wenhua
Published: July 2012

Modifications at C1, C7, C8, and C10 of genipin were conducted, and the neurotrophic effects of all derivatives were studied. Genipin derivatives 1–4 were obtained in mild to high yield. Compounds 1 and 4 are more stable than genipin if exposed to nucleophiles. All the derivatives display higher neurotrophic activities than genipin. Compound 4 is the most active, with the least optimal dose. Both genipin and 4 up‐regulated the activity of nNOS in PC12 cells. The effect of 4 is inhibited not only by 7‐NI, a specific inhibitor of nNOS, but also by L‐NIO, a specific inhibitor of eNOS; in the case of genipin, its effect is only inhibited by 7‐NI. All the results indicate that 4 is a promising lead compound for the development of new drugs in the treatment of neurodegenerative diseases with the ability to address multiple drug targets.
Microstructural and optoelectrical properties of transparent conducting ZnO:Al thin films for organic solar cells
Authors: You Zhong Zhi , Hua Gu Jin , Yong Yang Chun , Jin Hou
Published: July 2012

The Al‐doped zinc oxide (ZnO:Al) thin films were grown on glass substrates by the magnetron sputtering technique. The films were characterized with X‐ray diffractometer, four‐point probe and optical transmission spectroscopy, respectively. The dependence of microstructural, electrical and optical properties on deposition temperature was investigated. The results show that all the films have hexagonal wurtzite structure with highly c‐axis orientation. And the microstrural and optoelectrical properties of the films are observed to be subjected to the deposition temperature. The ZnO:Al film prepared at the deposition temperature of 650 K possesses the best optoelectrical properties, with the lowest electrical resistivity (6.1×10−4 Ω·cm), the highest average visible transmittance (85.3%) and the maximum figure of merit (0.41 Ω−1). The optical energy gap of the films was estimated from Tauc's law and observed to be an increasing tendency with the increment of the deposition temperature. Furthermore, the refractive index of the films was determined by the optical characterization methods and the dispersion behavior was studied by the single electronic oscillator model.