bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dielectric Behaviour at High Pressure of Cyclo‐Octanol
Authors: Poser Uwe , Würflinger Albert 
Published: March 2014

AbstractThe phase behaviour and dielectric relaxation of cyclooctanol has been studied in the temperature range 240 — 300 K and up to pressures of 300 MPa. Two recently found pressure‐induced solid phases have been confirmed and designated as orientationally disordered ones. The complex dielectric permittivity for the orientationally disordered phases is determined as a function of pressure and temperature for frequencies between 1 kHz and 13 MHz. The loss curves are described with modified Debye theories and the Jonscher equation. The results are compared with previous findings on smaller cyclic alcohol
Extraction of Citric Acid by n‐Octanol and n‐Hexanol
Authors: Apelblat Alexander , Manzurola Emanuel 
Published: March 2014

AbstractExtraction equilibria in the citric acid‐water‐n‐octanol and citric acid‐water‐n‐hexanol systems were investigated at 298.15 K. The proposed partition mechanism includes formation of the complex, H3Cit(H2O)4(ROH)4, with the equilibrium constant K = 0.102 for n‐octanol and K = 0.237 for n‐hexanol. Activities of alcohols in the organic phase and activity coefficients of citric acid in water were determined by a numerical integration of the Gibbs‐Duhem equation.
Löslichkeit und thermodynamische Daten von Eisen(II)‐Hydroxid durch analytische Bestimmung des Eisens und Leitfähigkeitsmessung im System Eisen‐Wasser
Authors: Bohnsack G. 
Published: March 2014

AbstractIn a solution of iron(II) hydroxide produced by equilibration of pure oxygen free water with pure metallic iron we have determined the constant of the protolysis equilibrium combining analysis of the iron concentration with conductivity measurement. — Following the reaction between steel wool and pure water in a closed system by conductivity measurement a conductivity maximum has shown a temporary supersaturation with a subsequent steady state of saturation of iron(II)‐hydroxide in a equilibrium with a not well defined solid. By determination of the iron concentration and of manganese and nickel as impurities we could estimate using the protolysis constant the composition of the saturated solution of iron(II)‐hydroxide. — From the measured data we could also derive the constants describing the properties of iron(II)‐hydroxid
1H‐NMR Studies of the Systems Ta1−xVxHy(0.0 ≤x≤ 1.0; 0 <y≤ 0.9), and Nb1−xVxHy(0.0 ≤x≤ 0.5; 0 <y≤ 0.9). Magnetic Susceptibility, Knight Shift, and Longitudinal Relaxation
Authors: Richter Karl‐Hermann , Weiss Alarich 
Published: March 2014

AbstractBoth the magnetic susceptibility χ(x, y) and the1H‐Knight shiftKH(x, y) of the ternary systems Ta1−xVxHyand Nb1−xVxHywere studied by high resolution1H‐NMR Fourier transform spectroscopy. χ(x, y) always increases as a function of the vanadium concentrationxand decreases with increasing hydrogen concentrationy. In contrast, the1H‐Knight shiftKH(x, y) is strongly influenced by vanadium at low hydrogen concentrations. For both systems the shape ofKH(x, y) behaves analogously to the shape ofKH(x, y) of the systems Ta1−xTixHyand Nb1−xTixHy. The same similarities were found with respect to the temperature dependence of the1H‐Knight shift.KHis nearly independent of temperature for the binary systems TaHyand NbHywhereas it increases with increasing temperature for the systems Ta0.9V0.1Hyand Nb0.9V0.1Hy. Such a behavior was observed for the ternary system Ta0.9Ti0.1Hy, too. From the temperature dependence of χ(T) andKH(T) we conclude that the V‐3d‐wavefunctions as well as the Ti‐3d‐wavefunctions produce a negative hyperfine field at the proton site. In contrast, we find a positive hyperfine field at the proton site caused by the spin part of the d‐electrons in the case of TaHyand NbHy. Additionally, measurements of the longitudinal relaxation timeT1were carried out on the systems TaHy—Ta0.9V0.1Hy. At low hydrogen concentrations the dipolar contribution toT1differs strongly for both systems. This may be a consequence of trapping processes of the hydrogen atoms in the neighborhood of the vanadium atoms.
Critical Assessment of Thermodynamic Properties and Phase‐Diagram Calculations of K‐KCl and K‐KBr Systems
Authors: Rand M. , Gaune‐Escard M. , Bros J. P. , Gaune P. 
Published: March 2014

AbstractAll the available thermodynamic information on the K‐KCl and K‐KBr systems has been collected and used, through an optimisation procedure, to check the thermodynamic consistency of those experimental thermodynamic data. Optimized sets of parameters for the excess Gibbs energy of mixing of the K‐KX liquid solutions have been obtained; the liquid phase was modelled as a simple mixture of K and KX, exactly equivalent to a “sublattice”‐type model, the excess Gibbs energies being represented by Redlich‐Kister polynomials. Agreement between calculated and experimental phase diagrams and thermodynamic functions is within the experimental uncertainties.
Die zweiten Virialkoeffizienten der Systeme N2–O2und N2–NO von 87 K bzw. 124 K bis 475 K
Authors: Fostiropoulos K. , Natour G. , Sommer J. , Schramm B. 
Published: March 2014

AbstractMeasurements of second interaction virial coefficients of mixtures N2–O2and N2–2NO are presented. Temperatures range from the boiling temperature of the gases up to 475 K. New experimental data of second virial coefficients for pure O2and NO are presented also and are critically compared with literature data. The amount of dimers in gaseous NO is calculated with the law of corresponding states.Some thermodynamic aspects of the N2–NO system are discussed.
The Dissolution of N2 and of H2 in Water from Room Temperature to 640 K
Authors: Alvarez Jorge , Crovetto Rosa , Fernández‐Prini Roberto 
Published: March 2014

AbstractThe solubilities of H2 and of N2 in water have been determined over a wide temperature range. The thermodynamic analysis of the data allowed the calculation of Henry's constants (k∞H) as function of temperature from room temperature to 636 K; other thermodynamic quantities of dissolution have been derived from the temperature dependence of k∞H. With a semiempirical perturbation method it is possible to describe the experimental behaviour and to predict the partial molar volume and heat capacity of the solutes over all the temperature range. This calculation procedure requires the knowledge of the hard‐sphere radii of the solute gases and their (linear) temperature dependence which may be determined from solubility data covering only a reduced temperature range extending to about 400 K.
Effect of Lipid Headgroups and (Nonelectrolyte) Solution on the Structural and Phase Properties of Bilayer Membranes
Authors: Cevc Gregor 
Published: March 2014

AbstractProperties of the biological and model membranes can be regulated by the lipid polar headgroups and their bathing solution. This occurs primarily via changes in the interfacial hydrophilicity and hydration, which are mostly a result of the lipid deprotonation or osmotic dehydration. Steric or electrostatic effects normaly play a minor role. Therefore, phosphate derivatization or protonation, further changes that decrease the lipid capacity for the hydrogen bonding and lower the interfacial affinity for binding water, as well as any system alterations that diminish the amount of interbilayer water can all cause the lipid chain melting phase transition temperature, the persistence of the lamellar lipid phase, and the colloidal stability of vesicle suspension, but also the height of the membrane permeability barrier to decrease, whereas lipid protonation or dealkylation have the reverse effect. – Lipid bilayers and their adjacent solution behave as single thermodynamic entity. Changes in the polar headgroup region and in the solvent composition consequently can regulate not only the membrane capacity for molecular or supramolecular reorganisation (e.g. phase changes or membrane fusion, respectively) but moreover may govern the short‐range intermembrane (e.g. hydration) forces and, to some extent, affect the membrane‐solute interactions. These effects are therefore of considerable interest and relevance for the studies and understanding of membrane binding and transport.
Intramolekulare Proteindynamik untersucht mit zeitaufgelöster Fourier Transform Infrarot‐Differenzspektroskopie
Authors: Gerwert Klaus 
Published: March 2014

AbstractThe intramolecular reactions of membrane proteins are investigated by the new developed time resolved FTIR difference spectroscopy technique. By this technique the kinetics of single groups in membrane proteins can be determined. As example the protonation kinetics of aspartic acids are shown. Simultaneously the absorbance change in the visible spectral region is measured at one wavelength. Thereby the IR‐Absorbance changes can be correlated to changes in the visible spectral region. The technique is applied to the lightdriven proton pump bacteriorhodopsin and to crystals of the photosynthetic reaction center of Rps. viridis.
Modulation of Gap Junctional Coupling in Pairs of Pancreatic Acinar Cells by cAMP, OAG and Protein Kinase C
Authors: Somogyi R. , Kolb H.‐A. 
Published: March 2014

AbstractJunctional coupling was studied in murine pancreatic acinar cells using the double whole cell patch clamp method. Independent of the electrolyte composition of the pipette solution, cell pairs spontaneously uncoupled. Addition of 5 mM ATP and 0.1 mM cAMP to the pipette electrolyte was sufficient to stabilize electrical coupling within an observation time of over one hour. At stable cell‐to‐cell‐coupling superfusion of a cell pair by 1‐oleyl‐2‐acetylglycerol (OAG) containing bath solutions induced a progressive decrease of coupling after a delay of about 10 minutes. Under these conditions stepwise changes of the junctional conductance of about 45 pS and 90 pS could be identified. Similarity, addition of protein kinase C to the pipette solution reduced junctional coupling. An antagonistic effect of protein kinase A and protein kinase C dependent processes on the permeability of gap junctions is discussed.
The Response of the Limulus Photoreceptor Cell to the Absorption of Single Photons
Authors: Stieve Hennig 
Published: March 2014

AbstractThe response of the visual cell of the horseshoe crab Limulus to light stimuli is described. Due to the absorption of a single photon, a rhodopsin molecule is light‐activated and starts a sequence of causal steps which lead to the generation of a relatively large elementary excitatory response, the “bump”. A bump is based on the concerted transient opening of a large number of sodium ion‐preferring channels through the cell membrane. The bump generating mechanism is discussed. – The “macroscopic” light response to higher stimulus intensities is believed to consist of a fused volley of bumps. Its intensity dependence is discussed. A conditioning pre‐illumination usually desensitizes the visual cell transiently. However, very weak pre‐illumination may cause an increase in sensitivity, “facilitation”.
Fluoreszenzkinetische Untersuchungen zum Mechanismus der cholinergen Reizung
Authors: Maelicke Alfred , Prinz Heino , Covarrubias Manual 
Published: March 2014

AbstractBased on equilibrium binding and stopped‐flow kinetic studies with the fluorescent cholinergic agonist NBD‐5‐acylcholine and acetylcholine receptor from electrocytes of Electrophorus electricus or Torpedo marmorata, we have developed a minimal model of cholinergic excitation. During the initial phase of association, the two agonist binding sites per receptor monomer are rapidly filled. The resulting state of low agonist affinity of fully occupied receptor is “activatable” in the sense that low energy opening events of the receptor integral cation channel may occur. The “activatable” state is lost either by dissociation of agonist or, in the continuous presence of agonist, by conformational transitions to state(s) of high agonist affinity. As such conformational transitions are also induced in the presence of cholinergic antagonists, the existence of ligand‐induced conformational transitions does not suffice by itself to explain the phenomenon of (agonist‐specific) desensitization. Our data are in contrast to previously proposed specific allosteric models of ligand interaction of the receptor.
Electrically and Chemically Gated Ion Channels in Skeletal Muscle
Authors: Neumcke B. , Lönnendonker U. , Woll K. H. 
Published: March 2014

AbstractThe surface membrane of skeletal muscle fibres contains ionic channels which are controlled by the electric field and regulated by intracellular ions. In patch clamp experiments on adult frog and mouse muscle fibres we have identified the following types of channels: anion‐selective channels, Ca‐activated K channels and ATP‐sensitive K channels. Some properties of these ion channels are described and possible physiological functions are discussed.
On the Structure of the ATP‐Synthase from Chloroplasts
Authors: Boekema Egbert J. , Fromme Petra , Gräber Peter 
Published: March 2014

AbstractThe H+‐translocating ATPase (“ATP‐synthase, CF0F1) was isolated from chloroplasts and characterized biochemically and by high resolution electron microscopy. The ATP‐synthase has a hydrophilic part, CF1, and a hydrophobic part, CF0, with subunit composition I, II, III,12, IV. The top view projection of CF1 (i.e. vertical to the membrane) reveals a pseudohexagonal arrangement of the large subunits α3β3, which ara arranged in two layers. The α‐ and β‐subunits are connected by a stalk with the membrane‐integrated CF0 part. The shape and dimensions of CF0F1 are given and a model for the subunit arrangement is described.
Electric Field‐Driven ATP Synthesis Catalyzed by the Membrane‐Bound ATP‐Synthase from Chloroplasts
Authors: Bauermeister Hans , Schlodder Eberhard , Gräber Peter 
Published: March 2014

AbstractWhen chloroplast vesicles, suspended in a conducting aqueous medium, are exposed to an external electric field pulse, the membrane‐bound ATP‐synthase can catalyze ATP synthesis similar to energization of the membrane by light pulses. Inhibitors which bind to the enzyme inhibit light‐induced ATP synthesis and external field‐induced ATP synthesis at the same concentration. With uncouplers, which increase the ion permeability of the membrane, a higher concentration is necessary to inhibit electric field‐induced ATP synthesis. This is due to the faster charging of the membrane capacity by an external electric field. The enzyme can exist in an oxidized and a reduced state. Both forms can catalyze field driven ATP synthesis, and the rates depend in a sigmoidal way on the field strength. For the same rate of ATP synthesis, the reduced form requires a lower field strength than the oxidized form.
Chromophore Location and Charge Displacement in Bacteriorhodopsin
Authors: Heyn M. P. , Braun D. , Dencher N. A. , Fahr A. , Holz M. , Lindau M. , Seiff F. , Wallat I. , Westerhausen J. 
Published: March 2014

AbstractUsing three selectively deuterated retinals, the in‐plane structure of the chromophore of bacteriorhodopsin was determined by neutron diffraction. The time‐resolved photovoltage of bacteriorhodopsin was analysed on the basis of distributed kinetics indicating the presence of three major phases in the charge displacement with time constants of 32 μs, 890 μs and 18 ms at 25°C, pH 7. Sixty to seventy percent of the relative charge displacement occurred in the slowest step. The current‐voltage characteristic of bacteriorhodopsin incorporated in planar lipid bilayers was measured and found to be distinctly non‐linear. Between −80 mV and +180 mV it can be approximated by a single exponential plus a constant. This behaviour can be explained in terms of a barrier model for the pump with the slowest step dominating the photocurrent and its voltage dependence. Combining the information from the current‐voltage dependence with the kinetic information, a stoichiometry of one proton pumped per bR cycling is obtained. There is no evidence for a reversal potential down to −160 mV.
H + H2: The Current Status
Authors: Buchenau H. , Toennies J. P. , Arnold J. , Wolfrum J. 
Published: March 2014

AbstractResults of experimental investigations on the thermal rate constants and the microscopic dynamics of the hydrogen exchange reaction, including the isotopic variants and the spectroscopy of the H3‐complex, are compared with recent predictions based on quasi‐classical, approximate and exact quantum, and variational transition state theory calculations.
Kinetics of Ion‐Molecule Reactions in Gases: Equilibrium and Nonequilibrium Theory with Applications
Authors: Stiller W. , Schuster R. 
Published: March 2014

AbstractFor calculating rate coefficients of ion‐molecule reactions the formalism of kinetic theory of weakly ionized diluted gaseous plasma is used. – Equilibrium rate coefficients of proton transfer reactions between ions and polar molecules show a weakly temperature‐dependent Arrhenius‐like behaviour. – Analogous nonequilibrium rate coefficients give a reaction‐induced kinetic isotope effect in reactions between small ions (H−, D−) with polar molecules (CH3CHO) in heavy carrier gases (xenon).
Reaktionen von H‐Atomen mit Cycloalkenen und 1‐Olefinen
Authors: Scherzer K. , Gebhardt J. , Olzmann M. 
Published: March 2014

AbstractThe reactions of hydrogen atoms with the cycloalkenes C5 to C8 and the n‐alkenes C2 to C8 have been studied at room‐temperature in a flow system. In the presence of an excess of H‐atoms two steps of chemical activation occur: 1) the addition of H‐atoms to the double bond and ii) the combination of the radicals formed with H‐atoms. The main processes are the stabilization (S) of the activated intermediates by collisions and the decomposition (D) via ring opening and degradation. It is shown that the ratio D/S decreases with increasing concentration and size of the hydrocarbon. To calculate the ratios D/S for the first and the second activation step the classical formalism for chemically activated systems is extended. A method based on the coupling of two conventional steady‐state master equations is presented to evaluate the contribution of either of the two reaction paths. It is shown that the second way, via activated alkanes, is more important under these conditions.
Formation of Solvated Ions by Electron Capture in van der Waals Aggregates
Authors: Oster Tatiana , Illenberger Eugen 
Published: March 2014

AbstractWe report on the formation of solvated anions in beams of molecular aggregates by resonant capture of low‐energy electrons. The initially generated negative ion can be effectively deactivated in the cluster environment (“built‐in 3‐body collision”). By this means anions which are normally inaccessible from the ground neutral state can be stabilized by intermolecular energy transfer. In these experiments halide ions solvated by H2O or CO2 are produced from mixed clusters of these molecules and CF3Cl or C2Cl4. The appearance of such products is found to depend strongly on the electronic state of the precursor anion.
Reactivity and Electronic Structures of Isolated Clusters
Authors: Rademann Klaus 
Published: March 2014

AbstractSome aspects of recent advances in the study of isolated clusters and their size dependent properties are reviewed. Reliable techniques for cluster generation and detection are briefly discussed. Methods for studying physical properties and electronic structures of isolated clusters and cluster ions are addressed in the context of relevant fundamental questions. Progress concerned with the exploration of solvated organic clusters, the interrogation of transition metal cluster reactivities and the investigation of electronic structures of metal clusters is documented by selected examples. In some cases, relations between isolated cluster properties and condensed phase behaviour are indicated.
Elementary Reactions of NH(a1Δ) with Saturated Hydrocarbons in the Gas Phase
Authors: Hack W. , Rathmann K. 
Published: March 2014

AbstractThe elementary reaction of NH(a1Δ) with the saturated hydrocarbons:

was studied for R = CH4, C2H6, C3,H8, and n‐C4H10 at room temperature in the gas phase at low pressure (10 < p/mbar ≤ 40). NH(a) was produced by HN3 laser photolysis (λL = 248 nm) and detected by laser induced fluorescence. Time resolution was obtained from the variable delay between the photolysis pulse and the detecting laser pulse. – The rate constants (in cm3/mol s) were found to be:

independent of pressure in the above given range. – The product NH2(X̃) and the quenching pathway (NH(X)) were followed directly and quantitatively by laser induced fluorescence. The quenching pathway was found to be unimportant([NH(X)]α /[NH(a)]0 < 1%) for all alkanes. The fraction of NH2(X̃) formed, {[NH2(X̃)]α/[NH(a)]0} decreases with increasing chain length from (CH4) = 1.0; (C2H6) = (0.34 ± 0.06); C3H8 = (0.20 ± 0.02) to n‐C4H10 = (0.07 ± 0.02). These ratios did not change with pressure (10 ≤ p/mbar ≤ 40). – The increase in the rate constants for the reactions with H–(CH2)n – H with increasing n (1 ≤ n ≤ 4) and the decrease in the NH2 yield demonstrate that NH2 is not formed by abstraction but by an insertion mechanism.
Analysis of Radicals from Flames by Scavenging with Dimethyl Disulfide
Authors: Hausmann M. , Homann K. H. 
Published: March 2014

AbstractLarger hydrocarbon radicals in flames, which are difficult to detect by optical methods, can be analyzed quantitatively by radical scavenging with dimethyl disulfide in the condensed phase. – Gas samples taken from a sooting ethyne/oxygen flame by a nozzle beam were frozen at liquid‐N2‐temperature on the inner surface of a hollow sphere simultaneously with the radical scavenger dimethyl disulfide. The latter was admitted in large excess as a gas and was condensed uniformly on the inner wall of the sphere. The mixture of condensable stable flame products and scavenging products in the excess CH3SSCH3 was separated and identified by GC/MS. – Larger hydrocarbons (CxHy, x ≥ 6) condensed quantitatively. H, CH3, C4H3 and the phenyl radical were scavenged as mono(methylthio) compounds; C2 and the carbenes CH2, C3H2, C5H2 yielded bis(methylthio) compounds; other bis(methylthio) compounds observed were C2nH2(SCH3)2 with n = 1, 2, 3 and 4. CH, C3H and C2H3 were identified by the respective tris(methylthio) compounds. Any consecutive reactions of radicals with stable flame products and their recombinations in the cold trap were suppressed by their scavenging reaction.
Energy and Charge Transfer in Clusters of Organic Molecules Following Resonant Electron Capture
Authors: Hashemi Reza , Kühn Alexander , Lotter Johannes , Illenberger Eugen 
Published: March 2014

AbstractNegative ion formation following resonant electron capture by molecules and molecular aggregates is studied in beam experiments for the prototype systems CF3Cl, CF4 and C2F4. Analysis of the excess kinetic energy of the reaction products is performed in order to observe the change in decomposition dynamics on proceeding from single molecules to clusters. It is shown that electron capture by aggregates may ultimately generate monomeric anions in their relaxed geometries not accessible in the isolated compound. In some cases a relaxation energy of several eV has to be distributed among the target cluster. Fragment ions formed with remarkably high translational energy are effectively slowed down when arising from aggregates at the same attachment energy. Clusters of tetrafluoroethylene show an additional resonance at low attachment energies which exclusively decomposes into (C2F4)−n, n ≥ 2.