bluuebunny/crossref_metadata_2025 huggingface dataset:
Orientational disorder in solids composed of the ellipsoid‐shaped molecules trichloromethyltrimethylsilane, Cl3CSi(CH3)3, t‐Butyltrichlorosilane, (CH3)3CSiCl3, and t‐Butyldimethylchlorosilane, (CH3)3CSi(CH3)2Cl
Authors: Bräuninger Sigmar , Dou Shi‐Qi , Fuess Hartmut , Schmahl Wolfgang , Strauß Roman , Weiss Alarich
Published: July 2012

The ethane structure‐related molecules Cl3CSi(CH3)3 (1), (H3C)3CSiCl3 (2), and (CH3)3CSi(CH3)2Cl (3) crystallize from the melt to an orientational disordered body centered cubic (plastic) phase I, Im3m, Z = 2. By DTA/DSC the following thermodynamic data have been determined (temperatures in K, ΔH in kJ mol−1). (1): Tm = 405.3; ΔHm = 7.36; ΔSm/R = 2.17; TI,II = 285.5; ΔHI,II = 11.16; ΔSI,II/R = 4.68. (2): Tm = 373.4; ΔHm = 6.69; ΔSm/R = 2.13; TI,II = 206.4; ΔHI,II = 6.01; ΔSI,II/R = 3.45. (3): Tm = 358.1; ΔHm = 5.66; ΔSm/R = 1.87; TI,II = 203.6; ΔHI,II = 7.75; ΔSI,II/R = 4.51. At 293 K the lattice constants of the bcc unit cells are (1): 796.6 (2) pm (303 K), (2): 794.5 (7) pm, (3): 803.6 (9) pm.

(1) Shows a two line 35Cl NQR spectrum (νi in MHz, T = 77 K) with ν1 = 37.213, ν2 = 37.033, fade out temperature Tf = 253 K; (2): Doublet, ν1 = 19.060, ν2 = 18.260, Tf = 177 K; (3): ν = 16.786, Tf = 200 K.

The 1H‐NMR line width and the second moment M2 (1H) of (2) show the orientationally disordered state above TI,II, hysteresis in TI,II, the freezing‐in of the t‐butyl group rotation below TI,II, and a freezing‐in of the individual CH3 group rotation below 100 K.
The role of RNA structure in RNA replication
Authors: Biebricher Christof K.
Published: July 2012

RNA replication by RNA replicases has two puzzling features: (i) its selectivity, i.e. only a few RNA species can be replicated, (ii) strand separation, i.e., a single‐stranded RNA template is used to produce a complementary replica; both template and replica are liberated as single‐stranded RNA. Sequence comparison of a great number of replicating RNA species did not reveal sequence homologies except for the invariant ends. However, a structural element required for the replication has been identified: 5′ termini were found to be involved in intramolecular base‐pairing while the 3′ termini were not. Artificially designed short RNA sequences having this structural property were synthesized and found to replicate. The results suggest that the RNA structures of template and replica participate directly in catalyzing the replication, in particular in the separation of strands during RNA replication.
Protein mediated networks. Random chemistry
Authors: Kauffman Stuart
Published: July 2012

Mathematical models of complex reaction systems suggest that such systems can exhibit a phase transition from subcritical to supracritical behavior. Supracritical behavior occurs if the diversity of substrates and potential catalysts exceeds a threshold. I will explore practical experimental avenues to study this phase transition, its role in creating libraries of organic molecules for drug discovery, approaches to study the emergence of collectively autocatalytic sets of peptides and other polymers, and a potential constraint on cells to remain subcritical.
Emergence of order in small autocatalytic sets maintained far from equilibrium: Application of a probabilistic receptor affinity distribution (RAD) model
Authors: Lancet Doron , Kedem Ora , Pilpel Yizhaq
Published: July 2012

We examined the behavior of auto‐catalytic sets of polymers by a computer simulation. Polymers are allowed to interact with each other, whereby each polymer molecule may catalyze the formation and degradation of others. The system is subjected to a set of thermodynamic and kinetic constraints, including a constant influx of free energy, which keeps the system away from chemical equilibrium and thus enables the effect of catalysis. The system is found to continuously change and probe many possible values in the composition space. In this simulation we make use of a Receptor Affinity Distribution (RAD) model to predict the probabilities of interaction and catalysis. Our results indicate that initially random sets of polymers, under the assumptions of the model, might accumulate information (i.e., clustering in the composition space). Sets will occupy a limited region of composition space, and temporarily reproduce themselves or disperse and give rise to other sets.
Determination of the rate constant and of product branching ratios in the reaction of CH3O2 with OCl between 233 and 300 K
Authors: Kukui A. S. , Jungkamp T. P. W. , Schindler R. N.
Published: July 2012

The reaction CH3O2 + OCl→prod (1) has been investigated in the temperature range 233–300 K using discharge flow mass‐spectrometric technique. A rate constant k1 (300 K) = (2.5±0.3) 10−12cm3 molecule−1 s−1 has been obtained observing the pseudo‐first‐order decay of CH3O2 radicals. The observed temperature dependence is described by

k1(233–300 K) = (2.0±0.1)10−12exp((80±50)/T)cm3 molecule−1 s−1.

The reaction channel (1a) CH3O2 + OCl→CH3OCl + O2 leading to CH3OCl formation was identified and found to be negatively temperature dependent with

k1a(233–300 K) = (1.5±0.3)·10−14exp ((920±200)/T)cm3 molecule−1 s−1.

It is shown that HCHO and HOCl result from the secondary reaction of OCl with CH3O.
Oxidative decarboxylation of cyclohexane monocarboxylic acid as a degenerate branching chain reaction II. Mechanism
Authors: Héberger K. , Keszler Á. , Vidóczy T. , Gál D. , Cotarca Livius , Delogu Pietro
Published: July 2012

Based on the experimental results obtained studying the oxidative decarboxylation of cyclohexane monocarboxylic acid and published earlier, a mechanism is suggested, according to which in the thermal oxidation two main chain carrier radicals exist: tertiary and secondary peroxy radicals yielding cyclohexanone as well as hydroxy and keto acids in parallel reaction sequences. Carbon dioxide is formed in both pathways independently.

The corresponding hydroperoxide molecules, formed during oxidation, decompose partly into radicals and partly into molecules resulting in degenerate branching and chemiluminescence phenomena, respectively. The rate determining termination is the cross combination process between secondary and tertiary peroxy radicals.

The combinatorial generation of the mechanism of the thermal process and its reduction enabled the construction of the sequence network of the formation of products indicating that the primary attack of the hydrogen abstraction (secondary or tertiary) determines the product distribution.
Von der Entropie zur Information — die physikalische Chemie der belebten Materie
Authors: Eigen Manfred
Published: July 2012

Hundred years ago physical chemistry was mainly concerned with equilibrium properties of macroscopic systems of matter. Energy and entropy were the basic concepts underlying various applications of the laws of thermodynamics. Particle physics and cosmology of our times have uncovered the limits of our understanding of these basic concepts. We had to learn “how strange the universe” is, before we may realize “how simple it is” (J.A. Wheeler, 1973). Physical chemistry of our days is increasingly dealing with material self‐organization far from equilibrium. A new concept is that of molecular storage and processing of information. This concept provides a physico‐chemical understanding of living matter. The paper describes necessary and sufficient conditions for generating information in molecular systems. The theoretical results are confronted with experimental findings obtained in vitro and in vivo.
Physikalische Chemie — Schnittstelle zwischen Naturwissenschaft und Technik
Authors: Felcht Utz‐Hellmuth
Published: July 2012

Physical chemistry appears on the surface to be an abstract science having only little direct relation to the chemical industry. On closer examination, however, it is very soon apparent that the laws developed within the field of physical chemistry to describe mass systems and mass transformation, as well as energy transfer and energy conversion, are of fundamental importance particularly to industrial chemistry. The application of these laws permits the theoretical treatment and elaboration of chemical processes and thus forms the basis for the realization of these processes on an industrial scale. Thermodynamic and kinetic studies of the chemical reaction are naturally of central importance, but the description of basic operations and measuring systems for process control and safety engineering, too, is only made possible by the application of physico‐chemical laws. This basic role of physical chemistry is described by means of examples from widely differing fields of the chemical industry.
Theoretische Chemie: Hilfe bei der Modellbildung oder Alternative zu Experimenten
Authors: Peyerimhoff Sigrid D.
Published: July 2012

A short historical introduction shows a few stations important for the field of theoretical chemistry whose appearance occurred 100 years ago under the term of mathematical physics or mathematical chemistry primarily in the area of physical chemistry. Present possibilities of the field are discussed in a number of examples: today quantumchemical calculations, computer simulations and modelling are a convenient and universally applicable instrument in many areas of chemistry for the interpretation of mechanisms as well as for quantitative prediction.
Reaktionen an Festkörper‐Oberflächen
Authors: Ertl G.
Published: July 2012

Chemical processes at solid surfaces form the basis for heterogeneous catalysis whose scientific investigation and industrial application were initiated at the beginning of this century. Despite early formulation of significant concepts, studies of the elementary steps on atomic scale started only during the past few decades in parallel to the development of powerful experimental tools. The present status will be illustrated by means of selected examples.
Stability constants of silver(I) complexes with diaza‐18‐crown ethers in polar solvents
Authors: Burchard T. , Cox B. G. , Firman P. , Schneider H.
Published: July 2012

The stability constants of Ag+ complexes with macrocyclic diaza‐crown ethers of constant ring size [18], but with different donor atom distributions in the ligand bridges, are strongly dependent upon solvent. The effect of solvent, however, is essentially independent of the ligand involved, and this extends even to bicyclic cryptand ligands. Thus, the stability constants of any one ligand are linearly related to those of the other ligands across a wide range of polar solvents. A more detailed analysis of the results in terms of the free energies of solvation and transfer of the species involved in the complexation reaction shows that, although the dominant influence is normally the solvation of Ag+, specific solvation of either the complexed cation or the free ligand can influence complex stabilities in some cases. Effects due to the former, although relatively weak, are evident in complexes of monocyclic diaza‐ligands in strongly coordinating solvents, such as dimethylformamide and dimethyl sulfoxide, and the latter is quite marked in solvents possessing acidic hydrogen atoms, such as water, methanol, and nitromethane.
Determination of candidate structures for Lennard‐Jones‐crystals through cell optimisation
Authors: Schön J. C. , Jansen M.
Published: July 2012

We show at the example of noble gases, using the Lennard‐Jones potential to approximate the interactions between the atoms, that the global minimisation of the energy through variation of both the basis vectors of the simulation cell and the relative positions of the atoms within the cell leads to structures that are good candidates for the actual structure of the material. During this optimisation, no restrictions were imposed on size, shape, or symmetry of the simulation cell.
Nuclear magnetic resonance of 69Ga in CdGa2Se4 and other defect chalcopyrites
Authors: Breuer A. , Siebert D.
Published: July 2012

By pulse FT‐NMR we investigated the resonance of the 69Ga isotope with nuclear spin I = 3/2 in single crystals of CdGa2S4, CdGa2Se4, HgGa2S4, and powders of CdGa2S4, CdGa2Se4, ZnGa2S4, ZnGa2Se4, HgGa2S4, and HgGa2Se4. Only the signal of the transition mI= ‐ 1/2 to mI= + 1/2 was analyzed by its second order shift. In case of crystals we used angular variation to obtain the electric field gradients (EFG). For CdGa2Se4 a small difference of the chemical shifts of about 70 ppm was revealed due to the different Ga positions. A characteristic twinning of many crystals was confirmed. Line broadening was different for annealed and quenched crystals and depended very strongly on the orientation of the crystals. This could be assigned to a partially disordered cation sublattice.
Hamilton‐Jacobi dynamics for the solution of time dependent quantum problems II. Wave packet propagation in two dimensional, nonlinearly coupled oscillators – exact and time‐dependent SCF‐solutions–
Authors: Gunkel Thomas , Bär Hans‐Jürgen , Engel Michael , Yurtsever Ersin , Brickmann Jürgen
Published: July 2012

Methods for the approximate numerical integration of the time dependent Schrödinger equation with given initial conditions (the initial wave packet) are presented. The methods are based on the Schrödinger representation of the quantum dynamic system. The quantum dynamic equations are transformed into Hamilton‐Jacobi type equations of motion as they occur in multi particle classical dynamics, i.e. standard techniques in molecular dynamics can be applied for the integration. The dynamics of minimum uncertainty Gaussian wave packets in strongly non‐harmonic, nonlinearly coupled oscillators are studied as examples. The numerically exact solutions are compared to time dependent SCF approximations of the wave packet.
PVTx‐Properties and virial coefficients of the water‐n‐hexane system
Authors: Abdulagatov I. M. , Bazaev A. R. , Ramazanova A. E.
Published: July 2012

PVTx‐data for the water‐n‐hexane system are reported in this paper. The data cover a temperature range from 523 to 623 K and pressure range from 2 to 16 MPa at different concentrations. The low pressure compressibility measurements were used to determine second and third virial coefficients for the water‐n‐hexane system. The values of the parameters in the square well potential are derived from virial coefficients data for pure components and binary mixtures water‐n‐hexane.
Determination of the product branching ratio in the reaction of NO3 with OCl at 300 K
Authors: Kukui A. , Jungkamp T. P. W. , Schindler R. N.
Published: July 2012

The relative importance of the product channels for OCl + NO3→ClOO + NO2 (1 a) and OClO + NO2 (1 b) have been reinvestigated at 300 K using discharge flow mass‐spectrometric technique. The ratio k1b/k1 = 0.32±0.1 has been obtained observing the build‐up of calibrated OClO signals as well as from pseudo‐first‐order decays of NO3 and OCl in excess of OCl and NO3, respectively.
Stability of Diffusion Profiles in quasi‐binary Solid Solutions (Ag, Na)Cl
Authors: Schimschal‐Thölke S. , Schmalzried H. , Martin M.
Published: July 2012

In binary or quasi‐binary systems the superposition of chemical diffusion and field‐driven migration may lead to unstable diffusion fronts. This means that an initially one‐dimensional transport geometry may become three (two)‐dimensional. This concept is tested with the solid solution AgCl‐NaCl above T=200°C, which is above the critical point of the miscibility gap. Morphological instabilities of the concentration profile in the inter‐diffusion zone are found if an external electric field is applied. This field must exceed a critical value and the AgCl‐side must be anodic in order to induce an instability of the diffusion front. Numerical solutions of the transport equations and the given boundary conditions corroborate the experimental results.
High Pressure Combustion – Ignition Temperatures to 1000 bar
Authors: Steinle J. U. , Franck E. U.
Published: July 2012

Ignition temperatures of gaseous mixtures of methane with oxygen or air at initial pressures between 50 and 1000 bar have been measured. Two cylindrical reaction vessels of 4 and 10 cm3 and one spherical vessel with 21 cm3 volume were applied which withstand dynamic pressures up to 6000 bar at 900 K (600°C). Most experiments used the “heat‐up” method with a high pressure gas mixture heated up inside and together with the reaction vessel until spontaneous rapid reaction began. Additional experiments were made with preheated empty vessels and with forced ignition by hot wires. Spontaneous ignition temperatures for stoichiometric methane‐air mixtures are around 870 K (600°C) at atmospheric pressure and decrease to 660 K (390°C) at 1100 bar ignition pressure. Semenov plots give straight lines for various reaction conditions. Effective activation energies could be derived. With the assumption of a global reaction order of 2, the activation energy for stoichiometric methane‐air is 359±4 kJ/mole, for stoichiometric methane‐oxygen it is 253±10 kJ/mol. Considering earlier experiments with “hydrothermal” supercritical flames, ignition with added high pressure steam were made.
Investigation of the Reaction of 3CH2 with NO at high Temperatures
Authors: Bauerle S. , Klatt M. , Gg. Wagner H.
Published: July 2012

The reaction 3CH2 + NO was studied behind incident shock waves over the temperature range 1100–2600 K by following the H and O atom formation with Atomic Resonance Absorption Spectroscopy (ARAS) and the OH radical formation with Laser Absorption. In the temperature range from 1100 to 2500 K the rate constant of the H atom formation formally attributed to a reaction channel giving HCNO+H (1 h) obtained on the basis of the experiments reported here is

k1h = 10(12.4 ± 0.2).exp (‐(25 ± 2) kJ mol−1/RT) cm3 mol−1 s−1.

The rate constant of the channel leading to HCN + OH (1d) was determined to be

k1d = 10(11.7 ± 0.3).exp (‐(12 ± 2) kJ mol−1/RT) cm3 mol−1 s−1.

The evaluation of the experimental profiles by means of computer simulation leads to an overall rate constant of about k1 = (1 ± 0.5)·1012cm3mol−1 s−1 without any noticeable temperature dependence within the error limits in the temperature range from 1200 to 2600 K. The contribution of a reaction channel leading directly or indirectly to O (or N) atoms was found to be less than 15% of the overall reaction at temperatures below 2000 K.
A Kinetic Study About the Reactions of NH(X3Σ−) with Hydrocarbons Part 3: Benzene, 1,3‐Butadiene and Acetylene
Authors: Röhrig M. , Römming H.‐J. , Gg. Wagner H.
Published: July 2012

The reactions of NH in its electronic ground state with benzene (1), 1,3‐butadiene (2) and acetylene (3) were investigated behind incident shock waves using narrow line width absorption detection of NH(X3Σ). The experiments were performed with very low initial concentrations of HN3 which was used as NH(X3Σ−) source to reduce the influence of secondary reactions. Thus it became possible to measure kinetic data for the reactions of NH (X3Σ−) with these hydrocarbons directly. The following rate constants were obtained in the temperature range 1100 to 1500 K, resp. 1400 to 1700 K (acetylene):

k1 = 10(14.2±0.3) exp (‐(76±8) kJ mol−1/RT) cm3/mol s

k2 = 10(13.9±0.3) exp (‐(45±7) kJ mol−1/RT) cm3/mol s

k3 = 10(14.7±0.3) exp (‐(59±9) kJ mol−1/RT) cm3/mol s
Kinetics of Photoinduced Electron Transfer Reactions of Some Anthraquinone Radical Anions with Various Inorganic Ions: Comparison with Marcus Cross‐Relation
Authors: Grampp Günter , Galán Manuel , Sacher Michael
Published: July 2012

The reactions of 2‐, 2,6‐ and 2,7‐anthraquinone (di) sulphonate radical ions with the paramagnetic ions Fe(CN)36, Cu2+, IrCl2‐6 and Fe3+ have been studied at different pH‐values at room temperature, in order to investigate the role of spin states on electron transfer. With 2‐anthraquinone sulphonate the rate constants are in the range 2.6 ‐ 7 × 108 mol−1 dm3 s−1, and for the other two anthraquinone derivatives the rate constants span over two orders of magnitude from 107 to 109 mol−1 dm3 s−1. The experimental rate constants have been compared with the predictions of the Marcus Cross‐Relation, taking also into account the contribution of the diffusion pathway in our calculations.

The predicted values are systematically larger than the experimental values. This systematic deviation is justified in the present work as due to the spin‐forbidden character of the reactions studied. The need for suited corrections in the current electron transfer theories has been stressed.
High Pressure Supercritical PVT‐Data of Water‐Sodium Hydroxide Mixtures and of Liquid Sodium Hydroxide to 673 K and 400 MPa
Authors: Kerschbaum S. , Franck E. U.
Published: July 2012

The density of homogeneous fluid mixtures of water and sodium hydroxide has been measured from 293 to 673 K and at pressures from 10 to 400 MPa. Measurements were performed at eight compositions between 10 and 90 weight percent NaOH and with pure molten NaOH. At sufficiently high pressure complete miscibility of NaOH and H2O exists above the melting temperature of NaOH at 595 K. A differential autoclave with internal heating within a space filled with high pressure argon and with an internal nickel bellows cell for the H2O–NaOH mixtures is described. Immediate results are given as specific mixture volumes and molar volumes. Molar volumes in dependence of composition have distinct minima near 30 mole percent NaOH. All excess volumes are negative. A semiempirical equation is proposed on the basis of a hydration model to describe molar and excess volumes. Partial molar volumes and estimated activity coefficients are given for 673 K and pressures at 100 and 400 MPa.
Dynamic Light Scattering Experiments with Aqueous Solutions of Polyelectrolytes with Hydrophobic Side Chains in the Presence of Salt
Authors: Gröhn F. , Topp A. , Belkoura L. , Woermann D.
Published: July 2012

Dynamic light scattering experiments are carried out with aqueous solutions of poly(4‐vinylpyridine) completely quarternized with dodecyl bromide and ethyl bromide in varying ratios in the presence of salt (KBr; αd + αe = 1; 0.010 ≤ αd ≤ 0.192; αd is the degree of quarternization by dodecyl bromide and αe that with ethyl bromide). Apparent diffusion coefficients Dapp (αd,c̄p) are calculated from the data (c̄p is the polymer concentration expressed in g dm−3). They are plotted as function of the reduced concentration variable λ = (cp*/cs) as well as of the degree of quarternization by dodecyl bromide αd at constant values of λ (cp* is the molar volume concentration of the repeating unit forming the polymer backbone; cs is the molar volume concentration of the added salt). The resulting curves indicate a characteristic change of the diffusive properties of the systems: For λ<< 1 one apparent diffusion coefficient is observed whereas for λ>> 1 a fast and a slow diffusive mode are detected. At a constant value of λ (λ ≈︁ 2.0) the appearance of a slow diffusive mode is induced by decreasing systematically αd (αd ≤ 0.192; αd + αe ≈︁ 1). It is predicted that the location of the “transition” on the λ‐axis is a function of αd.
In‐situ Optical Investigation of Oxygen Diffusion Profiles in SrTi03
Authors: Denk I. , Traub U. , Noll F. , Maier J.
Published: July 2012

The time evolution of oxygen stoichiometry profiles in Fe‐doped SrTi03 single crystals has been detected and analyzed in‐situ using an optical absorption technique. The profiles can be fitted according to Fick's second law by a constant chemical diffusion coefficient. The data obtained are in good agreement with earlier results from integral detection techniques and can be quantitatively understood by including the influence of internal coupling reactions to bare ambipolar transport via short range interaction.
Thermodynamic Properties for Solution of Hydrogen in Palladium‐Based Binary Alloys
Authors: Sakamoto Y. , Chen F. L. , Ura M. , Flanagan T. B.
Published: July 2012

The thermodynamic parameters for solution of hydrogen at infinite dilution and the (a+B) plateau thermodynamic properties for hydrogen absorption at moderate temperatures for a series of Pd‐based f.c.c binary alloys with relatively low solute metal content have been correlated from the viewpoint of whether the alloy lattice is expanded or contracted to parent Pd lattice. Newly determined data for Pd‐Zn, Pd‐Sb, Pd‐Bi, Pd‐Cr, Pd‐Mo and Pd‐Mn alloys are included. When alloys with solute metals in the same groups are compared, the lattice parameters of Pd binary alloys with the 4 d and 5 d transition elements are, in general, larger than those with the 3 d elements. The relative partial molar enthalpy, ΔH0H, at infinite dilution becomes more exothermic with an increase of lattice parameter for the lattice‐expanded alloys with the exception of Pd‐Pt alloys. Conversely, for contracted alloys, with the exceptions of Pd‐Li, Pd‐Zn, Pd‐Al and low Ti content Pd‐Ti alloys, the enthalpy becomes less exothermic with increasing lattice contraction. The dilute phase solubility at the same temperature as reflected by the relative chemical potential of dissolved hydrogen at infinite dilution, Δμ0H, increases with increasing lattice expansion for the expanded alloys, with the exceptions of Pd‐Pt and Pd‐Nb (Ta), whereas for the contracted alloys, the solubility decreases with increasing lattice contraction, with the exception of the Pd‐Li alloys. The standard free energy change, ΔG0plat'for B‐hydride formation in the expanded alloys decreases with increase of lattice expansion with the exceptions of the Pd‐Pt, Pd‐Zr, Pd‐Sb, Pd‐Nb(Ta) and Pd‐Mn alloys. For the contracted alloys, the B‐hydride becomes less stable with increasing lattice contraction except for the Pd‐Li alloys. The isobaric hydrogen solubilities in Pd alloys at relatively high pressures may be attributed to the influence of the solute metal atoms on the Pd band structure and to the exclusion of H from site occupation due to solute atoms in the nearest neighbor shells; both of these effects are independent of the lattice expansion and contraction.
A Capacitance and Infrared Study of the Electrical Double Layer Structure at Single Crystal Gold Electrodes in Acetonitrile
Authors: Panzram E. , Baumgärtel H. , Roelfs B. , Schröter C , Solomun T.
Published: July 2012

The electrical double layer at Au(100) and Au(111) electrodes in acetonitrile containing tetraethylammoniumper‐chlorate (TEAP) was studied by means of differential capacitance and in‐situ FTIR spectroscopy measurements. For both surfaces, a preponderant capacitance maximum was observed at a positive charge of about 8 μC cm−2. Two types of acetonitrile molecules were identified in the interfacial infrared spectra. One of these concerns adsorbed acetonitrile with a strongly blue shifted vCN mode at 2337 cm−1. The potential dependence of the spectra provides a clear evidence for dielectric saturation of the solvent and specific adsorption of the ions at large electrode charges. The spectra also indicate that the maximum ability of the solvent to reorientate in the interfacial field is in an adsorption geometry with the molecular axis inclined with respect to the surface. The data are discussed in context of the current models of the double layer, and compared with the related literature data obtained in an aqueous electrolyte.
A Kinetic Study About the Reactions of NH2(X̄2B1) Radicals with Saturated Hydrocarbons in the Gas Phase
Authors: Hennig G. , Wagner H. G. G.
Published: July 2012

The reactions of NH2(X̄2B1) with the hydrocarbons methane (1), ethane (2) and propane (3) were investigated behind incident shock waves at temperatures between 1500 K and 2100 K. The decay of NH2 was measured by laser absorption. NH2 was formed by the thermal decomposition of hydrazine. The following rate constants were obtained for the temperature range mentioned:

k1 = (1.2±0.6)·1013 exp(‐(63.4±3.4) kJ/mol/RT) cm3 mol−1 s−1

k2 = (9.7±0.3)·1012 exp(‐(48.0±1.8) kJ/mol/RT) cm3 mol−1 s−1

k3 = (1.7±0.4)·1013 exp(‐(44.6±2.0) kJ/mol/RT) cm3 mol−1 s−1.

These measurements extend the results obtained at low temperatures by Demissy and Lesclaux (330 K–250 K) and by Hack et al. (400 K–1080 K) into the range of interest for combustion processes.

The apparent energies of activation fit rather well into an Evans Polanyi plot. They correlate with the energies of activation of the corresponding reactions of OH(X2II)and those of CH3(X2A2) radicals.
Viscosity of N‐Pentane, N‐Heptane and Their Mixtures within the Temperature Range from 298 K up to Critical Points at the Saturation Vapor Pressure
Authors: Abdulagatov I. M. , Rasulov S. M.
Published: July 2012

The viscosity of n‐pentane, n‐heptane and their mixtures has been measured with a capillary flow method between 298 K and the critical temperatures at the saturation vapor pressure. The concentrations studied were 0.259, 0.419 and 0.745 mole fraction of n‐heptane. The maximal error of the experimental values of the viscosity is estimated to be ± 1.2% in the region far from the critical point and ± 5% in the immediate vicinity of the critical point. The viscosity obtained was compared to data by other authors with satisfactory agreement. The validity of the method has been confirmed by the measurement of the viscosity of standard liquids as water and toluene.
Surfactant Properties of Semifluorinated Alkanes in Hydrocarbon and Fluorocarbon Solvents
Authors: Binks B. P. , Fletcher P. D. I. , Thompson R. L.
Published: July 2012

The phase behaviour and aggregation of the semifluorinated alkane F‐(CF2)8‐(CH2)16‐H (abbreviated to F8H16) in hydrocarbon and perfluorinated solvents has been investigated. The variation of solubility with temperature for F8H16 in perfluorinated solvents shows highly non‐ideal behaviour and exhibits a sharp increase at a temperature a few degrees below the melting point of F8H16. The behaviour is similar to that in the region of the Krafft point of a conventional surfactant in water. With iso‐octane as solvent, the solubility shows only slight deviations from ideal behaviour. Vapour pressure osmometry (VPO) results confirm the near ideal behaviour of F8H16 in iso‐octane. For F8H16 in perfluorodecalin at 38 °C, VPO results show that aggregates are formed at concentrations above approximately 0.02 mole fraction. The aggregation number is 6 and is virtually independent of the SFA concentration. The results are discussed in terms of the antipathy between hydrocarbons and fluorocarbons as reflected in the values of the upper critical solution temperatures (UCST) of binary mixtures of hydrocarbons with perfluorinated solvents.
Thermodynamics of Aggregation in Droplet‐phase Water/AOT/Oil Microemulsions
Authors: Koper G. J. M. , Sager W. F. C. , Smeets J. , Bedeaux D.
Published: July 2012

We discuss the results of three experiments, namely dielectric permittivity, low shear viscosity, and electro‐optic birefringence measurements, that were designed to obtain quantitative information on the aggregation in droplet phase microemulsions. The data consistently yield a rather large binding free energy of −4 k T between two aggregated microemulsion droplets and we discuss possible explanations for this large value.
Lyotropic Phase Behaviour of Biological Amphiphiles
Authors: Seddon J. M.
Published: July 2012

A brief overview is given of the lyotropic phase behaviour exhibited by biological amphiphiles, with particular emphasis on the non‐lamellar liquid‐crystalline phases.
Thermal Diffusion in Crystalline Binary Compounds with Narrow Ranges of Homogeneity: (III) Experimental Study of the Soret Effect in β‐Ag2+δS
Authors: Korte C. , Janek J.
Published: July 2012

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

The electron transfer reactions of the cis‐tetraamminediaquocobalt(III) complex with hexacyanoferrate(II) and octacyanomolibdate(IV) in four different water‐cosolvent binary mixtures have been investigated. ket and KIP values have been experimentally determined and discussed within the framework of current theories on electron transfer reactions and ionic association. For this purpose, the standard formal potentials of hexacyanoferrate(II) and octacyanomolibdate(IV) were also determined.

Comparison of the second order rate constants (k12‐ ketKIP) to predictions of the Marcus Cross‐relation gives some indication of the adiabaticity of the processes investigated.
Formation of Fractal Clusters of Colloidal Copper Hydrous Oxides
Authors: Thies Michael , Hinze Ulrike , Paradies Henrich H.
Published: July 2012

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

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

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

According to some statements in the literature, it is very hard or virtually impossible to get meaningful relaxation data for macromolecular systems by methods involving electric field pulses (electric field jump and Joule temperature jump), mainly because of perturbations resulting from field induced orientation effects. These statements have been presented until recently, in spite of the fact that the magic angle technique for suppression of such effects has been described in the literature quite some time ago. Apparently there is not sufficient knowledge on the existence/validity/practicability of this technique. More than 20 years experience with magic angle detection is summarized, including a recent detailed comparison of magic angle fluorescence T‐jump data with corresponding stopped flow data for the case of ethidium intercalation into DNA double helices. The results demonstrate that chemical relaxation induced by application of electric field pulses to macromolecular solutions can be measured without perturbations, provided that appropriate procedures are used. Moreover, techniques using electric field pulses proved to be the only practicable approach to analysis of many macromolecular reactions.

It is not always necessary to suppress orientation effects; on the contrary, orientation effects can be very useful to follow reactions which cannot be detected by other procedures. A special case is demonstrated where reaction and orientation effects appear as a convolution product.
Enthalpies of dilution of some polycation solutions and exchange enthalpies of polycation counterions
Authors: Keller Markus , Lichtenthaler Rüdiger N. , Heintz A.
Published: July 2012

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

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

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

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

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

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

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

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

The dissolution process of silica gel in water is investigated in its dependence on dissolution time, pH (2 < pH < 10), and temperature (25°C, 45°C, 55°C). The dissolved amount of silica is depicted as a function of time and pH. A dissolution surface is formed. The saturation concentration at a certain temperature is relatively high at low pH‐levels. When the pH is increased, a minimum of solubility is found at pH about 4. A maximum seems to follow. Its position depends on the dissolution temperature. After this maximum a relatively constant region of amount of dissolved silica with a second small minimum is observed. If the pH‐value is as high as 10, the solubility increases drastically by the formation of an alkali silicate solution.

A model is developed for the interpretation of the experimental results. The model consists of four reactions with proton transfer which are assumed to be in equilibrium. Furthermore, four elementary reactions of monosilicic acid addition or elimination are considered. The model allows for the determination of the equilibrium constants of the proton transfer reactions as well as the corresponding enthalpies and entropies. The rate constants of the elementary reactions, and the activation enthalpies and entropies are estimated.

The expressions for the (overall) rate constants of dissolution and precipitation are derived, which are commonly used in the literature. They depend on the equilibrium constants of the proton transfer reactions, on the rate constants of the elementary reactions and on pH. Thus the course of the rate constant as a function of dissolution pH, as reported by several authors, could be established and interpreted.

As far as appropriate data are available in the literature, a general good agreement of thermodynamic and kinetic quantities with the results obtained in this work could be observed. Therefore they could be a base for further investigations.