bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chemical Reactions in Supercritical Water ‐ 1. Pyrolysis of tert.‐Butylbenzene
Authors: Kruse Andrea , Ebert K. H. 
Published: July 2012

AbstractSupercritical water is a powerful solvent and a favourable reaction medium for oxidation of organic material. The role of supercritical water in these processes is not fully understood. The influence of supercritical water on the pyrolysis of tert.‐butylbenzene as a model compound was investigated. Experiments were carried out in a flow reactor at pressures between 5 and 25 MPa, at temperatures between 505 and 540°C and residence times between 15 and 55 s. Water, nitrogen, and water‐nitrogen mixtures, respectively, were used as reaction media; no significant differences in the product formation rates and distributions were detected. In an experiment with D2O, instead of H2O, it was proved, that deuterium is incorporated in all the product substances in various amounts. Interpretating the results with a reaction model based on a radical mechanism it was made probable that H‐D exchange reactions occur with radical intermediates.
Tailoring Surface Electronic Properties to Promote Chemical Reactivity
Authors: Bertel E. , Sandl P. , Rendulic K. D. , Beutl M. 
Published: July 2012

AbstractOne of the foremost objectives in the search for improved catalysts is the promotion of molecule dissociation, which in many catalytic reactions is the rate limiting step. It is shown that modification of electronic surface states by surface dopants allows to control the dissociation barrier. The relation of this new type of promotion mechanism to the effect of surfactants in metal epitaxy opens a new perspective in the search for both, promoters and surfactants.
Observation of Fluorescence Background Suppression in Raman Scattering on Single Microparticles
Authors: Kaiser T. , Esen C. , Moritz H. , Borchers M. , Schweiger G. 
Published: July 2012

AbstractRaman scattering experiments were performed on single optically levitated microparticles. In comparison with bulk experiments an dramatic enhancement of the Raman scattering relative to the fluorescence scattering was observed. Two real‐world samples, a monomer for use in laser stereolithography and an engine lubricant, were investigated. Furthermore Dioctylphthalat (DOP), doped with fluorescent dye Coumarin 6, was studied by Raman spectroscopy in a droplet chain, on an optically levitated particle and in a cuvette. The combination of Raman spectroscopy and optical levitation could be a new offspring for analytical applications of Raman spectroscopy. Liquid and solid microparticles with a few nanograms in mass can be investigated by this technique with excellent signal‐to‐noise ratio.
Nonionic Microemulsions
Authors: Schubert K.‐V. , Kaler E. W. 
Published: July 2012

AbstractWe review and summarize the features of nonionic microemulsion phase behavior. Particular emphasis is given to the behavior of mixtures of oil, water or other polar materials with nonionic surfactants from the family of n‐alkyl polyglycol ethers, usually denoted as CiEj. The patterns of phase behavior are reviewed and the roles of various additives such as electrolytes and alcohols are discussed.
The Effect of Temperature on the Adsorption of Non‐Ionic Surfactants and Non‐Ionic Surfactant Mixtures at the Air‐Water Interface
Authors: Penfold J. , Staples E. , Thompson L. , Tucker I. , Thomas R. K. , Lu J. R. 
Published: July 2012

AbstractNeutron reflectivity has been used to study the effect of temperature on the adsorption of non‐ionic surfactants and non‐ionic surfactant mixtures at the air‐water interface. For a range of polyoxyethylene non‐ionic surfactants the adsorption is invariant with temperature in the range 25 to 50 c; however some subtle changes in the structure of the adsorbed layer are observed.For the non‐ionic mixture of monododecyltriethylene glycol, C12EO3, and monododecyloctaethylene glycol, C12EO18, measurements over a wide concentration range, from below to above the cmc (10−5 to 10−2 M), provide a direct qualitative confirmation of the abrupt change in surface composition at the cmc due to the onset on mixed micelle formation predicted recently by Nikas, Puvvada, and Blankschtein, Langmuir, 8 (1992) 2680.For the same non‐ionic mixtures and at concentrations below and above the cmc (at concentrations of 1.25 × 10−5 and 5 × 10−4 M) a change in surface composition with increasing temperature is observed. The surface becomes more rich in the least surface active component, the C12EO8. In the same temperature range the total adsorption from the mixture at the interface decreases slightly.
II. Theoretical Modeling: An Introduction
Authors: Widom B. 
Published: July 2012

AbstractThe major classes of models that have been applied and analyzed in the theoretical discussion of microemulsions are described. These include both continuum and lattice models, and models based on phenomenological free‐energy densities as well as those based on microscopic Hamiltonians. Some of the issues addressed by such models are the progression of microemulsion phase equilibria, the interfacial tensions, the wetting or non‐wetting of the interfaces, and the small‐angle X‐ray or neutron scattering from microemulsions. The ways in which the models address these issues are described and some characteristic results are quoted. Most of these matters are taken up later with more technical detail by other authors; the present paper is intended only to provide an overview.
Ginzburg‐Landau Theories of Ternary Amphiphilic Systems
Authors: Gompper G. 
Published: July 2012

AbstractGinzburg‐Landau models of ternary amphiphilic systems have been studied intensively over the last few years. A wide range of phenomena of amphiphile systems has been investigated with these models, such as the internal structure and the dynamical behavior of microemulsions, phase transitions between microemulsions, oil‐rich, water‐rich and lamellar phases, interfaces between coexisting phases and their wetting properties, and systems in confined geometry. The paper reviews some recent results of the Ginzburg‐Landau approach concerning these phenomena.
Length Scale for Configurational Entropy in Microemulsions
Authors: Reiss Howard , Kegel Willem K. , Groenewold Jan 
Published: July 2012

AbstractIn this paper we study the length scale that must be used in evaluating the mixing entropy in a microemulsion. The central idea involves the choice of a length scale in configuration space that is consistent with the physical definition of entropy in phase space. We show that this scale may be sensitive to the model employed in the description of a microemulsion, but that in most cases it is of the order of the cube root of the average molecular volume in the system. We also show that other much larger length scales used by workers in the field can be partially reconciled with the fundamental scale through a consideration of the constraints to which the microemulsion is subject. We have attempted to perform the analysis in as rigorous a manner as possible. Many interesting features appear and the importance of using the correct length scale as well as methods (some of which are extensions of current theory) for incorporating it into theories of microemulsions are discussed.
On the Physical Contribution to the Extend Real Associated Solution Model
Authors: Hofman T. , Casanova C. 
Published: July 2012

AbstractThe mixing rules and the expressions of the physical contributions to the excess functions of mixing given by the ERAS model are critically re‐examined. As a result, new and more rigorous equations are derived. Calculations performed on the typical systems confirm meaningful differences between the old and new formulation at low concentrations of the associated substance.
The Reactions of 1CH2(ã1A1) with C2HxF4‐x(x = 0, 2, 3, 4) and 1, 1‐C2HF2CI
Authors: Carstensen H.‐H. , Rehbein C. , Gg. Wagner H. 
Published: July 2012

AbstractThe rate constants of the reactions of 1CH2 with C2H4, CH2 = CF2, CHF = CHF, CF2 = CHF, C2F4, and CF2 = CHCl were investigated with a laser photolysis/laser induced fluorescence apparatus at room temperature under quasistationary conditions. 1CH2 was produced via photolysis of ketene. The obtained rate constants show a regular dependence on the amount of fluorine substitution: an increasing fluorine part leads to a decrease of the overall rate constant. This also holds for CF2 = CHCl, which shows nearly the same reactivity towards 1CH2 as CF2 = CHF does. Some of the investigated reactions were measured for both 1CH2(v = 0) and 1CH2(v = 1). The obtained rate constants are very similar.In the reactions of 1CH2 with CH2 = CF2, CF2 = CHF and C2F4 the radical 1CF2 could be detected as a reaction product. In the 1CH2 reactions with CHF = CHF and CF2 = CHF the radical 1CHF could be observed.These results underline the importance of the addition channel for this kind of reactions.
Dynamics and Molecular Order of the Liquid‐Crystalline Complexes of 5‐Octadecyloxyisophthalic Acid and Cyclic Oligo‐Amines, Investigated by 2H n. m. r. Spectroscopy
Authors: van Genderen Marcel H. P. , Pfaadt Marcus , Macho Volker , Valiyaveettil Suresh , Spiess Hans W. 
Published: July 2012

AbstractComplexes of 5‐octadecyloxyisophthalic acid with piperazine, 1,4,7‐triazacyclononane and 1,4,7,10‐hexaazacyclooctadecane were selectively deuterated in various positions, and investigated with variable‐temperature solidstate 2H n. m. r. spectroscopy. All systems form stable, enantiotropic liquid‐crystalline phases at high temperature, and the dynamics in these phases can be described by a single motional model. This model involves fast rotation around the director coupled with a rapid phenyl flip. Macroscopically oriented liquid‐crystalline phases with the director parallel to the magnetic field are found on cooling in a magnetic field of 7 T for the piperazine complexes, but only partial macroscopic order was achieved for the complexes with 1,4,7,10‐hexaazacyclooctadecane and 1,4,7‐triazacyclononane under these conditions, and also for the former in a magnetic field of 11 T. In contrast to the pure acid C18ISA, the stability of the phases is determined by the hydrogen/ionic bonds between the acid and the bases, and not by the alkyl‐alkyl interactions.
Catalysis by Manganese Oxide Monolayers Part 2: Zirconia Support
Authors: Ma J. , Chuah G. K. , Jaenicke S. , Gopalakrishnan R. , Tan K. L. 
Published: July 2012

AbstractThe catalytic and structural properties of two different preparations of manganese oxide supported on high surface area zirconia are compared. The catalyst were prepared by grafting from an alkoxide precursor and by conventional aqueous wet impregnation technique. Reaction of manganese ethoxide with the hydroxyl groups at the surface of the zirconia support is highly specific and allows manganese oxide to be deposited layer by layer. The zirconia used in this study has a mesoporous structure; pores with diameters ≦ 5.8 nm were found to be inaccessible to the manganese ethoxide precursor. Hence, only about half of the total surface area is available for the reaction with ethoxide. A quantitative evaluation of the XPS intensities for manganese and zirconia shows that about 2.5 layers of manganate are deposited after five grafting steps. Activity tests made on these catalysts confirm the monolayer buildup. The specific activity of the isolated manganese ions which result from the first grafting step is very low; the specific activity increases by an order of magnitude once the first monolayer is completed, and shows a further increase in the second and third layers. In contrast, impregnation with manganese acetate results in small manganate crystallites, which most likely form inside the pores. The specific activity of these catalysts and their selectivity towards acetone in isopropanol decomposition are very similar to that of bulk manganese dioxide whereas the grafted samples show a high selectivity towards propene.
Optical Detection of Electron Transport in Thin Films of Prussian Blue
Authors: Ochs S. , Grabner E. W. , Mohler E. 
Published: July 2012

AbstractPotassium‐iron(III)‐hexacyanoferrate(II) (Prussian blue) is deposited electrochemically as a thin film (thickness: 300 nm) on a Pt‐disk substrate electrode. The relative change in optical reflectivity of this electrode is detected time‐resolved upon galvanostatic reduction of Prussian blue to Everitt's salt and subsequent reoxidation. Considering different transport properties of electrons and cations within the film, the experimental result is fitted by numerical modelling. The specific diffusion coefficient for electrons is deduced as 5·10−11 cm2/s.
Transport of Photogenerated Charge Carriers Through Crystalline GaP Networks Investigated by Intensity Modulated Photocurrent Spectroscopy
Authors: Vanmaekelbergh D. , Iranzo Marín F. , van De Lagemaat J. 
Published: July 2012

AbstractThe transport of photogenerated electrons through porous n‐GaP electrodes has been investigated with Intensity Modulated Photocurrent Spectroscopy. Porous layers with a thickness of between 1 and 200 μm were formed on GaP substrates by anodic etching of crystalline n‐GaP electrodes. They consist of a network of crystalline GaP interpenetrated with the electrolyte. It is shown that the transit time of photogenerated electrons through the depleted porous network is larger than the RC response time. Hence, IMPS performed in the frequency window below (RC)−1 directly probes the transient photocurrent flow in the depleted porous network. The relatively long transit times observed with IMPS are attributed to strongly meandering paths of the photogenerated electrons through the crystalline network, probably determined by the potential distribution in the depleted network.
Metal Ion Induced Conformational Changes of Double‐Stranded Polynucleotides: Poly (dG‐m5dC) and Poly (dA‐dT)
Authors: Middendorf S. M. , Diebler H. 
Published: July 2012

AbstractLike poly(dG‐dC), also double‐stranded poly(dG‐m5dC) can adopt a left‐handed Z‐conformation. The concentrations of Ni2+ or Mg2+ which are required in order to induce the structural transition are much lower than in the case of the unmethylated polynucleotide. At ionic strength I = 0.001 M, one Ni2+ ion bound per 20 mononucleotide units is sufficient to trigger the conformational change. The kinetics of the binding of Ni2+ to the polynucleotide are characterized by a reaction effect with a time constant of 7–9 milliseconds (stopped‐flow and T‐jump), indicating innersphere binding. The kinetic data are consistent with a 3‐step mechanism which includes two inner‐sphere substitution processes, presumably involving a phosphate 0 atom and a guanine N7 atom. The slow kinetics of the BZ transition was monitored up to 1 hour. The reaction curves can be fitted excellently by 3 exponentials, the two shorter time constants being dependent on the Ni2+ concentration. A simple mechanism which is consistent with the experimental data is proposed and discussed.Also with poly(dA‐dT)·poly(dA‐dT) a drastic change in conformation after the addition of Ni2+ can be observed, presumably reflecting again a B→Z transition. Here, however, high concentrations of Ni2+ (0.075–0.55 M) and of NaCl (0.1–5 M) are required in order to start the transition. The rate of the conformational change is much faster than with poly(dG‐m5dC), the time constant was evaluated to be 0.9–1.9 seconds for 0.5–0.7 M of Ni2+ in 0.1 M NaCl solution.
Translational Diffusion of a Transient Charge‐Separated Species in Carbon Dioxide and Trifluoromethane Studied by the Transient Grating Method
Authors: Kanda D. , Kimura Y. , Terazima M. , Hirota N. 
Published: July 2012

AbstractBy means of the transient grating method, we have measured the translational diffusion constant of a transient charge‐separated species created by the photo‐isomerization of 1′,3′,3′‐trimethyl‐6‐nitrospiro[2H‐1‐benzopyran‐2,2′‐indoline] in carbon dioxide and trifluoromethane from ρr = 0.8 to 2.0, where ρr is the reduced density by the critical density of the solvent. It has been revealed that the effect of the charge‐separation on the diffusion constant is small in these fluids due to the large molecular size of the transient molecule. The viscosity dependence of the diffusion constant is well simulated by an empirical equation which also works well for benzene and naphthalene.
A Kinetic Analysis of γ‐Aminobutyrate Aminotransferase in Presence and Absence of Inhibitors
Authors: Porcelli Fernando , Scibona Giancarlo , Botrè Francesco , Lorenti Giampiero , Mazzei Franco , Botrè Claudio 
Published: July 2012

AbstractThe kinetics of the reaction catalyzed by γ‐aminobutyric acid transaminase (GABA‐T) is studied both in the absence and in the presence two inhibitors: n‐dipropylacetate (n‐DPA) and 4‐amino‐2‐azide‐butyric acid (GABA azide). A novel kinetic model is proposed, that is based on an experimentally derived rate equation, which describes the kinetics of the transamination process accounting for the competitive inhibition of the ketoacid and of the added inhibitor (n‐DPA, GABA azide). The consequence of the ketoacid inhibition on the primary and secondary double reciprocal plots of the initial velocity against the substrates concentration is examined. The kinetic parameters which describe the rate of the transamination reaction are derived and compared with data reported in the literature. The higher inhibition power of GABA azide with respect to n‐DPA is also assessed and discussed.
Chemical electrooptics and linear dichroism of polyelectrolytes and colloids
Authors: Kakorin Sergej , Neumann Eberhard 
Published: July 2012

AbstractRecently the controversial discussion on the reliability of electrooptical relaxation data of polyelectrolyte systems has been revived. It can be shown that chemical‐conformational contributions, for instance, to the dichroitic absorbance changes are exactly given by ΔACH=(ΔA∥+2·ΔA⊥)/3, where ΔA∥ and ΔA⊥ are the measured at the light polarization modes σ = 0° (∥) and σ = 90° (⊥), respectively. Alternatively, ΔACH=ΔAσ*, where σ* = 54.7° is the magic angle (for small absorbance changes). If ΔA∥ is measured at the various σ‐polarization modes according to ΔAσ cos2 σ+ΔA⊥ sin2 σ, the exact value of ΔACH is readily obtained. On the other hand, the linear dichroism ΔA = ΔA‐ΔA=ΔA∥‐ΔA∥+(ΔA‐ΔA can only be determined as an approximation of the difference ΔA−=ΔA∥‐ΔA⊥, if ΔA and ΔA are small or approximately equal.
A new route to polyelectrolytes: Radical initiation by the redox system Ce(IV)/sulfonic acid (sulfonate)
Authors: Rosengarten L. , Tauer K. 
Published: July 2012

AbstractRadical polymerization is the most commonly employed polymerization technique for the preparation of water‐soluble polymers. Unfortunately, not all water‐soluble monomers readily undergo radical homopolymerization in water. Here we report on a new redox‐initiator system for starting radical polymerizations in aqueous media. The initiator system consists of at least two components. One component (A) must contain an organic sulfonate or sulfonic acid, the other one is tetravalent Cerium. Results are presented for the following cases, which differ with respect to the properties of the component A:
I) If A is saturated it acts only as a reducing agent of the initiator system which is capable of starting radical polymerizations in the water phase. In this case the rate of polymerization is higher the higher the water solubility of the monomers.
However, if A is an unsaturated sulfonic compound (M) the reaction leads to hyperbranched products. This is due to the fact that M, which is for ordinary radical polymerizations a monofunctional monomer, becomes bifunctional in this special case of initiation.
On the other hand, if A is the water‐soluble polymer derived from M, one or more other monomers can be grafted onto the backbone of this polymer leading to graft‐blockcopolymers.
Ion binding in polyelectrolyte solutions. An account for noncoulombic interactions
Authors: Rebolj N. , Jamnik B. , Vlachy V. 
Published: July 2012

AbstractCanonical Monte Carlo method is used to study a refined model of polyelectrolyte solution. The discrete charges on a polyion are located periodically along the helix. The ion‐ion and ion‐polyion interactions are described by a solvent‐averaged potential which accounts for the desolvation of ions. The major parameters of the short‐range potential function are Gurney coefficients for the counterion‐counterion (Acc) and the charged group‐counterion interaction (Apc). From simulations, the self‐diffusion coefficient for counterions, D/Do, was calculated. This quantity is rather sensitive to the value of Apc and much less to the choice of the counterion‐counterion coefficient. The refined model is used to analyze a fraction of apparently free counterions, α (≈D/D0), as obtained from recent measurements of transport properties in aqueous solutions of lithium and cesium poly(styrenesulfonate). The values of Gurney parameters, which fit experimental results, are determined: for a good agreement with experimental data an additional repulsive interaction Apc≈3900 J/mol is required for lithium poly(styrenesulfonate) at 5°C. This value is smaller (≈1500 J/mol) for lithium salt at 35°C, and negative, ≈−130 J/mol, for cesium salt of poly(styrenesulfonic) acid.
Counterion induced bundle formation of rodlike polyelectrolytes
Authors: Tang Jay X. , Wong Shuen , Tran Phong T. , Janmey Paul A. 
Published: July 2012

AbstractA number of filamentous biopolymers including actin filaments (F‐actin), microtubules (MT), tobacco mosaic virus (TMV), and the filamentous bacteriophage fd form bundles under well‐defined conditions. All of these macromolecules are negatively charged rodlike assemblies, and lateral association is induced by a number of cations such as divalent and trivalent metal ions and homopolymers of basic peptides. The general features of bundle formation are largely independent of the specific structure of the biopolymers and the bundling agent used. They are also approximately independent of the concentration of macromolecules. However, a threshold concentration of bundling agent is required in order to form large lateral aggregates, detected by a sharp increase in light scattering and by electron microscopy. The threshold concentration varies strongly with the valence of the cations and increases with the ionic strength of the solution. The formation of bundles is reversible by polyanions such as nucleoside phosphates. This overall behavior is similar to the phenomenon of DNA condensation and can be explained by applying polyelectrolyte theories, including the concept of counterion condensation. Our results provide quantitative comparisons with a number of predictions of polyelectrolyte theories, including the calculation of apparent binding affinity and its dependence on ionic strength. They also support the prediction of an attractive interaction between the neighboring filaments due to sharing of counterion clouds. In addition, the simply detectable, reversible assembly of macromolecules in solution serves as a sensitive indicator of the active association of small ions and the formation of ion clusters. Association constants of Co(NH3)‐ATP and Lys18‐ATP were determined by application of this model.