bluuebunny/crossref_metadata_2025_split huggingface dataset:
Intramolecular charge transfer, photoisomerisation and rotational reorientation of trans‐4‐dimethylamino‐4′‐cyanostilbene in liquid solution
Authors: Il'Ichev Yurii V. , Zachariasse Klaas A. 
Published: July 2012

AbstractIn the excited singlet state of trans‐4‐dimethylamino‐4′‐cyanostilbene (DCS) ultrafast intramolecular charge transfer (ICT) takes place followed by trans‐cis photoisomerisation from a highly polar charge transfer (CT) state. The photoisomerisation of DCS is studied as a function of temperature in three homologous solvent classes, nalkanes, n‐alkylnitriles and n‐alcohols. The photoisomerisation activation barrier Etc increases with viscosity for DCS in n‐alkane solvents, whereas in the polar n‐alkylnitriles and n‐alcohols the separate influence of viscosity and polarity on the isomerisation reaction cannot be disentangled. The activation barrier for the trans‐cis photoisomerisation is considerably larger in acetonitrile and methanol, highly polar solvents of low viscosity, than in the nonpolar n‐heptane, due to the strongly polar character of the CT state as compared to the transition state of the isomerisation reaction. This polarity trend is reversed in solvents with the lowest polarity and the highest viscosity of the homologous series of the n‐alkylnitriles and the n‐alcohols. Simultaneous operation of polarity, viscosity and temperature as factors changing the potential energy surfaces, leads to isoviscosity plots that appear to indicate that the trans‐cis photoisomerisation of DCS does not depend on solvent viscosity. From measurements of fluorescence decay times as a function of pressure (to 4000 bar) it follows, however, that the photoisomerisation rate constant ktc decreases by a factor of 2.0 for a 3.3 fold viscosity increase, resulting in a fractional viscosity dependence, ktc = η−α with α = 0.61. When the increase of the permittivity with pressure is taken into account, α becomes 0.53. From the observation of a linear relationship between the rotational relaxation time τrot and the viscosity, 1/τrot=η−1.0 it is concluded that the Stokes‐Einstein‐Debye equation holds for the overall rotation of the DCS molecule, showing that viscosity is a good measure of solvent friction and that the fractional viscosity dependence with α < 1 is not due to a nonlinear viscosity behaviour.
Scavenging of hydrocarbon radicals from flames with dimethyl‐disulfide II. Hydrocarbon radicals in fuel‐rich low‐pressure flames of acetylene, ethylene, 1,3‐butadiene and methane with oxygen
Authors: Hausmann M. , Homann K.‐H. 
Published: July 2012

AbstractThe new technique of free‐jet condensation/scavenging with dimethyl‐disulfide has been applied for the quantitative analysis of hydrocarbon radicals and carbenes in flat premixed hydrocarbon/oxygen flames burning with fuel‐rich mixtures at 27 mbar. The results are reported as profiles of mole fractions of the radicals. The limit of detectability was about 1·10−7 mole fraction. Qualitatively the radicals are very similar with the four fuels, but there are large differences in their quantities. While in the methane flame only C1 and C2 radicals were present in detectable concentration, higher radicals up to naphthyl could be detected with the unsaturated fuels. Although methyl could not be determined quantitatively, it was found to be the major hydrocarbon radical in all flames. Methoxy radical was only found in the methane flame. Whereas, for example, C2, C3H2 and C3H are typical high‐temperature species, C2H is surprisingly formed at the beginning of the oxidation zone at relatively low temperature. Vinyl and the vinyl‐type radicals C2nH3 (n = 1 to 4) are in equilibrium with acetylene and the polyynes (C2nH2) at maximum flame temperature and in the burned gas. Since phenyl peaks always after benzene, it is concluded that it is mainly a degradation product from benzene and other lower aromatics. The mechanism of formation of C2H and C2, the equilibria of the C2nH3 and the relation between aliphatic and aromatic radicals are discussed.
Preferential solvation of some silver(I) salts in iso‐dielectric mixtures of methanol and N‐Methyl‐2‐pyrrolidinone at 30°
Authors: Varadarajan T.K. , Ramakrishna T.V. , Kalidas C. 
Published: July 2012

AbstractThe solvation behavior of various silver(I) salts, viz. silver (I) iodate, bromate and sulfate in iso‐dielectric solvent mixtures of methanol and N‐methyl‐2‐pyrrolidinone (NMP) has been investigated using Gibbs transfer energies and solvent transport number measurements. The Gibbs transfer energies of the salts were split into their individual ionic contributions using both negligible liquid junction potential method (nLJP) and the reference electrolyte method using tetraphenylarsonium tetraphenylborate (TATB). The results show a significant hetero‐selective solvation of all salts beyond XNMP = 0.5 with silver ion being selectively solvated by NMP and the anions by methanol.
Measurements of thermal conductivity of aqueous LiCl and LiBr solutions from 293 to 473 K at pressures up to 100 MPa
Authors: Abdulagatov I.M. , Magomedov U.B. 
Published: July 2012

AbstractHigh‐pressure thermal conductivities of H2O+LiCl and H2O + LiBr have been measured with a parallel‐plate apparatus. Data cover the pressure range from 0.1 to 100 MPa at temperatures from 293 to 473 K. The concentrations studied were 0.025, 0.05, 0.10. 0.15, 0.20, and 0.25 mass fraction of salts. The estimated accuracy of the method is about ± 1.6%. The pressure, temperature, and concentration dependence of the thermal conductivity has been studied. Measurements were made on six isobars, namely: 0.1, 20, 40, 60, 80, 100 MPa. The thermal conductivity shows a linear dependence on pressure and concentration at all isotherms. Along each isobar a given concentration shows the thermal‐conductivity maximum at temperatures about 413 K. The measured values of thermal conductivity are compared with the results of other investigators.
NMR study of liquid and supercritical benzene
Authors: Asahi Nobuyoshi , Nakamura Yoshio 
Published: July 2012

AbstractDensity, spin‐lattice relaxation time and self‐diffusion coefficient of benzene have been measured under vapor‐liquid coexistence from room temperature up to above the critical temperature. Measurements were made for four samples with the density in the supercritical region being respectively 0.302, 0.250, 0.154 and 0.101 g cm−3. The density has been determined by the NMR one‐dimensional projection technique, and the Carr‐Purcell‐Meiboom‐Gill method has been adopted to the measurement of the self‐diffusion coefficient. The results obtained have been discussed in terms of hard sphere models and various contributions to the relaxation rates have been separated and the correlation times for each molecular motion have been estimated at 470 K. It has been shown that the spin‐rotational relaxation is dominant near and above the critical temperature.
Raman spectral study of WCl6 in alkali chloride melts
Authors: Carountzos George , Kontoyannis Christos G. , Østvold Terje 
Published: July 2012

AbstractThe chemistry of tungsten chlorides in the LiCl/KCl eutectic has been investigated by Raman spectroscopy between 400 and 500°. It has been found that W(VI) is reduced to W(V) directly by the free Cl− ion in the melt and the octahedral complex ion WCL−6 is formed. Addition of metals (Al, Zn, Pb, W) causes further reduction of W(V). Depending on the metal added WCl2‐6 or W metal can be obtained.
The heterogeneous reaction of HONO and HBr on ice and on sulfuric acid
Authors: Seisel Sabine , Rossi Michel J. 
Published: July 2012

AbstractThe heterogeneous reactions of HONO with HBr on ice, solid and supercooled liquid H2SO4 solution (40–95 wt%) were studied in the temperature range 180 to 200 K for the solid substrates (ice, H2SO4) and 210 to 270 K for the liquid solutions of H2SO4 using a Knudsen flow reactor.The uptake coefficient of HONO onto frozen aqueous HBr solutions at 190 K was determined and resulted in a mean value of γ = (2.3 ± 1.2)·10−2. On ice the HBr uptake rate is high with a mean value of γ = 0.32±0.12 between 180 and 200 K and is unaffected by the presence of HONO. The uptake of HONO onto ice is a function of the HBr concentration in the condensed phase and for the highest HBr flows used an uptake coefficient of γ = 2.2·10−2 was found.On frozen H2SO4 solutions the uptake coefficient of HBr varies with the concentration of the solution from about 0.25 at 10 wt% to less than 1·10−4 in the absence and 5·10−4 in the presence of HONO at 95 wt%. The uptake of HONO in the presence of HBr was found to vary with the HBr concentration and to be approximately a factor of two lower than on the ice surface.On liquid H2SO4 the uptake coefficients of HBr and HONO both strongly depended on the concentration of the solution. HONO shows the greatest interaction at 95 wt% with γ = 2·10−2 and decreases to about 5·10−3 at 40 wt%. In comparison HBr only shows a weak interaction of γ of approximately 5·10−4 at 95 wt% and a strong interaction of γ = 4·10−2 at 40 wt%.On all three substrates the concurrent uptake of HONO and HBr was found to be reactive forming the only identified bromine containing reaction product BrNO. The variation of the substrates from strong acid liquid to solid neutral provides information about the nature of the heterogeneous interaction.
Singlet and triplet state quenching of aromatic cations by molecular oxygen
Authors: Wirp Christoph , Brauer Hans‐Dieter , Bendig J. 
Published: July 2012

AbstractRate constants of fluorescence quenching by molecular oxygen, kSq, of 4 acridizinium ions and of 7 protonated heterocyclic compounds as well as protonated 6‐aminochrysene have been determined in acetonitrile at room temperature. They adopt values in the range between 3.0×108 M−1 s−1 and 2.9×1010 M−1 s−1. Singlet oxygen (1O2) efficiencies for the oxygen quenching of the singlet state, ϕSΔ, and the triplet state, ϕTΔ, could be determined for most of the compounds. The results indicate that fluorescence quenching can be described here as competition between energy transfer and a process involving the second excited triplet state, kSq shows at first approximation a correlation with the energy gap between the singlet state and the second excited triplet state. Quenching of the first excited triplet state by oxygen is ruled mainly by energy transfer. Rate constants, kTq, could be determined for 5 compounds and vary between 6.0×108 M−1 s−1 and 1.1 × 109 M−1 s−1.
Magnetic field effects on the luminescence of p‐phenylenediamine derivatives
Authors: Sacher M. , Grampp G. 
Published: July 2012

AbstractA positive magnetic field effect (MFE) on the luminescence of three different N,N,N',N'‐tetraalkyl‐p‐phenylenediamines (TAPD) has been detected by field‐modulated MARY (MAgnetic Field Effects on Reaction Yields) spectroscopy in a binary solvent mixture of toluene/dimethylsulfoxide containing more than 20% vol. dimethylsulfoxide and in neat dimethylsulfoxide. The p‐phenylenediamine derivatives' luminescence in these solvents could be increased by application of small external magnetic fields in the order of less than 30 mT (1T = 104G) and the B1/2 values could be measured. In a comparative experiment the N,N‐dimethylaniline (DMA) fluorescence did not show such a behaviour. In conclusion a reaction scheme involving an electron transfer process between the p‐phenylenediamines and the solvent dimethylsulfoxide is suggested.
Experimental verification of gas phase bromine enrichment in reactions of HOBr with sea salt doped ice surfaces
Authors: Kirchner U. , Benter T. H. , Schindler R. N. 
Published: July 2012

AbstractSignificant gas phase bromine enrichment is experimentally verified on flowing gaseous HOBr over ice surfaces doped with sodium halides of sea salt composition. It is argued that formation of Br2Cl− in the condensed phase followed by its dissociation with release of Br2 into the gas phase accounts for this phenomenon.
Consideration of the thermodynamic stability of iodine species in the Bray‐Liebhafsky reaction
Authors: Stanisavljev Dragomir 
Published: July 2012

AbstractThe standard free energy of formation of IO* and HIO2 in water solution at 298 K are estimated to be ΔG0IO· = 120 kJ/mol and ΔGHIO2 = −75 kJ/mol. Values of standard reduction potentials for half‐reactions HIO2 + 2H++2e− → HIO + H2O, IO* + H+ + e− → HIO, IO−3 + 3H+ + 2e → HIO2 + H2O and HIO2 + H+ + e → IO* + H2O are calculated to be E0 = 1.35 V, E0 = 2.3 V, 0.92 V and E0 = 0.4 V. Energetic requirements during the process of oxidation of iodine in acidic media are introduced as an important criteria in examination of the models of the Bray‐Liebhafsky reaction mechanism.
Formation of Ca‐O clusters and their protonation and hydration in direct laser vaporization
Authors: Liu Xiang‐Hong , Zhang Xiao‐Guang , Wang Xiu‐Yan , Lou Nan‐Quan 
Published: July 2012

AbstractCalcium oxide clusters produced in the direct laser vaporization of different precursor solid samples CaO, Ca(OH)2 and CaCO3 have been investigated by a time‐of‐flight mass spectrometer. Besides [Ca(CaO)n]+ and [(CaO)n]+ clusters, considerable protonated clusters [H(CaO)n]+ and hydrated clusters [H(CaO)n(H2O)m]+ have also been found in the TOF mass spectra. The characteristic of the abundance distribution of the clusters shows that the formation process of calcium oxide clusters should proceed along the growth course of the rock salt structure, which is further supported by the reactivity of [H(CaO)n]+ clusters with H2O produced in the direct laser vaporization.
Complexing ability of monensin anion for alkali metal cations in binary mixtures of dipolar aprotic solvents
Authors: Wagner‐Czauderna E. , Rzeszotarska J. , Orłowska E. , Kalinowski M. K. 
Published: July 2012

AbstractCyclic voltammetric studies have been carried out on monensin anion complexes with the alkali metal cations in binary mixtures of dimethylsulfoxide with acetonitrile, acetone and hexamethylphosphoric triamide. respectively. The log Ks values obtained for the complexity constants can be well described by empirical relation log Ks = αDN + β, where DN stands for the effective donor number of a given solvent mixture and α and β mark the regression coefficients. This result is in agreement with the predominant role of cation solvation. The complexes show a sharp stability maximum for the Na+ complex in all media under investigation.
Size dependence of bond length and binding energy in palladium and gold clusters
Authors: Krüger Sven , Vent Stefan , Rösch Notker 
Published: July 2012

AbstractAll‐electron density functional calculations on a series of highly symmetric palladium clusters up to nuclearity 147 yield an essentially linear correlation between the average bond length and the average coordination. The average binding energy per atom is found to be proportional to the inverse cluster radius and thus mainly determined by the decreasing surface to volume ratio. Comparison to recently obtained results for the corresponding series of gold clusters confirms the wider validity of these size dependence relationships.
Synthesis and characterization of PbS nanoparticles in block copolymer micelles
Authors: Schneider T. , Haase M. , Kornowski A. , Naused S. , Weller H. , Förster S. , Antonietti M. 
Published: July 2012

AbstractPrecipitation of lead ions by hydrogen sulfide in the presence of amphiphilic block copoloymer micelles composed of polystyrene‐b‐poly(4)vinylpridine yields PbS nanoparticles. By adjusting the reaction conditions with respect to the lead‐to‐polymer ratio, temperature or proton concentration particles of different size (2 to 20 nm) and morphology (spheres, cubes or needles) have been prepared. These particles have been characterized by powder X‐ray diffraction and High Resolution Transmission Electron Microscopy (HRTEM).At a low lead content of the polymer micelles and relevated temperatures the formation of nanocrystalline PbS needles is preferred. These exhibit a structured absorption spectrum with two peaks at 375 and 580 nm. In polymer micelles with high lead content, PbS spheres (1 to 2 nm) are formed. Growth of these particles can be induced by increasing the proton concentration, resulting in particles with diameters up to 20 nm.
Physico‐chemical properties of crystalline nanoscale enzyme‐protein‐metal layer composites in biosensors
Authors: Pum Dietmar , Neubauer Angela , Sleytr Uwe B. , Pentzien Simone , Reetz Susanne , Kautek Wolfgang 
Published: July 2012

AbstractCrystalline bacterial cell surface proteins (S‐layers) are introduced as immobilization matrices for binding biologically functional molecules in the development of amperometric biosensors. Due to the crystalline character of S‐layers, functional groups are located in well defined position and orientation on the protein meshwork and thus allow to bind molecules in densely packed monolayers. One of the most critical procedures in the development of amperometric biosensors is the deposition of an electrical contact onto the sensing layer. Conventional, sputtering techniques using platinum or gold, or, more recently, pulsed laser deposition of precious metals under inert gas conditions allow to establish electrically conductive contacts on S‐layer‐based enzyme electrodes.
The influence of amphiphiles with different chemical structure on the properties of fluid interfaces
Authors: Haage Klaus , Fiedler Harald , Esser Alfija 
Published: July 2012

AbstractThe influence of the hydrophilic/hydrophobic balance in several structures of amphiphiles on the surface activity was investigated. The aim was to compare model compounds combining different polar groups like ionic groups in acyl oligoglycinates or nonionic glycosides with glycyl spacer groups or with oxyethylene spacer groups. These functional groups are important in technically used surfactants and in native based amphiphiles like carbohydrates and proteins and derivatives, thus they are of interest from theoretical and practical reasons. The influence of the different groups is shown by the adsorption isotherms and the coalescence of oil droplets separated by thin aqueous surfactant films. The surface and interfacial tension of the homologous pure model compounds have been measured and fitted with the Frumkin equation. The influence of these small spacer groups can result in an increase of the hydrophilic strength of the surfactant as well as in an increase of the hydrophobic strength, depending on the total hydrophilic/hydrophobic balance in the amphiphile.
Continuous ultrafiltration of reverse micelles in the ternary system Igepal CA 520/cyclohexane/water
Authors: Schomäcker Reinhard , Orlich Bernhard , Braun Gerhard 
Published: July 2012

AbstractThe ultrafiltration is a separation technique at the nanometer scale and is applicable for the rejection of reverse micelles, spherical aggregates of surfactants, at membrane surfaces. We investigated the continuous ultrafiltration of reverse micelles in the non‐ionic ternary system Igepal CA 520/cyclohexane/water. The dependence of flux velocity and rejection on transmembrane pressure, droplet size, concentration of surfactant and temperature is described. With increasing pressure we also found micelles beside surfactant monomers in the permeate. This effect is observed more strongly when using non‐ionic surfactants than using ionic surfactants. It is discussed on the basis of the flexibility of the micelles. The results of the ultrafiltration process are compared with theoretical models, which are developed for the ultrafiltration of macromolecules from aqueous solutions: the gel layer models, which are developed for the ultrafiltration of macromolecules from aqueous solutions: the gel layer model, the model of osmotic pressure and the force balance model.
Synthesis of organic polymer gels in microemulsions and lyotropic mesophases
Authors: Hentze Hans‐Peter , Göltner Christine G. , Antonietti Markus 
Published: July 2012

AbstractThe synthesis of fine polymer latices and ordered polymer gels by polymerization in microemulsions and lyotropic mesophases is described. For this purpose, a new class of surfactants based on the coupling of cetyl trimethylammonium groups with organic counterions was developed. Interface activity, critical micelle concentration as well as lyotropic liquid crystalline phase behavior of these surfactants were investigated, and very high efficiency and high phase stability was found.Systems optimized such do not only allow the synthesis of very small polymer latices (Rh≥7.5 nm) in reverse systems, but also the generation of gels with lamellar order. Due to the occurrence of phase transitions during polymerization, direct templating of the original lyotropic phase by the polymer gel is prevented, but the final polymer gels are highly ordered and reflect some of the characteristics of the surfactant template.
Study on the structure of reverse micelles of triton‐X‐100 at low water content
Authors: Kluge T. , Knoll H. , Helmstedt M. 
Published: July 2012

AbstractUV/VIS absorption and emission of Ru(bpy)2+3, and time‐resolved luminescence quenching of Ru(bpy)2+3 by methylviologene were studied in reverse micelles (water‐in‐cyclohexane microemulsion) of triton‐X‐100 at low water content (hexanol‐1 as cosurfactant). From experimental results it is concluded that the probe molecules Ru(bpy)2+3 were solubilized in two different small aggregates at mole fractions of 1% water. Dynamic light scattering experiments however show large aggregates in these samples indicating a secondary structure. Increasing the water content, small aggregates with a radius of a few nm were detected by both light scattering and luminescence quenching, as expected.
Thermally stable CaO surfaces on highly dispersed MgO — New aspects for methane activation
Authors: Hofmann P. , Knözinger E. , Diwald O. , Mustafa A. 
Published: July 2012

AbstractChemical Vapour Deposition (CVD), applied to the production of mixed oxides of magnesium and calcium, provides nanostructured particles with outstanding surface properties which are dominated by low coordinated sites and CaO enrichment. The resulting basic material should, therefore, be particularly well suited for methane activation. In addition, it turned out to be extremely thermally stable.In fact, FTIR spectroscopy clearly evidences efficient methane chemisorption on the new oxide material. EPR spectroscopy indicates the presence of new paramagnetic centres after the addition of methane. ‐ If the mixed oxide samples are exposed to UV irradiation (>320 nm) in the presence of a methane/oxygen mixture, IR bands appear which have to be attributed to larger homologous alkyl structures which are ‐ for different reasons ‐ not observed on the pure constituents (MgO, CaO). Thus relevant implications of the new oxide material are to be expected in the field of heterogeneous catalysis, in particular, of Oxidative Coupling of Methane (OCM).
Electrochemical investigation of the nanostructured composite (W, Ga)
Authors: Bolz H. , Schwitzgebel G. 
Published: July 2012

AbstractNanostructured composites (W,Ga)nc consist of tungsten crystallites 5‐10 nm thick and 10‐50 wt% gallium in the grain boundaries. Potentiometric measurements and cyclic voltammetry were performed in aqueous solution of Ga2(SO4)3. The electrode potential of the samples is 0.36 ± 0.03 V more positive than that of pure Ga. This value corresponds to the known binding energies of Ga layers on W single crystal surfaces (field ion microscopy). Therefore, there is strong evidence that the electrochemical behaviour is determined, in analogy to the under potential phenomena, by Ga monolayers in the surface regions of the grain boundaries.