bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis and characterization of oxycarbide glasses in the BaSiOC‐system and the influence of aluminum on the ability to incorporate carbon into the glass network
Authors: Lansmann V. , Hoffbauer W. , Wartner N. , Mader W. , Jansen M. 
Published: July 2012

AbstractSo far, only a few investigations about oxycarbide glasses prepared by a melting process are reported and no evidence has been provided for carbon being incorporated into the glass network. The present work describes the preparation and characterization of glasses in the BaSiOC and BaSiAlOC system prepared from the melt. The glasses were characterized by X‐ray diffraction, transmission electron microscopy, differential scanning calorimetry and 29Si‐ and 27Al‐MAS‐NMR Spectroscopy. By identifying SiO3C units in the BaSiOC system the first spectroscopic proof is given that in oxycarbide glasses prepared by a conventional melting process carbon is incorporated into the glass network. The substitution of silicon by aluminum results in a tighter network, which was unable to incorporate carbon.
Light induced nonequilibrium effects in gases
Authors: Schramm B. , Wörner T. 
Published: July 2012

AbstractIt is possible to disturb the equilibrium velocity distribution of molecules in a gas by absorption of narrow band laser light. This leads to light induced transport phenomena. We report on experiments, where we have measured the pressure difference caused by light induced viscous flow and where we have separated the two nuclear spin modifications of CH3F with the help of light induced drift.
Two‐dimensional nucleation initiated by athermal clusters
Authors: Donner C. , Pohlmann L. , Baumgärtel H. 
Published: July 2012

AbstractThe prepolarisation potential influences the two‐dimensional nucleation kinetics of adsorbed neutral molecules on a mercury electrode in the system 5‐bromocytosine/Na2SO4. It was shown that for prepolarisation potentials located near the phase transition potential a significant amount of large clusters is formed, which after the jump into the condensation region become overcritical nuclei with an athermal distribution. Significant differences exist in the kinetics at the cathodic and the anodic edge of the condensation region, respectively. This indicates that the potential dependence of the adsorption isotherm of the neutral molecules can not be symmetrical, as supported usually. These investigations show furthermore that the nucleation rate is not solely a function of the applied potential, but depends also on the prepolarisation conditions.
Highly dimerizable radical cation of 3,3′,5,5′‐tetramethylbenzidine
Authors: Awano Hiroshi , Ichihara Osamu , Sawada Kazutaka , Ohigashi Hiroji 
Published: July 2012

AbstractCation radical salts of 3,3′,5,5′‐tetramethylbenzidine (TMB) were studied in terms of dimerization of the radical cation, and compared with the salts of other aromatic diamines, including Wurster's blue perchlorate. ESR spectra of several TMB salts were measured in solid‐state, and analyzed by the singlet‐triplet model for a radical dimer. The singlet‐triplet energy separation has been obtained as 0.15 eV for (TMB)ClO4. The dimerization of the TMB radical cation in acetonitrile solution of (TMB)ClO4 was estimated from ESR and visible spectral results. In consequence, (TMB)+. is highly dimerizable in solution, compared with the systems of other diamines.
Electrocatalysis of the quinone/hydroquinone system by electrodes coated with substituted polyaniline
Authors: Malinauskas Albertas , Holze Rudolf 
Published: July 2012

AbstractPolymer films derived from N‐methylaniline (NMA), N(3‐sulphopropyl)‐aniline (NSPA), 2‐ and 3‐methylanilines (2‐MA and 3‐MA), and 2,3‐, 2,5‐ and 2,6‐dimethylanilines (2,3‐DMA, 2,5‐DMA and 2,6‐DMA), as well as of some copolymers, were obtained on a platinum electrode in acidic solution by potential cycling. Electrocatalytic properties of the resulting polymer coated electrodes towards the hydroquinone‐benzoquinone redox couple were investigated. The following sequence of catalytic activity was found: poly(2‐MA)>polyNMA = copoly (2‐MA+3‐MA) > copoly(NMA+NSPA) > polyNSPA>poly(3‐MA). With respect to the stability of catalytic effects observed at prolonged potential cycling, the following sequence can be drawn: poly(2‐MA) > polyNSPA≫copoly(2‐MA+3‐MA) = poly(3‐MA) > copoly(NMA+NSPA) > polyNMA. Thus, poly(2‐MA) was found to be the most effective and stable electrocatalyst in the redox couple investigated. The polymers derived from dimethylanilines were found to inhibit this redox process.
Application of a purely physical model (DISQUAC) to binary mixtures of phenol and organic solvents
Authors: Gonzalez J. A. , de la Fuente I. Garcia , Cobos J. C. 
Published: July 2012

AbstractA whole set of literature data on phase equilibria, vapor‐liquid equilibria, VLE, liquid‐liquid equilibria, LLE, and solid‐liquid equilibria, SLE, and on molar excess Gibbs energies, GE, molar excess enthalpies, HE and on activity coefficients at infinite dilution for phenol + organic solvents mixtures are examined in terms of the DISQUAC group contribution model. The interchange coefficients for OH(phenol)/aromatic; OH(phenol)/aliphatic and for OH(phenol)/C6H12 interactions are reported.DISQUAC yields a good representation of VLE, GE and HE, as well as of the temperature dependence of GE. DISQUAC predictions on SLE are similar to those encountered in other alcoholic solutions previously investigated, and are slightly worse than those given by the mean association number theory. LLE data are critically reviewed. The necessity of different third interchange coefficients for the OH(phenol)/aliphatic interactions in the series phenol + n‐alkanes for the longer n‐alkanes in order to improve LLE predictions is discussed. The larger discrepancies are found when predicting activity coefficients at infinite dilution.
The vapor composition and vapor pressure of ZnSe from a modified Knudsen technique between 1190 and 1310 K
Authors: Schönherr E. , Freiberg M. , Siche D. , Hartmann H. 
Published: July 2012

AbstractSolid ZnSe is evaporated from a Knudsen cell in vacuum. The effective molecular weight of the ZnSe vapor is directly determined by weighing the cell with and without effusion taking place. The rate of effusion is adjusted by a moveable furnace. An effective molecular weight of 135 ± 5 g/mol is found for temperatures between 1190 and 1310 K. The weight indicates the complete dissociation of the sublimed ZnSe into Zn and Se2 vapor. In that temperature range, the total equilibrium vapor pressure of solid ZnSe is estimated from the recoil force according to \documentclass{article}\pagestyle{empty}\begin{document}$ \log _{10} (P/{\rm kPa}) = - (12896 \pm 96){\rm K}/T + (9.19 \pm 0.08). $\end{document}
Synthesis and characterization of thiol‐stabilized CdTe nanocrystals
Authors: Rogach A. L. , Katsikas L. , Kornowski A. , Su Dangsheng , Eychmüller A. , Weller H. 
Published: July 2012

AbstractIn order to expand the range of high‐quality nanosized semiconductor materials that can be obtained as quantum dots through a wet chemical route a series of oxidize‐stable CdTe nanoclusters with narrow size distributions and extremely small particle sizes ranging from 1.3 to 2.4 nm has been prepared in aqueous solution using 2‐mercaptoethanol and 1‐thioglycerol as stabilizers. It has been investigated by means of UV‐vis absorption and photoluminescence spectroscopy, X‐ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and energy dispersive x‐ray analysis (EDX).
Adsorption and phase formation of uracil derivatives on gold and silver single‐crystal electrodes
Authors: Hölzle M. H. , Kolb D. M. , Krznarić D. , Ćosović B. 
Published: July 2012

AbstractThe adsorption of uracil, 6‐methyluracil, 5‐methyluracil (thymine) and 5,6‐dimethyluracil from aqueous solutions on Au(111) and Ag(111) has been investigated by cyclic voltammetry, capacity measurements and current transients, to elucidate the role of the electrode surface and of the intermolecular forces in the formation of ordered adlayers. From the calculated free adsorption enthalpies stability sequences for the condensed physisorbed phase were established. Our data show that the properties of the physisorbed adlayer are strongly influenced by the intermolecular forces, whereas in the chemisorbed state the influence of the substrate becomes dominant. For the chemisorbed molecules on Au(111) electrosorption valencies were estimated, which indicate an appreciable charge transfer.
Pressure driven transport across a cation exchange membrane in contact with mixed aqueous electrolyte solutions
Authors: Hahn O. , Woermann D. 
Published: July 2012

AbstractFiltration experiments with phenolsulfonic acid‐formaldehyde cation exchange membranes are carried out with aqueous solutions containing two electrolytes with a common anion: HCl/NaCl, HCl/CaCl2and NaCl/SrCl2. The concentration difference of each electrolyte between the high pressure phase and the filtrate in the stationary state has the same sign as the reflection coefficients of the electrolytes in the mixtures determined in independent experiments. This confirms theoretical predictions. Corresponding experiments with Nafion membranes show the influence of unstirred layers on the sign of the concentration difference in filtration experiments.
Metastable crystallization of LaZr2F11
Authors: Aasland S. , Julsrud S. , Grande T. 
Published: July 2012

AbstractFusion and crystallization of the compound LaZr2F11 were investigated by differential thermal analysis and powder X‐ray diffraction. The stable modification of LaZr2F11 was observed to melt congruently at 789±4°C. The melt was easily supercooled past the melting point, before a metastable phase, β‐LaZr2F11, crystallized. On further cooling β‐LaZr2F11 went through an exothermic solid‐solid phase transition to the stable modification α‐LaZr2F11. No solid‐solid phase transition was observed during reheating of α‐LaZr2F11. The melting point of β‐LaZr2F11 was observed approximately 10 K below the melting point of α‐LaZr2F11. β‐LaZr2F11 was confirmed metastable at all temperatures, but nucleates more readily from the supercooled melt than the stable modification α‐LaZr2F11.
Networks of anharmonic resonance systems in the rovibrational overtone spectra of the quasilinear molecule HCNO
Authors: Albert Sieghard , Winnewisser Manfred , Winnewisser Brenda P. 
Published: July 2012

AbstractThe infrared spectrum of fulminic acid, HCNO, has been measured in the range 700‐7000 cm−1 with a Bruker IFS 120 HR interferometer. More than 130 new vibrational levels have been identified. Power series coefficients of these levels are given. Each vibrational level with its rotational levels is locally or globally perturbed. It was possible to classify most of the interactions into a grand network of Coriolis‐ and/or Fermi‐type resonance systems by using the previously known basic resonance systems 00010/00002 and 00100/00004. In addition, a new basic resonance for HCNO could be identified in the system 00015/01000/00103. As a consequence of the many interactions many so called “resonance‐enhanced” rovibrational subbands have been assigned. The identification and partial analysis of the resonance systems have been carried out, first with the help of different presentations of reduced term values and second by determining the J‐value separation between e and f crossing points. In this paper, the resonance systems 01100/01004/00203/00115 and 00014/00110/00102, which are combinations of the above mentioned basic resonance systems, will be discussed. Some further resonance systems that can be deduced from these are discussed in detail, too.
Photosynthese und Photorezeption in Halobakterien
Authors: Oesterhelt Dieter 
Published: July 2012

AbstractThe photobiology of Halobacteria is reviewed here. Furthermore, the functions of halobacterial retinal proteins as ion pumps for photosynthesis and as sensors mediating phototaxis are described. The well‐characterized transport mechanism of bacteriorhodopsin allows the suggestion of a general functional model of all halobacterial retinal proteins due to their structural similarities. Experimental findings showing the respective interconversions of proton‐ and chloride (halide)‐pumps, of outward‐directed to inward‐directed pumps and of sensors to pumps confirm this model. From these findings a general concept of ion translocation is derived and described as the “IST” model.
Photosynthetic antennae. Photosynthetic light‐harvesting
Authors: van Grondelle Rienk , Monshouwer René , Valkunas Leonas 
Published: July 2012

AbstractThe peripheral light‐harvesting complex of the photosynthetic bacterium Rhodopseudomonas acidophila (LH2) and the major plant light‐harvesting complex LHCII have a very similar function: to absorb solar photons and to transfer the electronic excitation to the pigments surrounding the reaction center, the so‐called ‘core’. Nevertheless, their structures exhibit a dramatically different arrangement of the pigments. In LH2 the bacteriochlorophyll molecules are arranged in a highly symmetric ring, while in LHCII the positioning of the chlorophylls is very irregular. In both complexes the average distance between the pigments is 1 nm or less and, as a consequence, the electronic interaction between the pigments is strong ( > 100 cm−1). Therefore, the excitation transport in these photosynthetic light‐harvesting systems can not be described by a simple Förster type transfer mechanism, but new or other transfer mechanisms may be operative, for instance a mechanism in which the excitation is to some extent delocalized. Crucial parameters are the strength of the electronic coupling, the amount of energetic disorder and/or heterogeneity and the nature and strength of the interactions of the pigments with the protein. Here we will discuss the current status of the field of photosynthetic energy transfer in particular for LH2. We will evaluate a few simple models that contain some of the essential ingredients to describe the process of energy transfer and finally we will discuss some of the perspectives in this scientific field.
Photosynthetic oxygen evolution: H/D isotope effects and the coupling between electron and proton transfer during transitions S2⟹3 and S3⟹S4→S0
Authors: Bögershausen Oliver , Haumann Michael , Junge Wolfgang 
Published: July 2012

AbstractThe oxygen evolving complex (OEC) of photosystem II (PS II) incorporates a tetra Mn‐cluster, tyrosine (Yz) and probably one histidine residue (X) as redox cofactors. Four quanta of light drive the OEC through the increasingly oxidized states S0⟹S1⟹S2⟹S3⟹S4 to yield O2 during S4→S0. It has been speculated that some oxidized cofactor abstracts hydrogen from bound water. This implies that its oxidoreduction is electroneutral and linked to its deprotonation. To identify such steps we investigated the rates of electron transfer and proton release as function of the D2O/H2O ratio, the pH, and the temperature in thylakoids and PS II core particles. Upon oxidation of X on S2⟹S3, a rise of the pH from 5 to 8 increased the rate of the electron transfer to Yz by a factor of 2.5 and substitution of D2O for H2O gave an isotopic ratio of 2.1. Contrastingly, during all other transitions, including the O2‐evolving step S4→S0, the electron transfer rate was much less sensitive to these parameters (factors of ≤ 1.4). These results suggest a kinetical steering role of proton transfer only during S2⟹S3. We propose that X* (His*?) serves as a hydrogen acceptor for bound water during S4⟹S0.
On the influence of multiple scattering contributions to the extended X‐ray absorption fine structure (EXAFS) spectra of the photosystem II manganese complex
Authors: Dittmer Jens , Dan Holger 
Published: July 2012

AbstractThe catalytic center of photosynthetic water oxidation is a tetra‐nuclear manganese complex which presumably is covalently bound to the polypeptides of the Photosystem II (PS II) protein complex. Extended X‐ray Absorption Fine Structure (EXAFS) spectra were simulated for various likely structural elements of the PS II manganese complex. The influence of multiple scattering contributions to the EXFAS spectra is assessed. It is found that for distances below 3.5 Å multiple scattering contributions to the EXAFS spectrum of the PS II manganese complex are presumably negligible. However, for distances above 3.5 Å multiple scattering contributions to the EXAFS spectrum of the PS II manganese complex are likely to be of relevance. We conclude that the amino acid residues (glutamate, aspartate, histidine) which are ligands of the PS II manganese complex could give rise to the EXAFS Fourier peak at about 4 Å.
Pulsed EPR experiments on radical pairs in photosynthesis: Comparison of the donor‐acceptor distances in photosystem I and bacterial reaction centers
Authors: Zech Stephan G. , Lubitz Wolfgang , Bittl Robert 
Published: July 2012

AbstractPulsed EPR spectroscopy is applied to the radical pairs PQ in bacterial reaction centers of Rhodobacter sphaeroides R‐26 and PA in photosystem I from Synechococcus elongatus. For both radical pairs an out‐of‐phase echo was observed showing a deep modulation as a function of the spacing between the two microwave pulses. From the modulation frequency the dipolar and isotropic couplings between the radical pair spins were derived. For the bacterial reaction centers a dipolar coupling of D≈︁ −121 μT was obtained, resulting in a distance of about 28.4 Å between the electron spins of the radical pair. This value is in good agreement with the distance derived from the x‐ray structure of Rhodobacter sphaeroides R‐26. From the faster modulation in the PS I sample we obtained a dipolar coupling of D≈︁ −170μT, indicating a distance of 25.4 Å between the primary donor P700 and the acceptor quinone A1. For both radical pairs, only a small isotropic coupling of J ≈︁ 1 μT, consistent with transient EPR spectra, was found.
Biomimetic constructs. De‐novo design of redox proteins
Authors: Rau Harald K. , Haehnel Wolfgang 
Published: July 2012

AbstractA modular strategy for the de‐novo synthesis of four‐helix bundle proteins has been established. The individual helices and a cyclic decapeptide are purified to homogeneity after deprotection before they are coupled chemo‐ and regioselectively in predetermined orientations. The orientation of the helices relative to each other as well as of the N‐terminus is controlled by different side chain protecting groups. The new protein adapts the predicted structure of the heme binding core of the transmembrane cytochrome b to a soluble form. This protein with a molecular mass of 14,293 with antiparallel orientation of the four helices binds two heme groups in its hydrophobic interior via four histidines. Circular dichroism studies indicate a high helical content of the complex and a free energy of folding of −30.4kJ/mol. The two heme groups have midpoint potentials of −106 and −170 mV, respectively. The modular design of the de‐novo protein can easily be modified and provides the basis for detailed physical studies of molecular parameters.
Ivestigation of energy‐ and charge‐transfer processes using self‐organized porphyrin aggregates
Authors: Chernook Andrei V. , Shulga Alexander M. , Zenkevich Eduard I. , Rempel Ulrich , von Borczyskowski Christian 
Published: July 2012

AbstractSelf‐assembled triads and pentads are formed from Zn‐porphyrin or Zn‐chlorin dimers and pyridyl‐substituted free base of porphyrins, chlorins or tetrahydroporphyrins. A two‐point co‐ordination of the central Zn ions in the dimer with the nitrogen atoms of the pyridyl substituents of the free bases is essential for the complex formation. The complexation process has an equilibrium constant of the order of 107 M−1 at room temperature. An activation energy of the thermal dissociation of the complexes of 0.8 eV is found, which does not differ very much for different kinds of aggregates. Competing energy and charge transfer processes taking place in the aggregates have been identified by temperature dependent steady state fluorescence measurements.
Miscellanea. Femtosecond infrared spectroscopy on bacteriorhodopsin using a broad band carbon monoxide laser
Authors: Dziewior Reiner , Oilier Rolf 
Published: July 2012

AbstractA pump‐probe mid infrared transient absorption apparatus was built, employing a broad band continuous wave carbon monoxide laser and an optical gating technique resulting in femtosecond time resolution.It was used to monitor the all‐trans to 13‐cis isomerization of the retinal chromophore in Bacteriorhodopsin (BR). The C=C in‐phase stretch vibration, located at 1529cm−1 in the light adapted, unphotolyzed state BR570 served as marker band. Photoexcitation leads to a bleach centered at this wavenumber and to a partial recovery corresponding to the non unity quantum yield of the BR photocycle. On the picosecond time scale the high energy shoulder of this bleach is superimposed by newly created IR absorption strength, due to the corresponding vibrational modes of the J‐ and the K‐state.
Relativistic Effects in Heavy‐Element Chemistry
Authors: Heß Bernd Artur 
Published: July 2012

AbstractThe nature of relativistic effects in the electronic structure of atoms and molecules is explained and an account of theoretical methods for relativistic calculations in a quantum‐mechanical framework is given. The focus is on the requirement of reducing the number of degrees of freedom in the theory in order to obtain computationally efficient and still highly accurate approximations. Some applications illustrating the relativistic effects in coinage metal atoms and molecules are discussed.
Charge Transfer Like Complexes of Organic Dyes Adsorbed at Colloidal Silver studied by Cyclic Voltammetry, UV‐vis and SERS Spectroscopy
Authors: Nickel U. , Halbig P. , Gliemann H. , Schneider S. 
Published: July 2012

AbstractAfter adding cationic dyes like oxazine 170, malachite green, and crystal violet to a solution of colloidal silver sometimes an absorption band appears at wavelengths > 750 nm which is neither caused by the monomeric dye nor by a coagulation of the colloid. Based on electrochemical measurements this new absorption band is assigned to a chinhydron‐like adsorption geometry of the dye. Usually this band is only observed at low concentration of the dye, whereas at higher concentration the formation of H‐aggregates occurs. There seems to be a relationship between the intensity of this band and the SERS activity.
Non‐Cottrell Behaviour of Potentiostatic Processes in Mixed Conductors with Comparable Ionic and Electronic Conductivities
Authors: Preis Wolfgang 
Published: July 2012

AbstractA theoretical investigation of potentiostatic polarization processes in mixed conductors with arbitrary electronic transport numbers has been performed. As the potentiostatic polarization is accompanied by a chemical diffusion process inside the mixed conductor located between blocking electrodes, Fick's second law of diffusion has been solved for asymmetric electrochemical cells in order to obtain concentration profiles of the mobile species, current‐time relationships and the impedance of the asymmetric cell. Ohmic interfacial resistances as well as the ohmic bulk resistance owing to the total conductivity of the mixed conductor are considered. The theoretical results reveal that chemical diffusion processes in mixed conductors with comparable ionic and electronic conductivities show non‐Cottrell behaviour resulting in non‐Cottrell type current‐time relationships. These relations allow the exact description of the short‐time behaviour of potentiostatic diffusion processes occurring during chronoamperometric measurements. In addition, the non‐Cottrell behaviour of potentiostatic processes in mixed conductors with arbitrary electronic transport numbers employed in symmetric electrochemical cells is discussed.