bluuebunny/crossref_metadata_2025 huggingface dataset:
Discrimination between hydrogen atom and proton abstraction in the quenching of n, π* singlet‐excited states by protic solvents
Authors: Nau Werner M. , Greiner Gerhard , Rau Hermann , Olivucci Massimo , Robb Michael A.
Published: July 2012

The fluorescence quenching of the azoalkane 2,3‐diazabicyclo[2.2.2]oct‐2‐ene by protic solvents (methanol, methanol‐OD, water, deuterium oxide, acetic acid) has been examined. The pseudo‐unimolecular quenching rate constants (kq) vary from 0.30‐44×106s−1 and decrease upon deuteration of the solvent OH bonds, e.g., the isotope effect for methanol/methanol‐OD is ca. 8.5. This demonstrates that the hydroxylic hydrogens are predominantly responsible for the fluorescence quenching. The activation parameters were determined for methanol and methanol‐OD. The activation enthalpies are unexpectedly low (ΔH‡ = 1.8 kcal mol−1 for methanol) and increase upon deuteration (ΔH‡ = 3.0 kcal mol−1 for methanol‐OD), while the activation entropies remain the same (ΔS‡ ca. 17.5 cal K−1 mol−1. This provides evidence for a fully classical isotope effect related to differences in zero‐point vibrational energies. Tunneling appears to play no significant role. The quenching rate constants display no trend with the acidity of the solvent (pKa values) but with the homolytic bond dissociation energies of the OH bonds. This suggests the involvement of a hydrogen atom rather than a proton transfer. All important aspects (activation enthalpies, isotope effects, etc.) of this novel quenching mechanism of protic solvents are reproduced by MCSCF quantum‐chemical calculations with a complete active space of CAS (12,10) or CAS (8,7). Most importantly, the computed data indicate the occurrence of a conical intersection, i.e., a real surface crossing, which follows the transition state and provides an efficient trigger for radiationless return to the ground‐state energy surface (fluorescence quenching).
Proton transfer between carbon acids and methoxide: Studies in methanol, the gas phase and by ab initio MO calculations
Authors: Koch Heinz F. , Mishima Masaaki , Zuilhof Han
Published: July 2012

A detailed mechanism that features hydrogen‐bonded carbanions as well as free carbanions is presented for hydrogen transfer between carbon acids and methoxide ion in methanol. This is refined for several compounds by measuring their gas phase acidities, ΔG kcal/mol: C6H5CH(CF3)2 [335.3]; p‐C6H4CHClCF3 [337.4]; 9‐phenylfluorene [335.6]; C6F5H [349.2]. Ab initio molecular orbital calculations are reported to evaluate the stability of possible intermediates along the reaction pathway from 2‐hydro‐2‐phenyl‐perfluoropropane and methoxide ion to the carbanion and methanol. The intermediate, {C6H5C(CF3)2}−. HOCH3, is 6.8 kcal/mol more stable than the separated species, {C6H5C(CF3)2}− and CH3OH, and 43.2 kcal/mol more stable than C6H5CH(CF3)2 and −OCH3.
Ionic plastic phase in piperidinium hexafluorophosphate studied by solid NMR, X‐Ray diffraction, and thermal measurements
Authors: Ono Hiroshi , Ishimaru Shin'Ichi , Ikeda Ryuichi , Ishida Hiroyuki
Published: July 2012

Measurements of 1H, 19F, and 31P NMR, differential scanning calorimetry (DSC) and X‐ray powder diffraction were carried out in piperidinium hexafluorophosphate ([C5H10NH2]PF6). Three solid phases were observed by DSC in the range from 150 K to the melting point of 517 K. The highest‐temperature phase was determined to form a CsCl‐type cubic lattice with a=6.21(3) Å, Z=1, V=240(4) Å3, and Dx= 1.60(3) Mg m−3. From the NMR measurements in this phase, both cation and anion were revealed to perform self‐diffusion as well as isotropic rotation. These molecular motions and thermal properties indicate that this phase is an ionic plastic phase.
UV‐Vis spectroscopic study of molecular clustering in supercritical CO2‐acetone mixtures
Authors: Lu Jie , Han Buxing , Yan Haike
Published: July 2012

Solvatochromic behavior of acetone in supercritical CO2 was investigated over a wide range of pressures from 75 to 240 bar and at 318.15 K using UV‐Vis spectroscopy. Local density of CO2 about the solute was estimated from the solvatochromic shift of acetone based on the McRae‐Bayliss dielectric continuum model. The most remarkable aggregation of CO2 about the solute occurs at the reduced density of 0.5 ∼ 0.6. A simple clustering model was presented to estimate the excess solvent number about each solute molecule to the bulk region. In the near‐critical region, the excess number of CO2 is larger than the cluster size at infinite dilution defined by Debenedetti, which may be attributed to the formation of solute‐solute clusters.
LIF spectra of n‐propoxy and i‐propoxy radicals and kinetics of their reactions with O2 and NO2
Authors: Mund Ch. , Fockenberg Ch. , Zellner R.
Published: July 2012

Fluorescence excitation spectra of CH3CH2CH2O (n‐propoxy) and (CH3)2CHO (i‐propoxy) radicals were obtained using a combined laser photolysis/laser‐induced fluorescence (LIF) technique and the kinetics of reactions of these radicals with (1) O2 as a function of temperature and with (2) NO2 as a function of pressure have been determined.

Propoxy radicals were produced by excimer laser photolysis of the appropriate propyl nitrites at λ = 351 nm. The spectra of the (Ã←X̃) transitions show progressions of the CO‐stretching vibration in the electronically excited states with spacings of the bands of (560±10) cm−1 for i‐propoxy and (580±10) cm−1 for n‐propoxy. Fluorescence spectra taken after excitation in the (4,0) band at λ = 340.1 nm (i‐propoxy) and in the (1,0) band at λ = 342.4nm (n‐propoxy) show progressions of the CO‐stretching vibration in the electronic ground state of (900±60) cm−1 for i‐propoxy and (1000±50) cm−1 for n‐propoxy.

The Arrhenius expressions for the ractions of n‐propoxy and i‐propoxy with O2 have been determined to be k1 (n) = (1.4±0.6)×10−14 exp (0.9±0.5) kJ mol−1/RT) cm3 s−1 and k1 (i) = (1.0±0.3)×10−14 exp (‐(1.8±0.4) kJ mol−1/RT) cm3 s−1 in me range 218–313 K. The rate coefficients for the reactions of NO2 with n‐propoxy and i‐propoxy at T = 296 K were found to be independent of total pressure with k2(n) = (3.6±0.4)×10−11 cm3 s−1 (6.7–53 mbar) and k2(i)=(3.3±0.3)×10−11 cm3 s−1 (6.7–106 mbar).
Architecture of J‐aggregates studied by pressure‐dependent absorption and fluorescence measurements
Authors: Spitz Christian , Daehne Siegfried
Published: July 2012

The spectral shift of absorption and fluorescence bands as well as the fluorescence decay of four J‐aggregate forming 5,5′,6,6′‐tetrachlorobenzimidacarbocyanine dyes have been investigated in solution under high pressure up to 50 kbar0 The investigated dyes differ only in their 1,1′ and 3,3′ nitrogen substituents which do not influence the chromophore itself. Whereas the spectral behaviour of the monomeric dyes is comparable to that of aromatic and polyenic compounds, the J‐aggregates show some unusual spectral features.

Two types of J‐aggregates can be distinguished. One type exhibits a linear dependence of the absorption and fluorescence maximum on pressure wim vanishing Stokes shift over the whole pressure range. The second type is characterised by a limited shift of the absorption band to longer wavelengths whereas the Stokes shift increases even at pressures where the absorption energy remains constant.

The spectral behaviour of the first type is consistent with the well‐known chain‐shaped or brickstone‐like structure of J‐aggregates. As one dye of the second type is known to form optically active, Davydov‐split J‐aggregates the pressure‐dependent spectral behaviour of such dyes corroborates the assumption mat their J‐aggregates consist of helical cylindrical micelles.
Pressure‐jump investigations on the kinetics of the isotropic‐nematic phase transition of a liquid crystal: Time behavior of the scattered and transmitted light intensities for PCH 5
Authors: Sinanis S. , Schneider G.M.
Published: July 2012

A new optical high pressure cell was developed, which allows to induce pressure jumps within τ ≈︁ 0.5 ms and τ ≈︁ 50 ms and with an amplitude up to |ΔP| ≈︁ 6 MPa. With this cell the transmitted and scattered light intensities at fixed angles (θ = 20°, 50°, 80°, 110°, 140°) can be measured simultaneously as a function of time, e.g. at the phase transition isotropic‐nematic of a selected liquid crystal (here trans‐4‐n‐pentyl(4‐cyanophenyl)‐cyclohexane, PCH 5). The temperature changes during the pressure jumps are also registrated. The T(p) phase diagram of the liquid crystal is known from DSC measurements. Simultaneous time‐dependent measurements of transmitted and scattered light intensities allow a discussion of the processes that occur at the transition. The treatment of these processes has been approached according to existing theoretical models.
The structure of a methyl‐branched phospholipid monolayer in contact with hexadecane
Authors: Brezesinski Gerald , Bringezu Frank , Möhwald Helmuth
Published: July 2012

Monolayers of the methyl‐branched phospholipid l‐(2‐methylstearoyl)‐2‐hexadecylphosphatidylethanolamine (1) at the air/water interface and in contact with hexadecane are studied by pressure‐area isotherm measurements and grazing incidence x‐ray diffraction (GKD). The monolayers exhibit at both interfaces two diffraction peaks indicating a rectangular unit cell with next‐nearest neighbor (NNN) tilt at 20°C and at all lateral pressures investigated. Compared to the double‐chain DPPE, the introduction of the medryl side group changes the tilt direction from nearest neighbour (NN) to NNN, increases me tilt angle drastically and prevents the transition to the untilted hexagonal phase. The hexadecane contact decreases the tilt angle of (1) which shows that hexadecane is incorporated into the monolayer. However, the tilt angle can be reduced only to 13°. Comparison of the isotherm with the molecular areas determined by GIXD indicates that the monolayer consists of ordered and non‐ordered parts, the latter of which do not contribute to the diffraction pattern.
Investigation of charge transport across the Ag|AgI‐interface: (II) Dilatometric study of the anodic dissolution of silver
Authors: Majoni S. , Janek J.
Published: July 2012

The anodic dissolution of silver at the solid‐solid interface Ag|α‐AgI has been studied by means of a high precision (capacitive) dilatometer. The dilatometer signal corresponds to the change of the anode thickness during the dissolution experiment. Under galvanostatic conditions and in a definite pressure range the dilatometer signal oscillates periodically, i.e., me length change of the anode with time is not a simple and linear function of the current density. The mean length change is, as expected, proportional to the electric current. The oscillation modes of the dilatometer signal are correlated with simultaneous electrochemical oscillations at the anode and give evidence for the influence of morphological effects on the interface kinetics. From the combination of both electrochemical and dilatometric (mechanical) experiments, we draw conclusions on a possible mechanism of the observed oscillatory kinetics.
A new unifying structural model of heteropolymolybdate salts: Microstructure and thermal stability of a series of molecular oxides
Authors: Berndt S. , Herein D. , Zemlin F. , Beckmann E. , Weinberg G. , Schütze J. , Mestl G. , Schlögl R.
Published: July 2012

Powder X‐ray diffraction and cryo electron diffraction techniques supported by computer simulations were used to determine the secondary structures of the series of heteropoly acid (HPA) compounds CsxH4‐x PVMo11O40·nH2O (0≤x≤4). The structures of the caesium salts (2≤x≤4) are simple cubic with space group Pn3m. The free acid exhibits a triclinic lattice (P−1) for the majority of all crystals. A small fraction of thin crystals was detected with simple cubic structure (Pn3m). Computer simulations of the X‐ray diffraction patterns suggested that the structure of Cs2H2PVMo11O40·5H2O contains defects in the cation lattice. The caesium ion occupancy is 2/3. [H5O2]+‐groups occupy 1/3 of the cation positions. The diffraction pattern of Cs4PVMo11O40·5H2O could be simulated when only 3/4 of the anion positions are occupied. Cs3HPVMo11O40·7H2O crystallises in a simple cubic lattice without any defects.

The secondary structures of the investigated heteropoly salts can, therefore, be described by a single structure with variable site occupations, with the exception of Cs3HPVMo11O40·7H2O (caesium ion occupancy of 1 and poly anion occupancy of 1). All salts belong to one phase with large stoichiometric variations. A mixture of acid and caesium salt, with the acid epitactly grown on the salts, an intergrowth‐structure witii varying caesium ion content, mixed crystals as well as the coexistence of a nanocrystalline X‐ray‐invisible form of free acid besides caesium salt could be excluded for the partly neutralised materials. Selected physico‐chemical properties of the HPA compounds, which depend on the caesium ion content, will be rationalised widi the knowledge of the secondary structures.
Measurements of Henry's law constant for hydrogen in water utilizing a palladium differential resistance sensor
Authors: Yang Lietai , Sun Xiaodong , Steward F.R. , Morris D.R.
Published: July 2012

A differential‐resistance hydrogen sensor utilizing palladium, has been used for determining Henry's Law coefficient for hydrogen in water. This method does not necessitate equilibration of the gas and liquid phases. In the temperature range 187°C < T < 306°C, Henry's Law coefficient so determined is about 16 to 22% lower than the value determined from equilibration experiments.
Flame deposition of diamond films: An experimental study of the effects of stoichiometry, temperature, time and the influence of acetone
Authors: Bergmann Ulf , Lummer Karsten , Atakan Burak , Kohse‐Höinghaus Katharina
Published: July 2012

The deposition of diamond films in acetylene‐oxygen flames with different amounts of acetone in the source gas was investigated. Diamond films were deposited on molybdenum at temperatures between 1070 and 1420 K using a welding torch. The temperature as well as the stoichiometry dependence of the growth rate and quality of the diamond films were examined. The concept of supersaturation was adapted in order to have an transferable measure of the equivalence ratio. A sharp change of the diamond morphology from (111) to (100) planes between 1320 and 1370 K and between 6 and 7% supersaturation was found. The growth rate as a function of time was measured for deposition times between 2.5 and 180 min. Acetone influences the optimal conditions of the diamond deposition, the growth rate and the quality of the films. This influence was investigated in two different experiments. First, the acetone/acetylene ratio was varied with fixed supersaturation, whereas, in the second series, the supersaturation was increased by adding acetone, with keeping the acetylene flow fixed. It was found that small amounts of acetone have a positive effect on the film quality and increase the growth rate. This result may be qualitatively understood by an increase of hydrogen atom and methyl radical concentrations upon acetone addition.
Enhanced electrical conductivity of CuBr‐TiO2 composites: Dependence on temperature, volume fractions and grain sizes
Authors: Knauth P. , Albinet Gilbert , Debierre Jean‐Marc
Published: July 2012

Composites of a solid ionic conductor (copper(I) bromide) and an insulator (titanium dioxide) with carefully characterized purity and grain size are studied by impedance spectroscopy. The experimental dependence of electrical conductivity on temperature, volume fractions and grain sizes of the components is reported and interpreted in the framework of the space charge layer concept. An enhancement of conductivity by several decades compared with pure copper(I) bromide is observed and described by a percolation‐type model, which takes the effects of grain sizes and interfacial interactions into account.
Thermodynamics of alkanol + amine mixtures. Experimental results and ERAS model calculations of the heat of mixing
Authors: Heintz A. , Naicker P.K. , Verevkin S.P. , Pfestorf R.
Published: July 2012

Experimental data of the molar excess enthalpy of 17 binary alkanol+amine mixtures are presented obtained at 298.15 K by using an isoperibolic titration calorimeter (LKB 8700). The data are used for testing the ERAS model which accounts for self association and cross association of mixtures containing hydrogen bonds in the liquid state as well as for free volume effects based on an equation of state which incorporates the chainlike association of the molecules. Self association and cross association enthalpies of the hydrogen bonds are obtained as well as association constants providing an insight into the intermolecular structure of this kind of liquid mixtures.
Slow relaxation of conducting polymers: Differences between ring‐ and N‐substituted polyanilines
Authors: Malinauskas Albertas
Published: July 2012

A slow relaxation (“memory effect”) was found to proceed in a poly(o‐toluidine) layer, placed at platinum electrode, whereas no slow relaxation was observed in poly(N‐methylaniline). The difference between these two ring‐ and N‐methylsubstituted polyaniline derivatives is discussed in terms of redox and doping processes, taking place during their redox interconversion.
Rate constant for the reaction CH3+CH2(X̃3B1) at 298 K
Authors: Deters R. , Otting M. , Wagner H. Gg. , Temps F. , Dóbé S.
Published: July 2012

The rate constant for the reaction between CH3 and CH2 (X̃3B1 = 3CH2) radicals,

was determined at T=298 K and p=1.33 mbar in an isothermal discharge flow reactor. Far Infrared Laser Magnetic Resonance (FIR‐LMR) was employed for monitoring 3CH2 and CH3 radical concentration‐versus‐time profiles. CH3 was determined in the form of NO via the conversion reaction CH3+NO2 → CH3O+NO. The CH3 and 3CH2 radicals were generated by the reactions F+CH4 → CH3+HF and F+CH3 → 3CH2+HF. The rate constant for the recombination reaction

was determined together with the rate constant for reaction (1). The measurements gave a rate constant value for reaction (1) of k1 = (6.5±1.2)·1013 cm3/mol s.
An in situ UV‐Vis spectroelectrochemical investigation of the dichromate reduction at a polyaniline‐modified electrode
Authors: Malinauskas Albertas , Holze Rudolf
Published: July 2012

The electroreduction of dichromate at polyaniline (PANI) modified ITO glass electrodes in acidic solution was investigated with in situ UV‐Vis spectroelectrochemistry. It has been shown that under open circuit conditions dichromate does irreversibly oxidise the PANI layer. Under controlled potential conditions cathodic reduction of dichromate was shown to proceed at PANI‐modified electrodes. The overall rate of dichromate reduction was shown to be independent on the electrode potential of the PANI‐modified electrode in the range of ERHE=+0.2 to +0.8 V. From the data obtained it was concluded that a redox reaction between dichromate and PANI is the rate‐determining step of the overall electrocatalytic process.
Computer simulation of chiral liquid crystal phases — VII. The Chiral Gay‐Berne Discogen
Authors: Memmer R.
Published: July 2012

The phase structures of chiral discotic liquid crystals were studied by computer simulations. Bulk systems composed of uniaxial chiral discotic molecules with interactions described by the Gay‐Berne potential and an additive term for the energy of the chiral interaction were investigated using Monte Carlo (MC) simulations in the NVT ensemble. A discotic cholesteric phase (ND* and a discotic blue phase (BPDII) were observed along an isotherm in dependence on the chirality parameter describing the strength of the chiral interaction. All phases were characterised by order parameters, scalar and pseudoscalar orientational correlation functions, and visual representations of selected configurations.
Electrooxidation mechanism of glyoxylic acid on Au polycrystalline electrodes in acidic medium
Authors: Ocón P. , Velasco J. González
Published: July 2012

The electrooxidation mechanism of glyoxylic acid has been investigated on an Au polycrystalline electrode in acidic medium. The kinetic parameters deduced: Tafel slope, reaction order with respect to glyoxylic acid concentration, reaction order with respect to the pH, apparent activation enthalpy, entropy and Gibbs energy, and the final products detected after oxidation are in agreement with an electrooxidation mechanism beginning with an adsorption and a rate determining step in which the adsorbate becomes oxidized in a monoelectronic transfer reaction.
Angular axis distribution of asymmetric top molecules by the absorption of plane and circularly polarized light
Authors: Cong Shu‐Lin , Han Ke‐Li , Lou Nan‐Quan
Published: July 2012

Expressions used for describing optical preparation of aligned and oriented reagents are derived. The plane polarized light can only be used to control the alignment of reagents, and the circularly polarized light can be used to control the alignment and orientation of reagents. For asymmetric top molecules, the degree of alignment can often be chosen to be high, and the degree of orientation is often low. Specially, if reagents are symmetric top molecules, both degrees of alignment and orientation can often be chosen to be high for the K‐selected state.
Thermodynamic modelling of short range order using the compound energy formalism
Authors: Kusoffsky Alexandra , Sundman Bo
Published: July 2012

This paper describes an attempt to introduce a treatment of short range order within the compound energy formalism. The attempt is limited to binary alloys and phases with fcc or hcp structures.
Estimation of the thermodynamic stability of amorphous alloys Fe‐Si‐B and Co‐Si‐B
Authors: Kutsenok I. B. , Kunze S. , Mikhailovsky B. V. , Geiderikh V. A.
Published: July 2012

The estimation of thermodynamic functions of crystallization of amorphous alloys was carried out using a two‐stage procedure. The main approximation for this consists in the consideration of amorphous alloys as a supercooled metastable liquid solution. The first stage describes the thermodynamic properties of the melts Co‐Si‐B and Fe‐Si‐B by means of the ideal association model. A method of mathematical optimization was used to get the most reliable model parameters. All experimental thermodynamic data (integral and partial enthalpies, entropies and chemical potentials received by different experimental methods) available in the literature for both the ternary system and all composed binary systems were taken into account for this purpose. The second stage of estimation consists in the extrapolation of the calculated temperature and concentration dependences of the thermodynamic functions of the melts to low temperatures, using known models for the heat capacities of undercooled melts, and their comparison with appropriate thermodynamic functions of crystalline phases. The estimated values for the enthalpy of crystallization of the Fe‐B, Co‐Si‐B and Fe‐Si‐B amorphous alloys are in good agreement with experimental data.
Computer simulation of liquid ionic alloys and metal‐molten salt solutions
Authors: Koslowski T. H.
Published: July 2012

We present a numerical study of simple models of liquid ionic alloys and metal‐molten salt solutions. The microscopic structure is modeled using the primitive model of charged hard spheres, the electronic structure is described by a right‐binding Hamiltonian including the crucial component of Madelung potential fluctuations. We discuss the nature of the nonmetal‐metal crossover as a function of composition in these systems and present a computation of thermodynamic properties within the screened mean spherical approximation.
Interfacial properties of liquid alloys: An experimental study on Ga‐Bi and Ga‐Ge
Authors: Nattland D. , Chadli H. , Zell C.A. , Müller S.C. , Blanckenhagen B. V. , Freyland W.
Published: July 2012

Interfacial phase transitions like wetting and prewetting transitions are of considerable interest in physics and chemistry of condensed matter since they represent phase transitions in reduced dimensionality. Besides this interfacial properties are of profound practical and technological interest. Most systems studied experimentally in this respect are characterized by Van der Waals intermolecular interactions. However, in the last few years it was shown that Coulomb liquids like liquid alloys or metal molten salt solutions exhibit interfacial phase transitions similar to those known in Van der Waals systems.

In order to get more insight into these phenomena the fluid‐vapor interface of two different alloy systems have been studied using ellipsometry. Gallium‐bismuth is a binary alloy with large positive deviations from Raoult's law, exhibiting a distinct miscibility gap. Approaching liquid‐liquid coexistence a Bi‐rich film completely wets the fluid‐vapor interface. As can be estimated from the ellipsometric results the film thickness jumps at the monotectic temperature to a value of about 50 Å. In contrast, gallium‐germanium shows continuous miscibility and deviates much less from ideal mixing. As the Ge concentration in liquid Ga increases along the solid‐liquid coexistence curve the optical properties at the surface also vary continuously, which can be modelled within a simple effective medium approach.
Thermodynamically‐controlled processes on multicomponent alloy surfaces
Authors: Uebing Christian
Published: July 2012

The chemical composition of alloy surfaces is subject of segregation processes at elevated temperatures. In multicomponent alloy systems the joint surface enrichment of different solute atoms (cosegregation) is possible. Under thermodynamic control, i.e. when the temperature is sufficiently high to allow rapid bulk diffusion of the components, cosegregation may cause the formation of thermodynamically stable two‐dimensional chemical compounds (surface compounds), which are epitaxially arranged on alloy surfaces of suitable structure and orientation. The cosegregation‐induced surface confined formation of two‐dimensional chemical compounds must be distinguished from the precipitation of three‐dimensional compounds at surfaces (surface precipitates). According to the Gibbs phase rule, three‐dimensional precipitates can be formed upon oversaturation in coexistence with the saturated solid solution.

In this contribution the cosegregation‐induced growth of two‐ and three‐dimensional surface compounds and surface precipitates on several multicomponent alloy single crystals will be described and discussed.
III. Highly reactive and multicomponent systems: On the constitution and thermodynamics of Ni‐Gd alloys
Authors: Dischinger J. , Schaller H.‐J.
Published: July 2012

The thermodynamic properties of Ni‐Gd alloys were determined by electromotive force measurements between 873 and 1073 K on galvanic cells using CaF2 single crystals as solid electrolytes. Results yield a complete set of thermodynamic functions for the intermetallic phases (Ni), Ni17Gd2, Ni5Gd, Ni4Gd, Ni7Gd2, Ni3Gd, Ni2Gd, NiGd, Ni2Gd3, and NiGd3, as well as information on the phase relations. The system is characterized by pronounced negative deviations from ideality. The relative partial excess Gibbs energy of gadolinium at infinite dilution, ΔG (xGd→0), was determined to be ‐(104±5) kJ/mol. A comparison with analogous systems indicates the influence of the electronic structure of the components on thermodynamic properties of mixing. In order to fix the liquidus curve, differential thermal analysis was carried out over the entire range of composition.
Thermodynamics of solid Co‐Cr alloys by Knudsen cell mass spectrometry and computation of the phase diagram
Authors: Havrankova J. , Vrestal J. , Tomiska J.
Published: July 2012

Thermodynamic excess properties of cobalt‐chromium alloys in both the bcc solid and fcc solid phases have been investigated by Knudsen cell mass spectrometry in the temperature range 1580‐1790 K. The molar excess Gibbs energy, excess entropy and heat of mixing as well as the thermodynamic activities were determined from the ion intensities as a function of composition and temperature by fitting to a sub‐regular solution model and optimised to the phase equilibrium data (2 parameter T.A.P.‐series; Fcc phase: C in J/mol: CH1=‐10600, CH2=‐26500; C in J/(mol·K): Cs1=4.15, Cs2=‐26.0; Bcc phase: C in J/mol: CH1=19500, CH2 =‐29500; C in J/(mol·K): Cs1=19.4, Cs2=‐32.0). Solid Co‐Cr alloys at 1673 K are characterized in the fcc phase by negative molar excess Gibbs energy GE, prevailing negative molar excess entropies SE and exothermic molar heats of mixing HE, and in the bcc phase by negative and positive (at high Cr content) molar excess Gibbs energy GE, positive and slight negative (at higher Cr content) molar excess entropies SE and endothermic and slight exothermic (at higher Cr content) molar heats of mixing HE.

At 1673 K the following minimum and maximum excess properties result: a) Fcc phase, minimum values: HE=‐6400 J/mol (62 at.‐% Cr), SE=‐2.95 J/mol·K (70 at.‐% Cr), and GE=‐2650 J/mol (34 at.‐% Cr); b) Bcc phase, maximum values: HE=2300 J/mol (26 at.‐% Cr), SE=2.15 J/mol·K (26 at.‐% Cr), and GE=1090 J/mol (80 at.‐% Cr); bcc phase, minimum values: HE=‐140 J/mol (84 at.‐% Cr), SE=‐1.0 J/mol·K (82 at.‐%Cr), and GE=‐1300 J/mol (22 at.‐% Cr). The phase diagram has been recalculated by using these data, and the results of mass spectrometric investigations on the liquid phase.
Measurement of activity of gallium in liquid Ga‐Sb‐Ge alloys by EMF method with zirconia as solid electrolyte
Authors: Katayama Iwao , Fukuda Yutaka , Hattori Yoshiaki
Published: July 2012

The emf of galvanic cells with zirconia solid electrolytes was measured from 975 to 1242 K on binary Ga‐Ge alloys and from 1058 to 1236 K on ternary Ga‐Sb‐Ge alloys by use of Ga‐Ga2O3 as a reference electrode. From the emf values the activity of gallium in the liquid alloys is determined. At 1073 K the activity of gallium in the Ga‐Ge alloys and in the three pseudobinary alloys Ga‐(SbyGe1‐y) where y=0.25, 0.50 and 0.75 shows small negative deviations from ideality. Isoactivity curves in the ternary Ga‐Sb‐Ge alloys were derived by combining the activity data of Ga‐Sb, Ga‐Ge and the ternary alloys. The shape of the curves at 1073 K is simple in the Ga‐poor region, but shows a very small wavy form with increasing Ga concentration. Isovalues curves in the excess Gibbs energies of mixing in the ternary alloys are derived from Darken's method, and the results are compared with the model calculation proposed by Chou based on the experimental data in three binary systems. The shape of isovalue curves in ΔGxs is similar to those obtained from Chou's method, but the agreement between them in the values is not good.
Polyanionic clustering and electronic properties of the expanded equiatomic liquid alloy cesium‐lead
Authors: Hochgesand K. , Kurzhöfer R. , Leichtweiß O. , Winter R.
Published: July 2012

We present measurements of the electrical dc‐conductivity σ of the solid and liquid equiatomic Zintl‐alloy CsPb as a function of temperature in the range from 553 K to 2023 K. Due to significant charge transfer the alloy shows semiconducting behaviour. In the solid state the conductivity increases continuously from 0.2 Ω−1 cm−1 at 553 K up to 5 Ω−1 cm−1 at 800 K, where a drastic increase of σ is observed which is due to a rotor phase transition as discovered by Price, Saboungi et al. [1, 2]. In the liquid state (melting temperature Tm ≈︁ 870 K), σ reaches a maximum value of 1000 Ω−1 cm−1 around 1400 K. In addition, neutron diffraction measurements were carried out on the liquid from temperatures near the melting point up to 1900 K. The total Faber‐Ziman structure factors S(Q) exhibit a distinct prepeak remaining even up to the highest temperatures measured. This prepeak at 0.88–0.73 Å−1 is indicative of intermediate range ordering. We conclude that polyanions survive not only the melting process, but also persist through the whole temperature range up to about 1000 K above the melting point. RMC simulations were used to generate three‐dimensional models of the liquid and to determine the partial structure factors and pair correlation functions. With increasing temperature, the size of the polyanion clusters undergoes significant changes.
Thermodynamic study of intermediate phases in the Ru‐Ge, Ru‐Sn and Ru‐Si systems by Knudsen cell‐mass spectrometry
Authors: Ciccioli A. , Balducci G. , Gigli G. , Perring L. , Kuntz J.J. , Gachon J.C.
Published: July 2012

The enthalpies of formation of the intermediate phases in the systems Ru‐Ge and Ru‐Sn were measured by Knudsen cell‐mass spectrometry. The interest for these systems lies in their large implications in semiconducting materials and catalysts industry. The germanium and tin equilibrium vapour pressures were measured at various temperatures over two‐phase domains. The enthalpy changes of the decomposition reactions were determined by the second‐law method and the third‐law methods. Less extensive measurements have been carried out also for the Ru‐Si systems. The obtained values are compared with literature data and with those furnished by the semi‐empirical Miedema's model.
Properties of thermoreversible gels
Authors: Borchard W.
Published: July 2012

In a short survey chemical and physical aspects characterising thermoreversibly gelling systems are gathered. Rheological properties of the system gelatin/water for different polymer concentrations at various temperatures and varying angular frequencies are presented. The results are interpreted following the percolation theory. The relevant exponents of the storage and loss modulus are close to the percolation model of Arbabi and Sahimi. The pre‐gel properties favour the Zimm‐limit whereas the post‐gel properties are close to the Rouse‐limit. This controversial behaviour is discussed. The gel‐point has been determined by the divergence criterion of the dynamic viscosity at zero frequency when the storage modulus vanishes. The critical times in the percolation results agree fairly well with the time of gelation but not with the cross over time of the storage and loss modulus curves versus time at zero frequency.

An equilibrium aggregation model for the post gelation processes is presented which is based on the percolation approach. The time dependence of the storage modulus can be described in the total time range between gel point and the final equilibrium value after very long times.
Phase transitions of Poly(acrylic acid) Gels Grafted with Poly(N‐Isopropylacrylamide) Side Chains
Authors: Mikosch W. , Geissler E.
Published: July 2012

Poly(acrylic acid) (PAAc) hydrogels with poly(N‐isopropylacrylamide) (PNTPA) side chains display a phase transition on being subjected either to a change of temperature or of pH in the surrounding medium. Changes of pH induce volume transitions of the PAAc network, while the temperature influences the conformation of the PNIPA side chains. We describe the synthesis of this novel hybrid hydrogel, its phase diagram and preliminary results of local polymer structure investigations using contrast variation with small‐angle neutron scattering.
The volume transition in thermosensitive micronetworks as observed by small‐angle x‐ray scattering
Authors: Dingenouts N. , Norhausen Ch. , Ballauff M.
Published: July 2012

We present a study of the volume transition in colloidal particles composed of a temperature independent core and a shell of thermosensitive crosslinked polymer chains by small‐angle X‐ray scattering (SAXS). The poly(styrene) (PS) cores of the particles have a diameter of 80 nm whereas the shell composed of cross‐linked poly(N‐isopropylacrylamide) has a thickness of 32 nm in the swollen state at 25°C which shrinks to 18 nm at 50°C during a continuous volume transition. The SAXS‐intensities measured at high scattering angles could be described by a Lorenz‐type function at both states. This indicates the presence of marked liquid‐like local concentration fluctuations of the gel with a correlation length ξ of the order of a few nanometers even in the collapsed state (25°C: ξ = 3.2 nm; 50°C: ξ = 2.1 nm). The analysis thus shows that the core‐shell microgels behave in a distinctly different manner than ordinary thermosensitive gels. This is discussed in terms of the spatial constraint exerted by the core‐shell morphology onto the network.
Spherical microgel colloids — Hard spheres from soft matter
Authors: Bartsch E. , Kirsch S. , Lindner P. , Scherer T. , Stölken S.
Published: July 2012

While gels are usually considered to be soft materials, we demonstrate that it is possible to model hard sphere behaviour when the gel structure is confined to spherical objects of sizes in the colloidal range. We have measured the static structure factor of microgel spheres dispersed in good solvents, differing in size, crosslink density and swelling behaviour, by light scattering and small angle neutron scattering. Comparing with theoretical calculations for polydisperse hard spheres we show how the interactions in highly concentrated dispersions of spherical microgel colloids are determined by an interplay of the relative length of dangling polymer ends at the surface (determined by the average crosslink density and the particle size) and the swelling ratio (determined by the average crosslink density and the solvent quality). In addition the swelling ratio controls the volume fraction range in which colloidal behaviour is not superposed by the gel character. The latter leads to a loss of structural order due to the deformability of the microgel spheres, an effect that occurs at increasingly lower volume fractions if the swelling ratio increases. To achieve hard sphere behaviour up to very high volume fractions, thus, requires high crosslink densities and small swelling ratios.
Reversible gels of synthetic polymers: Phase relations, formation mechanisms and structure
Authors: Berghmans H. , Aerts L. , Buyse K. , Deberdt F. , Roels T. , De Rudder J. , Vereecke S.
Published: July 2012

The complex problem of thermoreversible gelation of solutions of synthetic polymers is discussed. Several possible mechanisms, based on supramolecular structure formation in solution, are discussed. The gelation of polyethylene solutions illustrates the structure formation through lamellar, folded chain crystallization. Gelation of solutions of stereoisomers of polystyrene and poly(methyl methacrylate) is more complex and two mechanisms can are proposed. The complex temperature‐concentration phase diagrams of syndiotactic polystyrene/solvent systems illustrate the competition between gelation by crystallization and the formation of elastic gels. The influence of chain conformation, participation of the solvent in the structure formation and the influence of solvent quality is discussed. Insight in the formation mechanism of elastic gels is obtained through the study of the gelation of solutions of syndiotactic poly(methyl methacrylate).
Gelierungstheorie: Versäumte Zusammenarbeit von Physik und Chemie
Authors: Stauffer D.
Published: July 2012

We describe how percolation theory, invented by Flory in 1941 to describe gelation, was in its later developments ignored by gelation theorists and only within the last decade confirmed experimentally. Also the mathematical theorems concerning uniqueness of the percolating network were long ignored and seem partially wrong or misleading. Finally, Flory's theory was applied to simulate stock market fluctuations.
Structure formation during precipitation reaction in gels: New liesegang patterns
Authors: Sydow U. , Plath P.J.
Published: July 2012

The paper reports on an investigation carried out into one‐ to three‐dimensional Liesegang systems (test tube arrangement) composed of different concentrations of lead nitrate in Agar gel with either potassium iodide or potassium dichromate as the precipitation reagent. A rich variety of different structure formations, including screw formations of the weakly soluble reaction product is documented.

Measurements of the progression of the precipitation front show a dependence of the diffusion path on time that which deviates from the Einstein‐Smoluchowski root mean square displacement. The measured exponent n of the displacement xn =f(t) is discussed in detail and interpreted as the dynamic dimension dw of the diffusion through the fractal medium of the gel, the backbone dimension of which could be estimated. A cellular automaton model is used to describe the DLA cluster formation of the precipitate as well as the geometrical shape of the Liesegang patterns.
Molecular dynamics study of electrolyte‐filled pores
Authors: Hartnig C. , Witschel W. , Spohr E.
Published: July 2012

The structure and dynamics of aqueous electrolyte solutions in cylindrical pores with pore radii of 11.1 Å have been investigated by molecular dynamics simulations. The pores serve as models for porous polymer membranes that have recently been produced. Polar functionalized pores were modeled by positive and negative surface charges on the cylinder surface. The observed correlation between ion mobility and the extent of contact ion pair formation with the surface charges provides a possible explanation for the experimentally observed ion selectivity in these pores.
Polymerization of styrene in microemulsion using gemini surfactants with hydrophilic and hydrophobic spacer groups
Authors: Dreja Michael , Tieke Bernd
Published: July 2012

The use of cationic gemini surfactants with various spacer groups in the polymerization of styrene in ternary microemulsion is reported. Gemini surfactants show a solubilization behaviour for styrene in water being superior over conventional single‐tail surfactants. Polymerization of the styrene‐in‐water microemulsions in the presence of a cross‐linker leads to spherical microgel particles of a size range being controlled by the surfactant/monomer ratio. For the two series of gemini surfactants with flexible hydrophobic alkylene spacer chains and flexible hydrophilic oligo(oxyethylene) spacers, the polymer particle size is significantly dependent on the length of the spacer chain. Both series also show the same dependence of the polymerization temperature on the particle size. If instead a hydrophobic aromatic unit is present as spacer group, the resulting particle size is no longer uniform. The results indicate that the process of particle formation and the resulting particle size are influenced by the microdroplet structure in the single phase microemulsion, which in turn is affected by the different interfacial properties of the surfactants.
Wetting phenomena near the bulk critical point of fluid mercury
Authors: Hensel F. , Yao M.
Published: July 2012

We have studied the adsorption of mercury on sapphire at temperatures and pressures close to the liquid‐vapour critical point (Tc= 1478°C, pc= 1673 bar, pc = 5.8 g/cm3) of mercury. The mercury film undergoes a first‐order phase transition known as prewetting. At low temperatures, the prewetting line meets the bulk coexistence curve tangentially at the wetting temperatures Tw = 1310°C. At high temperatures the prewetting line terminates at the prewetting critical point Tcpw = 1468°C and the prewetting pressure pcpw = 1586 bar lying close to the bulk critical point. In analogy with the line of compressibility maxima extending above the liquid‐vapor critical point, we can identify an extension of the prewetting phase line for T>Tcpw which marks the maximum in the two‐dimensional compressibility of the prewetting supercritical phase.
Synthesis, photoluminescence properties and theoretical insights on 1,3‐diphenyl‐5‐(9‐anthryl)‐2‐pyrazoline and ‐1H‐pyrazole
Authors: Dong Baoli , Wang Mingliang , Xu Chunxiang
Published: July 2012

1,3‐Diphenyl‐5‐(9‐anthryl)‐2‐pyrazoline and 1,3‐diphenyl‐5‐(9‐anthryl)‐1H‐pyrazole with an anthryl chromophore were synthesized and characterized using 1H NMR, 13C NMR, FT‐IR, mass spectrometry and elemental analysis. Their optical properties were characterized by UV–vis absorption and fluorescence spectroscopy. It was observed that the absorption and fluorescence spectra of the two compounds showed a red shift with respect to that of anthracene. Pyrazole exhibited high fluorescent quantum yields (Φf = 0.90 in toluene) while pyrazoline showed nearly no fluorescence in solution. The significant fluorescence divergence of the two similar compounds was investigated theoretically through density functional theory (DFT) calculations. The energetically lowest‐lying state S1 in the pyrazoline exhibited both characteristics of locally excited and electron‐transfer states that resulted in the fluorescence quenching of anthryl chromophore whereas the S1 state in the pyrazole corresponded to an optically allowed state that led to high fluorescence quantum yields in solutions. Copyright © 2012 John Wiley & Sons, Ltd.
Enzyme‐mediated methodologies for protein modification and bioconjugate synthesis
Authors: Matsumoto Takuya , Tanaka Tsutomu , Kondo Akihiko
Published: July 2012

Bioconjugates are valuable tools in many fields, including protein engineering and environmental and therapeutic research. Chemical methods are commonly used to synthesize protein‐protein and protein‐functional molecule bioconjugates because they permit easy tethering through covalent bonds. However, chemical methods often produce heterogeneous products and lead to degradation of protein activity due to random modifications. Recently, a number of techniques for modifying proteins or synthesizing bioconjugates have been reported, including more sophisticated chemical modification methods, utilization of noncovalent affinity, and protein splicing. Enzymatic methods in particular have attracted much attention due to the substrate specificity of enzymes, which enables site‐specific tethering of proteins to other proteins or functional molecules. Here, we discuss newly developed methods for protein modification and bioconjugate synthesis that exploit the properties of acyltransferases, ligases, and other enzymes.
The sweet tooth of biopharmaceuticals: Importance of recombinant protein glycosylation analysis
Authors: Lingg Nico , Zhang Peiqing , Song Zhiwei , Bardor Muriel
Published: July 2012

Biopharmaceuticals currently represent the fastest growing sector of the pharmaceutical industry, mainly driven by a rapid expansion in the manufacture of recombinant protein‐based drugs. Glycosylation is the most prominent post‐translational modification occurring on these protein drugs. It constitutes one of the critical quality attributes that requires thorough analysis for optimal efficacy and safety. This review examines the functional importance of glycosylation of recombinant protein drugs, illustrated using three examples of protein biopharmaceuticals: IgG antibodies, erythropoietin and glucocerebrosidase. Current analytical methods are reviewed as solutions for qualitative and quantitative measurements of glycosylation to monitor quality target product profiles of recombinant glycoprotein drugs. Finally, we propose a framework for designing the quality target product profile of recombinant glycoproteins and planning workflow for glycosylation analysis with the selection of available analytical methods and tools.
Ab Initio Based conformational study of the crystalline α‐chitin
Authors: Petrov Michal , Lymperakis Liverios , Friák Martin , Neugebauer Jörg
Published: July 2012

The equilibrium structure including the network of hydrogen bonds of an α‐chitin crystal is determined combining density‐functional theory (DFT), self‐consistent DFT‐based tight‐binding (SCC‐DFTB), and empirical forcefield molecular dynamics (MD) simulations. Based on the equilibrium geometry several possible crystal conformations (local energy minima) have been identified and related to hydrogen bond patterns. Our results provide new insight and allow to resolve the contradicting α‐chitin structural models proposed by various experiments. © 2012 Wiley Periodicals, Inc.